Summary
Although hydrogen has many useful properties, some have serious safety implications:
- Colourless and odourless
- Extremely reactive with oxygen and other oxidizers
- Low ignition energy
- High flame temperature
- Invisible flame in daylight conditions
- Negative Joule-Thomson coefficient; leaking gas warms and may spontaneously ignite
- Small molecular size promotes leaks and diffusion
- Very wide flammability limits in air mixtures
- Can diffuse into or react with certain metals, embrittling them
- The cryogenic liquid at 20K is even colder than frozen nitrogen, oxygen or argon
- Does not support life (can asphyxiate)
On the other hand, hydrogen's considerable buoyancy and lack of toxicity other than as an asphyxiant work in its favor.
Read more about this topic: Hydrogen Safety
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