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 Inert may refer to: * Chemically inert, not chemically reactive ** Inert gas ** Noble gas, historically called inert gas * Inert knowledge, information which one can express but not use * Inert waste, waste which is neither chemically nor biol ...

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 Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, espe ...

). Far smaller quantities of these are deadly. Notable examples of asphyxiant gases are methane, 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 mines,Terazawa K, Takatori T, Tomii S, Nakano K. ''Methane asphyxia. Coal mine accident investigation of distribution of gas.'' Am J Forensic Med Pathol. 1985 Sep;6(3):211-4.

submarines A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely o ...

refrigerator A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...

s,Gill JR, Ely SF, Hua Z.''Environmental gas displacement: three accidental deaths in the workplace.'' Am J Forensic Med Pathol. 2002 Mar;23(1):26-30. or other confined spaces ** Fire extinguisher systems that flood spaces with inert gases, such as computer

data center A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommunic ...

s and sealed vaults ** Large-scale natural release of gas, such as during the Lake Nyos disaster in which volcanically-released carbon dioxide killed 1,800 people. ** Release of helium boiled off by the energy released in a

magnet quench A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

such as the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...

or a

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

machine. ** Climbing inside an inflatable balloon filled with helium * Direct administration of gas ** Inadvertent administration of asphyxiant gas in respirators ** Use in

suicide Suicide is the act of intentionally causing one's own death. Mental disorders (including depression, bipolar disorder, schizophrenia, personality disorders, anxiety disorders), physical disorders (such as chronic fatigue syndrome), and s ...

and erotic asphyxiation

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. 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 loss of consciousness and death rapidly.

United States

The handling of compressed asphyxiant gases and the determination of appropriate environment for their use is regulated in the United States by the Occupational Safety and Health Administration (OSHA). The National Institute for Occupational Safety and Health (NIOSH) has an advisory role. OSHA requires employers who send workers into areas where the oxygen concentration is known or expected to be less than 19.5% to follow the provision of the Respiratory Protection Standard 9 CFR 1910.134 Generally, work in an oxygen depleted environment requires an SCBA or airline respirator. The regulation also requires an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, respirator fit testing, periodic workplace monitoring, and regular respirator maintenance, inspection, and cleaning." Containers should be labeled according to OSHA's Hazard Communication Standard

9 CFR 1910.1200 9 (nine) is the natural number following and preceding . Evolution of the Arabic digit In the beginning, various Indians wrote a digit 9 similar in shape to the modern closing question mark without the bottom dot. The Kshatrapa, Andhra and ...

These regulations were developed in accordance with the official recommendations of the

Compressed Gas Association The Compressed Gas Association (CGA) is an American trade association for the industrial and medical gas supply industries. The CGA publishes standards and practices that codify industry practices. In cases where government regulation is inspeci ...

(CGA) pamphlet P-1. The specific guidelines for prevention of asphyxiation due to displacement of oxygen by asphyxiant gases is covered under CGA's pamphlet SB-2, ''Oxygen-Deficient Atmospheres.'' Specific guidelines for use of gases other than air in back-up respirators is covered in pamphlet SB-28, ''Safety of Instrument Air Systems Backed Up by Gases Other Than Air.''

Odorized gas

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.

In mining

The dangers of excess concentrations of nontoxic gases has been recognized for centuries within the mining industry. The concept of black damp (or "stythe") reflects an understanding that certain gaseous mixtures could lead to death with prolonged exposure. Early mining deaths due to mining fires and explosions were often a result of encroaching asphyxiant gases as the fires consumed available oxygen. Early self-contained respirators were designed by mining engineers such as

Henry Fleuss Henry Albert Fleuss (13 June 1851 – 6 January 1933) was a pioneering diving engineer, and Master Diver for Siebe, Gorman & Co. of London. Fleuss was born in Marlborough, Wiltshire in 1851. In 1878 he was granted a patent which improved rebr ...

to help in rescue efforts after fires and floods. While canaries were typically used to detect carbon monoxide, tools such as the

Davy lamp The Davy lamp is a safety lamp for use in flammable atmospheres, invented in 1815 by Sir Humphry Davy.Geordie lamp were useful for detecting methane and carbon dioxide, two asphyxiant gases. When methane was present, the lamp would burn higher; when carbon dioxide was present, the lamp would gutter or extinguish. Modern methods to detect asphyxiant gases in mines led to the

Federal Mine Safety and Health Act of 1977 The Federal Mine Safety and Health Act of 1977 (Public Law 95-164) amended the Coal Mine Safety and Health Act of 1969. It can be found in the United States Code under Title 30, Mineral Lands and Mining, Chapter 22, Mine Safety and Health. The S. ...

in the United States which established ventilation standards in which mines should be "ventilated by a current of air containing not less than 19.5 volume per centum of oxygen, not more than 0.5 volume per centum of carbon dioxide".

References

{{Poisoning and toxicity Toxicology