Dr. Ahmed Abu Foulsite.iugaza.edu.ps/ishaban/files/2014/11/Noise-Pollution.pdf · 2 x 10-5 N/m2...
Transcript of Dr. Ahmed Abu Foulsite.iugaza.edu.ps/ishaban/files/2014/11/Noise-Pollution.pdf · 2 x 10-5 N/m2...
Dr Ahmed Abu Foul
Sound is a form of energy which is emitted by a vibrating
body and on reaching the ear causes the feeling of hearing
through nerves
Sounds produced by all vibrating bodies are not audible
The frequency limits of audibility are from 20 HZ to 20000
HZ
A sound generally consists of three inter-related elements-
the source the receiver and the transmission path
This transmission path is usually the atmosphere through
which the sound is propagated
The pressure waves spread out like ripples on a pond when a stone is
dropped into it except that sound waves fill the whole volume of air
whereas ripples are confined to the surface of the pond
Speed of Sound
In a free field sound propagates with the velocity c defined by
where TK and TR are the temperature in Kelvin and Rankin respectively
A simpler formula for the velocity of sound in air sufficiently accurate at
normal temperatures 0ndash30oC is
where TC is the temperature in centigrade
Example 1
Determine the speed of sound at 20oC (68oF) in both metric
and English units
Solution
The Kelvin temperature is TK = 2732 + 20 = 2932 K
and the Rankin temperature is TR = 4597 + 68 = 5277oR
The speed of sound c is then
Sounds of frequencies less than 20 HZ are called infrasonic
and greater than 20000 HZ are called ultrasonic
The intensity of sound is measured in sound pressure levels
(SPL) and common unit of measurement is decibel dB
The community (ambient) sound levels are measured in the A -
weighted SPL abbreviated dB(A)
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound is a form of energy which is emitted by a vibrating
body and on reaching the ear causes the feeling of hearing
through nerves
Sounds produced by all vibrating bodies are not audible
The frequency limits of audibility are from 20 HZ to 20000
HZ
A sound generally consists of three inter-related elements-
the source the receiver and the transmission path
This transmission path is usually the atmosphere through
which the sound is propagated
The pressure waves spread out like ripples on a pond when a stone is
dropped into it except that sound waves fill the whole volume of air
whereas ripples are confined to the surface of the pond
Speed of Sound
In a free field sound propagates with the velocity c defined by
where TK and TR are the temperature in Kelvin and Rankin respectively
A simpler formula for the velocity of sound in air sufficiently accurate at
normal temperatures 0ndash30oC is
where TC is the temperature in centigrade
Example 1
Determine the speed of sound at 20oC (68oF) in both metric
and English units
Solution
The Kelvin temperature is TK = 2732 + 20 = 2932 K
and the Rankin temperature is TR = 4597 + 68 = 5277oR
The speed of sound c is then
Sounds of frequencies less than 20 HZ are called infrasonic
and greater than 20000 HZ are called ultrasonic
The intensity of sound is measured in sound pressure levels
(SPL) and common unit of measurement is decibel dB
The community (ambient) sound levels are measured in the A -
weighted SPL abbreviated dB(A)
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
The pressure waves spread out like ripples on a pond when a stone is
dropped into it except that sound waves fill the whole volume of air
whereas ripples are confined to the surface of the pond
Speed of Sound
In a free field sound propagates with the velocity c defined by
where TK and TR are the temperature in Kelvin and Rankin respectively
A simpler formula for the velocity of sound in air sufficiently accurate at
normal temperatures 0ndash30oC is
where TC is the temperature in centigrade
Example 1
Determine the speed of sound at 20oC (68oF) in both metric
and English units
Solution
The Kelvin temperature is TK = 2732 + 20 = 2932 K
and the Rankin temperature is TR = 4597 + 68 = 5277oR
The speed of sound c is then
Sounds of frequencies less than 20 HZ are called infrasonic
and greater than 20000 HZ are called ultrasonic
The intensity of sound is measured in sound pressure levels
(SPL) and common unit of measurement is decibel dB
The community (ambient) sound levels are measured in the A -
weighted SPL abbreviated dB(A)
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 1
Determine the speed of sound at 20oC (68oF) in both metric
and English units
Solution
The Kelvin temperature is TK = 2732 + 20 = 2932 K
and the Rankin temperature is TR = 4597 + 68 = 5277oR
The speed of sound c is then
Sounds of frequencies less than 20 HZ are called infrasonic
and greater than 20000 HZ are called ultrasonic
The intensity of sound is measured in sound pressure levels
(SPL) and common unit of measurement is decibel dB
The community (ambient) sound levels are measured in the A -
weighted SPL abbreviated dB(A)
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sounds of frequencies less than 20 HZ are called infrasonic
and greater than 20000 HZ are called ultrasonic
The intensity of sound is measured in sound pressure levels
(SPL) and common unit of measurement is decibel dB
The community (ambient) sound levels are measured in the A -
weighted SPL abbreviated dB(A)
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
If a source of sound emits the same pressure fluctuation in
all directions in free space the surface with the same level
of pressure will be concentric spheres
As the waves propagate outward the spheres become larger
and larger and the energy emitted by the source spread over
an ever larger surface causing the amplitude to decay like
1r2 where r is the distance from the source
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Distance affects the intensity of sound For example if the sound
pressure level L1 in dB is measured at r1 meters then the sound
pressure level L2 in dB at r2 meters is given by
This is called geometrical decay Even if this did not happen sound
wave would decay anyway due to the small but finite viscosity of the
air and the absorbing capacity of most surfaces
Sound waves are characterized by their pressure amplitude and their
frequency
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
If the sound levels are measured in terms of pressure then
sound pressure level LP is given by
Lp=10XLog10(p2p0
2) = 20X Log10(pp0) in dB
The Lp is measured against a standard reference pressure Po =
2 x 10-5 Nm2 which is equivalent to zero decibels
The sound pressure is the pressure exerted at a point due to a
sound producing source
Definition of sound pressure
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 2
If the distance from a noise source is doubled find out the
noise levels
Given r2 = 2r1
We have L2 = L1 - 20log10 (r2r1)
Substituting we get
L2 = L1 - 20 log10 (2r1r1)
L2 = L1 - 20 log10(2)
ie L2 = L1 - 20 x 0301
= L1 - 602
ie the noise level will decrease by 6 dB for doubling of
distance from the source
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 3
The sound pressure level is measured at 5 x 10-4 Nm2 Find
out the noise level in dB
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Addition of sound levels
The effective sound levels form two or more sources cannot be
simply added algebraically
For example the effective sound level from two air
conditioners 60 dB(A) each say is not 60 + 60 = 120 dB (A)
but 60 + 3 = 63 dB(A) (See table 1)
Similarly the effective sound level of 57 dB 63 dB 63 dB 66
dB and 69 dB is 72 dB
The computation is illustrated below
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Addition of sound levels
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Adding noise sources and subtracting
background noise
10 log 2 = 3 dB
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
To get a measure of the magnitude of the noise we need its
root mean square value over a couple of periods (say 1s)
It turns out that for uncorrelated sources the resultant rms
pressure is such that is such that p2 = p2A + p2
B
This is illustrated in the diagram shown in the following
Fig
Addition of sound levels
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Chart method ndash adding decibels
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Chart method ndash subtracting background noise
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
0 16 Hz 20 kHz 5 MHz
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound waves travel at a specific speed ndash the speed of sound
ndash which is roughly c = 343 ms in air
This speed depends very little on the frequency of the wave
high frequencies ie 12 kHz travel as fast as a 50 Hz wave
However these two parameters define another important
one the wavelength
If T is the period of the pressure fluctuation then its
frequency is f=1T and the wavelength is defined by
=cT=cf
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Wavelength is the distance between two successive wave fronts (like
the distance between two wave crests with sea waves)
For sound waves at 50 Hz the wavelength is about 5m at 5kHz it is
about 7cm so there is a significant different
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 5 Determine the wavelength of a 125-Hz and an 8000-Hz tone at 20oC (68oF) in both metric and English units
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
What happens when a sound source such as a pistol is fired
out-of-doors in the absence of any nearby reflecting
surfaces as is seen in Fig 4
The sound waves will travel through the atmosphere from
the pistol to the receiver) who will only hear one crack
The farther the receiver is away the later the crack will
arrive and the weaker it will be
The direct sound wave is the only sound heard
The sound wave arrives at time t t = Rc
where R is the distance between the source and the receiver
and c is the speed of sound
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
If there is a large wall or building at a distance near the firing position as
evidenced in Fig 5 the receiver will hear a different sound
The first sound wave will be from the direct arrival and the second sound
wave from the reflected arrival off of the wall
The two sound waves will arrive at
t1 = R1c and t2 = R2c
The human ear is able to recognize individual sound impulses if they are
separated by a time period of about 50 ms
If the time difference between the direct sound and the reflected sound is
greater an echo will be heard if the time difference is less only one
modified crack will be heard as evidenced in Fig 5
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 6
Determine the time a receiver will hear a pistol shot when the distance between the pistol and the receiver is 200 m and there is a building behind the pistol 40 m away Make the calculation for the two temperature conditions minus10oC and 25oC Solution minus10oC 25oC
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound and human hearing ndash Frequency
Humans are less sensitive to low frequency sound and more
sensitive to high frequency sound Therefore sometimes the
dB scale is adjusted to take this into account
A-weighting (db(A)) adjusts overall scale so it better matches
what the human ear would hear
C-weighting (dB(C)) adjusts scale for loud or low frequency
sounds
B-weighting (dB(B)) adjusts by factors that are ldquoin betweenrdquo
the A-weighted factors and C-weighted factors (rarely used)
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound Level Meters are the instruments commonly used to
measure environmental noise
They have 3 main components
1 A microphone
2 Some filtering electronics (the weighting networks) and
3 Display
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Equivalent sound level (Leq) can be applied to any
fluctuation noise level
Itrsquos the constant noise level that over a given time expand
the same amount of energy as the fluctuating level over the
same period
Leq = 10 log Σ 10Li10(ti)
- n the number of samples taken
- Li the noise level in dBA of the ith sample
- ti fraction of total sample time
i=n
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Given two machines producing 80 dB each
what is the total SPLT
SPLT is the total sound pressure level
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 7
The noise levels at a particular location are 65dB 70dB and
78dB measured during an hour of the day Find out the
average noise levels at the location
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Consider the case where a noise level of 90 dBA exists for 10 mins
and is followed by a reduced noise level of 70 dBA for 30 mins What
is the equivalent continuous equal energy level for the 40 mins
period Assume a 5-min sampling interval
Solution if the sampling time is 5 mins then samples (n) is 8 and the
fraction of total sample time (ti) for each sample is 18 = 0125
Σ = (109010)(0250) + (107010)(0750)
= (25 x 108) + (750 x 106) = 258 x 108
and finally we take the log to find
Leq = 10 log (258 x 108) = 8411 or 84 dBA
2
t=1
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Physically there is no distinction between sound and
noise
Sound is a sensory perception and the complex
pattern of sound waves is labeled as noise music
speech etc
Noise has become a very important stress factor in
the environment of man
Sound and Noise
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound that is unwanted or disrupts onersquos quality of life is
called as noise When there is lot of noise in the
environment it is termed as noise pollution
Sound becomes undesirable when it disturbs the normal
activities such as working sleeping and during
conversations
It is an underrated environmental problem because of the
fact that we canrsquot see smell or taste it
World Health Organization stated that ldquoNoise must be
recognized as a major threat to human well-beingrdquo
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Normal level of tolerance is 80 dbA
Sound level below and above this is considered to be as noise pollution
Any sound above 80 dB can cause hearing loss
The loss is related to the intensity and length of exposure
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sound levels about 90 dBA with exposures of 8 hrs per day
will produce permanent hearing loss after many years
Increased blood pressure and hypertension were shown to
occur at sound levels of 85 dBA
Increased risk of hypertension for people living in areas
with road or air traffic noise at outdoor equivalent sound
levels above 70 dB(A) based on exposure between 600
am and 1000 pm
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Harmful Effects of Noise Are Related to the Noise
Dose
Is the Noise Harmful
Ask Yourself
How Loud How Long How Many Times
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Intensity of Noise (how loud)
Duration of Noise Exposure (how long)
Frequency (how many times during the day are they
exposed to such a noise)
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Regulated as an 8 hour Time Weighted Average
(TWA)
An 8 hr TWA of 90 dBA is designated as a Noise
Dose of 100
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
5 dB Halving Rule
For Each 5 dB Increase in Noise In order to be
Equivalent to the Previous Dose You Must Half the
Allowable Exposure Time
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
95 dBA over 4 Hour TWA Period
100 dBA over 2 Hour TWA Period
105 dBA over 1 Hour TWA Period
110 dBA over frac12 Hour TWA Period
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
OSHA Noise (permissible exposure limits PEL)
Presently industry is governed by noise regulations
adopted by OSHA (Occupational Safety and Health
Administration)
PEL same as originally adopted in 1971
ndash Criteria level (PEL) 90 dBA
ndash Threshold level 90 dBA
- Practical implication mdash Can be exposed to 89 dBA
forever
ndash Exchange rate 5 dB
bull 95 dBA for 4 hours is as bad as 90 dBA for 8 hours
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
The 5 dB Rule Can Be Useful in Estimating
Whether a Noise or an Activity Would Result in
Employees Being Exposed to Noise In Excess of the
PEL
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
An Employee Must Enter a Pump Room and
Conduct Preventative Maintenance
The Small Portable Sound Level Meter Reads 105
dBA Inside the Pump Room
How Long Could the Employee Stay in the Pump
Room Without Exceeding the Dose Equivalent
Noise Exposure of 90 dBA over an 8 hour TWA
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Employee Noise Exposure for 1 Hour at 105 dBA
Would Be the Dose Equivalent Exposure of 90 dBA
for an 8 Hr TWA
Administrative Controls
Likewise Limiting Employee Exposure Time to
Noise Can Help Reduce the Possibility of Hearing
Loss
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Hearing Conservation Amendment to PEL
1048714 Hearing Conservation Amendment (HCA) 1981ndash1983
1048714 Recognition that PEL was not protective
ndashAction level = 50 of PEL = hearing conservation program
require
ndashCriteria level = 90 dBA
ndashThreshold level = 80 dBA
ndashExchange rate = 5 dBA
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Table 1 presents permitted exposure times for various
noise levels
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
To calculate a permissible duration that is not addressed in this
table use the following equation
Where T is the permissible duration (in hours) and L is the
measured sound level (in dBA)
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
For mixed or varying-level noise the exposure may
not exceed a daily noise dose (Dt) of unity as
expressed in Eq (2)
where Dn is the actual duration of exposure at noise
level n and Tn is the noise exposure limit for noise
level n from Table 1
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Impact noises are generated by machines such as drop
hammers and punch presses and exposure to such noises must
not exceed a 140-dB peak sound pressure level
The peak sound pressure level also determines the maximum
number of impacts per day that an employee may be exposed
to as indicated in Table 2
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
If an employee is exposed to both steady noise and impulsive
noise throughout the day the combined effect can be handled
quite simply
For predictive purposes one needs to treat the ratio of the
number of impacts Nn at a given peak sound pressure level to
the maximum number of impacts allowed at that level and add
this fraction to the steady level calculation
The combined fractions from all sources should not exceed
unity
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Furthermore a hearing conservation program must be
implemented that will include at least an annual audiometric
test for employees exposed to noise levels greater than 85 dBA
for 8 h or whose noise dosage Dt meets or exceeds 05
Such a plan protects the workers by monitoring potential
deterioration of their hearing and protects employers from
unwarranted claims of damaged hearing prior to employment
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
Answer Borderline since dose = 100
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example
Given four hrs of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the PEL (Is this person
overexposed compared to PEL)
1048714 Answer No since dose lt100
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example
Given four hours of 90 dBA exposure two hours of 95
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Yes since dose is gt50
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example
Given four hours of 80 dBA exposure two hours of 90
dBA exposure and two hours of 85 dBA exposure
what is the dose using the HCA (Does this person
need to be in a hearing conservation program)
Answer Borderline since dose = 50
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 10 A group of factory workers are subjected to the following sound levels
daily
In addition they are exposed to 12 impulsive events from various
sources that have a sound level of 130 dB (peak) The workers are off-
site for lunch from 12 noon until 1 PM Determine if it is permissible for
the workers to work in this environment
The noise dosage from all events is
D = 316+1606+316+146+121000 = 0772
Therefore the workers can work in this environment but they should
have their hearing checked periodically because their exposure is greater
than 05
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Noise Exposure
In evaluating worker exposure to noise the industrial
hygienist should answer two main questions
1 Is the OSHA PEL met or exceeded
2 Does the worker need to be in the hearing
conservation program
Modern dosimeters calculate dose both ways
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
TLV and REL for Noise
The ACGIH TLV (Threshold Limit Value) and NIOSH REL (recommended exposure limit) recommended for noise is as
follows
ndash Criteria level = 85 dBA
ndash Threshold level = 80 dBA
ndash Exchange rate = 3 dBA
American Conference of Industrial Hygienists (ACGIH)
The National Institute for Occupational Safety and Health (NIOSH)
These guidelines are
much more
protective
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Employee Noise Exposures Often Depend on How
Close They Are to the Noise Source
Distance
Noise Quickly Decreases as You Move Away from
the Noise Source
6 dB Double Distance Rule
Noise Will Decrease 6 dB Each Time You Double
the Distance (free field point source only)
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Reducing the Action Level for Extended Work shifts
If a worker works longer than an 8‐hour shift the action level
(AL) for hearing conservation is reduced proportionally from
85 dBA using the following equation
Example
A worker works a 1075‐hour shift in a car parts
manufacturing plant What will be the workerrsquos reduced AL
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Converting a Single Dose Measurement to an 8‐hour TWA Sound Level
A dose measurement can be converted to an 8‐hour TWA sound level
using the following equation
Where the dose is a percentage and the TWA is on an A‐weighted scale
Example
A factory hires a health and safety consultant to measure the noise
exposure of the workers The consultant writes a report that states that
workers are exposed to a 183 dose according to the general industry
standard Convert this dose into an 8‐hour TWA
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Sources of noise
The sources of noise may vary according to daily activities
They sources may be
Domestic (movement of tools cutting and shedding of
fruitsvegetables etc)
Natural (shores birdsanimal shouts wind movement sea
tide movement water falls etc)
Commercial (vendor shouts automobiles aero planes
marriages laboratory machinery etc)
Industrial (generator sets boilers plant operations trolley
movement transport vehicles pumps motors etc)
The noise levels of some of the sources are summarized at the
following table
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Typical noise levels of some point sources
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
-Any kind of loud music can cause temporary and permanent hearing loss
-Items such as iPods can cause much damage to the ear
-Constant lsquopoundingrsquo music and noise that goes on for long periods of time are common causes of deafness
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Impacts of noise Why trouble about noise Often neglected noise induces a
severe impact on humans and on living organisms Some of
the adverse effects are summarized below
Annoyance (disturbance) It creates annoyance to the receptors
due to sound level fluctuations (variations) The a periodic
sound due to its irregular occurrences causes displeasure to
hearing and causes annoyance
Physiological effects The physiological features like
breathing amplitude blood pressure heart-beat rate pulse
rate blood cholesterol are effected
Loss of hearing Long exposure to high sound levels cause
loss of hearing This is mostly unnoticed but has an adverse
impact on hearing function
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Impacts of noise
Human performance The working performance of
workershuman will be affected as theyll be losing their
concentration
Nervous system It causes pain ringing in the ears feeling of
tiredness thereby effecting the functioning of human system
Sleeplessness It affects the sleeping there by inducing the
people to become restless and loose concentration and
presence of mind during their activities
Damage to material The buildings and materials may get
damaged by exposure to infrasonic ultrasonic waves and
even get collapsed
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Noise levels
As mentioned before the sound pressures perceived by
human range from 20 Pa to 200 Pa
This range is enormous (huge) As the intensity is
proportional to the square of the pressure its range of
variation is even greater
When a quantity varies over several orders of magnitudes it
is usually more helpful to look at its Logarithm and this is
what people working with noise do
A number of these logarithmic levels are used
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Noise levels
Intensity Level LI=Log10(II0) (in Bell)
where I0 = 10 - 12 Wm2 is a reference level which roughly corresponds to the lower threshold of hearing
These levels are actually non-dimensional numbers but they are commonly assigned a fictitious unit the lsquoBellrsquo
Most intensity levels are fairly small numbers in Bells one usually counts them in decibels (dB) ie a tenth of a Bell In decibel the intensity level is therefore
LI=10 Log10(II0) (dB)
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Leq Prediction
- Developed by the Ontario Ministry of Transportation and
Communication
Leq = 423 + 102 log (Vc + 6 Vt ) ndash 139 log D + 013 S
where Leq = energy equivalent sound level during 1 hr (dBA)
Vc = volume of automobiles (four tires only) (vehhr)
Vt = volume of trucks ( six or more tires) ( vehhr)
D = distance from edge of pavement to receiver (m)
S = average speed of traffic flow during 1 hr (kmhr)
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
If a new road is being planned it is not possible to assess
experimentally the impact of the new road on existing
neighboring areas
In this case noise calculations taking into account the most
common effects have been standardized to predict pressure
levels at some distance
See for example
httpwwwnplcoukacousticstechguidescrtn
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Control of Noise Pollution
The techniques employed for noise control can be
broadly classified as
1 Control at source
2 Control in the transmission path
3 Using protective equipment
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
1- Noise Control at Source
The noise pollution can be controlled at the source of
generation itself by employing techniques like
A Reducing the noise levels from domestic sectors
B Maintenance of automobiles
C Control over vibrations
D Low voice speaking
E Prohibition on usage of loud speakers
F Selection of machinery
G Maintenance of machines
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
80
The domestic noise coming from radio tape
recorders television sets mixers washing
machines cooking operations can be minimized by
their selective and careful operation
By usage of carpets or any absorbing material the
noise generated from felling of items in house can
be minimized
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
81
Regular servicing and change of vehicles will
reduce the noise levels
Fixing of silencers to automobiles two wheelers
etc will reduce the noise levels
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
PH 0101 UNIT 1 LECTURE 9 82
The vibrations of materials may be controlled using
proper foundations rubber padding etc to reduce the noise levels caused by vibrations
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
PH 0101 UNIT 1 LECTURE 9 83
Speaking at low voices enough for communication
reduces the excess noise levels
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
84
By not permitting the usage of loudspeakers in the
habitant zones except for important meetings
functions
Now-a-days the urban administration of the metro
cities in India is becoming stringent on usage of
loudspeakers
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
85
Optimum selection of machinery tools or equipment
reduces excess noise levels
For example selection of chairs or selection of
certain machinery equipment which generate less
noise (sound) due to its superior technology etc is
also an important factor in noise minimization
strategy
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
86
Proper lubrication (using oil) and maintenance of machines vehicles etc will reduce noise levels
For example it is a common experience that many
parts of a vehicle will become loose while on a rugged path of journey
If these loose parts are not properly fitted they will generate noise and cause annoyance to the driverpassenger
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
2- Control in the transmission path
The change in the transmission path will increase the length of
travel for the wave and get absorbed refractedradiated in the
surrounding environment The available techniques are briefly
discussed below
1 Installation of barriers
1 Design of building
bull Installation of panels or enclosures
bull Green belt development
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
88
Installation of barriers between noise source and receiver can attenuate the noise levels
The barrier may be either close to the source or receiver subjected to the condition that Rltlt D or in other words to increase the transverse length for the sound wave
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
PH 0101 UNIT 1 LECTURE 9 89
R D
Source Receiver
Barrier
Barrier close to source
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
D
Barrier
Receiver
Source
R
At very large distances the barrier becomes less effective because
of the possibility of refractive atmospheric effects
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
91
A sound source may be enclosed with a paneled structure such as room as a means of reducing the noise levels at the receiver
The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic (audio) absorption within the enclosure and the details of the panel penetrations which may include windows or doors
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Climate
Easy in installation
Durability - resistance to degradation from compression
moisture decomposition etc
Easy of replacement at end of life
Cost effectiveness
Toxicity
Flammability
Environmental impact and sustainability
Consideration of materials used
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Approximate reduction of outside noise provided by typical exterior wall construction
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Brick
Glass
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Hardwood
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Softwood
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Fiberglass rigid panel
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Polystyrene Cementitious foam
Air-entrained concrete
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Example 11
What barrier dimensions are necessary in order that
the barrier provide 20 dB attenuation at 500 HZ
From fig (next slide) we see that H2R must be at
least 10 ft in order to achieve the desired attenuation
This can be accomplished by selecting different values
for H and R for example
H = 55 ft R = 3ft H = 10 ft R= 10 ft H = 175 ft R
= 30 ft etc
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
104
Green belt development can attenuate the sound
levels
The degree of attenuation varies with species of
greenbelt
The legal regulations direct the industries to develop
greenbelt four times the built-up area for attenuation
of various atmospheric pollutants including noise
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
PH 0101 UNIT 1 LECTURE 9 105
Protective equipment usage is the ultimate step in noise control technology ie after noise reduction at source andor after the diversion or engineered control of transmission path of noise
The usage of protective equipment and the workerrsquos exposure to the high noise levels can be minimized by following
(a) Job rotation (b) Exposure reduction (c) Hearing protection
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
106
By rotating the job between the workers working at a particular noise source the adverse impacts can be reduced
(b) Exposure reduction
The schedule of the workers should be planned in such a
way that they should not be over exposed to the high noise levels
(c) Hearing protection
Equipment like earmuffs ear plugs etc are the commonly
used for hearing protection Attenuation provided by ear-
muffs vary widely in respect to their size shape seal material etc
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Noise Management Strategy
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
Day-night equivalent noise levels (Ldn) The day night equivalent noise levels of a community can be expressed as Ldn dB(A)=10 x log10 [1524 (10Ld10) + 924 (10 (Ln + 10)10)] (3)
where Ld = day-equivalent noise levels (from 6 AM - 9 PM) dB (A)
Ln = night equivalent noise levels (from 9 PM - 6 AM) dB (A) The day hours in respect to assessment of noise levels is fixed from 6 AM - 9 PM (ie 15 hrs) and night hours from 9 PM - 6 AM (ie 9 hrs) A sound level of 10 dB is added to Ln due to the low ambient sound levels during night for assessing the Ldn values
THE END
HAVE A NICE DAY
THE END
HAVE A NICE DAY