Flammable hydrogen mixtures are easily ignited by static electricity, electrical sparks, and open flames.
The most effective way to extinguish a hydrogen fire is to shut off the flow of hydrogen. A central shutoff valve is typically required and an automatic shut-off system should be considered. If it is not possible or safe to turn off the hydrogen flow, the usual fire-fighting procedure is to prevent the fire from spreading, protect adjacent equipment and let the fire burn until the hydrogen is consumed.
If a hydrogen fire is extinguished without stopping the hydrogen flow, an explosive mixture may form, creating a more serious hazard. See Incident Procedures.
The risk of blast effects can be managed by reducing the consequence (e.g., by maintaining adequate separation distance between hydrogen storage vessels and other structures) or by driving the probability of the event to a very low level. Data on separation distances is currently under review at NFPA, and more information will be available in the near future.
The OSHA standard 29 CFR 1910.103 was based on NFPA 50A and 50B (which have since been combined into NFPA 55). 29 CFR 1910.103 applies to standard industrial storage practice for quantities up to 75,000 gallons of liquid hydrogen and 15,000 standard cubic feet of gaseous hydrogen. (The acknowledged hazard is fire, which is mitigated by time-tested ASME vessel design.)
If planned operating conditions exceed the above limits (e.g., larger quantities of hydrogen or greater potential for a system breach), then two options can be considered:
- Follow the guidelines of DoD 6055.9.
- Prepare a hazard review for design and operation that meets OSHA requirements (see 29 CFR 1910.119) and demonstrates adequate safety for the proposed system/operation.
OSHA standard 29 CFR 1910.103 indicates that locating a hydrogen system in a room designed with some fire resistance, proper venting, and explosion venting is preferable to a "normal" room that doesn't have any special design features. For buildings or rooms with the potential to accumulate quantities of hydrogen greater than 400 SCF, explosion venting should be provided in the roof or exterior walls in accordance with the OSHA standard.