EN ISO 9612:2025

SLOVENSKI STANDARD
01-november-2025
Nadomešča:
SIST EN ISO 9612:2009
Akustika - Določanje izpostavljenosti hrupu v delovnem okolju - Metodologija (ISO
9612:2025)
Acoustics - Determination of occupational noise exposure - Methodology (ISO
9612:2025)
Akustik - Bestimmung der Lärmexposition am Arbeitsplatz - Verfahren der
Genauigkeitsklasse 2 (Ingenieurverfahren) (ISO 9612:2025)
Acoustique - Détermination de l'exposition au bruit en milieu de travail - Méthodologie
(ISO 9612:2025)
Ta slovenski standard je istoveten z: EN ISO 9612:2025
ICS:
13.140 Vpliv hrupa na ljudi Noise with respect to human
beings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 9612
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2025
EUROPÄISCHE NORM
ICS 13.140 Supersedes EN ISO 9612:2009
English Version
Acoustics - Determination of occupational noise exposure -
Methodology (ISO 9612:2025)
Acoustique - Détermination de l'exposition au bruit en Akustik - Bestimmung der Lärmexposition am
milieu de travail - Méthodologie (ISO 9612:2025) Arbeitsplatz - Methodik (ISO 9612:2025)
This European Standard was approved by CEN on 5 March 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9612:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 9612:2025) has been prepared by Technical Committee ISO/TC 43 "Acoustics"
in collaboration with Technical Committee CEN/TC 211 “Acoustics” the secretariat of which is held by
DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2025, and conflicting national standards
shall be withdrawn at the latest by December 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 9612:2009.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 9612:2025 has been approved by CEN as EN ISO 9612:2025 without any modification.

International
Standard
ISO 9612
Third edition
Acoustics — Determination of
2025-05
occupational noise exposure —
Methodology
Acoustique — Détermination de l’exposition au bruit en milieu de
travail — Méthodologie
Reference number
ISO 9612:2025(en) © ISO 2025
ISO 9612:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 9612:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Instrumentation . 5
5.1 Sound level meters and personal sound exposure meters .5
5.2 Calibrator . .5
5.3 Periodic verification .6
6 Methodology – Chronological steps . 6
6.1 Step 1: Work analysis .6
6.2 Step 2: Selection of the measurement strategy .6
6.3 Step 3: Measurements .6
6.4 Step 4: Error handling and uncertainties .6
6.5 Step 5: Calculation and presentation of results and uncertainty .6
7 Work analysis . 6
7.1 General .6
7.2 Defining homogeneous noise exposure groups (HEG) .7
7.3 Determination of a nominal day .7
8 Selection of measurement strategies. 8
8.1 General .8
8.2 Measurement strategies .8
9 Strategy 1 – Task-based measurement . 8
9.1 Dividing the nominal day into tasks .8
9.2 Duration of tasks .8
9.3 Measurement of L for tasks .
pT,,Aeq
m
9.3.1 General .9
9.3.2 Number of measurements . .9
9.3.3 Time and duration of measurements .10
9.3.4 Calculation of the A-weighted equivalent continuous sound pressure level .10
9.4 Calculation of contribution from each task to daily noise exposure level .10
9.5 Determination of daily noise exposure level .11
10 Strategy 2 – Job-based measurement .12
10.1 General . 12
10.2 Measurement plan – Number, duration and distribution of measurements . 12
10.3 Measurements . 12
10.4 Determination of daily noise exposure levels for workers in a homogeneous noise
exposure group . 13
11 Strategy 3 — Full-day measurement .13
11.1 General . 13
11.2 Observing work activities and monitoring measurements .14
11.3 Measurements .14
11.4 Determination of daily noise exposure level . 15
12 Measurements .15
12.1 Selection of instrumentation . 15
12.2 Field calibration . 15
12.3 Instrument worn by the worker . 15

iii
ISO 9612:2025(en)
12.4 Integrating-averaging sound level meter .16
13 Sources of uncertainty and errors . 17
13.1 General .17
13.2 Mechanical impacts on microphone .17
13.3 Wind and airflows .18
13.4 Relevance of sound contributions .18
14 Calculation of measurement uncertainties and presentation of the final results .18
15 Information to be reported .18
Annex A (informative) Example of a checklist to ensure that significant noise events are
detected during the work analysis .21
Annex B (informative) Guidance to the selection of measurement strategy .22
Annex C (normative) Evaluation of measurement uncertainties .25
Annex D (informative) Example showing calculation of daily noise exposure level using task-
based measurements .34
Annex E (informative) Example showing calculation of daily noise exposure level using
job-based measurements .39
Annex F (informative) Sample calculation of daily noise exposure level using full-day
measurements .42
Annex G (informative) Example calculation of daily noise exposure level for flexible workers .45
Annex H (normative) Uncertainty calculation for peak sound pressure levels .49
Bibliography .53

iv
ISO 9612:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 211,
Acoustics, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO 9612:2009), which has been technically
revised.
The main changes are as follows:
— A reshaping of the guidance on measurement of L for the task-based strategy (9.3).
pT,,Aeq
m
— A revision of the measurement plan for the job-based strategy (10.2).
— The addition of Homogeneous noise Exposure Groups (HEG) sampling requirements for the full-day
measurement strategy and the addition of criteria to validate sampling (11.3).
— Some precisions and clarifications on the instrumentation section.
— Some additions to the test report section: number of peak events, L .
EX,,89h 5 %
— The addition of C.7 in Annex C, which gives the formulae to calculate the measurement uncertainty
when multiple nominal days are used. An Annex H is also introduced to clarify uncertainty of peak
measurements.
— The introduction of a new Annex G.
— The introduction of a new Annex H.
— A full revision of the Excel calculation file attached to this document.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO 9612:2025(en)
Introduction
This document provides a stepwise approach to the determination of occupational noise exposure from
noise level measurements. The procedure contains the following major steps: work analysis, selection of
measurement strategy, measurements, error handling and uncertainty evaluations, calculations, and
presentation of results. This document specifies three different measurement strategies: task-based
measurement; job-based measurement; and full-day measurement. This document gives guidance on
selecting an appropriate measurement strategy for a particular work situation and purpose of investigation.
This document also provides an informative spreadsheet to allow calculation of measurement results and
uncertainties. ISO is not responsible for errors that shall arise or occur with the use of this spreadsheet.
This document recognizes the use of hand-held sound level meters as well as personal sound exposure
meters. The methods specified optimize the effort required for obtaining a given accuracy.

vi
International Standard ISO 9612:2025(en)
Acoustics — Determination of occupational noise exposure —
Methodology
1 Scope
This document specifies a method for measuring workers’ exposure to noise in a working environment and
calculating the noise exposure level. This document deals with A-weighted levels but is applicable also to
C-weighted levels. Three different strategies for measurement are specified. The method is applicable for
detailed noise exposure studies or epidemiological studies of hearing damage or other adverse effects.
The measuring process requires observation and analysis of the noise exposure conditions so that the quality
of the measurements can be controlled. This document provides methods for estimating the uncertainty of
the results.
This document is not intended for assessment of masking of oral communication or assessment of infrasound,
ultrasound and non-auditory effects of noise. It does not apply to the measurement of the noise exposure of
the ear when hearing protectors are worn.
Results of the measurements performed in accordance with this document can provide useful information
when defining priorities for noise control measures.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 1999, Acoustics — Estimation of noise-induced hearing loss
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
IEC 60942, Electroacoustics — Sound calibrators
IEC 61252, Electroacoustics — Specifications for personal sound exposure meters
IEC 61672-1, Electroacoustics — Sound level meters — Part 1: Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

ISO 9612:2025(en)
3.1
A-weighted equivalent continuous sound pressure level
L
pT,A,eq
ten times the logarithm to the base 10 of the ratio of the time average of the square of the A-weighted sound
pressure, p , during a stated time interval of duration T (starting at t and ending at t ), to the square of a
A 1 2
reference value, p , expressed in decibels:
t
 2 
pt dt
()
A
 ∫ 
t
T
L =10 lg dB
 
pT,,Aeq
 p 
 
 
where the reference sound pressure, p , is 20 μPa
[9]
Note 1 to entry: Adapted from ISO/TR 25417:2007 .
3.2
A-weighted noise exposure level normalized to an 8 h work day

L
EX,8h
daily noise exposure level, in decibels, given by the formula:
T 
e
LL=+10 lg dB
EX,,8hApT,eq
 
e
T
 
where
L
is the A-weighted equivalent continuous sound pressure level for T ;
pT,,Aeq
e
e
T is the effective duration, in hours, of the working day;
e
T is the reference duration, T = 8 h.
0 0
Note 1 to entry: If the effective duration of the working day, T , is equal to 8 h, then L equals L .
e EX,8h p,,Aeqh8
Note 2 to entry: If the average or normalized exposure over a number of days is desired, the following formula can be used:
1 X
 01, ⋅L 
EX,,8h x
L =10 lg 10 dB
EX,8h ∑
 
x=1
X
 
where L is the daily noise exposure level for day x.
EX,8h, x
The value of X is chosen according to the purpose of the averaging process. For example, X = 5 leads to a daily noise
exposure level normalized to a nominal week of five 8 h working days.
[9]
Note 3 to entry: This definition differs from that given in ISO/TR 25417:2007 .
3.3
nominal day
working day over which it is chosen to determine the noise exposure
Note 1 to entry: The nominal day is determined from the work analysis and depends on the purpose of the
measurements. See also 7.3.
Note 2 to entry: The noise exposure level is normally calculated on a daily basis, but there can be circumstances where
the use of weekly or longer noise exposure periods is considered appropriate.
Note 3 to entry: The nominal day can be a synthesized working day that includes fragments of different real working
days of a week or of several consecutive weeks.

ISO 9612:2025(en)
3.4
C-weighted peak sound pressure level
L
p,Cpeak
ten times the logarithm to the base 10 of the ratio of the square of the C-weighted peak sound pressure,
p , to the square of a reference value, p , expressed in decibels
Cpeak 0
p
Cpeak
L =10lg dB
p,Cpeak
p
where the reference sound pressure, p is 20 μPa
3.5
task
distinct part of a worker´s occupational activity
Note 1 to entry: Figure 1 illustrates the hierarchy of jobs and tasks.
3.6
job
overall occupational activity that is carried out by a worker, consisting of all the tasks performed by the
worker during the entire working day or shift
Note 1 to entry: A worker often has a job title that describes his or her job, sometimes complemented with an additional
description to ensure clear identification, e.g. "welder - process line A".
Note 2 to entry: Figure 1 illustrates the hierarchy of jobs and tasks.
Key
Job 1 scaffolders Task 1 planning
Job 2 welders Task 2 grinding
Job 3 painters Task 3 welding
Job 4 store keepers
Figure 1 — An example illustrating the hierarchy of jobs and tasks
4 Symbols
Symbol Description Unit
c sensitivity coefficient related to each input quantity
i
c sensitivity coefficient associated with job noise level sampling
c sensitivity coefficient associated with noise level sampling of task m
1a,m
c sensitivity coefficient associated with estimation of duration of task m
1b,m
c sensitivity coefficient associated with measurement instrumentation
ISO 9612:2025(en)
Symbol Description Unit
c sensitivity coefficient associated with microphone position
i task sample number
I total number of task samples
j number of observations of task duration
J total number of observations of task duration
k coverage factor related to a confidence interval
K denominator as given in C.3.3, Note 2
N
L A-weighted noise exposure level normalized to a nominal 8 h working day dB
EX,8h
A-weighted noise exposure level normalized to a nominal 8 h working day averaged over a dB
L
EX,8h
number of days
L A-weighted noise exposure level including its associated uncertainty - 95 % level of confi- dB
EX,8h,95 %
dence
NOTE Statistically, assuming a normal distribution of the noise exposure measurements,
for 95 % of the samplings the noise exposure will be equal to or below this level
L A-weighted noise exposure level of task m contributing to the daily noise exposure level dB
EX,8h,m
L A-weighted equivalent continuous sound pressure level over a period T dB
pT,,Aeq
A-weighted equivalent continuous sound pressure level for task m dB
L
pT,,Aeq
m
A-weighted equivalent continuous sound pressure level of sample i for task m dB
L
pT,,Aeq ,i
m
L A-weighted equivalent continuous sound pressure level of job sample n dB
pT,,Aeq
n
A-weighted equivalent continuous sound pressure level for the effective duration of the dB
L
pT,,Aeq
e
working day
L C-weighted peak sound pressure level dB
p,Cpeak
m task number
M total number of tasks
n Job/day sample numbers
N total number of job/day samples
n number of workers in a homogeneous noise exposure group
G
−5
Pa
p reference sound pressure; p = 2 × 10 Pa
0 0
p A-weighted sound pressure Pa
A
C-weighted peak sound pressure Pa
p
Cpeak
Q correction for measurement instrumentation dB
correction for microphone position dB
Q
T time period over which an average is taken h
h
T reference duration; T = 8 h
0 0
T effective duration of the working day h
e
duration of task m h
T
m
duration of sample j of task m h
T
mj,
T duration of sample n (job or full-day approaches) h
n
U expanded uncertainty dB
u combined standard uncertainty dB
standard uncertainty of each input quantity dB
u
i
standard uncertainty of the energy average of a number of measurements of A-weighted dB
u
equivalent continuous sound pressure level
standard uncertainty due to noise level sampling of task m dB
u
1,am
ISO 9612:2025(en)
Symbol Description Unit
u standard uncertainty due to the estimation of duration of task m h
1,bm
standard uncertainty due to the instrumentation dB
u
standard uncertainty due to the instrumentation in the task method dB
u
2,m
u standard uncertainty due to microphone position dB
expanded uncertainty for multiple nominal days dB
U
x day number for multiple nominal days
X total number of days for multiple nominal days
5 Instrumentation
5.1 Sound level meters and personal sound exposure meters
Measurements can be made by using either integrating-averaging sound level meters or personal sound
exposure meters.
Sound level meters, including the microphone and associated cables, shall meet the requirements for
IEC 61672-1, class 1 or class 2 instrumentation. Class 1 instrumentation is preferred and should be used
when measuring at very low temperatures or when the noise is dominated by high frequencies (see also
NOTES 2 and 4).
Personal sound exposure meters, including the microphone and cable, shall meet the requirements specified
in IEC 61252. Personal sound exposure meters also fulfilling the requirements of IEC 61672-1, class 1, are
recommended when measuring at very low temperatures or when the noise is dominated by high frequencies
(see also NOTES 2 and 4).
NOTE 1 Personal sound exposure meter is often referred to as "noise dose meter" or "noise dosimeter".
NOTE 2 For IEC 61672-1, class 1 instruments, the specified tolerance limits are applied for the temperature range
from -10 °C to +50 °C. For instrumentation in accordance with IEC 61672-1, class 2, and for personal sound exposure
meters in accordance with IEC 61252, the influence of variations in the air temperature on the measured signal level
is specified over the range from 0 °C to +40 °C. In order to maintain accuracy when performing measurements outside
this temperature range, it can be necessary to use an instrument for which the manufacturer specifies compliance for
a wider temperature range. Alternatively, a sound level meter in accordance with IEC 61672-1, class 1, can be selected.
In cold conditions, the measuring instrument can be kept warm, e.g. under clothing, such that only the microphone is
exposed to low temperatures.
NOTE 3 The choice of the instrumentation influences the uncertainty of the measurements.
NOTE 4 For personal sound exposure meters, IEC 61252 allows wide tolerances in the frequency characteristics
above 4 000 Hz, which can lead to incorrect measurement of high frequency sound such as that from air nozzles. In
order to reduce the uncertainty when measuring noise dominated by high frequencies, it can be necessary to use
a measuring instrument for which the manufacturer specifies high frequency characteristics within a narrower
tolerance range. Alternatively, a sound level meter specified in accordance with IEC 61672-1, class 1 or 2, can be selected
in the following way. Due to the tolerances defined in IEC 61672-1, class 2 sound level meters can be appropriate for
measurements up to 8 kHz. Measurements up to 16 kHz can only be performed by using a sound level meter meeting
the requirements of class 1. Assessment of airborne sound beyond 16 kHz can produce unreliable results even when
using class 1 sound level meters (see also Clause 1).
Personal sound exposure meters can have a cut-off level at around 70 dB. This can influence the value of the
measured noise exposure, but only at low exposure levels.
5.2 Calibrator
For class 1 measuring instrument, the sound calibrator shall conform to class 1 specifications of IEC 60942.
For class 2 measuring instrument, the sound calibrator shall conform to either class 1 or 2 specifications of
IEC 60942.
ISO 9612:2025(en)
5.3 Periodic verification
The calibration of the sound calibrator and the compliance of the integrating-averaging sound level meter
with the requirements of IEC 61672-1, IEC 61252 and other relevant standards shall be verified at intervals
in a laboratory making calibrations traceable to appropriate standards.
Unless national regulations dictate otherwise, it is recommended that the sound calibrator and the
compliance of the integrating-averaging sound level meter with the requirements of IEC 61672-1 be verified
at intervals not exceeding 2 years.
The date for the last periodic verification, the name of the laboratory that performed it, and the outcome
shall be recorded and given in the measurement report.
6 Methodology – Chronological steps
6.1 Step 1: Work analysis
The work analysis shall provide sufficient information about the work and the workers under consideration
so that an appropriate measurement strategy can be selected and measurements can be planned. Work
analysis shall be carried out in accordance with Clause 7.
6.2 Step 2: Selection of the measurement strategy
A measurement strategy shall be selected from task-based measurement, job-based measurement and full-day
measurement as specified in Clause 8. More than one measurement strategy can be used, if relevant (see B.6).
6.3 Step 3: Measurements
The basic measurement quantity shall be L . In addition, L shall be measured, if relevant. The
pT,,Aeq p,C
peak
measurements shall follow the chosen strategy as specified in one of Clauses 9, 10 or 11 and comply with the
requirements of Clause 12.
6.4 Step 4: Error handling and uncertainties
Sources of errors and uncertainties that shall influence the result shall be evaluated in accordance with
Clauses 13 and 14.
6.5 Step 5: Calculation and presentation of results and uncertainty
Calculate L as specified for the selected strategy (see Clauses 9, 10, and 11) and the uncertainty as
EX,8h
specified in Annex C. The results and uncertainties can be calculated by using the spreadsheet in https://
standards .iso .org/ iso/ 9612/ ed -3/ en.
The results shall be presented as specified in Clause 15. Annexes D, E and F provide practical examples for
the task-based, job-based, and full-day measurements, respectively.
7 Work analysis
7.1 General
Work analysis is required in all situations. It shall provide the information necessary to
a) describe the activities of the enterprise and the jobs of the workers under consideration,
b) define homogeneous noise exposure groups (see 7.2), if relevant,
c) determine a nominal day or several nominal days, as appropriate, for each worker or group,

ISO 9612:2025(en)
d) identify tasks which make up the jobs, if relevant,
e) identify possible significant noise events,
f) choose the measurement strategy, and
g) establish the measurement plan.
The work shall be analysed with emphasis put on production, process, organization, workers and activities.
The measurements shall be performed by using the task-based, job-based or full-day strategy. Whichever
strategy is used, it is essential to identify all events which are significant with regard to noise exposure and
to make sure that the measurement plan takes them into account. See Annex A for an example of a checklist.
NOTE The order in which the items above are performed can depend on the complexity of the situation on site.
The items are strongly connected, and the process can therefore be iterative in complex situations, i.e. increased
knowledge about one of the items can result in a new description or redefinition of others.
7.2 Defining homogeneous noise exposure groups (HEG)
Measurement efforts can be reduced by defining homogeneous noise exposure groups. These are groups
of workers that are performing the same job and are expected to have similar noise exposures during the
working day. If used, the homogeneous noise exposure group shall be clearly identified.
NOTE The term "similar noise exposure group" is sometimes used instead of "homogeneous noise exposure group".
Homogeneous noise exposure groups can be defined in a number of ways. For example, it may be possible to
define such groups according to job title, function, work area or profession. Alternatively, the groups can be
defined by analysing the work according to production process or work activity criteria.
In whichever way the groups are defined, they should be verified in consultation with the workers and
supervisors, and ultimately by evaluating the measurement results, see 10.4.
7.3 Determination of a nominal day
A nominal day, including work periods and breaks, shall be determined in consultation with both workers
and management. The work shall be studied in order to obtain an overview and understanding of all factors,
which can influence the noise exposure. See Annex A for more details.
Issues that shall be addressed are:
a) tasks (content and duration) and variation within tasks;
b) main noise sources and noisy work areas;
c) work pattern and any significant noise events, resulting in a change of the noise level or which can result
in peak levels exceeding regional regulation limits;
d) number and duration of breaks, meetings, etc., and whether they should be regarded as a part of the
nominal day.
Measurements shall be planned to ensure that all significant noise events are included. For each of the events,
it shall be recorded when it occurred, its nature, duration and daily frequency. An example of a checklist to
ensure that significant noise events are detected during the work analysis is given in Annex A.
In some cases, the work and consequently the noise exposure, varies from day to day so that there is no
typical daily exposure, e.g. for workers who work in different locations or jobs each day. In these cases, the
nominal day can be defined from work situations during several days, e.g. one week. See also Notes to 3.2
and 3.3.
Any indicators that characterize the work with respect to noise shall be identified, quantified, and reported.
Examples of such indicators are: type of production in process; materials; quantities; thickness of work
pieces; adjustment; speed; and number of workers involved.

ISO 9612:2025(en)
If the purpose of measurements is to estimate the long-term risk of hearing impairment of workers, then the
nominal day chosen shall be representative of the average exposure over the period under consideration, in
accordance with ISO 1999.
8 Selection of measurement strategies
8.1 General
The selection of an appropriate measurement strategy is influenced by several factors such as the purpose
of the measurements, complexity of the work situation, number of workers involved, effective duration of
the working day, time available for measurement and analysis, and amount of detailed information required.
8.2 Measurement strategies
Three measurement strategies for the determination of workplace noise exposure are offered by this
document. These are:
a) task-based measurement: the work performed during the day is analysed and split up into a number of
representative tasks, and for each task separate measurements of sound pressure level are taken (see
Clause 9);
b) job-based measurement: a number of random samples of sound pressure level are taken during the
performance of particular jobs (see Clause 10);
c) full-day measurement: sound pressure level is measured continuously over complete working days (see
Clause 11).
Detailed guidance on the choice of the measurement strategy is given in Annex B.
A guidance for the evaluation of the daily noise exposure level of workers who perform several types of
work in a same day or over several days is provided in Annex G.
9 Strategy 1 – Task-based measurement
9.1 Dividing the nominal day into tasks
For the workers or homogeneous noise exposure groups under evaluation, the nominal day shall be divided
into tasks. Each task shall be defined such that L is likely to be repeatable.
...