Abu Dhabi Environment,
Health and Safety Management
System Regulatory Framework
(EHSMS)
Technical Guideline - Noise
Draft
July 2009
2 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
TABLE OF CONTENTS
1. Introduction............................................................................................................ 3
2. Purpose / Objectives.............................................................................................. 4
3. Purpose / Objectives.............................................................................................. 5
3.1 Standards on Noise Measurement .............................................................. 5
3.2 Environmental Noise Terminologies and Acoustic Principles....................... 6
4. Instrumentation...................................................................................................... 7
4.1 Equipment................................................................................................... 7
4.1.1 Sound Level Meter .................................................................................. 7
4.1.2 Sound Calibrator ..................................................................................... 8
4.1.3 Microphone Support ................................................................................ 8
4.2 Calibration................................................................................................... 8
4.2.1 Certificates of Conformance .................................................................... 8
4.2.2 Regular Calibration.................................................................................. 9
5. Measurement Considerations .............................................................................. 10
5.1 Unattended Measurement......................................................................... 10
5.2 Attended Measurement ............................................................................. 10
5.3 Permanent Noise Monitoring Station ......................................................... 10
5.4 Local Meteorological Conditions................................................................ 11
6. Measurement Procedures.................................................................................... 12
6.1 Selection of Measurement Time Intervals.................................................. 12
6.2 Microphone Position.................................................................................. 12
6.2.1 Outdoor Measurement........................................................................... 12
6.2.1 Indoor.................................................................................................... 12
6.3 Observe Position....................................................................................... 13
6.4 Field Checks ............................................................................................. 13
6.5 Measurement Parameters......................................................................... 13
7. Measurement of Industrial and Commercial Activities .......................................... 15
8. Measurement of Road Traffic............................................................................... 16
9. Calculation........................................................................................................... 18
10. Reporting ............................................................................................................. 19
11. References .......................................................................................................... 20
Tables:
Table 3.01 Noise Measurement Standards and Guidelines....................................... 6
Appendix:
Noise Parameters and Terminology ............................................................................. 21
3 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
1. Introduction
In 2005 the Environment Agency - Abu Dhabi (EAD) was established under Law
No. (16) of 2005 pertaining to the Reorganization of the Abu Dhabi Environment
Agency. EAD is the general agency established as an independent entity
concerned with environmental affairs in the Emirate of Abu Dhabi.
EAD is responsible for the protection of the environment and wildlife and for the
implementation of federal and local related legislation pertaining to the
environment. The main legislation governing the environment is Federal Law
No.24 of 1999 for the Protection and Development of the Environment (hereafter
referred to as Federal Law 24). The Competent Authority is responsible for the
supervision and implementation of the Abu Dhabi Emirate Environmental Health
and Safety Management Systems (EHSMS).
This technical guideline forms part of the regulatory framework of the EHSMS
and has been prepared in accordance with the AD EHSMS Code of Practice 14 –
Noise Management, and the AD EHSMS Noise Management Standard. It is
designed to provide guidance for collecting water and groundwater samples for
the assessment of surface water and groundwater quality.
This technical guideline provides an introduction to the international standards
applicable to the measurement of environmental noise, and the general
requirements for measuring and calculating sound pressure levels.
4 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
2. Purpose / Objectives
This guideline provides information for the purpose of monitoring noise to provide
a consistent approach for assessments conducted by EAD and shall be
considered as minimum requirements. The guideline aims to provide general
direction on appropriate collection and quality assurance procedures during the
undertaking of environmental monitoring to obtain representative samples, which
faithfully represent the environment from which they were taken.
This guideline assumes that:
• an appropriate level of site conceptualization has been completed as part of a
Preliminary Site Investigation; and
• a suitable monitoring plan has been established to achieve the objectives of a
study.
This short-form guideline is not intended to be comprehensive and further
information should be sought from international standards and codes where
considered relevant for the purpose of completing noise assessment.
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3. Purpose / Objectives
Prior to undertaking air sampling, the objectives of the investigation should be
established. These should define how and why samples are to be collected.
These objectives will guide the development of the investigation strategy and
sampling plan.
The sampling objectives will be site specific and depend on the purpose of the
investigation and will be guided by the Data Quality Objectives (DQOs). These
objectives should be established at the outset of the investigation and can be
developed using the seven (7)-step process presented below:
Step 1. State the Problem - define the problem that requires assessment /
investigation.
Step 2. Identify the Goal of the Study - identify the study question(s) and state
how the environmental data will be used in meeting the objectives of the study.
Step 3. Identify the Information Inputs - identify the data and information
required to answer the study question(s).
Step 4. Define the Boundaries of the Study - define the spatial and temporal
limits of the study. Specify the target sample population for the study.
Step 5. Develop the Analytical Approach - develop an analytic approach that
will guide how you analyse the study results and draw conclusions from the data.
Step 6. Specify Performance or Acceptance Criteria - determine what data
quality assessment criteria will be used to assess data Precision, Accuracy,
Representativeness and Comparability and Completeness (PARCC parameters).
Step 7. Develop a Plan for Obtaining the Data - develop a sampling, analysis
and quality plan (SAQP) that meets the performance criteria.
A site recognisance should be undertaken prior to establishing on site to gain
information on the site characteristics and to provide input into the sampling plan.
3.1 Standards on Noise Measurement
Environmental noise assessment shall be performed in accordance with current
international standards. The International Organization for Standardization (ISO)
has issued standards on environmental noise measurement and calculations
which enable procedures to be defined and results to be compared:
Assessment of Environmental Noise:
6 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
• ISO 1996-1:2003 - Acoustics - Description, measurement and assessment of
environmental noise - Part 1: Basic quantities and assessment procedures;
and
• ISO 1996-2:2007 - Acoustics - Description, measurement and assessment of
environmental noise -- Part 2: Determination of environmental noise levels.
Calculation
• ISO 9613 - Acoustics – Attenuation of sound during propagation outdoors.
• For the noise management standards under Abu Dhabi Environment, Health
and Safety Management Framework, the applicable noise measurement
standards are shown in Table 3.01.
Table 3.01 Noise Measurement Standards and Guidelines
Noise Measurement Standard Measurement Guideline
Community Noise -- World Health Organization (1999), Guidelines for Community Noise
Construction Equipment (Sound Power Level)
European Union, Official Journal L376, 30/12/1981, p. 0049 - 0055
--
Vehicles (Motor Vehicles, Motor Cycles)
European Union, Official Journal L42, 23.2.1970, p. 16 - 20
--
Railway Equipment Official Journal of the European Union (8.2.2006), L37
--
Occupational Noise
(Noise Exposure Assessment)
� NIOSH Publication No. 98-126, Criteria for a Recommended Standard: Occupational Noise Exposure
� American National Standard Measurement of Occupational Noise Exposure, ANSI S12.12-1996 (ANSI 1991a)
--
3.2 Environmental Noise Terminologies and Acoustic Principles
The environmental noise parameters, terminologies and acoustic principles are
well defined in the standards shown in Section 2 and the literature stipulated in
Section 9. This Section highlights the characteristics of noise as follows.
Sound can be defined as any pressure variation that the human ear can detect;
20 Pa corresponds to the average person’s threshold of hearing, 100 Pa will
cause pain (i.e. threshold of pain). In view of human ears response
logarithmically rather than linearly to stimuli, acoustic parameters are expressed
as a logarithmic ratio of the measured valued to a reference value. This
7 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
logarithmic ratio is called a decibel (i.e. dB). This manageable scale from 0 dB at
the threshold of hearing (20 FPa) to 130 dB at the threshold of pain (about 100
Pa). An increase of 6 dB representing a doubling of sound pressure.
The number of pressure variations per second is the frequency of sound which is
measured in hertz (Hz). The normal hearing ranges from about 20 Hz to 20000
Hz (20kHz).
Human ears are less sensitive at very low and very high frequencies. To account
for this, weighting filters are applied to sound measuring. The most common
frequency weighting is “A-weighting”, the noise measurement results are denoted
as dB(A) which conforms approximately to the response of the human ear.
Frequency analysis shall be applied to tones measurements.
Appropriate measurement methods and parameters shall be adopted for different
types of noise including continuous noise (e.g. a running pump), intermittent
noise (e.g. an airplane passes by of which the noise level increases and
decreases rapidly) and impulsive noise (e.g. a piling driver).
The major factors affecting noise level and noise propagation:
• type of noise source (point source and line source);
• distance from the noise source;
• obstacles (e.g. buildings, noise barriers);
• ground absorption;
• reflection;
• atmosphere absorption;
• wind speed; ambient temperature and temperature gradient; and
• precipitation and humidity.
4. Instrumentation
4.1 Equipment
4.1.1 Sound Level Meter
(a) Hand-held integrated sound level meters are widely used for environmental
noise measurement as they are equipped with built in loggers enabling
recording of statistical values and enabling a wide range of parameters to
be measured and displayed simultaneously.
(b) There are two types of sound level meter, namely, Type 1 and Type 2.
Both types have the same design goals and differ mainly in the tolerance
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limits. Tolerance limits for Type 2 specifications are greater than those for
Type 1 specification.
(c) Type 1 sound level meter complying with the International Electrotechnical
Commission (IEC) standard shall be used for environmental noise
assessment:
• IEC 61672 : 2003 "Electroacoustics - sound level meters.
4.1.2 Sound Calibrator
A sound calibrator shall be used for direct calibration of sound level meter before
and after noise measurment. The sound calibrator shall comply with the
standards shown below.
• EN/IEC 60942 (2003) Class LS and Class 1; and
• ANSI S1.40 – 1984
4.1.3 Microphone Support
(a) Sound level meter and the microphone shall be supported on suitable
stands (e.g. a tripod), where appropriate.
(b) For the modern sound level measurment instrument, the microphone is
attached directly to the body of the sound level meter. When
measurements are carried out at a low sound level environment, the
microphone can be directly mounted on the tripod and a cable used to
connect the microphone to the body of the sound level meter. In doing so,
the influence of the operator on the sound level measurement results could
be minimised.
(c) The sound level meter and attached microphone can be hand-held for short
term measurments.
4.2 Calibration
4.2.1 Certificates of Conformance
In general, reputable sound measurement equipment suppliers issue a
Certificate of Conformance (COC) with each instrument. The COC states that
the instrument complies with published specifications and applicable standards.
This COC should not be considered as a Certificate of Calibration.
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4.2.2 Regular Calibration
Sound level meters and calibrators used for noise measurement shall be
calibrated at regular time intervals (usually at annually) at an accredited
calibration laboratory under the internationally recognised accreditation scheme.
Certified calibration of a sound level meter or a sound level calibrator is a full
examination of the instrument’s conformance to relevant standards. The
calibration certificate provides all test results, calibration uncertainty, location and
condition of calibration, and a traceability statement. All measurements shall
have the proper traceability according to national or international standard.
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5. Measurement Considerations
The noise measurement considerations for each occasion are vary. In general,
the factors shown below shall be considered:
• unattended or attended measurement;
• requiring a permanent monitoring station or not; and
• local meteorological conditions.
5.1 Unattended Measurement
(a) Modern sound level meters can be left on site to record environmental
noise levels, real time data and reports can be sent to the operator’s office
via a variety of data transmittal means. This is the most convenient and
economical way to measure noise level, and enables long-term monitoring.
(b) For unattended measurement, the equipment setup shall consider:
• possibility of remote access to data and setup;
• a wide measurement range;
• data logging frequency;
• sound recording for noise source identification;
• storage capacity of data;
• back-up power supply;
• weatherproof microphone and equipment; and
• free from human and other interference.
5.2 Attended Measurement
In some circumstances, it is important that the operator be present on-site:
• power source for operating the sound level meter is intermittent or unreliable;
• change the setting of the sound level meter;
• identify noise sources;
• prevent interference with equipment or measurement; and
• unexpected events or interruptions may occur.
5.3 Permanent Noise Monitoring Station
(a) Permanent or long-term noise monitoring (e.g. 24 hours a day, 365 days a
year or a long period) is applicable to the study of noise trend, noise
mapping, checking the compliance of legal noise limits, and enhancing
public awareness (allowing instant reading, long-term and short-term
11 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
average noise levels be shown on a public display system such as a
website).
(b) The basic requirements of a permanent noise monitoring station shall
include:
• type 1 sound level meter / instrument;
• a weatherproof microphone made of corrosive resistant materials and
with built-in protection against humidity;
• a mechanism allowing automatic performance of acoustic verification
and system checks;
• real time readings, frequency analysis and immediate calculation of
indices (subject to the noise monitoring objectives);
• data analysis and storage devices and information transmission system;
and
• connected to a control centre for viewing and analysing data from
several positions (where applicable).
5.4 Local Meteorological Conditions
(a) The weather conditions shall be representative of noise exposure situation
under consideration as sound pressure levels vary with the weather
conditions.
(b) In general, the measurement shall be carried out at the following
conditions:
• downwind; and
• in dry conditions (no rain) with a wind speed of less than 5 m/s.
(c) A microphone windshield shall be used for all outdoor measurements.
Windshields shall be of a type applicable to the microphone in use.
12 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
6. Measurement Procedures
6.1 Selection of Measurement Time Intervals
(a) The selected measurement intervals shall cover all significant variation in
noise emissions and propagation.
(b) For noise measurement from single events (e.g. aeroplane fly-over),
measurement time intervals shall be chosen so the sound exposure level
(LE) can be determined.
(c) If the noise displays periodicity, the measurement time interval shall cover
an integer number of at least three periods.
6.2 Microphone Position
6.2.1 Outdoor Measurement
(a) Most outdoor measurements are essentially free-field. A free field position
refers to a position where there are no reflecting surfaces other than the
ground close enough to influence the sound pressure level. The distance
from the microphone to any sound-reflecting surface apart from the ground
shall be at least twice the distance from the microphone to the dominating
part of the sound source. In general, The measurement site shall be
located at a point 1m from the exterior of the noise sensitive receiver
building façade and be at a position 1.2 m above the ground.
(b) If there is a problem with access to the normal measurement position, an
alternative position can be chose, and a correction to the measurement
shall be made (e.g. a correction of +3dB(A)) shall be made to the free field
measurement).
(c) If measuring in a free-field environment, point a free-field microphone (IEC)
directly towards the source. If using a random incidence microphone
(ANSI), orient the microphone 70o to 80o from the spimd source.
(d) The microphone shall be 1.2 m above ground level. For general noise
mapping, use a microphone height of 4.0+0.5m in multi-story story
residential areas. In one-storey residential areas and recreational areas,
use a microphone height of 1.2 m.
6.2.1 Indoor
(a) Rooms smaller than 300 m3:
13 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
• at least three discrete positions evenly distributed in the areas of the
room where affected persons preferably spend time shall be identified
for measurement.
• if dominant low-frequency noise is suspected, one of the three positions
shall be in a corner and no rotating microphone is allowed. The corner
position shall be 0.5m from all boundary surfaces in a corner with the
heaviest walls and without any wall openings near than 0.5m.
• the other microphones shall be positioned at least 0.5m from walls,
ceiling or floor, and at least 1 m from significant sound-transmission
elements such as windows or air-intake openings. The distance
between neighbouring microphone positions shall be at least 0.7 m.
(b) Rooms larger than 300 m3:
• more microphone positions can be appropriate. For low frequency
noise, one third of the extra positions shall be corner positions.
6.3 Observe Position
(a) People on site may affect the noise measurement results significant. The
noise measurement observer shall be away from the microphone. People,
other than those critical to the measurement, shall be excluded from the
measurement site, where possible.
(b) Ideally, an extension cable shall be used to connect the microphone and
the sound level meter to minimise the effect of presence of people.
6.4 Field Checks
(a) Immediately before and after each series of measurements, a calibrated
sound calibrator (generating a known sound pressure level at a known
frequency, usually 1 kHz and 94 dB) shall be applied to the microphone to
check the performance of the measurement system. Measurements may
be accepted as valid only if the calibration levels from before and after the
noise measurement agree to within 1 dB.
(b) Should measurement carried out for a long period of time (e.g. over a day
or more), the measurement system shall be checked either acoustically or
electrically at regular intervals (e.g. once or twice a day).
6.5 Measurement Parameters
Depends on the purpose of measurement and the operation of the source, sound
level can be expressed as in a variety of terms, including but are not limited to:
14 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
(a) Equivalent continuous sound pressure level, LeqT:
It is a measure of the averaged energy in a varying sound level and is
known as the essential averaged parameter. For short-term averaging, Leq
shall be measured for at least 10 minutes (ISO 1996-2:2007).
(b) Sound exposure level, LE:
LE is suitable for event measurements (e.g. rail noise, aircraft noise) /
intermittent noise. Measure each event during a time period shall be long
enough to include all important noise contributions. For a pass-by,
measure until the sound pressure level has dropped at least 10 dB below
the maximum level.
(c) N percent exceedance level, LN:
An analysis of statistical distributions of sound levels is a useful tool for
noise assessment. Apart from showing the variability of noise level, this
parameter is prominent in many standards as the basis for assessing
background noise.
(d) Impulsive noise:
Impulsive noise is noise from impacts or explosions (e.g. from a pile driver,
gunshot), it is brief and abrupt. As per ISO 1996-2:2007, there is no
generally accepted method to detect impulsive sound using objective
measurements. For describing impulsive noise, the noise source and
repetition rate shall be recorded.
(e) Tonal sound:
The presence of a prominent, discrete-frequency spectral component (tone)
Tones can be identified objectively using frequency analysis, detailed in
ISO 1996-2:2007.
(f) Low frequency noise:
Low frequency noise (e.g. large diesel engines in ships and power plants)
has significant acoustic energy. ISO 1996-2:2007 details the measurement
methods valid down to the 16 Hz octave band (the microphone shall be at
least 16 m from the nearest significant reflecting surface other than the
ground in order to be a free-field measurement).
15 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
7. Measurement of Industrial and Commercial Activities
(a) Site Selection:
Noise measurement shall be carried out at noise sensitive receiver’s
premises. If it is not possible, measurement locations shall be on publicly
accessible land at positions that are representative of the areas of the
receptor premises under consideration.
(b) Microphone Position:
The microphone shall be:
• set at 1.2 m above the ground;
• at least 1 m from any reflecting surface other than the ground; and
• orientated to the incident sound from the noise source
(c) Parameter and Measurement Intervals:
• the measurement parameters shall include but are not limited to:
� Leq, Lmax; and
� other statistical measures (e.g. L10, L50, L90);
• the measurement duration shall be representative of the situation
under consideration, noise level shall be logged at 15 minute intervals.
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8. Measurement of Road Traffic
Road traffic measurement is detailed in ISO 1996-2:2007.
(a) Site Selection:
Site selection noise measurement of a roadway depends upon the purpose
of noise measurement. In general, noise measurement will be carried out:
• at a critical noise sensitive receiver premises in order to evaluate the
noise level of a road; or
• at a location of a potential noise sensitive receiver / development.
• the received noise level is affected by:
• road geometry (e.g. intersections, ramps, grades);
• topography (e.g. nature of ground surface between the road and the
measurement site); and
• buildings and other reflective surfaces which may result in scattering of
shielding of sound.
(b) Microphone Location:
The microphone shall be:
• set 1 meter from the façade of a building on a noise sensitive receiver
premises; and
• set 1.2 to 1.5 meters above the ground or 1.2 to 1.5 meters above the
floor level of podium, if any.
The axis of maximum sensitivity of the microphone shall be normal to the
traffic stream and directed towards the road.
(c) Measurement Conditions:
Measurement shall be carried out under the conditions shown below:
• the road section for measurement shall be dry; and
• the peaks of wind noise at the microphone shall be at least 10 dB(A)
below the measured L10 noise statistics.
Traffic conditions (e.g. traffic volume, speed) of weekdays, weekends or
public holidays may be vary. Noise measurement shall be carried out at the
traffic conditions that are appropriate to the measurement objectives.
17 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
(d) Parameters and Measurement Duration:
• a series of Leq, L10 and Lmax measurements, each representing 1 hour of
traffic shall be recorded over 24 hours.
• the Lmax (sound pressure level) shall be determined based on the sound
pressure level measured during at least 30 pass-bys of vehicles of the
category considered.
• traffic conditions shall be recorded during the measurement time
interval:
• traffic count: the number of vehicle pass-bys (distinct between ‘heavy’
and ‘light’ types1);
• the average traffic speed; and
• pavement type of relevant sections of the road being measured.
(e) Measuring Equipment:
The set up of sound level meter shall be as follows:
• a-weighting frequency;
• fast time response; and
• acquiring data on Leq(1-hr) , L10(1-hr) and L10(1-hr) over 24 hours.
1 As per ISO 1996-2:2007, a heavy vehicle is one exceeding the mass 3,500Kg.
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9. Calculation
(a) Measurement uncertainty
The uncertainty of sound pressure levels depends on the sound source,
measurement time interval, weather conditions, the distance from the
sound source, the measurement method and instrumentation. Guidelines
on the estimation of uncertainty are given in Table 1 of ISO 1996-2:2007.
(b) Rounding of noise levels
All noise measurements shall be rounded to the nearest whole dB(A), with
values of 0.5 or more being rounded upwards.
(c) Noise level prediction
• noise level at a receiver point and noise propagation from one
measurement point to another can be calculated instead of being
measured.
• calculation is applicable to the situations shown below:
� noise mapping;
� comparison of alternative development and noise reduction
scenarios;
� prediction of future noise levels;
� limited access to the measurement position.
• as per ISO 1996-2:2007, there are no internationally recognized
complete calculation methods. However, a list of national calculation
methods for traffic and industrial noise is shown in the said Standard.
• when calculating instead of measuring sound pressure level, it is
necessary to have data on source noise emission, preferably as a
source sound power level and the position of a point source creating the
same sound pressure levels in the environment as the real source. In
general, this data are given in the established calculation models. In
addition, sound propagation (modeling) shall be related to well defined
meteorological and ground conditions.
• the calculation shall be calibrated. It involves some form of valid
measurements at selected positions where the measured levels can be
compared to the calculated ones.
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10. Reporting
The noise measurement report shall provide information on the items shown
below:
• the purpose of measurement;
• the standard adopted for measurement;
• date, time and location for measurement;
• time of intervals and duration of each measurement (start and stop time),
time and duration of interruption of measurement (if any);
• number of measurement made;
• meteorological conditions (including wind speed, wind direction, cloud cover,
temperature, barometric pressure, humidity, rain);
• equipment (the model and serial numbers of sound level meter and acoustic
calibrator);
• equipment calibration certificate shall attached with the noise measurement
report;
• equipment set up (e.g. coordinates of the sound level meter / microphone and
its height above ground; distance between the microphone and façade, time
of intervals and duration for the measurements, fast / slow response mode,
frequency band, measurement range);
• description of monitoring location and sound sources under investigation (e.g.
any identified noise source);
• other necessary information as per the objective of noise monitoring (e.g.
traffic count);
• measurement results and their correction and adjustment (where
appropriate);
• method(s) used to extrapolate the measured values to other conditions
(where appropriate); and
• calibration data acquired before and after the measurement.
20 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
11. References
• American National Standard Measurement of Occupational Noise Exposure,
ANSI S12.12-1996 (ANSI 1991a).
• Bruel & Kjaer (1984), Measuring Sound.
• Bruel & Kjaer (2001), Environmental Noise.
• European Union, Official Journal L376, 30/12/1981, p. 0049 – 0055.
• European Union, Official Journal L42, 23.2.1970, p. 16 – 20.
• ISO 1996-2, Acoustics – Description, Measurement and Assessment of
Environmental Noise – Part 2: Determination of Environmental Noise Level.
• NIOSH Publication No. 98-126, Criteria for a Recommended Standard:
Occupational Noise Exposure.
• Official Journal of the European Union (8.2.2006), L37.
• World Health Organisation (1999), Guidelines for Community Noise.
21 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
Appendix A
Noise Parameters and Terminology
22 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
A wide range of parameters are used to assess environment noise, the definitions of this
parameters are well addressed in the international recognized standards. The
parameters used commonly in noise measurement are shown below.
(a) Sound Pressure and Sound Pressure Level
Sound pressure is the instantaneous difference between the actual pressure
produced by a sound wave and the average or barometric pressure at a given
point in space, it is measured in pascals (Pa), 1 Pa = 1 newton per square metre
(N/m2).
Sound Pressure Level (SPL, expressing in dB) = 20 log10 (p/p0)
dB: The sound pressure level of a sound in decibels, is equal to 20 times the
logarithm to base 10 of the ratio of the RMS sound pressure to the reference
sound pressure 20 mPa (2 × 10-5 Pa).
(b) A Weighted Sound Level
‘A weighted sound level” is a measure of sound pressure level designed to reflect
the acuity of the human ear. Human ear is less efficient at low and high
frequencies than at medium or speech-range frequencies. For describing a sound
containing a wide range of frequencies in a manner representative of the ear’s
response, it is necessary to reduce the effects of the low and high frequencies with
respect to the medium frequencies. The resultant sound level is called A-weighted
(the unit is dB(A)) which is commonly called noise level.
(c) A Weighted-Equivalent Continuous Noise Level
A weighted-equivalent continuous noise level (LAeq,T), a widely used noise
parameter, calculates a constant level of noise with the same energy content as
the varying acoustic noise signal being measured:
• ‘A’ denotes that A-weighting has been included;
• ‘eq’ indicates that an equivalent level has been calculated; and
• ‘T’ denotes the duration of measurement.
(d) Sound Exposure Level
Sound exposure level (SEL, expressing in LAE) is closely related to LAeq for
assessment of events (e.g. aircraft). The LAE value contains the same amount of
acoustic energy over a normalised one second period as the actual noise event
under consideration.
(e) Sound Power and Sound Power Level
Sound power (expressing in watt) if the total sound energy radiated by a sound
source per unit time, it is essentially independent of the surroundings. Given the
23 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
sound power is known, the sound pressure at a point can be calculated according
to acoustic principles.
Sound Power Level (LW or PWL), in dB, at which a source produces sound energy
per unit of time, usually given in octave bands. A power expressed in dB above
the standard reference level of 1 picowatt.
Sound Power Level = 10 log10 (W/W0), where W is the emitted power and W0 is the
reference power (10-12 W).
(f) Fast, Slow and Impulse Time Weightings
For the provision of visual indication of fluctuating noise levels, standardised
response times (Fast - F, Slow - S and Impulse - I) are originally built into noise
measuring instruments.
(g) LAFMax, LASMax or LAIMax
Maximum A-weighted noise level measured with Fast (F), Slow (S) or Impulse (I)
time weighting. They are the highest level of environmental noise occurring during
the measurement time.
(h) LAFN, T Percentile Levels
The level of A-weighted noise exceeded for N% of the measurement time.
24 of 24 AD EHSMS – Technical Guideline – Noise Draft July 2009
© Environment Agency Abu Dhabi 2009
This document is and shall remain the property of the Environment Agency Abu Dhabi. The document
may only be used for the purposes for which it was intended. Unauthorised use or reproduction of this
document is prohibited.
Document Status
Reviewer Approved for Issue Rev No.
Author Name Signature Name Signature Date
A. G. Jukes
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