Store flammable gas cylinders such as hydrogen, separated from oxidizing (e.g. oxygen), toxic, pyrophoric, corrosive, and reactive Class 2, 3, or 4 gases. Non-reactive gases, such as helium, may be co-located. See codes and standards such as NFPA 2 [7.2.1.1 Incompatible Materials] for further guidance.

Sprinkler systems and other fire suppression means are prescribed per building and fire codes to limit fire spread to other materials. In the case of a hydrogen leak and fire, it is best practice to isolate the hydrogen source, and let any residual hydrogen gas burn out. Even if the initial fire is extinguished, additional leaking hydrogen may accumulate and ignite with the potential for an explosion. 

In general, indoor storage should be limited and the use of hydrogen indoors should be the least necessary. Look to store flammable gases outdoors in dedicated protected area when practicable. Check to see what adopted building and fire codes in your jurisdiction say. NFPA 2, Hydrogen Technology Code, Sections 6.4.1 and 16.3 prescribe requirements to limit hydrogen storage and use in laboratories. NFPA also prescribes requirements for ventilation, gas cabinets, electrical classification, and fume hood operations. Consider outdoor or dedicated storage facilities if you need more than one standard-sized cylinder of hydrogen to support your work.

There are many potential sources of delayed ignition. Hydrogen is easily ignited, and the larger the cloud, the more likely it is for it to find an ignition source. The cloud itself may serve as an ignition source as the force of the gas release may cause dust or other contaminants to mix in the air creating a static charge which ignites the hydrogen. Similarly, the force of the release can cause surrounding materials and equipment to create an ignition source from impingement. Examples include doors being pushed against surrounding equipment, crushed stone being blown against equipment leading to an impact and spark, etc. The release may also be larger than the hazard assessment or codes anticipated, thereby extending the vapor cloud into areas with other ignition sources such as unclassified electrical equipment, hazardous activity by personnel, or surrounding equipment. 

The oxygen in sprayed water would not be a hazard for delayed ignition

There is currently a published ASME BPV Code Case describing pressure design requirements for pressure design of electrolyzers. If the Code Case is adopted by the jurisdiction where a new electrolyzer will be installed, the new electrolyzer will have to meet the requirements in the Code Case. The responsible ASME committee is working to revise the Code Case and intends to incorporate the Code Case into ASME BPV Section VIII, Division 1. If the requirements of the Code Case are so incorporated, then jurisdictions that adopt this Section will also automatically adopt the requirements for new electrolyzers. The incorporation is unlikely to occur before the 2027 edition of the ASME BPV Code.

At least three of the ASME B31 piping codes are logical choices:

• ASME B31.1, Power Piping
• ASME B31.3, Process Piping
• ASME B31.12 Hydrogen Piping and Pipelines

Considerations for code selection include:

• Requirements imposed by the authority having jurisdiction, whether by direct reference or by reference from another applicable code or standard.
• Code(s) used for other piping systems at the site. The people who have to operate and maintain the piping will be better served with fewer piping codes. The piping codes are complex and have different requirements. The people who have to operate and maintain the piping will likely be more successful if they have to learn requirements from fewer codes.

In the absence of these factors, ASME B31.12 is probably the most logical choice.

All three codes are suitable for liquid and gaseous hydrogen at pressures 15,000 psi (100 MPa) and higher. For pressures higher than 15,000 psi (100 MPa), the designation of high pressure fluid service in accordance with Chapter IX of ASME B31.3 may be a more economical choice and should be considered.

Safety codes globally have a requirement to provide a positive means to isolate energy sources and hazardous substances prior to performing maintenance. For gaseous hydrogen systems, methods such as a blind flange, a double block valve arrangement or a double block and bleed valve arrangement can provide that positive isolation.

Installing a blind flange requires breaking the supply line and inserting a solid insert that blocks the flow. The disadvantage of this approach is that it is more laborious than the other options and a method of isolation is needed to safely install the blind flange. The components involved are a lower cost than the other options but that cost is offset by the additional labor and system down-time required. For these reasons, they typically are only used for long term isolation.

A double valve arrangement is an effective approach that can be implemented quickly. A disadvantage of the double valve is that hydrogen may leak through the first valve and allow pressure to build between the valves without any indication. Aside from leading to a false sense of security, the pressure may also push its way through the second valve into the downstream plumbing and work area. While it may seem unlikely for two valves to leak, there sometimes is a common mode failure where both valves are damaged at the same time.

A double-block-and-bleed valve arrangement has a third valve to act as a means to vent, or "bleed" pressure between the two block valves. . In this configuration, leak through of the first valve cannot pressurize the second blocking valve, thereby eliminating the leak-through failure mode of the double block valve arrangement. For hydrogen systems, the outlet of the bleed valve should be routed to a safe venting location. A double block and bleed system can also be automated. In that situation the block valves are designed to fail closed and the bleed valve to fail open. Double block and bleed valves can also be used to safety depressurize and vent the downstream section prior to the isolation.

The requirements of the code used for the original construction apply. The piping may meet the requirements of more than one code. In which case, the code used for changing the rating may be different than the original code of construction. In any case, the re-rated system should meet all of the requirements of the selected code. Note that if the original proof test of the system was not high enough meet the requirement for the new service, the piping will have to be tested at the higher pressure.

The code used for repair and alterations of an existing system depends on the code used for construction as well as on the requirements imposed by the jurisdiction. Note that getting a permit from the jurisdiction may be necessary for an extensive alteration.

Note that getting a permit from the jurisdiction may be necessary for an extensive alteration.

NFPA 2 Annex G provides a summary of the conflicts with 29 CFR 1910.103. This is language that has been in NFPA 55 for several cycles as this conflict has existed for many years. The requirements in the Federal Regulations were established in the early 1970s. Since that time, OSHA has not had sufficient resources to update the applicable provisions.

The primary difference between OSHA and NFPA requirements is the separation distances for bulk hydrogen storage systems. The separation distances were changed by NFPA several years ago based on scientific analysis of leak data. When evaluating installations involving CFR referenced standards such as the ASME Boiler and Pressure Vessel Code, OSHA inspectors are taught to accept compliance with later editions of the standards as meeting the requirements of the regulation. The same may be true for the differences between OSHA 49 CFR 1910.103 and NFPA 2.

See attached response from OSHA on the general topic of NFPA codes/standards.