1.1 This Standard supersedes IGEM/H/2 Edition 1, Communication 1843 which is obsolete.

1.2 This Hydrogen Enabling Standard was commissioned by the Hydrogen Skills and Standards for Heat (HSS4H) programme to provide evidence to support the UK Government’s 2025 consultation on the role of hydrogen in heating. The Standard has been prepared to support the initial coordinated community-based village trial for 100% Hydrogen (see Sub-Section 2.4) and to support the training and assessment program for Gas Safe Register licensed engineers who are to be engaged in the trial.

Note:  In 2023 the UK Government decided not to progress with initial village trials planned for Whitby and Redcar. The document will still be relevant to any future trial that takes place.

1.3 The Standard sets down the specific additional requirements and procedures, to that which are normally followed in other normative standards, to enable engineers to carry out work on new low -pressure Hydrogen domestic installations and existing low-pressure Natural Gas domestic installations repurposed for Hydrogen, during the initial community-based village trial.

1.4 The aim of the document is to identify the differences in practices and procedures that will be required for domestic Hydrogen installations. However, this cannot be an exhaustive list.

1.5 This IGEM Standard provides the key technical & safety engineering requirements, in conjunction with applicable UK Regulations, to support a training and assessment programme for engineers involved in the Hydrogen community trials. This Standard can also be used to support employers to develop their own site-specific work practices and procedures for their employees to use and follow. As such, Appendices A8 & A9 are provided as exemplars to assist trial operators in this new field of activity.  

1.6 Standards and research being undertaken by the HSS4H and other research-based programs are to support the UK Government’s policy decision and the village trial. The practices and procedures recommended in this Standard reflect the current maturity of knowledge and experience of Hydrogen operation and will be reviewed over time as the operational evidence base becomes more established.  

1.7 Some procedures and equipment required by this Standard may only be applicable during the initial trials. If the UK Government’s policy decision supports conversion, further research, and development, in conjunction with experience gained from trials, may result in different approaches being adopted in the future, which will be incorporated into future guidance.

1.8 Many of the methods and equipment required for these activities are still being developed and finalised and updates to this document will be required as information becomes available.

1.9 If the UK Government’s policy decision supports converting the Natural Gas system to Hydrogen, this document will be superseded by normative Standards and procedures once they are fully developed.

1.10 This Standard makes use of the terms “must”, “shall” and “should” when prescribing particular procedures:

• the term “must” identifies a requirement by law in Great Britain (GB) at the time of publication
• the term “shall” prescribes a procedure which, it is intended, will be complied with in full and without deviation
• the term “should” prescribes a procedure which, it is intended, will be complied with unless, after prior consideration, deviation is considered to be acceptable.

Such terms may have different meanings when used in legislation, or Health and Safety Executive (HSE) Approved Code of Practice (ACoP) or guidance, and reference needs to be made to such statutory Legislation or official guidance for information on legal obligations.

1.11 It is now widely accepted that the majority of accidents in industry generally are in some measure attributable to human as well as technical factors. People who initiated actions that caused or contributed to accidents might have acted in a more appropriate manner to prevent them.

To assist in the control of risk and proper management of these human factors, due regard is to be taken of HSG48 and HSG65.

1.12 The primary responsibility for compliance with legal duties relating to health and safety at work rests with the employer. The fact that certain employees, for example "responsible engineers" are allowed to exercise their professional judgement does not allow employers to abrogate their primary responsibilities.

Note:  The responsible engineer is a suitably qualified, competent, and experienced engineer appointed to be responsible for the execution and for approval of activities designated by their employer.  

Employers are required to:

• have done everything to ensure, so far as is reasonably practicable, that there are no better protective measures that can be taken other than relying on the exercise of professional judgement by "responsible engineers"
• have done everything to ensure, so far as is reasonably practicable, that "responsible engineers" have the skills, training, experience, and personal qualities necessary for the proper exercise of professional judgement
• have systems and procedures in place to ensure that the exercise of professional judgement by "responsible engineers" is subject to appropriate monitoring and review.

Employers shall not require "responsible engineers" to undertake tasks which would necessitate the exercise of professional judgement that is not within their competence. There should be written procedures defining the extent to which "responsible engineers" can exercise their professional judgement. When "responsible engineers" are asked to undertake tasks which deviate from this they are to refer the matter for higher review.

1.13 Notwithstanding Sub-Section 1.10, where new and better techniques are developed and proved, they are to be adopted without waiting for the modification of this Standard. Amendments to this Standard will be issued when necessary and their publication will be announced in the Journal of IGEM and other publications as appropriate.

1.14 The document identifies (via notes) where confirmation is outstanding, or where an explanation of a recommendation given in the draft is required, for example: (Note:  exact details of size and flow limits to be determined.) 

1.15 Evidence to support these recommendations is referenced throughout the document and is based on work published at the time of writing.  

1.16 This Standard assumes that the Trial Operator has ensured that new or repurposed gas services to premises have been commissioned and that Hydrogen is available at the emergency control valve (ECV).  

1.17 This Standard was published in December 2024.

2.1 This Standard covers gas utilization activities associated with the design, installation, commissioning, and maintenance of low-pressure Hydrogen gas installations, downstream of the Emergency Control Valve (ECV), in domestic premises, forming part of a UK Government-approved coordinated community-based trial.
Note: This Standard assumes a supply of Hydrogen gas is available upstream of the ECV and that the new, or the conversion of, the low-pressure supply network to Hydrogen has been completed.

2.2 This Standard applies to both new installations for Hydrogen and repurposed Natural Gas installations for Hydrogen.

Note 1: The Standard uses the terminology - ‘new installations’ and ‘repurposed installations’ to reflect this.

Note 2: Where all or parts of an existing Natural Gas installation is to be repurposed for Hydrogen, it will have been covered by a risk assessment (which may be generic) to ensure the components are suitable for use or otherwise replace (see Section 6).

Note 3: The range of Hydrogen appliances available for the initial trials may be limited. Therefore, this Standard focuses on the installation of those appliances that will be used in the trials and will be available for both training and assessment of competence.

Note 4: The principles of this standard can be applied to the repurposing of other fuel gas installations, e.g. LPG.

2.3 Trials will also include industrial and commercial (non-domestic) premises. These installations are covered by a separate Standard, IGEM/H/3 Hydrogen Enabling Standard – Non-Domestic.
Larger domestic premises will also be covered by IGEM/H/3.

Note: This is due to large domestic premises having a primary meter size greater than 20 m3h-1 requiring individual assessment of excess flow mitigation provision.

2.4 The Hydrogen gas supplied to trial installations is assumed to be nominally 100% Hydrogen, though it may contain small quantities of other components and the odorant. Blends of Hydrogen and Natural Gas are not within the scope of this document.

Note 1: The term 100% is used to differentiate between Hydrogen and Hydrogen blended with Natural Gas.

Note 2: IGEM/H/1 Reference Standard and PAS 4444 details the gas quality information.

2.5 The Standard applies to new and repurposed Hydrogen installation pipework and meters having the following:

• connection to a Hydrogen low pressure (LP) supply network and,
• maximum Operating Pressure (MOP) at the outlet of the ECV not exceeding 75 mbar and,
• nominal contracted metering pressure (Pm) not exceeding 30 mbar (normally 21 mbar) and,
• nominal bore pipework of not greater than 35 mm and,
• a maximum badged capacity through the primary meter of not exceeding 20 m3h-1 and,
• a maximum installation volume of 0.035 m3 and,
• individual appliance heat input not exceeding 70 kW.

Note 1: The supply Network Operator may choose to provide a higher than normal minimum pressure at the outlet of the ECV to assist in the repurposing of the downstream pipework, subject to the required approvals.

Note 2: Larger domestic installations outside this scope, will follow the recommendations given in IGEM/H/3 Hydrogen Enabling Standard – Non-Domestic.

2.6 All pressures quoted are gauge pressure unless otherwise stated.

2.7 The following types of premises and plant are excluded:

• multi-occupancy buildings (as defined by IGEM/G/5)
• caravan parks and boats, yachts, and other vessels
• individual appliances exceeding 70 kW
• gas boosters
• gas engines
• gas compressors
• gas turbines
• processes and industrial plant
• bottled gas supplies.

2.8 Italicised text is informative and does not represent formal requirements.

2.9 Appendices are informative and do not represent formal requirements unless specifically referenced in the main Sections via the prescriptive terms “must”, “shall” or “should”.