ISO 15664:2025
(Main)Acoustics — Noise control design procedures for open plant
Acoustics — Noise control design procedures for open plant
This document defines the procedures for noise control of primarily open plants and the requirements on equipment suppliers for reporting and testing of noise. It is applicable to the following: — specification of procedures for noise control during engineering of a new plant and modification/extension of existing plants (construction and commissioning noise procedures are outside the scope of this document); — definition of responsibilities of parties involved, viz. “end-user”, “engineering contractor” and “equipment supplier”; — description of general procedures to arrive at noise requirements for individual equipment, based on overall noise requirements for the plant. Input to purchase specifications is presented in REF Annex_sec_A \r \h Annex A. A schematic flowchart, reviewing the noise control process, is presented in REF Annex_sec_B \r \h Annex B 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000C00000041006E006E00650078005F007300650063005F0042000000 and a summary of action items is presented in REF Annex_sec_C \r \h Annex C 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000C00000041006E006E00650078005F007300650063005F0043000000 . An example of an equipment noise data sheet is presented in REF Annex_sec_E \r \h Annex E 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000C00000041006E006E00650078005F007300650063005F0045000000 .
Acoustique — Modes opératoires de contrôle du bruit dans les installations ouvertes
La présente Norme internationale définit les procédures de maîtrise du bruit dans les installations principalement ouvertes. Elle s'applique aux tâches suivantes: _ la spécification des procédures de maîtrise du bruit pendant l'étude d'une nouvelle installation et la modification/extension d'installations existantes (les procédures relatives au bruit pendant la construction sont en dehors du domaine d'application de la présente Norme internationale mais il convient de les prendre en considération); _ la définition des responsabilités des parties concernées, à savoir «l'utilisateur final», «l'entrepreneur d'ingénierie» et le «fournisseur d'équipement»; _ la description des procédures générales permettant de satisfaire aux exigences relatives au bruit de chaque équipement, en se fondant sur les exigences relatives au bruit global de l'installation. Un organigramme schématique, présentant le processus de maîtrise du bruit, figure en annexe A et un récapitulatif des actions est présenté à l'annexe B. NOTE En ce qui concerne les méthodes techniques spécifiques d'étude et d'analyse de l'acoustique des installations, il convient d'utiliser d'autres normes et d'autres ouvrages.
General Information
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Standards Content (Sample)
International
Standard
ISO 15664
Second edition
Acoustics — Noise control design
2025-12
procedures for open plant
Acoustique — Modes opératoires de contrôle du bruit dans les
installations ouvertes
Reference number
© ISO 2025
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ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 General terms .2
3.2 Terms specific to noise .2
4 General requirements . 5
5 General noise limits (immission requirements) . 6
5.1 In-plant noise .6
5.1.1 General .6
5.1.2 Emergency area noise limit .6
5.1.3 Work area noise limit .6
5.1.4 Restricted area.6
5.1.5 Modification/extension of an existing plant . .7
5.2 Environmental noise .7
5.3 Exceptional or infrequent operating conditions .7
5.4 Additional restrictions for tonal or impulsive noise.7
6 Equipment noise limits (emission requirements) . 8
6.1 General .8
6.1.1 Default equipment noise limits .8
6.1.2 Noise control measures .8
6.2 Equipment emitting noise to external environment .9
6.3 Equipment emitting intermittent or fluctuating noise .9
6.4 Equipment located outside the work area .9
6.5 Additional restrictions for tonal or impulsive noise.9
6.6 Equipment noise data sheets .9
6.6.1 Noise limits .10
6.6.2 Noise acceptance testing .10
6.6.3 Noise guarantees .10
6.7 Equipment selection .10
6.7.1 Bid comparison .10
7 Noise abatement .11
7.1 Silencers .11
7.2 Acoustic enclosures .11
7.3 Sound absorption .11
8 Project control . .11
8.1 Noise control documentation .11
8.2 Engineering phase reports . 12
8.3 Equipment noise test . 12
8.4 Plant noise acceptance test. 12
8.5 Remedial action . 13
Annex A (normative) Requirements on equipment suppliers for reporting and testing on noise . 14
Annex B (informative) Noise control flowchart .16
Annex C (informative) Summary of action items and allocation of responsibility . 17
Annex D (informative) Noise aspects of specific equipment . 19
Annex E (informative) Example of equipment noise data sheet .21
Annex F (informative) Documents to be made available to the noise control engineers .22
iii
Annex G (informative) Example of format for the noise allocation report.24
Annex H (informative) Example of format for the noise control report .25
Annex I (informative) Example of format for the noise verification report .26
Bibliography .28
iv
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.
This second edition cancels and replaces the first edition (ISO 15664:2001), which has been technically
revised.
The main changes are as follows:
— The scope of this document has been updated to reflect that requirements for suppliers of noise-emitting
equipment have been defined.
— Supplementary specification to this document as defined in S-717 by the Joint Industry Programme 33
(JIP33) of the International Association of Oil and Gas Producers (IOGP) has been added in a new annex
(see Annex A).
— The equipment noise data sheet (see Annex E) has been updated.
— A recommended area noise limit has been included to be used where area noise limits are not defined
elsewhere.
— Clause 6 has been updated to reflect changes in acoustic engineering work practises and the use of
computational noise modelling tools.
— Annex C from the first edition was deleted and replaced by a new Annex C.
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
Introduction
Achieving acceptable environmental and occupational noise conditions requires procedures for the noise
control design of open plants. This is a common challenge in oil refineries, chemical plants, gas plants,
onshore and offshore oil and gas production facilities, unenclosed powerplants, steelworks, gravel washing
plants, cement plants, concrete batch plants, sawmills and other continuous, batch or intermittent operation
plants located in the open.
The users of this document should be familiar with the type of plant involved and have sufficient technical
expertise and experience in industrial plant noise control design. This document is intended to be flexible
to suit the nature and location of the plant being designed, and the technical abilities of the parties involved.
It is specifically intended that the end-user and the contractor agree on the nature and extent of the work to
be done, the reporting on the work, and which party carries out what work.
This document is not intended specifically to be a contract document, except for Annex A which is considered
suitable for procurement specifications of individual equipment.
A list of standards related to this document is given in the Bibliography.
vi
International Standard ISO 15664:2025(en)
Acoustics — Noise control design procedures for open plant
1 Scope
This document defines the procedures for noise control of primarily open plants and the requirements on
equipment suppliers for reporting and testing of noise.
It is applicable to the following:
— specification of procedures for noise control during engineering of a new plant and modification/
extension of existing plants (construction and commissioning noise procedures are outside the scope of
this document);
— definition of responsibilities of parties involved, viz. “end-user”, “engineering contractor” and “equipment
supplier”;
— description of general procedures to arrive at noise requirements for individual equipment, based on
overall noise requirements for the plant.
Input to purchase specifications is presented in Annex A.
A schematic flowchart, reviewing the noise control process, is presented in Annex B and a summary of action
items is presented in Annex C.
An example of an equipment noise data sheet is presented in Annex E.
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.
ANSI S12.12, Method for the determination of sound power levels of noise sources using sound intensity
ISO 1996-2:2017, Acoustics — Description, measurement and assessment of environmental noise — Part 2:
Determination of sound pressure levels
ISO 3741, Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound
pressure — Precision methods for reverberation test rooms
ISO 3743 (all parts), Acoustics — Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Engineering methods for small, movable sources in reverberant fields
ISO 3744, Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound
pressure — Engineering methods for an essentially free field over a reflecting plane
ISO 3745, Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound
pressure — Precision methods for anechoic rooms and hemi-anechoic rooms
ISO 3746, Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound
pressure — Survey method using an enveloping measurement surface over a reflecting plane
ISO 3747, Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound
pressure — Engineering/survey methods for use in situ in a reverberant environment
ISO 3864, Safety colours and safety signs
ISO/TS 7849-2, Acoustics — Determination of airborne sound power levels emitted by machinery using vibration
measurement — Part 2: Engineering method including determination of the adequate radiation factor
ISO 9614 (all parts), Acoustics — Determination of sound power levels of noise sources using sound intensity
ISO/TS 20065, Acoustics — Objective method for assessing the audibility of tones in noise — Engineering method
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/
3.1 General terms
3.1.1
end-user
party which initiates the project and ultimately owns or operates the plant, or pays for its design and
construction
Note 1 to entry: The end-user will generally specify the technical objectives and/or requirements.
3.1.2
contractor
party which carries out all or part of the design, engineering, procurement, construction and commissioning
for the project
3.1.3
manufacturer
supplier
party which manufactures or supplies equipment and services to perform the duties specified by the
contractor (3.1.2)
3.1.4
work area
any position not less than 1 m from equipment surfaces accessible to personnel, and any position where a
worker's ear may be exposed to noise in the normal course of duty
Note 1 to entry: The work area also includes any platform, walkway or ladder.
3.1.5
project specification
document defining the scope of a project
Note 1 to entry: It can contain descriptions of the process, project management, responsibilities and engineering
requirements. These include safety and environmental requirements.
3.1.6
regulatory authorities
local, regional, national, or other authorities that specify and enforce criteria for environmental and
occupational health noise
3.2 Terms specific to noise
3.2.1
noise limit
noise levels not to be exceeded and given as a sound power level, sound pressure level, or noise exposure level
3.2.1.1
regulatory noise limits
noise limits set by regulatory authorities (3.1.6)
3.2.1.3
contractual noise limits
noise limits set by the end-user (3.1.1) as part of a legal contract between the end-user (3.1.1) and the
contractor (3.1.2), considering regulatory noise limits (3.2.1.1) and company requirements
3.2.1.4
area noise limits
noise limits set by the end-user (3.1.1) or contractor (3.1.2) for a work area (3.1.4) given as A-weighted
equivalent continuous sound pressure level
3.2.1.5
equipment noise limits
noise limits set by an end-user (3.1.1) or contractor (3.1.2) for a manufacturer/supplier (3.1.3) for an individual
equipment item
3.2.2
tonal noise
noise which is dominated by one or several clearly distinguishable tone(s)
Note 1 to entry: See ISO 1996-2 and ISO/TS 20065.
3.2.3
impulsive noise
sound characterized by brief bursts of sound pressure
Note 1 to entry: The duration of a single impulsive sound is usually less than 1 s. See ISO 1996-1 and ISO/PAS 1996-3.
3.2.4
fluctuating noise
noise whose level varies continuously and to an appreciable extent during the period of observation
[SOURCE: ISO 12001:1996, 3.19.1., modified — reference to figure deleted.]
3.2.5
intermittent noise
noise whose level abruptly drops to the level of the ambient noise several times during the period of
observation. The time during which the level remains at a constant value clearly above that of the ambient”.
[SOURCE: ISO 12001:2009, 3.19.2, modified — adjusted, so that only levels above the ambient are defined as
intermittent noise.]
3.2.6
noise emission
airborne sound radiated by a well-defined noise source, such as a machine, equipment, part of a plant, or an
entire plant
Note 1 to entry: See ISO 12001 and ISO 11690-1.
3.2.7
noise immission
total amount of noise from all contributing sources at a given receiver position
Note 1 to entry: See ISO 11690-1.
3.2.8
noise exposure
all noises that arrive, over a specific time period, T, at a person’s ear in the actual situation
Note 1 to entry: See ISO 11690-1; for the purposes of this document, this term is also used for specific positions in the
environment.
[SOURCE: ISO 11690-1:2020, 3.3.2., modified — “of a person” deleted, reference to figures deleted.]
3.2.9
equivalent continuous sound pressure level
L
pT,eq
ten times the logarithm to the base 10 of the ratio of the time-average of the square sound pressure, p, during
a stated time interval of duration T (starting at t and ending at t ), to the square of a reference value, p ,
1 2 0
expressed in decibels
t
2
pt dt
()
∫
t
T
LL==10lg dB
pT,,pTeq
p
where the reference value, p is 20 μPa
Note 1 to entry: Because of practical limitations of the measuring instruments, p is always understood to denote the
square of a frequency-weighted, frequency-band-limited or time-weighted sound pressure. If specific frequency and
time weightings as specified in IEC 61672-1 and/or specific frequency bands are applied, this should be indicated by
appropriate subscripts, e.g. L denotes the A-weighted sound pressure level with time weighting F.
pA, F
Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007, 8-22.
[SOURCE: ISO/TR 25417:2007, 2.3]
3.2.10
sound pressure level
L
p
quantity given by:
p
RMS
L =10lg dB
p
p
where p is the root-mean-square sound pressure in the time domain and p is the reference value of
RMS 0
sound pressure
[SOURCE: ISO 80000-8:2020, 8-14]
3.2.11
sound power level
L
W
quantity given by:
P
m
L =10lg dB
W
P
where P is the magnitude of the time-averaged sound power and P is the reference value of sound power 1 pW
m 0
[SOURCE: ISO 80000-8:2020, 8-15]
3.2.12
peak emission sound pressure level
L
p,peak
ten times the logarithm to the base 10 of the ratio of the square of the peak emission sound pressure, p ,
peak
to the square of a reference value, p , expressed in decibels
p
peak
L =10lg dB
p,peak
p
where the reference value, p , is 20 μPa
Note 1 to entry: The peak emission sound pressure level is usually C-weighted and denoted L
pC,peak
[SOURCE: ISO 11204:2010, 3.5]
4 General requirements
The control of noise in a plant is necessary for the following reasons:
— to prevent noise-induced hearing loss;
— to reduce work, speech and concentration interference;
— to provide quiet living accommodation for personnel;
— to protect the environment;
— to prevent annoyance and adverse impact to the neighbouring community.
Noise limits can be given for each of the above aspects of noise control, relative to certain areas inside or
outside the plant. For the purposes of this document, they are referred to as “general noise limits” and are
specified in Clause 5.
Noise limits for each item of equipment shall be derived from the general noise limits, as applicable for the
equipment in its specific position in the plant. These are commonly referred to as “equipment noise limits”.
Procedures for deriving equipment noise limits are specified in Clause 6.
Each potential noise source shall be subject to the requirements of this document.
Recommendations for noise limits can be found in International Standards, e.g. ISO 11690-1 (workplace),
ISO 9921 (speech communication) and ISO 1996 series (environment). Requirements for noise limits can
also be provided by National Codes of Practice or statutory regulations or legislation.
The specified limits shall be met for the design operating conditions of the plant. They shall also hold for other
operating conditions which occur occasionally, such as start-up, shutdown, regeneration, and maintenance,
unless otherwise specified by the end-user and agreed upon with the contractor. In emergency situations
(e.g. relief valve operation), a higher noise limit may be allowable, and the limit specified for such conditions
shall not be exceeded.
This document deals with noise from more or less stationary equipment; however, noise radiated from mobile
noise sources operating on the site, such as transportation vehicles (lorries, trucks, railway equipment) or
mobile maintenance equipment in the plant or workshops, also needs to be considered. Noise due to mobile
sources is more important if relatively high numbers of vehicles are present near the boundaries of the plant
or if the plant is located near sensitive receivers. Regulatory authorities may also require consideration of
noise emissions from mobile equipment. The end user and contractor shall agree whether or not this type of
mobile source noise is to be considered as part of the noise control procedures.
The planning and scope of the noise control engineering for a plant is based heavily on the project
specification. It is vital that all noise limits and any other noise requirements specified by the end-user be
carefully and completely defined in the project specification. This is particularly true where more than one
contractor is involved or where the plant (or part thereof) might be operated by other than the end-user or
contractor.
This document defines a number of specific tasks that may be performed during a project. These tasks
are assigned an action item (B1, B2, B3, etc.). The responsibility for the execution of these action items is
assigned to either the end-user or the contractor as stated in Annex C, where a summary of the action items
is included.
5 General noise limits (immission requirements)
5.1 In-plant noise
5.1.1 General
The end-user shall investigate all regulatory noise limits in the plant including but not limited to hearing
conservation, speech and work interference, and accommodation noise levels (B1).
In-plant noise limits shall be defined as area noise limits, i.e. as maximum sound pressure levels for work areas.
The most stringent noise limits and other requirements shall be determined from the requirements of
regulatory authorities and end-users. The applicable contractual noise limits shall be stated in the project
specification (B2).
Any deviations from applicable requirements shall be justified and documented.
Where there are no regulatory noise limits, the guidelines of ISO 11690-1 and other International Standards
should be considered.
As a rule, a noise limit of 85 dB A-weighted sound pressure level may be used for general plant areas where
area noise limits cannot be derived from end-user or authority regulations to reduce the risk of hearing loss
(see ISO 1999).
5.1.2 Emergency area noise limit
The emergency area noise limit is the sound pressure level anywhere in the work area that shall not be
exceeded in any situation, including emergencies (i.e. pressure relief valves, emergency flaring, and other
safety equipment).
The emergency area noise limit is determined as part of action item (B2).
An emergency area noise limit expressed as peak emission sound pressure level of L = 140 dB, or
pC,peak
alternatively L = 115 dB, should be used for general plant work areas where noise limits cannot be derived
pA
from end-user or regulatory requirements.
5.1.3 Work area noise limit
The work area noise limit, which can be different for different areas, is the noise level that shall not be
exceeded in order to comply with the limits as determined in action item (B2).
5.1.4 Restricted area
Restricted areas are those work areas in the plant where, according to the state of the art, it is not reasonably
practicable to reduce the noise level at or below the work area limit. The emergency area noise limit remains
valid in such areas.
If it is unavoidable that the work area noise limit will be exceeded around a particular equipment, action
should be taken to limit the area involved as far as is economically and technically feasible. This can include
the erection of an acoustic enclosure. Areas inside acoustic enclosures around such equipment may be
restricted areas.
The contractor shall identify the potential restricted areas to the end-user. Written permission shall be
obtained from the end-user to designate an area as a restricted area. The end-user and contractor shall
discuss and agree the noise levels that may be permitted in these noise restricted areas, taking into account
the regulatory noise limits (B3).
Permanent warning signs to indicate the mandatory use of hearing protection shall be erected at the
boundaries of restricted areas (B4). The signs shall be of the type specified in ISO 3864.
5.1.5 Modification/extension of an existing plant
When adding a new equipment or modules to existing facilities with area noise levels exceeding the work
area noise limit, the sound level contribution of the new facilities shall have an overall equivalent continuous
sound pressure level equal to or lower than the work area noise limit on a stand-alone basis and should not
increase the existing noise level.
5.2 Environmental noise
Limits for environmental noise are often set by regulatory authorities and can be linked to existing noise
levels. The regulations can also include methods for measurement and calculation of environmental noise
immission based on the sound power emitted by noise sources. Regulations can include requirements for
permits and environmental assessments. See ISO 1996-1 and ISO 1996-2.
The end-user shall investigate applicable regulations, Codes of Practice, legislation and other guides for
applicable noise limits. Consider discussing interpretation of these with the regulatory authorities to avoid
misunderstandings (B5).
Environmental noise limits are often different for day, evening, and nights, and for weekends.
Where requirements for environmental noise do not exist or are insufficient, the potential for adverse
community reaction to noise shall still be considered at the project definition stage (B6). This may include
additional road, rail or marine movements. Guidance in such cases can be sought from those in similar
countries or from WHO documents.
Authorities usually specify environmental noise limits for normal, and sometimes for emergency operation,
as a sound pressure level limit at specified locations in the vicinity of the plant or at the plant boundary line
(B7). Such limits can be converted into contractual noise limits in terms of sound power level for the plant as
a whole and/or its composing parts. In these cases, the resultant sound power level limits shall be included
in the project specification.
Calculation of environmental noise immission based on source sound power levels and vice versa shall
be carried out in accordance with recognized calculation models specified or agreed by authorities, the
contractor, and the end-user. Examples of recognized calculation methods (e.g. those in ISO 9613-1 and
ISO 9613-2) are given in the Bibliography.
NOTE There are many ways to convert sound pressure level limits into sound power level limits for composing
parts of a plant or large equipment items.
5.3 Exceptional or infrequent operating conditions
It shall be ensured that any allowances for occasional higher noise levels that can be acceptable to regulatory
authorities (such as for start-up, shutdown, and maintenance activities) are included in the project
specification (B8).
5.4 Additional restrictions for tonal or impulsive noise
Further restrictions can apply if the noise contains tonal or impulsive components, and these shall be
considered when specifying equipment noise limits (see 6.5).
6 Equipment noise limits (emission requirements)
6.1 General
Emission requirements shall be set for all equipment that contributes to in-plant or environmental noise
levels. Noise limits for individual equipment shall be determined at an early stage of the project and shall
ensure conformity with the immission limits of the plant.
Equipment noise limits shall be derived from the immission requirements identified as in-plant noise
limits (B2) and/or environmental noise limits (B7), or any other limits that may be stated in the project
specification.
Equipment noise limits shall be included in contract documentation to suppliers (see 6.6 and A.1).
Equipment noise limits can be specified as sound power levels and/or as sound pressure levels at a relevant
distance (typically at 1 meter), see Annex E. The allocation of emission requirements for individual
equipment items can best be performed using acoustic calculations (see, for example, ISO/TR 11690-3),
vendor data, noise declarations (see, for example, ISO 4871), databases and experience, considering the type,
size and operating conditions of the equipment. It can be necessary to add an allowance to accommodate
future expansion, changes in operations and/or items that may have been omitted from the calculation.
When setting emission requirements to individual equipment, all contributing noise sources, and the
acoustic properties of the surrounding environment shall be considered. It can therefore be more cost
effective to allocate higher noise limits to large or high-powered equipment than to simply allocate the same
noise limit to each item of equipment.
If equipment consists of components (e.g. a driver and a driven part), the work area noise limit applied to
each component separately will not ensure that the assembled equipment meets the work area noise limit.
For such equipment, more stringent limits shall be specified on the data sheets for the separate components.
The noise limit per component shall be based on acoustic calculations.
6.1.1 Default equipment noise limits
If detailed noise calculations are not completed before equipment is sent for bid, equipment noise levels
should be specified a minimum of 5 dB less than the most stringent area noise limit (e.g. an equipment
A-weighted sound level of 80 dB would be specified to meet an A-weighted area noise limit of 85 dB). Care
should be taken to understand that the number of similar sources needs to be considered in setting a default
value to avoid the total sound level for an area exceeding the area limit. It shall be recognized that situations
can exist where total noise levels can exceed the area noise limit when using default emission levels.
Similarly, default emission levels cannot guarantee conformity with environmental noise limits.
6.1.2 Noise control measures
The derivation of the sound power level limit for each item of equipment is an iterative process. When the
results of the investigation indicate that one or more of the limits will be exceeded, the noise control engineer
shall consider different strategies to ensure conformity. Noise control measures may include replacing the
equipment by an alternative item that emits less noise, relocating the equipment to increase the distance
to an operator or to a community, using natural or man-made screening and sound barriers and using
sound insulation or acoustic enclosures. In most cases, reducing the noise at source is the better solution.
For recommended practice for the design of low-noise machinery refer, for example, to ISO/TR 11688-1 and
ISO/TR 11688-2.
A further reduction of the equipment noise limit shall be made when several items of equipment or equipment
packages are to be mounted close together, or when the equipment is placed in a reverberant area.
Some additional information on the noise aspects of specific equipment is listed in Annex D.
6.2 Equipment emitting noise to external environment
Noise propagation calculations shall be carried out in accordance with recognized calculation models
specified or agreed by the authorities and end-users (see, for example, ISO 9613-2). It can then be decided
if individual equipment sound level limits can be increased or decreased so that the community sound
pressure level limit is met.
Consideration shall be given to all noise sources when there are several facilities contributing to
environmental noise levels. The reliability of the sound levels used, and an allowance for items that may
have been omitted from the calculation, should also be considered.
6.3 Equipment emitting intermittent or fluctuating noise
Where the general noise limits of 5.1 and 5.2 are complied with, but equipment emits an intermittent or
fluctuating noise (e.g. depressurizing, boiler blow-down, sump pump), the estimated equivalent continuous
sound pressure level, L , shall not exceed the equipment limits specified. A maximum instantaneous
pT,eq
level may be set by the end-user or authorities and should consider all intermittent noise sources that may
operate together.
6.4 Equipment located outside the work area
The equipment noise limit is normally set as a sound power level or sound pressure limit at 1 m from the
equipment. Where the nearest accessible position is more than 1 m away, an equipment noise limit for 1 m
may be set higher and should be calculated. This could be the case for vent stacks, ducted fan intakes and
other not normally accessible equipment.
Although from the work area noise limit point of view this increase might be permissible, it might conflict
with the environmental noise limit. This can be the case with flare noise, for instance. The most stringent
requirement based on the work area noise limit and the environmental noise limit shall be applied.
6.5 Additional restrictions for tonal or impulsive noise
Further restrictions can apply when the noise of an equipment item contains tonal and/or impulsive
components, and the relevant sound source contributes significantly. An objective method for determination
of the audibility of tones in environmental noise can be found in ISO/TS 20065 or, alternatively, by using the
simplified method in Annex A. For determination of impulsive noise refer to ISO 1996-3.
6.6 Equipment noise data sheets
Equipment noise data sheets shall be prepared by the contractor for all relevant items of equipment or an
equipment package, if such a package will be provided by a single supplier (B9). If components of a package
will be provided by different suppliers, separate equipment noise data sheets shall be prepared by each
supplier. If a single supplier is providing an entire equipment package (i.e. compressor, gearbox, and motor)
the supplier shall be responsible for providing an equipment noise datasheet for the entire equipment
package, incorporating noise data from any sub suppliers.
The equipment noise data sheet shall be returned with the tender and contain:
— noise guarantees for the equipment for any of the conditions of operation for which the equipment can
be expected to be used;
— unsilenced A-weighted sound power and sound pressure levels;
— octave band sound levels;
— A-weighted sound power and sound pressure levels together with details of any noise control measures
that are necessary to meet the specified noise limits;
— method used to determine the equipment noise emission;
— details of any tonal, impulsive, intermittent or fluctuating noise levels,
— test standard to be used in the noise acceptance test (accepted test standards are given in Annex A);
— after acceptance test is conducted, the declared sound power and sound pressure levels in octave-bands
and the A-weighted overall levels of the equipment, including all the sound measurement locations used
to determine equipment noise emission.
6.6.1 Noise limits
The equipment noise limits shall be stated either as a sound pressure level limit at a specified distance,
usually at 1 m from the equipment surface or at the operator’s position, or as a sound power level limit, or
both, and defined as an overall A-weighted value in decibels and, where considered more appropriate, the
corresponding 31,5 Hz to 8 kHz octave-band spectrum may be specified. See Annex A and Annex E.
6.6.2 Noise acceptance testing
Requirements for noise acceptance testing shall be included. Any adjustments for tonal or intermittent noise
shall be clearly stated.
6.6.3 Noise guarantees
All guaranteed noise levels quoted shall include upper measuring tolerances. If spectrum sound levels
are included in the guarantee, then these may have different tolerances to those for the total sound levels.
The noise control engineer should consider the test method tolerances when setting the noise limits for
individual equipment items.
If guarantees have been provided in some other way, specification of equipment noise limits on individual
data/requisition sheets is not required. For example, where a supplier provides all the pumps or motors in a
project, a list of guaranteed equipment noise levels and spectra per item will be acceptable.
NOTE The sound power level limit and sound pressure level limit need not be related or equivalent since they can
originate from different general limits, i.e. the sound power limit can originate from the environmental noise limit and
the sound pressure limit from the work area noise limit.
6.7 Equipment selection
It shall be ensured
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