National foreword

This British Standard is the UK implementation of ISO 5149‑3:2026. It supersedes BS ISO 5149‑3:2014+A1:2021, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee RHE/18, Refrigeration safety.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 November 2026.

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.

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:

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;
secondary cooling or heating systems;
the location of the refrigerating systems;
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

3 Terms and definitions

4 Location of refrigerating equipment

4.1 General

4.2 Refrigerating equipment located in the open air

4.3 Refrigerating equipment located in a machinery room

4.4 Refrigerating equipment located in the occupied space

4.5 Refrigerating equipment located in an area not designated as an occupied space or a machinery room

4.6 Refrigerating equipment located in a class IV ventilated enclosure within an occupied space

4.7 Piping duct or shaft

5 Classification

5.1 General

5.2 Classification of system locations

5.3 Classification of access to occupied spaces, machinery rooms and open air

5.4 Classification of refrigerants

6 Determining the room volume and room area used in refrigerant quantity limit calculations

6.1 General

6.2 Space volume and area calculations

7 Setting refrigerant quantity limits

7.1 General

7.2 Defining toxicity and flammability classes, toxicity factor, lower flammability limit and cap factors

7.3 Establishing the refrigerant quantity limit

7.4 Refrigerant charge limit calculation for Path A safety concept

7.5 Advanced methods for charge limit based on both flammability and toxicity

7.6 Refrigerant charge limit with ventilation

7.7 Charge limit determined by test

7.8 Additional requirements for spaces below ground

7.9 Ensuring safety by other methods – Path B safety concept

8 Machinery rooms

8.1 Occupancy of machinery rooms and separate refrigeration machinery rooms

8.2 Venting from or through the machinery room

8.3 Combustion equipment and air compressors

8.4 Open flame

8.5 Storage

8.6 Remote emergency switch

8.7 Exterior openings of the machinery room

8.8 Piping and ducting

8.9 Normal lighting

8.10 Emergency lighting

8.11 Dimensions and accessibility

8.12 Doors, walls and ducts

8.13 Ventilation

8.14 Additional measures for flammable refrigerants

8.15 Additional requirements for R-717

9 Requirements for additional measures

9.1 General

9.2 Potential leak points in piping

9.3 Ventilation

9.4 Safety shut-off valves

10 Electrical installations

10.1 General requirements

10.2 Main power supply

10.3 Electrical equipment in machinery rooms in which a refrigerating system contains flammable refrigerants

11 Safety alarms

11.1 General

11.2 Alarm system power

11.3 Alarm system warning

11.4 Additional alarm system requirements for R-717 systems with charges above 4 500 kg

12 Detection systems

12.1 General

12.2 Location of detection systems

12.3 Function of the detection systems

12.4 Type and performance of a detection system

12.5 Installation

13 Instruction manuals, notices and inspections

13.1 Instruction manual

13.2 Warning notice

13.3 Visual inspection of site

13.4 Maintenance of the site

14 Heat sources and temporary high temperatures located at the site

15 Heat-transfer fluid

15.1 General

15.2 Ingestion

15.3 Water and soil contamination

15.4 Personal exposure (toxicity)

15.5 Pressure

15.6 Marking

15.7 Freezing point

15.8 Decomposition point

15.9 Flash point

15.10 Auto-ignition temperature

15.11 Thermal expansion

15.12 Corrosion protection

Bibliography