What is an unsafe level of oxygen


Air normally contains 21% oxygen by volume, although oxygen levels of 19.5% — 23.5% by volume are considered to be safe.

Some situations can cause the level of oxygen to dramatically decrease, leading to an oxygen-deficient atmosphere and possible asphyxiation. This may occur, for example, if oxygen in the atmosphere is:

  1. displaced by gases produced during biological processes, for example, methane in a sewer
  2. displaced during purging of a confined space with an inert gas to remove flammable or toxic fumes ie nitrogen
  3. depleted inside metal tanks and vessels through surface oxidation (for example, when rust forms)
  4. consumed during combustion of flammable substances
  5. absorbed or reacts with grains, wood chips, soil or chemicals in sealed silos.

Too much oxygen can increase the risk of fire or explosion. Oxygen-enriched atmospheres may occur if:

  1. chemical reactions cause the production of oxygen, for example certain reactions with hydrogen peroxide
  2. there is a leak of oxygen from an oxygen tank or fitting while using oxy-acetylene equipment.

Gas detection trianing