Asphyxiant gas

Asphyxiant gas

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An asphyxiant gas is a non-toxic or minimally toxic gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 which reduces or diplaces the normal oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 concentration in breathing air. Prolonged breathing of oxygen depleted air can lead to death by asphyxia
Asphyxia or asphyxiation is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs...

tion (suffocation). Because asphyxiant gases are relatively inert
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...

 and odorless, their presence in high concentration may not be noticed until the effects of elevated blood carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

Hypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...

) are recognized by the body.

Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

 gases, by contrast, cause death by other mechanisms, such as competing with oxygen on the cellular level (e.g., carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

) or directly damaging the respiratory system
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...

 (e.g., phosgene
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...


Notable examples of asphyxiant gases are nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

, and helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

. The Earth's atmosphere is made of 79% asphyxiant gases (mainly nitrogen), and 21% oxygen.

Asphyxia hazard

Asphyxiant gases in the breathing air are normally not hazardous. Only where elevated concentrations of asphyxiant gases displace the normal oxygen concentration a hazard exists. Examples are:
  • Environmental gas displacement
    • Confined spaces, combined with accidental gas leaks, such as mines
      Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

      , submarines, refrigerator
      A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

      s, or other confined spaces
    • Fire extinguisher
      Fire extinguisher
      A fire extinguisher or extinguisher, flame entinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations...

       systems that flood spaces with inert gases, such as computer data center
      Data center
      A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems...

      s and sealed vaults
    • Large-scale release of gas, such as during the Lake Nyos
      Lake Nyos
      Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...

       disaster in which volcanically-released carbon dioxide was responsible for the death of 1,800 people.
    • Release of Helium boiled off by the energy released in a Magnet quench such as the LHC
      Large Hadron Collider
      The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....

       or a MRI
      Magnetic resonance imaging
      Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

  • Direct administration of gas
    • Exclusive administration, such as inhaling the contents of a balloon filled with helium
      Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

    • Inadvertent administration of asphyxiant gas in respirators
    • Use in suicide
      Suicide is the act of intentionally causing one's own death. Suicide is often committed out of despair or attributed to some underlying mental disorder, such as depression, bipolar disorder, schizophrenia, alcoholism, or drug abuse...

       and erotic asphyxiation
      Erotic asphyxiation
      Erotic asphyxiation or breath control play is the intentional restriction of oxygen to the brain for sexual arousal. The sexual preference for that behavior is variously called asphyxiophilia, autoerotic asphyxia, hypoxyphilia. Colloquially, a person engaging in the activity is sometimes called a...

    • Execution
      Capital punishment
      Capital punishment, the death penalty, or execution is the sentence of death upon a person by the state as a punishment for an offence. Crimes that can result in a death penalty are known as capital crimes or capital offences. The term capital originates from the Latin capitalis, literally...

       in gas chamber
      Gas chamber
      A gas chamber is an apparatus for killing humans or animals with gas, consisting of a sealed chamber into which a poisonous or asphyxiant gas is introduced. The most commonly used poisonous agent is hydrogen cyanide; carbon dioxide and carbon monoxide have also been used...

  • Contained gas environment
    • Climbing inside an inflatable balloon filled with helium

United States

The handling of compressed asphyxiant gases and the determination of appropriate environment for their use is regulated in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 by the Occupational Safety and Health Administration
Occupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...

 (OSHA). The National Institute for Occupational Safety and Health
National Institute for Occupational Safety and Health
The National Institute for Occupational Safety and Health 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 Centers for Disease Control and Prevention within the U.S...

 (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 [29 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 [29 CFR 1910.1200]. These regulations were developed in accordance with the official recommendations of the Compressed Gas Association
Compressed Gas Association
The Compressed Gas Association is the oldest major industrial and medical gas association in the world.In January 1913, Robert King sent a letter to the 75 manufacturers of compressed gases in the United States inviting them to attend a meeting in New York for the purpose of organizing a new...

 (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 is an organosulfur compound that contains a carbon-bonded sulfhydryl group...

s) are chemically reactive. This is not a problem with natural gas burned as a fuel, but a major use of asphyxiants such as nitrogen, helium, argon and krypton is to protect reactive materials from the atmosphere.

Asphyxiant gases in mining

The dangers of excess concentrations of non-toxic gases has been recognized for centuries within the mining industry. The concepts of black damp (or "stythe") and afterdamp
Afterdamp is the toxic mixture of gases left in a mine following an explosion caused by firedamp, which itself can initiate a much larger explosion of coal dust. It consists of carbon dioxide, carbon monoxide and nitrogen. Hydrogen sulfide, another highly toxic gas, may also be present...

 reflect 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 respirator
A respirator is a device designed to protect the wearer from inhaling harmful dusts, fumes, vapors, or gases. Respirators come in a wide range of types and sizes used by the military, private industry, and the public...

s were designed by mining engineers such as Henry Fleuss
Henry Fleuss
Henry Albert Fleuss was a pioneering diving engineer, and Master Diver for Siebe, Gorman & Co. of London.Fleuss was born in Marlborough, Wiltshire in 1851....

 to help in rescue efforts after fires and floods. While canaries
The Atlantic Canary , also called the Island Canary, Canary or Common Canary, is a small passerine bird belonging to the genus Serinus in the finch family, Fringillidae. It is native to the Canary Islands, the Azores, and Madeira. Wild birds are mostly yellow-green, with brownish streaking on the...

 were typically used to detect carbon monoxide, tools such as the Davy lamp
Davy lamp
The Davy lamp is a safety lamp with a wick and oil vessel burning originally a heavy vegetable oil, devised in 1815 by Sir Humphry Davy. It was created for use in coal mines, allowing deep seams to be mined despite the presence of methane and other flammable gases, called firedamp or minedamp.Sir...

 and the Geordie lamp
Geordie lamp
The Geordie lamp was invented by George Stephenson in 1815 as a solution to explosions due to firedamp in coal mines.Although controversy arose between Stephenson's design and the Davy lamp, , Stephenson's original design worked on significantly different principles...

 were useful for detecting methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 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
Mine Safety and Health Act of 1977
The Federal Mine Safety and Health Act of 1977 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...

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..."