Oxygen (O₂) Gas Sensors are used to protect againist oxygen depletion due to inert gas such as: Nitrogen, Argon, Helium and against Oxygen-enriched environments due to increased the risk of fire or explosion.
Air normally contains 20.9 per cent oxygen by volume, although oxygen levels of 19.5 per cent to 23.5 per cent by volume are considered to be safe. Atmospheres deficient in oxygen do not provide adequate sensory warning of danger and most simple asphyxiants are odourless. Unconsciousness and death can rapidly ensue in an environment which is deficient in oxygen. There have been a considerable number of deaths among inappropriately protected workers who have entered confined spaces or tanks before these spaces were adequately vented or gas-tested. The WHS Regulations and the Confined Spaces Code of Practice detail the precautions which should be observed in such environments.