...when compared to Hydrogen. Hydrogen burns, Gasoline fumes explode.
From: Twenty Hydrogen Myths #E03-05
AMORY B. LOVINS, CEO, ROCKY MOUNTAIN INSTITUTE
20 June 2003, corrected and updated 17 February 2005
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http://www.rmi.org/images/other/Energy/E03-05_20HydrogenMyths.pdf> from Page 9
...Myth #2. Hydrogen is too dangerous, explosive, or “volatile” for common use as a fuel.
The hydrogen industry has an enviable safety record spanning more than a half-century. Any fuel
is hazardous and needs due care, but hydrogen’s hazards are different and generally more tractable
than those of hydrocarbon fuels.
It’s extremely buoyant — 14.4 times lighter than air (natural
gas is only 1.7 times lighter than air). Hydrogen is four times more diffusive than natural gas
or 12 times more than gasoline fumes, so leaking hydrogen rapidly disperses up and away from
its source. If ignited, hydrogen burns rapidly with a nonluminous flame that can’t readily scorch
you at a distance, emitting only one-tenth the radiant heat of a hydrocarbon fire and burning 7%
cooler than gasoline. Although firefighters dislike hydrogen’s clear flame because they need a
viewing device to see it in daylight, victims generally aren’t burned unless they’re actually in the
flame, nor are they choked by smoke.
Hydrogen mixtures in air are hard to explode, requiring a constrained volume of elongated shape.In high-school chemistry experiments, hydrogen detonates with a “pop” when lit in a test tube,
but if it were in free air rather than a long cylindrical enclosure, it wouldn’t detonate at all. Explosion
requires at least twice as rich a mixture of hydrogen as of natural gas, though hydrogen’s
explosive potential continues to a fourfold higher upper limit. Hydrogen does ignite easily,
needing 14 times less energy than natural gas, but that’s of dubious relevance because even natural
gas can be ignited by a static-electricity spark. Unlike natural gas, however, leaking hydrogen
encountering an ignition source is far likelier to burn than to explode, even inside a building,
because it burns at concentrations far below its lower explosive limit.
Ignition also requires a
fourfold higher minimum concentration of hydrogen than of gasoline vapor. In short, in the vast
majority of cases, leaking hydrogen, if lit, will burn but not explode. And in the rare cases where
it might explode,
its theoretical explosive power per unit volume of gas is 22 times weaker than
that of gasoline vapor. It is not, as has been claimed, “essentially a liquid or gaseous form of dynamite.”
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