Dazo Water Fuel Technology

2.2.3 Liquid Hydrogen Leaks

Leaking liquid hydrogen may spread on the ground for a short distance, but the liquid will quickly evaporate, creating a cloud of gaseous hydrogen over the liquid pool. The distance of spread and the rate of evaporation will depend on the size of the leak and on ambient conditions. The hydrogen cloud over the liquid pool will be very cold and dense, but will rise and dissipate as it is warmed by surrounding air. Often the cold hydrogen will condense water vapor in the air, creating a visible fog in the area of the leak. Frost or ice may also form on the storage vessel or lines in the area of the leak.
The cloud of cold gaseous hydrogen may move horizontally as it warms and rises, and may extend beyond the area of visible fog. This hydrogen cloud may be cold enough to cause frostbite to exposed skin and should be avoided.

Leaking liquid hydrogen is so cold that it can liquefy the oxygen and nitrogen in surrounding air. If liquid oxygen drips onto combustible material (for example, asphalt), it will significantly increase the fire hazard. This is not of major concern for the volumes of liquid hydrogen likely to be carried on a typical commercial vehicle. However, liquid hydrogen storage tanks at fuel stations, which are likely to contain a much greater volume of fuel, should always be constructed over pads made of noncombustible material, such as concrete.

For the same reason, the insulation on the exterior of all liquid hydrogen storage tanks and lines, both at the fuel station and on a vehicle, should be vapor sealed to ensure that air cannot contact the cold inner surface.