Asphyxiant gas

:dablink|For main article see Asphyxia. An asphyxiant gas is a non-toxic or minimally toxic gas which dilutes or displaces the oxygen containing atmosphere, leading to death by asphyxiation if breathed long enough. Toxic gases in large enough concentrations to cause asphyxia lead to death by other mechanisms such as interaction with the respiratory system by competing with oxygen (such as carbon monoxide) or causing direct damage (such as phosgene). Because asphyxiant gases are relatively inert, their presence in large quantities may not be noticed until the effects of elevated blood carbon dioxide are recognized by the body. Asphyxiation is not an intrinsic gas property, but arises from its ability to cause death by asphyxiation without causing other symptoms. Notable examples of asphyxiant gases are nitrogen, argon, and helium. The earth's atmosphere is made of 79% asphyxiant gases (mainly nitrogen), and 21% oxygen. This is an example of how all safe, breathable atmospheres are made up of a high enough concentration of oxygen together with at least one asphyxiant gas.

Examples of asphyxia by asphyxiant gas

:dablink|For main article see Asphyxia.This means that asphyxiant gases are normally hazardous only in special circumstances, due to the exclusion of the naturally abundant oxygen in Earth's atmosphere:
* Environmental gas displacement
** breathing in a confined space, 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. PMID 3870672] , submarines [ [http://www.southcoasttoday.com/daily/08-00/08-16-00/a08wn013.htm Discussion of the Kursk disaster and death on submarines] ] [Kirk JC. "Proposed minimum requirements for the operational characteristics and testing of submersible atmosphere monitoring and control units." Life Support Biosph Sci. 1998;5(3):287-94. PMID 11876195] , refrigeratorsGill 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. PMID 11953489] , or other confined spaces [Sahli BP, Armstrong CW."Confined space fatalities in Virginia." J Occup Med. 1992 Sep;34(9):910-7. PMID 1447597]
** fire extinguisher systems that flood spaces with inert gases - such as computer data centers and sealed vaultsGill 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. PMID 11953489]
** due to a large-scale release of gas, even larger areas can be affected given enough asphyxiant gas, such as during the Lake Nyos disaster in which volcanically-released carbon dioxide was responsible for the death of 1,800 people. [ [http://www.bbc.co.uk/science/horizon/2001/killerlakes.shtml BBC article on the Lake Nyos incident] ]
* Direct administration of asphyxiant gas
** exclusive administration of a gas, such as from inhaling the contents of a balloon filled with heliumFact|date=February 2007
** inadvertent administration of asphyxiant gas in respirators [ [http://www.osha.gov/dts/shib/shib042704.html OSHA article on asphyxiant gases in respirators] ]
** asphyxiant gases are also used in suicide [Gallagher KE, Smith DM, Mellen PF. "Suicidal asphyxiation by using pure helium gas: case report, review, and discussion of the influence of the internet." Am J Forensic Med Pathol. 2003 Dec;24(4):361-3. PMID 14634476] [Gilson T, Parks BO, Porterfield CM. "Suicide with inert gases: addendum to Final Exit." Am J Forensic Med Pathol. 2003 Sep;24(3):306-8. PMID 12960671] and erotic asphyxiation. [Shields LB, Hunsaker DM, Hunsaker JC 3rd, Wetli CV, Hutchins KD, Holmes RM. "Atypical autoerotic death: part II." Am J Forensic Med Pathol. 2005 Mar;26(1):53-62. PMID 15725777]
*Contained asphyxiant gas environment
** climbing inside an inflatable balloon filled with helium [Yoshitome K, Ishikawa T, Inagaki S, Yamamoto Y, Miyaishi S, Ishizu H. "A case of suffocation by an advertising balloon filled with pure helium gas." Acta Med Okayama. 2002 Feb;56(1):53-5. PMID 11873946]

Handling of asphyxiant gases

US

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) and National Institute for Occupational Safety and Health (NIOSH). OSHA requirements for the use of asphyxiant gases mandate the provision of respiratory protective devices under the Respiratory Protection Standard [29 CFR 1910.134] . This includes "respirator selection, 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." [ [http://www.osha.gov/SLTC/healthguidelines/nitrogen/recognition.html OSHA page for nitrogen, a representative asphyxiant gas] ] [NIOSH [1987a] . NIOSH guide to industrial respiratory protection. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-116.] 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 Compressed Gas Association (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." [http://www.cganet.com/publication_detail.asp?id=SB-2 Link to pamphlet SB-2] 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." [http://www.cganet.com/publication_detail.asp?id=SB-28 Link to pamphlet SB-28]

Odorized asphyxiant gas

Because of the potential danger of inadvertent asphyxiant gas leaks in the workplace, there have been proposals to odorize some commonly used atmospheric gases such as nitrogen and argon so that their presence can be detected by smell. However, the Compressed Gas Associated has published a position paper arguing against this practice. Their arguments include concern that odorized gas will lead to more relaxed handling of the gases, that the ability to smell is variable among workers, and that there are impracticalities involved in assigning a different smell to each gas. [ [http://www.specgasreport.com/archive/oderizing.htm] Summary of CGA position on odorizing. Accessed 10/11/06] [ [http://www.cganet.com/publication_detail.asp?id=PS-1] Full text of CGA position on odorizing. Accessed 10/11/06]

UK

In the United Kingdom gasses are covered by COSHH.

The asphyxiant, and potentially explosive, natural gas is given an odour artificially.

Historical aspects

:dablink|see Davy lamp.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 reflect an understanding that certain gaseous mixtures could lead to death with prolonged exposure. [ [http://www.msha.gov/century/mag/magcvr.asp Mine Safety and Heath Administration article about mine fire survival. Accessed 10/12/06] ] 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 in order to help in rescue efforts after fires and floods. While canaries were typically used to detect carbon monoxide, tools such as the Davy Safety Lamp and the 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 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..." [ [http://www.msha.gov/REGS/ACT/ACT2.HTM#14 MSHA copy of the Mine Act of 1977. Accessed 10/12/06] ]

References

ee also

* Mining accidents
* Davy lamp
* Geordie lamp