Flammable hydrogen releases can result in deflagration and transition to a detonation. Whether the
deflagration transitions to a detonation depends on numerous parameters such as cloud size, hydrogen
concentration, confinement, and congestion. Releases into confined or congested areas are more
susceptible to generating significant deflagration over-pressures and more likely to…

There are numerous models that can be used to assess the consequence and risk of leaks and releases.
One such model is HYRAM which is publicly available from Sandia and the US DOE.

Emergency response procedures must be developed for each system based on its design. The
procedures generally include steps to clear personnel from the immediate area, isolate the hydrogen,
shut down the equipment, contact local responders, and protect surrounding equipment/structures until
the hazard is mitigated or the incident is over.

In most cases, it is not necessary to depressurize hydrogen systems in an emergency. Pressure vessels are usually isolated in an emergency. The best actions to assure safety during an emergency should be identified during the hazard analysis.

Requirements for TPRD/PRD’s depend on the local regulations. Some jurisdictions require them, some do not. Others make them optional based on results of performance testing.

This is a complicated subject. Thermally activated pressure relief devices can be an important safeguard for hydrogen vessels if properly designed and installed in accordance with code requirement. Requirements vary globally and often depend on the type of vessel and its intended service (e.g. mobile or stationary). However, as with any device, TPRD’s offer both advantages and disadvantages.…

No, this is not a common or preferred approach. Isolating the source of hydrogen is the best safety practice. Water systems could extinguish the flame but allow the gas to continue leaking and result in an explosion if reignited.

Situations where extinguishing a hydrogen leak prior to stopping flow is safer are rare. Hydrogen releases have a high potential for inadvertent re-ignition and subsequent explosion. Some vent stacks might be equipped with an extinguishing system, but these often can be more hazardous than allowing a properly designed vent stack to continue to burn until the source is isolated.

Releases from high pressure hydrogen systems often make a sound. In those cases, sound might be the
easiest way for a person to know there is a hazard. However, leaks can be relatively small and diffuse,
thereby not making much sound, or alternately large and so loud that they can be very difficult to find. In
both cases, it can be hazardous to move into or through an area.

There is no consensus on the “correct” answer. Small leaks of short duration have a much lower
probability of ignition compared to large releases. Ignition probability is affected by the operating
conditions, whether the release is from a leak or vent stack, and the surrounding environment. Since the
probability of ignition is high, hazard analyses will usually assume the hydrogen…