As mentioned earlier, the chemical and petrochemical industries have been using hydrogen in their operations for many years, and the space industry for several decades. Within industrial settings, the production, storage and transportation infrastructures have been developed for the safe use of hydrogen. However, it must be borne in mind that hydrogen is a volatile, dangerous and explosive gas. Perhaps the most vivid image of this was the fire that destroyed the Hindenburg Zeppelin in 1937 while landing in Lakehurst, New Jersey. Initially, hydrogen used to keep the airship aloft was blamed for the disaster, but later investigations showed the real cause of the accident to be the extremely flammable lacquer (it had similar properties to rocket fuel) which was painted onto the outer hull of the airship and ignited due to electrostatic discharges. The ensuing fire helped by hydrogen burned the entire airship in about only 30 seconds.
In the past, hydrogen has also been used in many homes (the owners were most often unaware) in the form of town gas, which contained up to 60% hydrogen in a mixture with carbon monoxide. It was due in part to the high toxicity of CO, and not necessarily because of hydrogen, that town gas has been replaced by natural gas. Due to its unique physical properties compared to liquid and gaseous hydrocarbon fuels, the safety issues associated with the use of hydrogen are quite specific since, being small and light, hydrogen is a most leak-prone gas. Hydrogen itself is non-toxic, but it is explosive and flammable. Moreover, being colorless, odorless and tasteless, it is difficult to detect leaks. In the case of natural gas, which is also odorless, colorless and tasteless, sulfur compounds are added to make leaks readily detectable, but the addition of such odorants is impractical in the case of hydrogen. In addition, the odorants would leak at different rates compared to the extremely small hydrogen molecule. Consequently, it is necessary to use sensors for hydrogen detection, though even these have been found to be relatively ineffective. Additives could also contaminate and poison the hydrogen fuel cells. Hydrogen is flammable over a wide range of concentrations in air (from 4 to 75%), and the minimum energy necessary for its ignition (0.005 mcal) is about 20-fold lower than that for natural gas and gasoline. Common electronic devices such as a cell phone or even the friction of simply sliding over a motor car seat can cause ignition if the correct concentration of hydrogen in air is present [89,95]. Hydrogen burns with a scarcely, almost invisible, slightly bluish flame, which means that a person could actually step unknowingly into hydrogen flames. Hydrogen, as mentioned earlier, can also cause many metals (including steel) to become brittle over time, raising the risk of cracks and fractures that would result in failures with possible catastrophic consequences, especially in high-pressure systems. Hence, specialized materials or/and liners would be necessary for hydrogen storage.
Until now, the good safety record of hydrogen use in industry has been largely due to the numerous precautions, codes and standards required for hydrogen handling by trained professionals. It is also related to the fact that most hydrogen is produced on-site and so is not transported over long distances in large quantities. However, if hydrogen were to be handled by the wider public and by people with no formal training or awareness of its potential danger, then it would be vital that strict new safeguards be introduced. Such safety measures would most likely be very costly to introduce, and public compliance difficult to ensure.
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