National foreword

This British Standard is the UK implementation of EN ISO 22734‑1:2025. It is identical to ISO 22734‑1:2025. It supersedes BS ISO 22734:2019, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee GSE/6.

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 31 July 2025.

This European Standard was approved by CEN on 29 June 2025.

CEN and CENELEC 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 and CENELEC 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 and CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.

CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czechia, 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 foreword

This document (EN ISO 22734‑1:2025) has been prepared by Technical Committee ISO/TC 197 "Hydrogen technologies" in collaboration with Technical Committee CEN-CENELEC/ JTC 6 “Hydrogen in energy systems” the secretariat of which is held by NEN.

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 January 2026, and conflicting national standards shall be withdrawn at the latest by January 2026.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN-CENELEC shall not be held responsible for identifying any or all such patent rights.

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 and CENELEC websites.

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 22734‑1:2025 has been approved by CEN-CENELEC as EN ISO 22734‑1:2025 without any modification.

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 197, Hydrogen technologies, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/CLC/JTC 6, Hydrogen in energy systems, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This first edition of ISO 22734‑1 cancels and replaces ISO 22734:2019.

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.

Introduction

The electrochemical cells of a hydrogen generator system dissociate water molecules (H₂O) into two hydrogen (H₂) gas molecules and one oxygen (O₂) gas molecule when direct electrical current (e-) is applied. H₂ gas forms at the negative (-) cathode electrode and O₂ gas forms at the positive (+) anode electrode. An ion transport medium between the electrodes, a solid electrolyte membrane or a liquid electrolyte held in a microporous diaphragm, additionally functions to keep product H₂ and O₂ gases separate.

Water electrolysis hydrogen generator systems include the cell(s), electrical conditioning, gas processing, feed water, electrolyte management, cooling, ventilation, and control equipment. Gas compression, feed water conditioning, and other auxiliary equipment can be included. These systems can scale from small self-contained appliances to a group of factory-matched modules comprising large plant size installations.

This document is intended to assess water electrolysis hydrogen generator safety and may be used for certification purposes.

NOTE See ISO/IEC 17000 for further guidance on certification.

1 Scope

1.1 General

This document specifies the safety requirements of hydrogen gas generation appliances or systems that use electrochemical reactions to electrolyse water to produce hydrogen, herein referred to as hydrogen generators.

1.2 Applicable hydrogen generators

This document is applicable to:

hydrogen generator appliances or systems (containerised, or skid mounted, complete hydrogen generation systems);
factory-matched modules (supplied by the same manufacturer) that, when connected together, form a complete hydrogen generation system;
hydrogen generators intended for industrial, commercial and residential applications;
hydrogen generators intended for indoor or outdoor environments.

NOTE When this document is applied to hydrogen gas generation appliances or systems intended for installation into buildings, additional requirements for the design of the building are likely to apply. These building requirements are not addressed in this document. Additionally, the hydrogen generator enclosure requirements in this document do not necessarily translate to requirements for a building.

Guidance for hydrogen generators that also provide oxygen used for industrial and commercial applications is provided in this document, however additional considerations can apply.

1.3 Applicable ion transport mediums

This document is applicable to hydrogen generators that use the following types of ion transport medium:

aqueous alkaline (basic) electrolytes, such as solutions of potassium hydroxide or sodium hydroxide;
aqueous acidic electrolytes, such as dilute sulphuric acid;
solid polymeric materials with acidic function group additions, such as acid proton exchange membrane (PEM);
solid polymeric materials with basic function group additions, such as anion exchange membrane (AEM).

1.4 Applicability to large scale hydrogen generators

This document is applicable to large scale hydrogen generators assembled on site.

NOTE 1 Large scale water electrolysis systems typically have a production rate of 100 kg/hour or more and can be assembled using modules or equipment from various manufacturers.

NOTE 2 Building requirements are not addressed in this document and the hydrogen generator enclosure requirements in this document do not necessarily translate to requirements for a building.

1.5 Applicability to certain hydrogen generator subassemblies

This document is applicable to:

electrochemical cell stacks (as stand-alone products);
modules (sub-systems) for integration into larger hydrogen generation systems.

In such cases, the entirety of this document will not be applicable, and the specific sections relevant to the product are established in order to develop a product conformance strategy.

1.6 Excluded hydrogen generators

This document is not applicable to the following:

residential hydrogen generators that also supply oxygen as a product;
hydrogen generators that can also be used to generate electricity, such as reversible fuel cells (refer to IEC 62282‑8‑101, IEC 62282‑8‑102 and IEC 62282‑8‑201);
hydrogen generators that use solid oxide electrolyte (refer to IEC 62282‑8‑101 and IEC 62282‑8‑201).

2 Normative references

3 Terms and definitions

4 Requirements

4.1 Operating conditions

4.2 Risk management

4.3 Chemical reaction equipment

4.4 Mechanical equipment

4.5 Electrical equipment and wiring

4.6 Control systems

4.7 Enclosure requirements

5 Test methods

5.1 General

5.2 Type (qualification) tests

5.3 Routine tests

6 Marking and labelling

6.1 General requirements

6.2 Hydrogen generator marking

6.3 Marking of equipment

6.4 Warning labels

7 Documentation

7.1 General

7.2 Hydrogen generator ratings

7.3 Hydrogen generator installation

7.4 Hydrogen generator operation

7.5 Hydrogen generator maintenance

Bibliography

BS EN ISO 22734-1:2025

Hydrogen generators using water electrolysis - Safety

Current

Published:

31 Jul 2025