Safety *

Cavendish and Priestly at first thought of hydrogen as pure phlogiston. After experiments and the passing of the phlogiston theory, Lavoisier eventually suggested the name of hydrogen. Properties which are frequently mentioned as making hydrogen especially hazardous are the wide combustibility and detonability ranges. The high diffusivity of hydrogen in air can make hydrogen either more or less safe than slower diffusing combustible gases. The low flame emissivity is also ambiguous in its safety considerations. Combustion of hydrogen within closed spaces can cause serious pressure escalations. In the case of an unconfined ignition of an H₂-air mixture, a simple combustion or deflagration usually occurs resulting in overpressure up to 7 kPa. The handling of hydrogen gas does not present any low temperature problems, as a rule. However, if hydrogen gas which is stored at high pressure is allowed to vent rapidly, the temperature of gas discharged will become colder as the venting proceeds.