AD EHSMS - Technical Guideline - Noise

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


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.


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.


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:


• 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


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


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.


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.


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


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.


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:


• 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:


(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).


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.


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.


(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.


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.


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.


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.


Appendix A

Noise Parameters and Terminology


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


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.


© 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

AD EHSMS - Technical Guideline - Noise

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