Can a wet mist system be used to prevent an H2 explosion? Is it considered experimental?

There are two parts for such a system to be effective. First, the system would have to activate quickly enough to establish a water mist throughout the region of interest (i.e., region occupied by a flammable gas mixture) before it could be ignited. This is challenging in terms of timing, and the impact of spraying water inside an enclosure filled with equipment not designed to get wet can be an issue. Second, such a system has to provide a sufficient density of water droplets in the right size range to have the desired effect. For conventional vapor cloud explosions (e.g., large vapor cloud occupying a portion of a process unit at a refinery or chemical plant), experimental work has examined the effect of water sprays. Getting a high enough density of the right sized water droplets has been shown to be effective at slowing the flame front, and hence reducing the resulting blast load. The goal has not been to put the flame out (i.e., quench the flame), as this would be much more difficult, but rather to absorb some of the combustion energy and hence slow the flame. 

The same type of research has been done for mine explosions in the U.S. For a hydrogen-air mixture inside an enclosure, it is theoretically possible to use a water spray (from a fast-acting system triggered on detection) to slow down the flame. This could reduce the demand on an explosion venting system or reduce the structural capacity required for a given vent system. There are a number of recent publications on this topic (i.e., slowing the flame front propagation velocity, reducing the maximum blast pressure, and/or extinguishing the flame for hydrogen or mixtures containing hydrogen). However, the HSP is not aware of any such system for hydrogen explosion prevention or mitigation in industrial applications being available for purchase.