>liquid hydrogen
Accidentally released liquid hydrogen will evaporate very quickly to form a clearly visible cloud of condensed water. It is a common rule of thumb that the explosive part of the cloud more or less coincides with the visible part, but this is not a reliable guidance for safety purposes. On cessation of the release, the cloud will rapidly warm, rise up, and dissolve in a matter of a few minutes.
Puddles or pools of cryogenic liquid may form, if the rate of release is high enough to compete with evaporation. The heat of evaporation per unit mass of liquid hydrogen is about the same as for methane or propane, whereas it is much less per unit liquid volume. This feature and the greater temperature difference with the environment will cause pools of liquid hydrogen to evaporate faster than those of the other liquids. If such a hydrogen pool is ignited, the fire will have a smaller extension than for the other gases and will be much shorter in duration.