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…
Documents such as NFPA 2, Hydrogen Technologies Code, and the International Fire Code have quantity thresholds that differentiate requirements for the design of systems and enclosures. However, even the smaller quantities present a hazard under specific conditions, especially for systems that have the potential to release hydrogen into a confined or unvented space. Good engineering judgement…
Dispersion and radiation analysis should be conducted to ensure that the hydrogen cloud will not interfere with the flight path of aircraft. In addition, there may be maximum height requirements due to airport requirements depending on the location of the stack.
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.
Flare-less compression style fittings are commonly used. Choose tubing materials and tube wall thicknesses suitable for hydrogen and pressures you are using. Make sure all tubing joints are properly made, mechanically supported to minimize stress and vibration, are in a ventilated space, and are easily accessible for inspection and leak testing.
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…
Purging is not recommended as a continuous part of vent stack operation. However, maintenance activity is a transient event and it’s prudent and recommended to purge a vent system prior to performing maintenance. It’s always possible that hydrogen could be leaking internally from a valve or other component and therefore create a hazard. Of particular note, care must be taken that proper…
We are not aware of a study for blended NG/H2. However, for high concentrations of NG, the vent system should be similar to NG, which still recommends a vent system as NG is less dense than air. For nearly pure hydrogen the recommendations of this presentation are in effect.
NFPA 2 provides Tables in Chapters 7 and 8 that specify the hazardous area classifications surrounding vent stack outlets. These are based on typical vent systems and flows, but are only applicable for smaller systems. The designer of a vent system should apply the principles of documents such as IEC 60079-10-1 (also required by NFPA 2) or NFPA 497 to evaluate larger vent releases where the…
We would not open the vent system to inspect the internal piping without a good reason.
It is recommended to check for water in the vent stack trap
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