Although all fuels are hazardous, hydrogen's hazards are different from and generally more easily managed than those of hydrocarbon fuels. It's 14.4 times lighter than air, four times more diffusive than natural gas, and 12 times more diffusive than gasoline—so leaking hydrogen rapidly rises away from its source. Also, it needs at least four times the concentration of gasoline fumes to ignite, it burns with a nonluminous flame that can't scorch you at a distance, and its burning emits no choking smoke or fumes—only water.

Hydrogen-air mixtures are hard to make explode. Hydrogen does ignite easily, with only a tenth as much energy as natural gas, which a static spark can ignite. However, unlike natural gas, ignited hydrogen burns at lower concentrations than can explode, and it can't explode in open air. The 1937 Hindenburg disaster was investigated by NASA scientist Dr. Addison Bain in the late 1990s. He found that probably nobody aboard was killed by a hydrogen fire; the 35 onboard who died as a result of the fire were killed by jumping out or by the burning propeller-engine diesel fuel, flammable furnishings, and dirigible itself, which—coated with a paste containing aluminum powder and chemically similar to rocket fuel—was easily set alight by a spark. The clear hydrogen flames swirled harmlessly above the 62 surviving passengers as they rode the flaming dirigible safely to earth.
 

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