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Toxic or asphyxiating atmospheres

Hazard Knowledge

Toxic or asphyxiating atmospheres (also known as irrespirable atmospheres) are caused by the presence of toxic gases or vapours, or the lack of sufficient oxygen. Working in this type of atmosphere can lead to asphyxia, unconsciousness or death.

Environments where asphyxiant gases may be present include:

  • Where contaminants have been processed or stored
  • Where there is sewage, sludge or other deposits, especially if gases are released when it is disturbed
  • In spaces where contaminants can enter, or are produced by equipment in use
  • Where exhaust gases from engine driven equipment, machinery or vehicles have accumulated
  • Where naturally occurring biological processes produce toxic gases, especially in poorly-ventilated spaces
  • Where gases from leaks, failure or damage to machinery, pipes or cylinders have accumulated
  • In spaces such as pipes, sewers or manholes

Oxygen deficiency can result from industrial processes or the storage of products, including:

  • Purging confined spaces with an inert gas to remove flammable or toxic gases, vapours or aerosols
  • Naturally occurring biological or chemical processes that consume oxygen
  • Transportation or storage of wood pellets, used as a biofuel, which may consume oxygen and produce carbon monoxide gas
  • When spaces are left completely closed or poorly ventilated for extended periods
  • Limestone chippings, associated with drainage operations, that can produce increased levels of carbon dioxide when they get wet
  • Burning operations and work such as welding and grinding, which consume oxygen
  • Displacement of air during pipe freezing
  • The gradual depletion of oxygen as workers breathe in confined spaces if there is an inadequate supply of replacement air

The intentional reduction of oxygen, to create a hypoxic atmosphere, can be used to:

  • Inhibit or suppress fire, using Redox or gaseous systems – for further information see the BRE supplementary information
  • Extend the shelf life of produce
  • Reduce the effects of oxidation