Asphyxiant gas

An asphyxiant gas, also known as a simple asphyxiant, is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation). Because asphyxiant gases are relatively inert and odorless, their presence in high concentration may not be noticed, except in the case of carbon dioxide (hypercapnia).

Toxic gases, by contrast, cause death by other mechanisms, such as competing with oxygen on the cellular level (e.g. carbon monoxide) or directly damaging the respiratory system (e.g. phosgene). Far smaller quantities of these are deadly.

Notable examples of asphyxiant gases are methane,^[1] nitrogen, argon, helium, butane and propane. Along with trace gases such as carbon dioxide and ozone, these compose 79% of Earth's atmosphere.

Asphyxia hazard

Asphyxiant gases in the breathing air are normally not hazardous. Only where elevated concentrations of asphyxiant gases displace the normal oxygen concentration does a hazard exist. Examples are:

• Environmental gas displacement
  • Confined spaces, combined with accidental gas leaks, such as
    submarines,^[2][3] refrigerators,^[4] or other confined spaces^[5]
  • inert gases, such as computer data centers and sealed vaults^[4]
  • Large-scale natural release of gas, such as during the Lake Nyos disaster in which volcanically-released carbon dioxide killed 1,800 people.^[6]
  • Release of
    magnet quench such as the Large Hadron Collider or a magnetic resonance imaging
    machine.
  • Climbing inside an inflatable balloon filled with helium[7]
• Direct administration of gas
  • Inadvertent administration of asphyxiant gas in
    respirators^[8]
  • Use in suicide^[9][10] and erotic asphyxiation^[11]

Risk management

The risk of breathing asphyxiant gases is frequently underestimated leading to fatalities, typically from breathing helium in domestic circumstances and nitrogen in industrial environments.^[12]

The term asphyxiation is often mistakenly associated with the strong desire to breathe that occurs if breathing is prevented. This desire is stimulated from increasing levels of carbon dioxide. However, asphyxiant gases may displace carbon dioxide along with oxygen, preventing the victim from feeling short of breath. In addition the gases may also displace oxygen from cells, leading to

United States

The handling of compressed asphyxiant gases and the determination of appropriate environment for their use is regulated in the

To decrease the risk of asphyxiation, there have been proposals to add warning odors to some commonly used gases such as nitrogen and argon. However, CGA has argued against this practice. They are concerned that odorizing may decrease worker vigilance, not everyone can smell the odorants, and assigning a different smell to each gas may be impractical. Another difficulty is that most odorants (e.g., the thiols) are chemically reactive. This is not a problem with natural gas intended to be burned as fuel, which is routinely odorized, but a major use of asphyxiants such as nitrogen, helium, argon and krypton is to protect reactive materials from the atmosphere.^[17][18]

In mining

The dangers of excess concentrations of nontoxic gases has been recognized for centuries within the mining industry. The concept of

• Inert gas asphyxiation
  • Controlled atmosphere killing
    , a method of execution using asphyxiant gases
• Limnic eruption
  • Lake Kivu
  • Lake Monoun
  • Lake Nyos
  • Mazuku
• Mining accidents

References