ISO 5149-3

• Abstract:

  ISO 5149-3:2014 is applicable to the installation site (plant space and services). It specifies requirements for the site for safety, which could be needed because of, but not directly connected with, the refrigerating system and its ancillary components. ISO 5149-3:2014 is applicable to new refrigerating systems, extensions or modifications of existing systems, and for used systems being transferred to and operated on another site. It also applies in the case of the conversion of a system for another refrigerant.

• Status: Not Published
• ICS: 27.080 - Heat pumps
• ICS: 27.200 - Refrigerating technology
• Technical Committee: ISO/TC 86/SC 1 - Safety and environmental requirements for refrigerating systems
• Drafting Committee: ISO/TC 86/SC 1 - Safety and environmental requirements for refrigerating systems
• Current Stage: 6000 - International Standard under publication
• Start Date: 22-Sep-2026
• Completion Date: 26-Sep-2026

• Revises: ISO 5149-3:2014/Amd 1:2021 - Refrigerating systems and heat pumps — Safety and environmental requirements — Part 3: Installation site — Amendment 1: Update of the requirements for machinery rooms and emergency mechanical ventilation
• Effective Date: 19-Nov-2022
• Revises: ISO 5149-3:2014 - Refrigerating systems and heat pumps — Safety and environmental requirements — Part 3: Installation site
• Effective Date: 19-Nov-2022

Overview

ISO 5149-3 is a key international standard for the safety and environmental requirements of refrigerating systems and heat pumps, with a specific focus on the installation site, classification, and selection criteria. It is designed to support safe planning and operation at the plant space level, helping organizations address site-related risks that are not directly part of the refrigerating system itself.

This standard is relevant for:

• New refrigerating systems
• Extensions or modifications of existing systems
• Used systems transferred to a different site
• System conversions for another refrigerant

For engineers, designers, facility managers, and compliance teams, ISO 5149-3 provides a practical framework for identifying site conditions that support safe installation and ongoing operation.

Key Topics

ISO 5149-3 covers the selection and assessment of the installation environment, including the relationship between the refrigerating equipment and the surrounding space. It supports decision-making for different installation configurations and helps define the conditions needed for safer system placement.

Key topics include:

• Installation site requirements for plant spaces and services
• Classification of system locations such as occupied spaces, machinery rooms, open air, and ventilated enclosures
• Refrigerant quantity limit considerations linked to space volume and area
• Machinery room requirements, including accessibility, ventilation, lighting, and emergency provisions
• Detection and alarm systems for safety monitoring
• Instruction manuals, notices, and inspections to support site maintenance and awareness
• Additional measures for specific refrigerant and site conditions
• Heat-transfer fluid considerations related to safety and environmental performance

The standard also supports a structured approach to risk reduction by addressing site-based factors that influence refrigerant safety, ventilation design, and emergency preparedness.

Applications

ISO 5149-3 is widely applicable across industries that use refrigeration and heat pump technology. It is especially valuable in environments where safe installation and site planning are essential for operational reliability and compliance.

Typical applications include:

• Commercial refrigeration in retail, food storage, and distribution
• Industrial refrigeration for process cooling and manufacturing
• Heat pump installations in buildings and facilities
• Machinery room planning for centralized refrigeration systems
• Retrofits and upgrades where existing systems are relocated or modified
• Refrigerant conversion projects requiring reassessment of site suitability

By applying ISO 5149-3, organizations can improve site safety, support regulatory alignment, and strengthen the overall design of refrigerating systems and heat pumps.

Related Standards

ISO 5149-3 is part of the ISO 5149 series, which addresses the broader safety and environmental requirements for refrigerating systems and heat pumps. It is intended to be used alongside other related parts of the series for a more complete compliance strategy.

Related standards and document areas include:

• ISO 5149-1 - General requirements and basic definitions
• ISO 5149-2 - Design, construction, testing, marking, and documentation
• ISO 5149-4 - Operation, maintenance, repair, and recovery
• Supporting annexes and normative references within ISO 5149-3

Together, these standards provide a coordinated approach to refrigeration safety, heat pump installation, and environmental risk management across the system lifecycle.

FINAL DRAFT
International
Standard
ISO/FDIS 5149-3
ISO/TC 86/SC 1
Refrigerating systems and heat
Secretariat: ANSI
pumps — Safety and environmental
Voting begins on:
requirements —
2026-07-27
Part 3:
Voting terminates on:
2026-09-21
Installation site, classification and
selection criteria
Systèmes frigorifiques et pompes à chaleur — Exigences de
sécurité et d'environnement —
Partie 3: Site d'installation, classification et critères de sélection
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 5149-3:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 5149-3:2026(en)
International
Standard
ISO/FDIS 5149-3
ISO/TC 86/SC 1
Refrigerating systems and heat
Secretariat: ANSI
pumps — Safety and environmental
Voting begins on:
requirements —
Part 3:
Voting terminates on:
Installation site, classification and
selection criteria
Systèmes frigorifiques et pompes à chaleur — Exigences de
sécurité et d'environnement —
Partie 3: Site d'installation, classification et critères de sélection
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
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Phone: [phone]
Email: [e-mail]
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Published in Switzerland Reference number
ISO/FDIS 5149-3:2026(en) © ISO 2026

ii
ISO/FDIS 5149-3:2026(en)
Contents Page
Foreword .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Location of refrigerating equipment . 2
4.1 General .2
4.2 Refrigerating equipment located in the open air .3
4.3 Refrigerating equipment located in a machinery room .3
4.4 Refrigerating equipment located in the occupied space .3
4.5 Refrigerating equipment located in an area not designated as an occupied space or a
machinery room .3
4.6 Refrigerating equipment located in a class IV ventilated enclosure within an occupied
space .4
4.7 Piping duct or shaft .4
5 Classification . 4
5.1 General .4
5.2 Classification of system locations .4
5.2.1 Class I – Mechanical equipment located within the occupied space .4
5.2.2 Class II – Compressors and pressure vessels outside the occupied space .4
5.2.3 Class III – Machinery room or open air .5
5.2.4 Class IV – Ventilated enclosures .5
5.3 Classification of access to occupied spaces, machinery rooms and open air .5
5.4 Classification of refrigerants .6
6 Determining the room volume and room area used in refrigerant quantity limit
calculations. 6
6.1 General .6
6.2 Space volume and area calculations .6
7 Setting refrigerant quantity limits. 7
7.1 General .7
7.2 Defining toxicity and flammability classes, toxicity factor, lower flammability limit
and cap factors.7
7.3 Establishing the refrigerant quantity limit .8
7.4 Refrigerant charge limit calculation for Path A safety concept .9
7.4.1 General .9
7.4.2 Refrigerant charge limit based on toxicity .9
7.4.3 Refrigerant charge limit based on flammability .9
7.5 Advanced methods for charge limit based on both flammability and toxicity . 13
7.5.1 General . 13
7.5.2 Charge limit calculation . 13
7.6 Refrigerant charge limit with ventilation . 15
7.6.1 Refrigerant charge limit with ventilation based on toxicity . 15
7.6.2 Refrigerant charge limit with ventilation based on flammability .17
7.7 Charge limit determined by test .19
7.8 Additional requirements for spaces below ground .19
7.9 Ensuring safety by other methods – Path B safety concept . 20
7.9.1 General . 20
7.9.2 Applicable measures . 20
8 Machinery rooms .21
8.1 Occupancy of machinery rooms and separate refrigeration machinery rooms .21
8.2 Venting from or through the machinery room .21
8.3 Combustion equipment and air compressors .21
8.4 Open flame .21

iii
ISO/FDIS 5149-3:2026(en)
8.5 Storage .21
8.6 Remote emergency switch .21
8.7 Exterior openings of the machinery room .21
8.8 Piping and ducting. 22
8.9 Normal lighting . 22
8.10 Emergency lighting . 22
8.11 Dimensions and accessibility . . 22
8.12 Doors, walls and ducts . 22
8.12.1 Doors and openings . 22
8.12.2 Emergency. 22
8.12.3 Walls, floor and ceiling . . 23
8.12.4 Service ducts . 23
8.12.5 Ventilation ducts . . 23
8.13 Ventilation . 23
8.13.1 General . 23
8.13.2 Ventilation for temperature control under normal operating conditions . 23
8.13.3 Ventilation when people are present in the machinery room. 23
8.13.4 Emergency mechanical ventilation .24
8.13.5 Required airflow for emergency mechanical ventilation .24
8.13.6 Mechanical ventilation openings .24
8.14 Additional measures for flammable refrigerants .24
8.14.1 General .24
8.14.2 Emergency exhaust ventilation .24
8.14.3 Maximum surface temperature . 25
8.15 Additional requirements for R-717 . 25
8.15.1 Drainage . 25
8.15.2 Specific equipment for emergency washing . 25
8.15.3 Fire sprinkler systems . 25
8.15.4 Doors and openings . 25
9 Requirements for additional measures .25
9.1 General . 25
9.2 Potential leak points in piping . 26
9.3 Ventilation . 26
9.3.1 General . 26
9.3.2 Dilution transfer openings for natural ventilation for systems in accordance
with 7.5. 26
9.3.3 Mechanical ventilation . 26
9.4 Safety shut-off valves .27
9.4.1 General .27
9.4.2 Location .27
9.4.3 Design .27
10 Electrical installations .28
10.1 General requirements . 28
10.2 Main power supply . 28
10.3 Electrical equipment in machinery rooms in which a refrigerating system contains
flammable refrigerants . 28
11 Safety alarms .28
11.1 General . 28
11.2 Alarm system power . 28
11.3 Alarm system warning . 28
11.3.1 General . 28
11.3.2 Alarm for machinery room . 29
11.3.3 Alarm for occupied space . 29
11.4 Additional alarm system requirements for R-717 systems with charges above 4 500 kg . 29
12 Detection systems .29
12.1 General . 29
12.2 Location of detection systems . 29

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ISO/FDIS 5149-3:2026(en)
12.3 Function of the detection systems . 29
12.4 Type and performance of a detection system . 29
12.4.1 General . 29
12.4.2 Refrigerant detection systems for R-717 . 30
12.5 Installation . 30
13 Instruction manuals, notices and inspections .30
13.1 Instruction manual . 30
13.2 Warning notice . 30
13.3 Visual inspection of site . 30
13.4 Maintenance of the site .31
14 Heat sources and temporary high temperatures located at the site .31
15 Heat-transfer fluid .31
15.1 General .31
15.2 Ingestion.32
15.3 Water and soil contamination .32
15.4 Personal exposure (toxicity) .32
15.5 Pressure .32
15.6 Marking .32
15.7 Freezing point .32
15.8 Decomposition point .32
15.9 Flash point .32
15.10 Auto-ignition temperature .32
15.11 Thermal expansion . 33
15.12 Corrosion protection . 33
Annex A (informative) Examples of classification and access category in Clause 5 .34
Annex B (normative) Safety classification and information about refrigerants .36
Annex C (normative) Determination of the releasable charge .43
Annex D (normative) Determination of the release height . 47
Annex E (normative) Determination of estimated height reached by the airflow .49
Annex F (normative) Charge limit determination using surrounding concentration test .51
Bibliography .54

v
ISO/FDIS 5149-3:2026(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 required 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 86, Refrigeration and air-conditioning,
Subcommittee SC 1, Safety and environmental requirements for refrigerating systems.
This second edition cancels and replaces the first edition (ISO 5149-3:2014), which has been technically
revised. It also incorporates the Amendment ISO 5149-3:2014/Amd 1:2021.
The main changes are as follows:
— integration of Clause 5 to Clause 8 and Annex A of ISO 5149-1:2014 in this document;
— introduction of Path A and Path B safety concepts and related safety provisions;
— introduction of the releasable charge concept;
— partial alignment of the document with EN 378-3.
A list of all parts in the ISO 5149 series can be found on the ISO website.
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.

vi
FINAL DRAFT International Standard ISO/FDIS 5149-3:2026(en)
Refrigerating systems and heat pumps — Safety and
environmental requirements —
Part 3:
Installation site, classification and selection criteria
1 Scope
This document specifies:
— the classification and selection criteria applicable to refrigerating systems;
— safety requirements for the installation site of refrigerating systems and their ancillary components.
These classification and selection criteria are used in ISO 5149-2 and ISO 5149-4.
This document is applicable to:
a) refrigerating systems, stationary or mobile, of all sizes, except vehicle air conditioning systems covered
by a specific product standard, e.g. ISO 13043 and SAE J 639;
b) secondary cooling or heating systems;
c) the location of the refrigerating systems;
d) parts replaced and components added after publication of this document if they are not identical in
function and in capacity.
This document is applicable:
— to new refrigerating systems, extensions or modifications of already existing systems;
— for used systems, being transferred to and operated on another site;
— in the case of the conversion of a system for another refrigerant.
This document is only applicable to systems containing refrigerants which have a safety group classification
and are listed in ISO 817.
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 817:2024, Refrigerants — Designation and safety classification
ISO 5149-1, Refrigerating systems and heat pumps — Safety and environmental requirements — Part 1:
Vocabulary
1)
ISO 5149-2:— , Refrigerating systems and heat pumps — Safety and environmental requirements — Part 2:
Design, construction, testing, marking and documentation
1) Under preparation. Stage at the time of publication: ISO/FDIS 5149-2:2026.

ISO/FDIS 5149-3:2026(en)
ISO 5149-4, Refrigerating systems and heat pumps — Safety and environmental requirements — Part 4:
Operation, maintenance, repair and recovery
ISO 12100, Safety of machinery — General principles for design — Risk assessment and risk reduction
ISO 13850, Safety of machinery — Emergency stop function — Principles for design
ISO 22712, Refrigerating systems and heat pumps — Competence of personnel
IEC 60079-10-1, Explosive atmospheres — Part 10-1: Classification of areas — Explosive gas atmospheres
IEC 60204-1, Safety of machinery — Electrical equipment of machines — Part 1: General requirements
IEC 60364-1, Low-voltage electrical installations — Part 1: Fundamental principles, assessment of general
characteristics, definitions
IEC 60364-5, Electrical installations of buildings — Part 5: Selection and erection of electrical equipment
IEC 62990-3, Workplace atmospheres — Part 3. Gas detectors. Electrical apparatus for the detection and
measurement of oxygen — Performance requirements and test methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5149-1 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/
For the user's convenience, the list of abbreviated terms used in this document is given in Table 1.
Table 1 — Additional abbreviated terms
Abbreviated term Description
ATEL acute toxicity exposure limit
CL concentration limit
CLAM concentration limit with additional measures
GWP global warming potential
LFL lower flammability limit
ODL oxygen deprivation limit
ppm parts per million by volume
RV room volume
SDS safety data sheet
TF toxicity factor
4 Location of refrigerating equipment
4.1 General
Refrigerating equipment can be sited outside the building in the open air, in a designated machinery room,
in occupied areas or in areas not designated as occupied or as a machinery room.
The refrigerating equipment can be contained in a class IV ventilated enclosure provided by the manufacturer.

ISO/FDIS 5149-3:2026(en)
4.2 Refrigerating equipment located in the open air
Refrigerating equipment sited in the open air shall be positioned to avoid refrigerant flowing from the
equipment into the building or otherwise endangering people and property.
NOTE Possible methods to achieve this include one or more of the following:
— location of the refrigerant-containing part of the refrigeration system (except piping) at least 6 m away from any
opening to the building;
— for refrigerant heavier than air use of barriers of at least 1 m height between the system location and the inlet
ventilation opening to block the flow of leaked or vented refrigerant;
— for refrigerant heavier than air location of the inlet ventilation opening at least 1 m above the level at which the
system is installed.
The discharge opening from safety relief devices or associated discharge pipes shall be positioned according
to the manufacturer's instructions and oriented to direct vented refrigerant away from inlet ventilation
openings. Alternatively, for flammable refrigerants, the distance to the inlet ventilation opening may be
determined in accordance with IEC 60079-10-1.
4.3 Refrigerating equipment located in a machinery room
When a machinery room is chosen as the location for refrigerating equipment, it shall meet the requirements
specified in Clause 8.
A risk assessment based on the safety concept for the refrigerating system (as determined by the
manufacturer and including the charge and safety classification of the refrigerant used) shall be conducted
to determine whether it is necessary to place the refrigerating system in a separate refrigeration machinery
room.
NOTE Where housing around refrigerating equipment is sufficiently large for people to enter, the housing is
considered as a machinery room and requirements for such rooms apply.
4.4 Refrigerating equipment located in the occupied space
The requirements shall be as specified in Clause 5, Clause 6 and Clause 7.
4.5 Refrigerating equipment located in an area not designated as an occupied space or a
machinery room
For any equipment located in a space that cannot be sealed from an occupied space, the location shall be
treated as an occupied space in accordance with 4.4.
Where compressors or pressure vessels are located in an indoor space that is sealed from any occupied
space, the location shall be treated as an occupied space in accordance with 4.4 or a machinery room in
accordance with Clause 8.
Where equipment (not including compressors and pressure vessels) containing non-permanent joints is
located in an unoccupied space that is sealed from any occupied space, the requirements of Clause 8 shall
apply. If mechanical ventilation is required according to 8.13, ventilation shall be from an extractor hood
positioned adjacent to the equipment and the ventilation rate shall be more than 0,05 m /s per ventilator.
In the case of equipment subject to adverse conditions, for example severe vibration or a corrosive
atmosphere, the ventilation rate shall be more than 0,5 m /s per extractor hood.
If mechanical ventilation is required, refrigerant gas detectors shall activate the ventilation in accordance
with the requirements given in Clause 12.
NOTE 1 Severe vibration can be caused by unbalanced dynamic loads or hydraulic shock during defrost operation.
NOTE 2 The ventilation rate is deemed sufficient to ventilate a volume of 18 m .

ISO/FDIS 5149-3:2026(en)
4.6 Refrigerating equipment located in a class IV ventilated enclosure within an occupied
space
The class IV ventilated enclosure containing the refrigerating equipment shall be installed in accordance
with the design specified in ISO 5149-2:—, 6.2.17. The class IV ventilated enclosure shall have a sufficient
make up air source to replace any exhausted air. The ventilation from the enclosure shall be to the open air
or to a room having a minimum volume as specified in 7.3 for an occupied space.
4.7 Piping duct or shaft
Where hand-operated shut-off devices are mounted in a piping duct or shaft designed for human entry, the
duct or shaft shall have more than one escape exit. The duct shall have an internal height of at least 1,2 m.
5 Classification
5.1 General
For the purpose of this document, refrigerating systems shall be classified according to:
— the location in which the system is installed;
— the type of people who have access to the place in which the system is installed;
— the toxicity and flammability characteristics of the refrigerant.
There are four classes of location and three access categories for refrigerating systems or parts of
refrigerating systems. Where a refrigerating system contains parts installed in several spaces, each space
shall be considered individually. The charge limits shall be calculated for each of them, according to Clause 7.
For installations with multiple refrigerating systems, each refrigerating system shall be evaluated
independently.
Examples of classification of system locations, categorisation of access and classification of refrigerants are
given in Annex A.
5.2 Classification of system locations
5.2.1 Class I – Mechanical equipment located within the occupied space
If the refrigerating system or any of its refrigerant-containing parts are located indoors in an occupied space
or a non-occupied space which is not sealed from the occupied space or which can leak into the occupied
space, then the system is considered to be of class I unless the system conforms to the requirements in 5.2.2
or 5.2.4.
EXAMPLE Integral display unit.
5.2.2 Class II – Compressors and pressure vessels outside the occupied space
If all compressors and pressure vessels are outside the occupied space and refrigerant leaks from
compressors or pressure vessels cannot flow into the occupied space, then the requirements for a class II
location shall apply to any refrigerant-containing part in the occupied space or that can leak refrigerant into
the occupied space. Coil-type heat exchangers and pipework, including valves, may be located in an occupied
space.
Refrigerant can leak into the occupied space through heat-transfer fluid if, for example:
— the heat-transfer fluid is ventilation air;
— the heat-transfer fluid is an open spray system;

ISO/FDIS 5149-3:2026(en)
— leakage of the refrigerant into the occupied space is caused by leakage of the refrigerant into the
heat-transfer fluid;
— there is a heat-transfer fluid relief valve or an automatic purge point that vents into the space.
Leakage via the heat-transfer fluid is not considered for systems that conform to ISO 5149-2:—, 6.2.9.5 on
the protection of the secondary cooling and heating system.
EXAMPLE Cold store.
5.2.3 Class III – Machinery room or open air
If all of the refrigerant-containing parts are located in a machinery room or the open air, then the
requirements for a class III location shall apply. The machinery room shall conform to the requirements of
Clause 8.
EXAMPLE Water-cooled chiller.
5.2.4 Class IV – Ventilated enclosures
If, with the intent of preventing migration of leaked refrigerant to the surrounding area,
refrigerant-containing parts are located in a ventilated enclosure that conforms to the requirements of 4.6
and ISO 5149-2:—, 6.2.17, then the requirements for a class IV location shall apply.
EXAMPLE Heat pump within a ventilated enclosure.
5.3 Classification of access to occupied spaces, machinery rooms and open air
For the purpose of this document, access classification shall be determined according to Table 2.
The access category is defined according to Table 2 by consideration of the group of occupants who are least
familiar with the safety precautions. For example, in a supermarket, department store or transport terminus,
an unregu
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Published in Switzerland.
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ISO/FDIS 5149-3:2026(en)
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Foreword . ix
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Location of refrigerating equipment . 3
4.1 General. 3
4.2 Refrigerating equipment located in the open air . 3
4.3 Refrigerating equipment located in a machinery room . 3
4.4 Refrigerating equipment located in the occupied space . 4
4.5 Refrigerating equipment located in an area not designated as an occupied space or a
machinery room . 4
4.6 Refrigerating equipment located in a class IV ventilated enclosure within an occupied
space . 4
4.7 Piping duct or shaft . 4
5 Classification. 4
5.1 General. 4
5.2 Classification of system locations . 5
5.3 Classification of access to occupied spaces, machinery rooms and open air . 6
5.4 Classification of refrigerants . 7
6 Determining the room volume and room area used in refrigerant quantity limit
calculations . 7
6.1 General. 7
6.2 Space volume and area calculations . 7
7 Setting refrigerant quantity limits . 8
7.1 General. 8
7.2 Defining toxicity and flammability classes, toxicity factor, lower flammability limit and
cap factors . 8
7.3 Establishing the refrigerant quantity limit . 9
7.4 Refrigerant charge limit calculation for Path A safety concept . 10
7.5 Advanced methods for charge limit based on both flammability and toxicity . 14
7.6 Refrigerant charge limit with ventilation . 16
7.7 Charge limit determined by test . 20
7.8 Additional requirements for spaces below ground . 20
7.9 Ensuring safety by other methods – Path B safety concept . 20
8 Machinery rooms . 22
8.1 Occupancy of machinery rooms and separate refrigeration machinery rooms . 22
8.2 Venting from or through the machinery room . 22
8.3 Combustion equipment and air compressors . 22
8.4 Open flame . 22
8.5 Storage . 22
8.6 Remote emergency switch . 22
8.7 Exterior openings of the machinery room . 23
8.8 Piping and ducting . 23
8.9 Normal lighting . 23
8.10 Emergency lighting . 23
8.11 Dimensions and accessibility . 23
8.12 Doors, walls and ducts . 23
8.13 Ventilation . 24
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ISO/DISFDIS 5149-3:20252026(en)
8.14 Additional measures for flammable refrigerants . 25
8.15 Additional requirements for R-717 . 26
9 Requirements for additional measures . 27
9.1 General. 27
9.2 Potential leak points in piping . 27
9.3 Ventilation . 27
9.4 Safety shut-off valves . 28
10 Electrical installations . 29
10.1 General requirements . 29
10.2 Main power supply . 29
10.3 Electrical equipment in machinery rooms in which a refrigerating system contains
flammable refrigerants . 29
11 Safety alarms . 29
11.1 General. 29
11.2 Alarm system power . 30
11.3 Alarm system warning . 30
11.4 Additional alarm system requirements for R-717 systems with charges above 4 500 kg . 30
12 Detection systems . 30
12.1 General. 30
12.2 Location of detection systems . 30
12.3 Function of the detection systems . 31
12.4 Type and performance of a detection system. 31
12.5 Installation . 31
13 Instruction manuals, notices and inspections . 32
13.1 Instruction manual . 32
13.2 Warning notice . 32
13.3 Visual inspection of site . 32
13.4 Maintenance of the site . 32
14 Heat sources and temporary high temperatures located at the site . 33
15 Heat-transfer fluid . 33
15.1 General. 33
15.2 Ingestion . 33
15.3 Water and soil contamination . 33
15.4 Personal exposure (toxicity) . 33
15.5 Pressure . 33
15.6 Marking . 34
15.7 Freezing point . 34
15.8 Decomposition point . 34
15.9 Flash point . 34
15.10 Auto-ignition temperature . 34
15.11 Thermal expansion . 34
15.12 Corrosion protection . 34
Annex A (informative) Examples of classification and access category in Clause 5 . 35
Annex B (normative) Safety classification and information about refrigerants . 37
Annex C (normative) Determination of the releasable charge . 45
Annex D (normative) Determination of the release height . 49
Annex E (normative) Determination of estimated height reached by the airflow . 52
Annex F (normative) Charge limit determination using surrounding concentration test . 56
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ISO/FDIS 5149-3:2026(en)
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Bibliography . 60

Foreword . vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Location of refrigerating equipment . 2
4.1 General. 2
4.2 Refrigerating equipment located in the open air . 2
4.3 Refrigerating equipment located in a machinery room . 3
4.4 Refrigerating equipment located in the occupied space . 3
4.5 Refrigerating equipment located in an area not designated as an occupied space or a
machinery room . 3
4.6 Refrigerating equipment located in a ventilated enclosure within an occupied space . 3
4.7 Piping duct or shaft . 3
5 Classification. 4
5.1 General. 4
5.2 Classification of system locations . 4
5.2.1 Class I – Mechanical equipment located within the occupied space . 4
5.2.2 Class II – Compressors and pressure vessels outside the occupied space . 4
5.2.3 Class III – Machinery room or open air . 5
5.2.4 Class IV – Ventilated enclosures . 5
5.3 Classification of access to occupied spaces, machinery rooms and open air . 5
5.4 Classification of refrigerants . 6
6 Determining the room volume and room area used in refrigerant quantity limit
calculations . 6
6.1 General. 6
6.2 Space volume and area calculations . 6
7 Setting refrigerant quantity limits . 7
7.1 General. 7
7.2 Defining toxicity and flammability classes, toxicity factor, lower flammability limit and
cap factors . 7
7.3 Establishing the refrigerant quantity limit . 8
7.4 Refrigerant charge limit calculation for Path A safety concept . 9
7.4.1 General. 9
7.4.2 Refrigerant charge limit based on toxicity . 9
7.4.3 Refrigerant charge limit based on flammability . 9
7.5 Advanced methods for charge limit based on both flammability and toxicity . 13
7.5.1 General. 13
7.5.2 Charge limit calculation . 14
7.6 Refrigerant charge limit with ventilation . 16
7.6.1 Refrigerant charge limit with ventilation based on toxicity . 16
7.6.2 Refrigerant charge limit with ventilation based on flammability . 18
7.7 Charge limit determined by test . 20
7.8 Additional requirements for spaces below ground . 20
7.9 Ensuring safety by other methods – Path B safety concept . 20
7.9.1 General. 20
7.9.2 Applicable measures . 21
8 Machinery rooms . 21
8.1 Occupancy of machinery rooms and separate refrigeration machinery rooms . 21
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ISO/DISFDIS 5149-3:20252026(en)
8.2 Venting from or through the machinery room . 22
8.3 Combustion equipment and air compressors . 22
8.4 Open flame . 22
8.5 Storage . 22
8.6 Remote emergency switch . 22
8.7 Exterior openings of the machinery room . 22
8.8 Piping and ducting . 22
8.9 Normal lighting . 23
8.10 Emergency lighting . 23
8.11 Dimensions and accessibility . 23
8.12 Doors, walls and ducts . 23
8.12.1 Doors and openings . 23
8.12.2 Emergency . 23
8.12.3 Walls, floor and ceiling. 23
8.12.4 Service ducts . 23
8.12.5 Ventilation ducts . 24
8.13 Ventilation . 24
8.13.1 General. 24
8.13.2 Ventilation for temperature control under normal operating conditions . 24
8.13.3 Ventilation when machinery room is occupied . 24
8.13.4 Emergency mechanical ventilation . 24
8.13.5 Required airflow for emergency mechanical ventilation . 25
8.13.6 Mechanical ventilation openings . 25
8.14 Additional measures for flammable refrigerants (classes 2L, 2 and 3) . 25
8.14.1 General. 25
8.14.2 Emergency exhaust ventilation . 25
8.14.3 Maximum surface temperature . 25
8.15 Additional requirements for R-717 . 26
8.15.1 Drainage . 26
8.15.2 Specific equipment for emergency washing . 26
8.15.3 Fire sprinkler systems . 26
8.15.4 Doors and openings . 26
9 Requirements for advanced measures . 26
9.1 Potential leak points in piping . 26
9.2 Ventilation . 27
9.2.1 General. 27
9.2.2 Dilution transfer openings for natural ventilation . 27
9.2.3 Mechanical ventilation . 27
9.3 Safety shut-off valves . 28
9.3.1 General. 28
9.3.2 Location . 28
9.3.3 Design . 28
10 Electrical installations . 28
10.1 General requirements . 28
10.2 Main power supply . 29
10.3 Electrical equipment in machinery rooms in which a refrigerating system contains
flammable refrigerants . 29
11 Safety alarms . 29
11.1 General. 29
11.2 Alarm system power . 29
11.3 Alarm system warning . 29
11.3.1 General. 29
11.3.2 Alarm for machinery room . 29
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ISO/FDIS 5149-3:2026(en)
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11.3.3 Alarm for occupied space . 30
11.4 Additional alarm system requirements for R-717 systems with charges above 4 500 kg . 30
12 Detection systems . 30
12.1 General. 30
12.2 Location of detection systems . 30
12.3 Function of the detection systems . 30
12.4 Type and performance of a detection system. 30
12.4.1 General. 30
12.4.2 Refrigerant detection systems for R-717 . 30
12.5 Installation . 31
13 Instruction manuals, notices, and inspections . 31
13.1 Instruction manual . 31
13.2 Warning notice . 31
13.3 Visual inspection of site . 31
13.4 Maintenance of the site . 32
14 Heat sources and temporary high temperatures located at the site . 32
15 Heat-transfer fluid . 32
15.1 General. 32
15.2 Ingestion . 33
15.3 Water and soil contamination . 33
15.4 Personal exposure (toxicity) . 33
15.5 Pressure . 33
15.6 Marking . 33
15.7 Freezing point . 33
15.8 Decomposition point . 33
15.9 Flash point . 33
15.10 Auto-ignition temperature . 33
15.11 Thermal expansion . 34
15.12 Corrosion protection . 34
Annex A (informative) Examples of classification and access category in Clause 5 . 35
A.1 Examples of classification . 35
A.2 Examples of access categories . 35
Annex B (normative) Safety classification and information about refrigerants . 37
Annex C (normative) Determination of the releasable charge . 45
C.1 General . 45
C.2 Determination by testing . 45
C.2.1 Conditions . 45
C.2.2 Test set-up . 45
C.2.3 Test method . 46
C.2.4 Determination of the small leak orifice size . 47
C.3 Determination by calculation . 47
C.3.1 General . 47
C.3.2 Refrigerant with high latent heat . 48
C.3.3 Effect of sublimation . 48
Annex D (normative) Determination of the release height . 49
Annex E (normative) Determination of estimated height reached by the airflow . 51
Annex F (normative) Charge limit determination using surrounding concentration test . 54
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ISO/DISFDIS 5149-3:20252026(en)
F.1 General . 54
F.2 Testing room requirements . 54
F.2.1 Testing room dimensions . 54
F.2.2 Testing room tightness . 54
F.2.3 Gas sensors . 54
F.3 Simulated leak . 55
F.4 Installation of the test object and gas sensors . 55
F.5 Simulated leak . 56
F.6 Concentration measurement . 56
F.7 Acceptance criteria . 56
Bibliography . 57

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ISO/FDIS 5149-3:2026(en)
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Foreword Formatted: Adjust space between Latin and Asian text,
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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
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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