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Hydrogen Explained

Hydrogen Safety

Hydrogen is no more dangerous than petrol or other fossil fuels, the risks are simply different.

Unfortunately many people still harbour misconceptions about hydrogen due to the Hindenburg disaster. Contrary to popular belief, the main cause of the Hindenburg disaster was not the hydrogen that the airship contained, but rather the highly reactive coating of iron oxide and reflective aluminium paint on it's shell. These chemicals reacted fiercely together when the ship was struck by lightening in an electrical storm and caused an intense fire. Once the shell had burnt through the hydrogen then also ignited.

Hydrogen is actually a relatively safe gas to handle provided that the risks are properly assessed. Some of the more common risks are listed below:

Fire

Fire Fire is perhaps the most obvious risk, but it is important to recognise that hydrogen combusts differently to most other fuels. It burns rapidly with an invisible flame. This presents a danger in that it is harder to see, but at the same time the rapid combustion will mean that the fire is more likely to extinguish quickly.

Leaks and Embrittlement

Bottle As hydrogen atoms are very small and light they tend to leak out of containers more readily. This risk can be reduced through the use of hydrogen detection equipment and pressure-tested vessels. Typically, the industry standard is to pressure test vessels to between 150% and 200% of their intended capacity to provide a large safety margin. In addition to leaks, hydrogen can also cause some materials to become brittle. This is because the atoms are small enough to penetrate most structures and alter their composition. Some materials are better than others at resisting this effect, notably stainless steel due to its hardness rating.

Asphyxiation

Exclamation mark This can happen when hydrogen fills an enclosed space and dilutes the concentration of oxygen to below levels that are able to support life. Although this is mentioned as a hazard it is normally very unlikely as the gas is more likely to explode/combust before the concentration gets this high.

Explosion

Explosion Similarly to most fossil fuels, hydrogen can present a risk of explosion. The greatest risk tends to be presented in confined spaces, as hydrogen is a light gas and would otherwise disperse quickly before reaching an explosive concentration. The explosive concentrations for hydrogen in air are between 18.3 and 59 percent by volume.

Liquid Hydrogen

Exclamation mark Liquid hydrogen intesifies the risks listed above and very careful handling is required. Infact, cryogenic hydrogen presents simlar explosion characteristics to TNT! It is preferred not to store hydrogen in liquid form for these reasons and also due to the fact that it typically evaporates from most storage vessels at a rate of 1% a day.

Once the above risks have been assessed and procedures put in place, hydrogen is a relatively safe gas to use. It has been used in industry for a number of years with an excellent safety record. Common uses include:

  • Refinement of petroleum
  • Soldering and brazing
  • Weather balloons
  • Rocket fuel
  • Clean fuel for automotive vehicles
  • Fertilizer production (NH3)
  • Energy storage
Scientist

More information about hydrogen and fuel cell safety can be found at http://www.hydrogensafety.info