Exposure between these products is bidirectional. A hazard analysis should consider what happens to
alternate fueling equipment if an incident with one of the fuels occurs. Care must be taken to have the
appropriate separation distance and mitigations according to the applicable codes. Limited experience
with existing stations has shown that these multi-fuel stations can be successful when installed per code
rules.

Each installation should be evaluated based on the results of a hazard analysis considering both of these
scenarios. Separation distances as listed in documents such as NFPA 2, Hydrogen Technologies Code, are
a minimum starting point but may need to be adjusted based on analysis. Recent work by NFPA 2 has
also included overpressure criteria, but the consequences can vary depending on system design and
surroundings.

Guidance for location of vent stacks is provided by NFPA 2, Hydrogen Technologies Code, which also references CGA G5.5, Hydrogen Vent Systems, for additional guidance. Minimum distances to vent stack outlets should be determined from dispersion and radiation analyses. The height of the vent stack and orientation of the release will affect the minimum separation distance.

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.

These distances are based primarily on hydrogen piping releases and resultant vapor clouds and jet flames based on pipe diameter and pressure. It’s important to note that many facilities have issues such as confinement and congestion, so it may be applicable to apply contemporary engineering models to assess risk.

There is technically no upper limit for GH2 storage listed within the separation distance tables within Chapter 7 of NFPA 2. For LH2, there is a 75000-gallon upper limit for the LH2 storage separation distance tables within Chapter 8 for LH2. 
It’s important to note that many facilities have site specific issues such as large quantities, confinement, and congestion, so it may be applicable to apply contemporary engineering dispersion and radiation models to fully assess risk.
ISO TC 197 is actively developing LH2 tank standards based on recent research results in the European program described at http://preslhy.eu/. This process is usually slow because of the many nations involved and time inherently needed to reach the consensus required by the ISO standard development process.

The Global Asset Protection Services (GAPS) standard was written 20 years ago for property loss prevention at crowded chemical plants and is intended for existing and new oil and chemical facilities to limit explosion over-pressure and fire exposure damage; thus, the purpose is different than NFPA 2. NFPA distances were based on studies from the 1960s as well as qualitative factors that were deemed successful based on applied experience over the years. A risk informed approach as described within Annex E of NFPA 2 was applied to GH2 separation distances in the 2011 edition. These were further revised in 2020. Similar changes as described in Annex N of NFPA 2 were applied to LH2 distances in the 2023 edition.

These distances are based primarily on hydrogen piping releases as a function of pipe diameter and pressure. Exposures were aggregated into three groups and separation distances applied to each as applicable based on unignited vapor clouds, radiation exposure from jet fires, and overpressure. It’s important to note that many facilities have site specific issues such as large quantities, confinement, and congestion, so it may be applicable to apply contemporary engineering models to fully assess risk.
 

Previous versions of NFPA 55 listed overhead power lines within the separation distance tables with no voltage distinction. The separation distances were 15 ft for GH2 and 25 ft for LH2 for all overhead electrical lines. The current edition of NFPA 2 includes these in overhead utilities; the distance for GH2 and LH2 will vary with pressure and diameter of the hydrogen piping. In practice, high voltage overhead power transmission lines used larger distances for safety, but this was mainly due to the easement required for these lines that would exclude hydrogen (and other) systems. For safety, if a best practice was that if the failure of an uninsulated power line could touch the system, then the lines are too close. The UK has some distance criteria under ENA Technical Specification 43-8 Overhead line clearances.