Work environmentksz.pwr.edu.pl/wp-content/uploads/katjac8795/pdf/3_Noise...Hearing loss Prolonged...
Transcript of Work environmentksz.pwr.edu.pl/wp-content/uploads/katjac8795/pdf/3_Noise...Hearing loss Prolonged...
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Work environment
Noise
Why it is important problem?
1.7 million workers in the U.S. between 50-
59 years of age have compensable noise-
induced hearing loss
About 17% of the working population are
employed in jobs with noise exposure higher
than the OSHA standard of 85 dBA
In Poland ~13 milion citizens are in risk
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Occupations under hazardous conditions in Poland,
2011
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Sound
Sound
Normal Atmospheric Pressure
Sound
Pressure
A pressure wave traveling through air, water or othermedia that the human ear can detect.
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Sound radiates outward from the source
in all directions and the sound intensify
diminishes with distance from the source
Sound characteristics
Frequency
Number of times per
second a vibrating
body traces one
complete cycle of
motion
Cycles/second =
Hertz ( Hz) = f
Sound chaaracteristics
Wavelength (λ)
Distance measured between two analogous
points on two successive parts of a wave
Distance a sound wave travels in one cycle
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Sound characteristics
Velocity (c)
The speed at which analogous pressure points on
successive parts of a sound wave pass a given point
Speed of sound is always equal to the product of
wavelength and the frequency
c = f * λ
Speed of sound
344 m/s in air
1433 m/s in water
3962 m/s in wood
5029 m/s in steel
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Sound characteristics
Sound Pressure Level (Lp)
the sound pressure referenced to 20 µPa,
which is the threshold of hearing at a
reference frequency of 1000Hz
Unit: decibel [dB]
Lp = 10 log (p/p0)2
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Decibel
One dB is the minimum difference in
loudness that is usually perceptible
By definition, the decibel is a dimensionless
unit used to express the logarithm of the
ratio of a measured quantity to a reference
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Source
Threshold of Hearing (TOH)
Rustling Leaves
Whisper
Normal Conversation
Busy Street Traffic
Vacuum Cleaner
Large Orchestra
Walkman at Maximum Level
Front Rows of Rock Concert
Threshold of Pain
Intensity
Level
0 dB
10 dB
20 dB
60 dB
70 dB
80 dB
98 dB
100 dB
110 dB
130 dB
# of Times
Greater Than
TOH
100
101
102
106
107
108
109.8
1010
1011
1013
Military Jet Takeoff 140 dB 1014
Instant Perforation of Eardrum 160 dB 1016
Distance Vs Loudness (db)
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65
70
75
80
85
90
0 1 2 3 4 5 6 7 8 9 10
Distance from Origin
Lo
ud
ness (
db
)
How Much Does the Sound Intensity
Diminish with Distance from the Source?
Distance 1 or D1
Distance 2 or D2
The Change in the Decibels from D1 to D2 is 20 * log (D2/D1)
When the distance doubles, the decline is ~ 6 db
Why Does the Sound not Decline as
Computed?
Sound is reflected from
the concrete floor
Sound is reflected from
the block walls
Sound is reflected from
other objects
Hearing
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Hearing sense functions
Main defense sense – receive far signals independly
from their layout
Localize pottentally dangerous objects in space
(direction and distance)
Specific sounds alarm for the whole organismus
(„fight or escape”)
Homing system for sight
Interpersonal communication
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HOW DO WE HEAR?
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SOUND RECEPTORS
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Audiogram
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Noise
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Noise
Any unwanted sound or vibratory energy
Noise Induced Hearing Loss
Exposure to noise causes a
loss of sensitivity to high
frequency (high pitch)
sound
Continued exposure
results in damage to mid
frequency region
One can experience
progressive high
frequency hearing loss
and not be aware of it
until it becomes severe
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Noise is possibly annoying,
but it is not physically painful
The effects of noise on hearing loss
occur slowly, unnoticed from day to
day exposure to equipment
surrounding workers
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Fellow Workers on most construction projects
also do not wear hearing protection
Hearing protection might be regarded
as a bother to many construction
workers
Noise measuring
A weighted scale
Gives a single number measure of noise level by
integrating sound levels at all frequencies
Gives a scale for noise level as experienced or
perceived by the human ear
Sound level meter – dosimeter - Measures and
stores sound level measurements and
integrates these measurements over time,
providing an average noise exposure reading for
a given period of time
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Noise classification
infrasonic (2-50 Hz)
Audible (20Hz – 10 000 Hz)
ultrasonic (10-100 kHz)
Noise classification
Continous
Impact
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Noise classification
industrial
municipal
Traffic
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Industrial noise
Energetics
Wood industry
Stone treatment
Trade and servises
Metal industry
Mining
Entertainment places (i.e. clubs)
Food industry
Other
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Acoustic map of Wroclaw
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Noise influence on human organismus
Impact on hearing organ
Adaptation
Fatigue
Acoustic trauma
Physiological impact
Psychological – anxiety disorders,
deconcentration, longer reaction time
Hormonal
Equilibrium disorders
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Hearing loss
Prolonged exposure to sound
levels greater than 85 decibels
will result in hearing loss
Occupational hearing loss is the hearing
impairment of one or both ears, partial or
complete, that results from one’s employment
Acoustic trauma – damage to the sensorineural
elements of the inner ear due to injury
Noise-induced hearing loss – cumulative permanent
sensorineural hearing loss
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Damaging of Corti
aparatus
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Noise Exposure Factors
Intensity Loudness
Frequency
Duration Length of exposure
Distance from the source
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Noise Exposure Standards
Occupational Safety And Health
Administration’s(OSHA) Noise Standard,
Code of Federal Regulations Section 29, Part
1910 Sub Part 95 (CFR 29 1910.95)
Permissible Exposure Limit (PEL) - 90 dB
Polish law – 85 dB
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How can we easy estimate the noise
level? Rule of Thumb
If you have to raise your voice to be heard
by someone less than 1 m away, than you
need hearing protection
Signs of risk
Ringing in the ears
the need to shouting to the co-worker
temporary hearing loss
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Doubling Rate
The number of decibels of continuous noise
exposure which results in a halving of the
allowed exposure time
OSHA
8 hours at 90 dB
4 Hours at 95 dB
2 hours at 100 dB
1 hour at 105 dB
30 minutes at 110 dB
15 minutes at 115 dB
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Noise reduction methods
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Noise reduction methods
Technical
Emission reduction silent devices,
automatization, maintenance
Transmission reduction housings, screens, traps
Immission reduction personal hearing protection
Administrative
Law regulations
Organizational work time, breaks, workstation
layout
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Soundproofing housings
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Acoustic screens
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Acoustic screens and traps
Source of
noise
Reflecting
ceiling
Screen
Source of
noise
Sound
absorbing
material
Screen
Personal Hearing Protection
NRR - Noise Reduction Rating
In order to ensure maximum hearing
protection two variables are important:
the fit of the hearing protector
the importance of wearing the hearing protector
during the entire time the wearer is exposed to
excessive or dangerous noise levels
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Personal hearing protection
Types
Canal Caps
Earplugs
Ear Muffs
NRR of 22 NRR of 29 NRR of 30
DOUBLING UP!
Use of insert earplugs and circumaural earmuffs together
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Active method
Additional sound
source
Noise
Silence
Basic principles
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1. Reduce the noise level of the
source itself
Identify why the machine makes noise
Examine the possibility of making design
changes
1. Maintenance
2. Substitution of materials (plastic for metal)
3. Substitution of equipment
Maintenance
replacement or adjustment of worn or loose
parts
balancing of unbalanced equipment
lubrication of moving parts
use of properly shaped and sharpened
cutting tools
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Substitution of equipment
electric for pneumatic (e.g. hand tools);
stepped dies rather than single-operation
dies
rotating shears rather than square shears
hydraulic rather than mechanical presses
presses rather than hammers
belt conveyors rather than roller conveyors
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2. Enclose the source
This stops the sound emission at the source
Make sure the reduction is sufficient
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3. Increase the distance between the
source and nearby people
This will help to decrease the sound before
it reaches the people around it
Noise levels decrease approximately with
the square of the distance between the
source and the receiver
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4. Place sound-absorbing and
reflecting barriers in the noise path
Absorbing materials will help reduce the
sound level energy
Reflecting barriers will direct some of that
energy away from surrounding personnel so
that the sound wave will need to go a large
distance before encountering people
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