Knowledge and understanding
Understand all associated hazard knowledge
Liquid hydrogen and helium are sufficiently cold to liquefy air. Nitrogen will evaporate more rapidly from the liquefied air than oxygen. This will leave behind a liquid air mixture that has a higher concentration of oxygen than normal air. When this evaporates, an atmosphere with a higher concentration of oxygen is created.
Liquid oxygen is also a frequently used cryogenic material and is transported by road and stored at premises. A release of liquid oxygen will inevitably result in elevated oxygen levels as the oxygen evaporates into the atmosphere.
Other situations where an oxygen-enriched atmosphere might occur because of certain chemical reactions include:
- Decomposition of hydrogen peroxide or another oxidising source
- Chemical oxygen generators
- Electrolysis of water
By far the most likely situation for an oxygen enrichment to be encountered is through the transport/storage of cryogenic oxygen.
Cryogenic materials can create a fire hazard through three possible routes:
- The cryogenic material is a liquefied flammable gas (e.g. methane as liquefied natural gas (LNG))
- The cryogenic material is liquefied oxygen; as this evaporates, the atmospheric oxygen concentration will be raised, increasing the potential for combustible materials to burn
- Certain cryogenic materials (liquid hydrogen and helium) are sufficiently cold to liquefy air and when this evaporates nitrogen will be released first; when oxygen subsequently evaporates this will also lead to an increase in the atmospheric concentration of oxygen
- Control measureRecognise consequences on processes using cryogenic materials
- Control measureSubstance identification