This document describes specific functional requirements of stations for the injection of hydrogen fuel gas into transmission and distribution systems for fuel gases (natural gas, biomethane, SNG, hydrogen fuel gas, fuel gas mixtures, etc.) in accordance with European technical rules that ensure the interoperability of systems in addition to the general functional requirements of EN xxxxx-1 (WI 00234087). This standard complements Part 1 by specifying the technical safety requirements to be observed in respect of the chemical and physical properties of hydrogen fuel gas. It furthermore complements the requirements on pipelines specified in EN 12007-3 and EN 1594 by describing the specific requirements in respect of hydrogen. Additionally, it explains how to handle hydrogen measurements during the course of injection. This document represents the state of the art at the time of its preparation. This document does not apply to injection stations operating prior to the publication of this European Standard. This standard specifies common basic principles for gas infrastructure. Users of this document are expected to be aware of more detailed national standards and/or codes of practice in the CEN member countries. This document is intended to be applied in association with these national standards and/or codes of practice setting out the above-mentioned basic principles. In the event of conflicts in terms of more restrictive requirements in national legislation/regulation with the requirements of this document, the national legislation/regulation takes precedence as illustrated in CEN/TR 13737 (all parts). CEN/TR 13737 (all parts) gives: — clarification of all legislations/regulations applicable in a member state; — if appropriate, more restrictive national requirements; — a national contact point for the latest information.