Asphyxiant
A substance that displaces or reduces the availability of oxygen in the breathing zone, leading to oxygen deficiency and potentially unconsciousness or death. Simple asphyxiants have no direct toxic effect but reduce oxygen concentration; chemical asphyxiants interfere with oxygen use by body tissues.
Also known as
By jurisdiction
UK HSE
“asphyxiant”Close equivalentCOSHH 2002 applies to asphyxiants as substances hazardous to health. Simple asphyxiants such as nitrogen, argon, carbon dioxide and methane are listed in HSE EH40 with an advisory note on oxygen deficiency risk. Confined space regulations address asphyxiation as a key risk requiring atmospheric monitoring.
Irish HSA
“asphyxiant”Close equivalentThe Chemical Agents Regulations 2001 apply to asphyxiants. The General Application Regulations 2007 identify oxygen deficiency as a specified risk in confined spaces. HSA guidance requires atmospheric monitoring for oxygen levels before and during confined space entry.
US OSHA
“asphyxiant”Close equivalent“OSHA addresses asphyxiation risk through 29 CFR 1910.146 (permit-required confined spaces), which requires atmospheric testing for oxygen concentration, flammable gases, and toxic air contaminants before entry. Oxygen-deficient atmosphere is defined as containing less than 19.5 per cent oxygen. HazCom also covers simple asphyxiants.”
Practitioner note: Simple asphyxiants give no warning. Nitrogen, argon and carbon dioxide displace oxygen without odour or irritation, so confined space entry depends on atmospheric testing, never on how the air seems.