An asphyxiant gas, also known as a simple asphyxiant, is a nontoxic or minimally toxic

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

which reduces or displaces the normal oxygen concentration in breathing

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

. Breathing of oxygen-depleted air can lead to death by

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

tion (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 Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous p ...

Toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

gases, by contrast, cause death by other mechanisms, such as competing with oxygen on the cellular level (e.g.

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...

) 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, esp ...

). Far smaller quantities of these are deadly. Notable examples of asphyxiant gases are methane, nitrogen,

argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

, 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 op ...

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 t ...

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 An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

, 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 telecommuni ...

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, nic ...

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 hundre ...

or a magnetic resonance imaging machine. ** Climbing inside an inflatable balloon filled with helium * Direct administration of gas ** Inadvertent administration of asphyxiant gas in respirators ** Use in suicide 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 Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...

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 The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...

(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 A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...

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 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 inspe ...

(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

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

s) 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 Blackdamp (also known as stythe or choke damp) is an asphyxiant, reducing the available oxygen content of air to a level incapable of sustaining human or animal life. It is not a single gas but a mixture of unbreathable gases left after oxygen is ...

(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 and the

Geordie lamp The Geordie lamp was a safety lamp for use in flammable atmospheres, invented by George Stephenson in 1815 as a miner's lamp to prevent explosions due to firedamp in coal mines. Origin In 1815, Stephenson was the engine-wright at the Killingw ...

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 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