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  Hydrogen: safety

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The public opinion generally perceives hydrogenas a dangerous, inflammable, explosive gas. This is certainly true; however, the full truth is that the majority of current liquid and gaseous fuels are dangerous, inflammable and explosive, and that hydrogen has had a particularly bad press. In particular, the Hindenburg disaster in 1937, where a hydrogen-filled Zeppelin was destroyed in a fire, has influenced people's perception of hydrogen over the last sixty years and unreasonably so. Rigorous testing has led to the belief amongst many experts that hydrogen is no more dangerous than any other fuel – gasoline, natural gas, kerosene – and is in many cases safer.

Hydrogen safety issues

The simple reaction of many people, when considering the issue of hydrogen as a fuel for the first time, is to say "but won't it explode?"

The truth is that hydrogen is in effect highly explosive in confined spaces, because of its high flame speed; however, the shape of the space in which the hydrogen is confined plays an important part, as does the mode of ignition. On the other hand, hydrogen also has a high dispersion coefficient and therefore it is almost impossible to cause a hydrogen explosion in an open area; for the same reason, a hydrogen fire will burn out much more quickly than a gasoline or methane fire. It is also worth pointing out that pure hydrogen is not intrinsically explosive: it must be mixed with air or oxygen before detonation can occur.

Hydrogen is also flammable and explosive over a much wider range of mixtures than any conventional fuel, but its lower limits of 4% and 13% respectively in air are better than gasoline (1% and 1.1%) and similar to those of natural gas (5.3% and 6.3%). Thanks to its fast dispersion and low density, hydrogen does not pool on the ground like gasoline or LPG and is therefore less of a hazard apart from the first few seconds after a spillage. Calculations and experiments involving kerosene (aviation fuel) suggest that a fire in a hydrogen-fuelled aircraft would last a tenth of the time, produce much less heat and spread over a smaller area than a comparable kerosene fire. This would certainly save lives if the fire occurred on the ground.

In addition, further aspects must be considered apart from fire hazard: hydrogen is neither toxic nor corrosive, therefore leaks cannot cause local environmental harm.

Finally, an interesting point is that when safety experts at industrial gas companies are contacted, they usually express a preference for working with hydrogen over many other fuel gases.

The Hindenburg

The most famous (in fact, the only famous) accident involving hydrogen directly was the Hindenburg disaster that occurred in Lakehurst, New Jersey in 1937. Thirty five people died in the tragedy, but later analysis showed that 27 of these deaths were due to people jumping from the burning airship in mid-air. The other eight were people who were killed by burning upholstery or diesel fumes. The most recent research, carried out by Addison Bain, a retired NASA hydrogen specialist, shows that the detonation was caused by the high-volatility paint that was used to paint the outside of the balloon – akin to coating it with rocket fuel. Although the hydrogen burned once the Zeppelin had caught fire, the 62 people who stayed on board and avoided the toxic smoke from the furnishings all survived.

Safe design

Because of its properties and also the bad press to which hydrogen is accustomed, companies producing or using hydrogen have to ensure that they have extensive safety procedures. This is a sensible precaution, but does not appear to be comparable with what is currently requested for handling conventional fuels. If gasoline automobiles were to be introduced now, rather than having evolved over the past 100 years, the safety requirements would probably be much more stringent than they actually are.

In fact, familiarity appears to water down risk perception, as the following example wonderfully describes:

“A new source of power… called gasoline has been produced by a Boston engineer. Instead of burning the fuel under a boiler, it is exploded inside the cylinder of an engine…

The dangers are obvious. Stores of gasoline in the hands of people interested primarily in profit would constitute a fire and explosive hazard of the first rank.

Horseless carriages propelled by gasoline might attain speeds of 14, or even 20 miles per hour. The menace to our people of [vehicles of] this type hurtling through our streets and along our roads and poisoning the atmosphere would call for prompt legislative action even if the military and economic implications were not so overwhelming… the cost of producing [gasoline] is far beyond the financial capacity of private industry…

In addition the development of this new power may displace the use of horses, which would wreck our agriculture.”

US Congressional Record, 1875


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