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Argument: Hydrogen in cars is less dangerous than gasoline

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Supporting quotations

Arthur St. Antoine. "Hydrogen, Fuel Cells, and Reality". Motor Trend. - How safe is hydrogen? Hydrogen is highly flammable over a wide range of concentrations, but upon release it rises four times faster than natural gas, whereas gasoline vapors and propane can gather in strong concentrations on the ground.

Amory B. Lovins said in an interview with Motor Trends, "The tanks are extraordinarily strong. Remember that the pressure inside makes them kind of rubbery in a crash. One manufacturer spent about a decade trying to destroy 5000-psi tanks every way it could think of and never got one to fail ungracefully. The issue with 10,000 psi tanks may be a little different. Using current materials, the space and weight penalties are significant enough that you have to ask yourself if it's worth it, or whether it would be better to put the money into lightening the platform rather than increasing the pressure."[1]

Amory Lovins, CEO of Rocky Mountain Institute. "Twenty Hydrogen Myths". Rocky Mountain Institute. 20 June 2003 - 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.34 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.35 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.36 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.”

Contrary to a popular misunderstanding, these safety attributes actually helped save 62 lives in the 1937 Hindenburg disaster. An investigation by NASA scientist Dr. Addison Bain found38 that the disaster would have been essentially unchanged even if the dirigible were lifted not by hydrogen but by nonflammable helium, and that probably nobody aboard was killed by a hydrogen fire. (There was no explosion.) The 35% who died were killed by jumping out, or by the burning diesel oil, canopy, and debris (the cloth canopy was coated with what nowadays would be called rocket fuel). The other 65% survived, riding the flaming dirigible to earth as the clear hydrogen flames swirled harmlessly above them. This would hardly be the case if an aircraft with only liquid hydrocarbons caught fire while aloft. It emphasizes that hydrogen is generally at least as safe as natural gas or LPG, and is arguably inherently safer than gasoline,39 although the character of their risks is not identical. For example, leaking hydrogen gas will accumulate near the ceiling of an airtight garage, while gasoline fumes or propane will accumulate near the floor — a greater risk to people because they’re typically near the floor, not the roof. Standing in a carpet of fire is far more dangerous than standing below a nearly non-luminous clear flame that goes upwards. Lingering perceptions that hydrogen is unusually dangerous are likely to be dispelled by the kinds of compelling videotaped demonstrations now becoming available, such as a comparison of a hydrogen fire with a gasoline fire. First, a hydrogen leak was created, assuming a very unlikely triple failure of redundant protective devices (industry norms for hydrogen leak detection and safety interlocks are convincingly effective). The tested leak, deliberately caused at the highest- pressure location, discharged the entire 1.54-kg hydrogen inventory of the fuel-cell car in ~100 s, but the resulting vertical flame plume raised the car’s interior temperature by at most 1–2 F° (0.6–1.1 C°), and its outside temperature nearest the flame by no more than a car experiences sitting in the sun. The passenger compartment was unharmed. But then in the second test, a 2.5- fold-lower-energy leak from a 1.6-mm (1/16") hole in a gasoline fuel line gutted the car’s interior and would have killed anyone trapped inside.40 Because the hydrogen-leak test didn’t damage the car, both tests were conducted successively using the same car.41 Finally, of course, there is no connection whatever between ordinary hydrogen gas, whose chemical reactions make it useful as a fuel, and the special isotopes whose thermonuclear reactions power hydrogen bombs. A hydrogen bomb can’t be made with ordinary hydrogen, nor can the conditions that trigger nuclear fusion in a hydrogen bomb occur in a hydrogen accident; they’re achieved, with difficulty, only by using an atomic bomb.

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