{{Short description|Insufficient oxygen in breathed air}} '''Inert gas asphyxiation''' is a form of asphyxiation that results from breathing a physiologically inert gas in the absence of oxygen, or a low amount of oxygen (hypoxia),<ref>European Industrial Gases Association (2009), ''[http://www.linde-gas.com/internet.global.lindegas.global/en/images/Hazards%20of%20inert%20gases%20and%20oxygen%20depletion17_13909.pdf Hazards of Inert Gases and Oxygen Depletion]'', {{Webarchive|url=https://web.archive.org/web/20170517121748/http://www.linde-gas.com/internet.global.lindegas.global/en/images/Hazards%20of%20inert%20gases%20and%20oxygen%20depletion17_13909.pdf |date=2017-05-17 }}, IGC Doc 44/09/E</ref> rather than atmospheric air (which is composed largely of nitrogen and oxygen). Examples of physiologically inert gases, which have caused accidental or deliberate death by this mechanism, are argon, xenon, helium and nitrogen.<ref>{{Cite journal |last1=Steiner |first1=A. R. |last2=Axiak Flammer |first2=S. |last3=Beausoleil |first3=N. J. |last4=Berg |first4=C. |last5=Bettschart-Wolfensberger |first5=R. |last6=García Pinillos |first6=R. |last7=Golledge |first7=H. D. |last8=Marahrens |first8=M. |last9=Meyer |first9=R. |last10=Schnitzer |first10=T. |last11=Toscano |first11=M. J. |last12=Turner |first12=P. V. |last13=Weary |first13=D. M. |last14=Gent |first14=T. C. |date=2 November 2019 |title=Humanely Ending the Life of Animals: Research Priorities to Identify Alternatives to Carbon Dioxide |journal=Animals |volume=9 |issue=11 |pages=911 |doi=10.3390/ani9110911 |doi-access=free |pmid=31684044 |pmc=6912382 }}</ref> The term "physiologically inert" is used to indicate a gas that has no toxic or anesthetic properties and does not act upon the heart or hemoglobin. Instead, the gas acts as a simple diluent to reduce the oxygen concentration in inspired gas and blood to dangerously low levels, thereby eventually depriving cells in the body of oxygen.<ref name="Wilkenfield"/>
According to the U.S. Chemical Safety and Hazard Investigation Board, in humans, "breathing an oxygen deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths. The exposed person has no warning and cannot sense that the oxygen level is too low." In the US, at least 80 people died from accidental nitrogen asphyxiation between 1992 and 2002.<ref name="CSB.gov Safety Bulletin"/> Hazards with inert gases and the risks of asphyxiation are well-established.<ref>[https://web.archive.org/web/20141129043944/http://www.asiaiga.org/docs/AIGA%20008_11_Hazards%20of%20inert%20gases%20and%20oxygen%20depletion.pdf "Hazards of Inert Gases and Oxygen Depletion"]. Singapore: Asia Industrial Gases Association.</ref>
An occasional cause of accidental death in humans, inert gas asphyxia has been used as a suicide method. Inert gas asphyxia has been advocated by proponents of euthanasia, using a gas-retaining plastic hood device colloquially referred to as a suicide bag. Nitrogen asphyxiation has been approved in some places as a method of capital punishment. In the world's first instance of its use, on January 25, 2024, Alabama executed convicted murderer Kenneth Eugene Smith via this method. It has since been used seven more times, six times in Alabama and once in Louisiana, which first used it on March 18, 2025.<ref>{{cite web | url=https://www.cnn.com/2024/01/25/us/kenneth-smith-nitrogen-gas-execution-alabama | title=Alabama puts to death Kenneth Smith in first known execution using nitrogen gas | website=CNN | date=25 January 2024 | access-date=26 January 2024 | archive-date=26 January 2024 | archive-url=https://web.archive.org/web/20240126024427/https://www.cnn.com/2024/01/25/us/kenneth-smith-nitrogen-gas-execution-alabama | url-status=live }}</ref><ref>{{Cite web |last=Pilkington |first=Ed |date=March 19, 2025 |title=Louisiana uses nitrogen gas for first time in death row execution |url=https://www.theguardian.com/us-news/2025/mar/18/louisiana-nitrogen-gas-execution-jessie-hoffman-jr |access-date=October 26, 2025 |website=The Guardian}}</ref> Alternatively, the term hypoxia has been used but this usage is flawed given that hypoxia does not necessarily imply death. On the other hand, asphyxiation is technically incorrect given respiration continues and the carbon dioxide metabolically produced from the oxygen inhaled prior to inert gas asphyxiation can be exhaled without restriction, which can prevent acidosis and the strong urge to breathe caused by hypercapnia.<ref>{{Cite report |url=https://dpic-cdn.org/production/legacy/Copeland%20Report_Nitrogen-Hypoxia.pdf |title=Nitrogen Induced Hypoxia as a Form of Capital Punishment |first1=Michael |last1=Copland |first2=Thom |last2=Parr |first3=Christine |last3=Paras |access-date=2023-11-02 |archive-date=2023-10-22 |archive-url=https://web.archive.org/web/20231022232603/https://dpic-cdn.org/production/legacy/Copeland%20Report_Nitrogen-Hypoxia.pdf |url-status=live }}</ref>
== Process == When humans breathe in an asphyxiant gas or any other physiologically inert gas, they exhale carbon dioxide without re-supplying oxygen. Physiologically inert gases (those that have no toxic effect, but merely dilute or displace oxygen) are generally free of odor and taste. Accordingly, the human subject detects little abnormal sensation as the oxygen level falls. This leads to asphyxiation (death from lack of oxygen) without the painful and traumatic feeling of suffocation (the hypercapnic alarm response, which in humans arises mostly from carbon dioxide levels rising), or the side effects of poisoning. In scuba diving rebreather accidents, a slow decrease in oxygen breathing gas content can produce variable or no sensation.<ref name = "Hamilton"/> By contrast, suddenly breathing pure inert gas causes oxygen levels in the blood to fall precipitously, and may lead to unconsciousness in only a few breaths, with no symptoms at all.<ref name="CSB.gov Safety Bulletin"/> Some animals are better equipped than humans to detect hypoxia, and these species are less comfortable in low-oxygen environments that result from inert gas exposure, though still more averse to CO<sub>2</sub> exposure.<ref name="Joanna-thesis" />
== Physiology ==
A typical human breathes between 12 and 20 times per minute at a rate influenced primarily by carbon dioxide concentration, and thus pH, in the blood. With each breath, a volume of about 0.6 litres is exchanged from an active lung volume of about three litres. The normal composition of the Earth's atmosphere is about 78% nitrogen, 21% oxygen, and 1% argon, carbon dioxide, and other gases. After just two or three breaths of nitrogen, the oxygen concentration in the lungs would be low enough for some oxygen already in the bloodstream to exchange back to the lungs and be eliminated by exhalation. Unconsciousness in cases of accidental asphyxia can occur within one minute. Loss of consciousness results from critical hypoxia, when arterial oxygen saturation is less than 60%.<ref name="Fisher" />
At oxygen concentrations in air of 4 to 6%, there is "loss of consciousness in 40 seconds and death within a few minutes".<ref name="DiMaio"/> At an altitude over {{convert|43000|ft|abbr=on}}, where the ambient oxygen concentration is equivalent to a concentration of 3.6% at sea level, an average individual can perform flying duties efficiently for only 9 to 12 seconds without oxygen supplementation.<ref name="Fisher"/> The US Air Force trains air crews to recognize their subjective signs of approaching hypoxia. Some individuals experience headache, dizziness, fatigue, nausea and euphoria, and some become unconscious without warning.<ref name="Fisher" /> Loss of consciousness may be accompanied by convulsions,<ref name="Fisher" /> and is followed by cyanosis and cardiac arrest. In a 1963 study by the RAF Institute of Aviation Medicine,<ref name="RAF">{{cite journal |author =J. Ernsting |title =The effect of brief profound hypoxia upon the arterial and venous oxygen tensions in man| journal = Journal of Physiology | volume = 169 | pages = 292–311 | year =1963 |issue =2| pmc=1368754 | doi = 10.1113/jphysiol.1963.sp007257 | pmid = 14079668}}</ref> subjects were asked to hyperventilate in a nitrogen atmosphere. Among the results:
{{blockquote|When the duration of over-ventilation with nitrogen was greater than 8–10 sec the subject reported a transient dimming of vision. In the experiments in which nitrogen breathing was carried out for 15–16 sec the subject experienced some general clouding of consciousness and impairment of vision. Vision was frequently lost in these experiments for a short period. In the few experiments in which nitrogen was breathed for 17–20 sec unconsciousness supervened and was accompanied on most occasions by a generalized convulsion. The duration of the interval between the start of over-ventilation with nitrogen and the onset of symptoms was 12–14 sec.}}
The study did not report how much discomfort the subjects felt.<ref name=RAF/>
== Animals == ===Slaughter=== {{Main|Animal slaughter}}
''Controlled atmosphere killing'' (''CAK'') or ''controlled atmosphere stunning'' (''CAS'') is a method for slaughtering or stunning animals such as swine, poultry,<ref>{{Cite web |last=Doorn |first=Dick Van |date=2016-03-16 |title=CO2 stunning for poultry - worldwide interest |url=https://www.poultryworld.net/health-nutrition/co2-stunning-for-poultry-worldwide-interest/ |access-date=2023-03-15 |website=Poultry World |language=en-US |archive-date=2023-09-24 |archive-url=https://web.archive.org/web/20230924081812/https://www.poultryworld.net/health-nutrition/co2-stunning-for-poultry-worldwide-interest/ |url-status=live }}</ref> or cane toads by placing the animals in a container in which the atmosphere lacks oxygen and consists of an asphyxiant gas (one or more of argon, nitrogen or carbon dioxide), causing the animals to lose consciousness. Argon and nitrogen are important components of a gassing process which seem to cause no pain in some species, and for this reason many consider some types of controlled atmosphere killing more humane than other methods of killing.<ref name="Auto40-1"/><ref name="awfc"/> Others species such as pigs show aversion to highly concentrated nitrogen and argon.<ref>{{Cite web |title=AVMA Guidelines for the Euthanasia of Animals: 2020 Edition |url=https://www.avma.org/sites/default/files/2020-02/Guidelines-on-Euthanasia-2020.pdf |access-date=2025-07-28 |website=www.avma.org |quote="Hypoxia produced by N2 and Ar appears to reduce, but not eliminate, aversive responses in pigs"}}</ref> Most animals are stunned by carbon dioxide.<ref>{{cite journal |last1=Andy Coghlan |title=A more humane way of slaughtering chickens might get EU approval |journal=New Scientist |date=Feb 3, 2018 |url=https://www.newscientist.com/article/2159895-a-more-humane-way-of-slaughtering-chickens-might-get-eu-approval |access-date=June 24, 2018 |archive-date=June 24, 2018 |archive-url=https://web.archive.org/web/20180624204842/https://www.newscientist.com/article/2159895-a-more-humane-way-of-slaughtering-chickens-might-get-eu-approval/ |url-status=live }}</ref><ref>{{Cite web |title=Is carbon dioxide stunning of pigs humane? – RSPCA Knowledgebase |url=https://kb.rspca.org.au/knowledge-base/is-carbon-dioxide-stunning-of-pigs-humane/ |access-date=2023-03-15 |language=en-AU |archive-date=2023-03-15 |archive-url=https://web.archive.org/web/20230315194402/https://kb.rspca.org.au/knowledge-base/is-carbon-dioxide-stunning-of-pigs-humane/ |url-status=live }}</ref>
If carbon dioxide is used, controlled atmosphere killing is not the same as inert gas asphyxia, because carbon dioxide at high concentrations (above 5%) is not biologically inert, but rather is toxic and also produces initial distress in some animal species.<ref>{{cite journal |last1=Archie Campbell |title=Humane execution and the fear of the tumbril |journal=New Scientist |date=Mar 10, 2018 |url=https://www.newscientist.com/letter/mg23731680-900-humane-execution-and-the-fear-of-the-tumbril-3 |access-date=June 24, 2018 |archive-date=June 24, 2018 |archive-url=https://web.archive.org/web/20180624204708/https://www.newscientist.com/letter/mg23731680-900-humane-execution-and-the-fear-of-the-tumbril-3/ |url-status=live }}</ref> The addition of toxic carbon dioxide to hypoxic atmospheres used in slaughter without animal distress is a complex and highly species-specific matter, which also depends on the concentration of carbon dioxide.<ref>{{cite web|url=http://kb.rspca.org.au/What-is-CO2-stunning_118.html|archive-url=https://web.archive.org/web/20140409003755/http://kb.rspca.org.au/What-is-CO2-stunning_118.html|url-status=dead|archive-date=April 9, 2014|title=When is carbon dioxide stunning used in abattoirs?|publisher=RSPCA|access-date=June 14, 2013}}</ref><ref>{{cite journal |author1=Jong E.C. |author2=Barnett J.L. |author3=Hemsworth P.H. | year = 2000 | title = The aversiveness of carbon dioxide stunning in pigs and a comparison of the CO2 stunner crate vs. the V-restrainer | journal = Applied Animal Behaviour Science | volume = 67 | issue = 1–2| pages = 67–76 | doi = 10.1016/S0168-1591(99)00103-3 | pmid = 10719190}}</ref><ref>Raj, A.B.M. and Gregory, N.G., (1995).</ref>
=== Euthanasia === Diving animals such as rats and minks and burrowing animals are sensitive to low-oxygen atmospheres and will avoid them. For this reason, the use of inert gas (hypoxic) atmospheres (without CO<sub>2</sub>) for euthanasia is also species-specific.<ref>{{cite thesis |last1=Makowska |first1=Inez Joanna |title=Alternatives to carbon dioxide euthanasia for laboratory rats |url=https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/24/items/1.0066849 |publisher=University of British Columbia |access-date=28 August 2023 |doi=10.14288/1.0066849 |date=2008 |archive-date=28 August 2023 |archive-url=https://web.archive.org/web/20230828204925/https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/24/items/1.0066849 |url-status=live }}</ref>
== Accidental deaths and injury ==
Accidental nitrogen asphyxiation is a possible hazard where large quantities of nitrogen are used. It causes several deaths per year in the United States,<ref name="CSB"/> which is asserted to be more than from any other industrial gas. In one accident in 1981, shortly before the launch of the first Space Shuttle mission, five technicians lost consciousness and two of them died after they entered the aft compartment of the orbiter. Nitrogen had been used to flush oxygen from the compartment as a precaution against fire. They were not wearing air packs because of a last-minute change in safety procedures.<ref name="Time"/>
During a pool party in Mexico in 2013, eight party-goers were rendered unconscious and one 21-year-old male went into a coma after liquid nitrogen was poured into the pool.<ref>{{cite news| url=http://www.nydailynews.com/life-style/health/liquid-nitrogen-jagermeister-mexican-pool-party-sickens-guests-article-1.1376739| work=NY Daily Times| title=Liquid nitrogen at Jägermeister Mexican pool party sickens guests: one man in a coma, eight others ill| access-date=2014-11-16| archive-date=2021-01-27| archive-url=https://web.archive.org/web/20210127164439/https://www.nydailynews.com/life-style/health/liquid-nitrogen-jagermeister-mexican-pool-party-sickens-guests-article-1.1376739| url-status=live}}</ref><ref>{{cite web|url = http://blog.chembark.com/2013/06/18/awful-idea-liquid-nitrogen-at-a-pool-party/|title = Awful Idea: Liquid Nitrogen at a Pool Party|work = chembark.com|date = 18 June 2013|first = Paul|last = Bracher|access-date = 27 November 2014|archive-date = 1 February 2020|archive-url = https://web.archive.org/web/20200201162638/http://blog.chembark.com/2013/06/18/awful-idea-liquid-nitrogen-at-a-pool-party/|url-status = live}}</ref> Occasional deaths are reported from recreational inhalation of helium, but these are very rarely from direct inhalation from small balloons. The inhalation from larger helium balloons has been reportedly fatal.<ref>{{cite news | url=https://www.foxnews.com/story/2-college-students-found-dead-inside-helium-balloon-in-florida | work=Fox News | title=2 College Students Found Dead Inside Helium Balloon in Florida | date=2006-06-04 | access-date=2013-06-15 | archive-date=2013-06-19 | archive-url=https://web.archive.org/web/20130619052035/http://www.foxnews.com/story/0,2933,198108,00.html | url-status=live }}</ref> A fatal fall from a tree occurred after the inhalation of helium from a toy balloon, which caused the person to become either unconscious or lightheaded.<ref>Lung ruptures and fatal gas embolisms have occurred from inhalation from a pressure tank and although this was reported as a helium inhalation death, it differs greatly from the process of inert gas asphyxiation. See [https://www.foxnews.com/health/teen-dies-after-inhaling-helium-at-party gas embolism helium death]</ref> In 2015, a technician at a health spa was asphyxiated while conducting unsupervised cryotherapy using nitrogen.<ref>{{Cite news|url=http://www.ktnv.com/news/osha-investigating-henderson-cryochamber-death|title=Coroner rules cryochamber death due to lack of oxygen|last=Saeidi|first=Mahsa|date=2015-11-11|newspaper=KTNV|language=en-US|access-date=2016-10-17 |archive-url = https://web.archive.org/web/20161018211047/http://www.ktnv.com/news/osha-investigating-henderson-cryochamber-death | archive-date = 2016-10-18 | url-status = dead}}</ref><ref>{{Cite news|title = Death of Woman in Tank at a Nevada Cryotherapy Center Raises Questions About Safety|url = https://www.nytimes.com/2015/10/27/us/death-of-woman-in-tank-at-a-nevada-cryotherapy-center-raises-questions-about-safety.html|newspaper = The New York Times|date = 2015-10-26|access-date = 2016-01-26|issn = 0362-4331|first1 = Kimberley|last1 = Mcgee|first2 = Julie|last2 = Turkewitz|archive-date = 2021-05-16|archive-url = https://web.archive.org/web/20210516102442/https://www.nytimes.com/2015/10/27/us/death-of-woman-in-tank-at-a-nevada-cryotherapy-center-raises-questions-about-safety.html|url-status = live}}</ref> In 2021, six people died of asphyxiation and 11 more were hospitalized following a liquid nitrogen leak at a poultry plant in Gainesville, Georgia.<ref>{{Cite web|last=Amy|first=Jeff|date=January 28, 2021|title=Liquid nitrogen leak at Georgia poultry plant kills 6|url=https://apnews.com/article/georgia-gainesville-34698174274717f4ec84b6964782e9fe|access-date=January 28, 2021|website=Associated Press|archive-date=January 30, 2021|archive-url=https://web.archive.org/web/20210130043531/https://apnews.com/article/georgia-gainesville-34698174274717f4ec84b6964782e9fe|url-status=live}}</ref><ref>{{cite news |last1=Sharpe |first1=Joshua |title=Cause of death released for Gainesville poultry plant workers |url=https://www.ajc.com/news/crime/cause-of-death-released-for-gainesville-poultry-plant-workers/YTA3R2KQPJGZ3POKJATKNRWCHE/ |access-date=June 23, 2021 |publisher=The Atlanta Journal-Constitution |date=March 12, 2021 |archive-date=June 24, 2021 |archive-url=https://web.archive.org/web/20210624204845/https://www.ajc.com/news/crime/cause-of-death-released-for-gainesville-poultry-plant-workers/YTA3R2KQPJGZ3POKJATKNRWCHE/ |url-status=live }}</ref>
== Suicide == {{main|Suicide bag}}
{{Suicide sidebar}} Use of inert gas for suicide was first proposed by a Canadian, Dr Bruce Dunn.<ref>Dunn B, ''Nitrogen and other Inert Gases.'' In: Smith K, Docker C, Hofsess J, Dunn B, "Beyond Final Exit", published by the Right to Die Society of Canada 1995, pp.65-71. The book was distributed internationally by Canadian, American, and British organizations. See also Exit (Right-to-Die Organisation)</ref> Dunn commented that "...the acquisition of a compressed gas cylinder, an appropriate pressure reducing regulator, and suitable administration equipment... [was] not inaccessible to a determined individual, but relatively difficult for a member of the public to acquire casually or quickly".<ref>"Dunn B, ''Beyond Final Exit,'' p.70. Dunn's work and other chapters from ''Beyond Final Exit'' was also publicised on the Canadian website (now offline) called DeathNET. Côte R, ''In Search of Gentle Death'', Corinthian Books 2012, page 314.</ref> Dunn collaborated with other researchers, notably the Canadian campaigner John Hofsess, who in 1997 formed the group "NuTech" with Derek Humphry and Philip Nitschke.<ref>See: Euthanasia device</ref> Two years later, NuTech had streamlined Dunn's work by using readily-available party balloon cylinders of helium.<ref>Humphry, Derek (2014). [http://www.finalexit.org "Obtaining drugs via the internet and using helium hood kits"] {{Webarchive|url=https://web.archive.org/web/20150917204714/http://www.finalexit.org/ |date=2015-09-17 }}. finalexit.org.</ref>
The method of suicide based on self-administration of helium in a bag, a colloquial name being the "exit bag" or suicide bag, has been referenced by some medical euthanasia advocacy groups.<ref>{{cite journal|title=Suicidal asphyxiation with helium: report of three cases.|vauthors=Grassberger M, Krauskopf A | pmid=17571238 | doi=10.1007/s00508-007-0785-4|volume=119|year=2007|journal=Wien. Klin. Wochenschr.|issue=9–10 |pages=323–5|s2cid=22894287 }}</ref> Originally, such bags were used with helium, and 30 deaths were reported with use of them from 2001 to 2005, and another 79 from 2005 to 2009. This suggested to one set of reviewers that the popularity of the technique was increasing, as also did the increase in helium suicides in Sweden during the latter half of the same decade.<ref name = "Austin"/>
After attempts were made by authorities to control helium sales in Australia, a new method was introduced that instead uses nitrogen.<ref>{{cite journal | pmid = 18725778 | doi=10.1097/PAF.0b013e318183240c | volume=29 | title=Case report of suicide by inhalation of nitrogen gas. | date=Sep 2008 | journal=Am J Forensic Med Pathol | pages=235–7 | vauthors=Harding BE, Wolf BC| issue=3 }}</ref> Nitrogen became the main gas promoted by euthanasia advocates, such as Philip Nitschke, who founded a company called ''Max Dog Brewing'' in order to import canisters of nitrogen into Australia.<ref name="death in a can">{{cite news |url=https://www.vice.com/en/article/death-in-a-can-australias-euthanasia-loophole/ |title=Death in a Can: Australia's Euthanasia Loophole |work=VICE Australia |publisher=VICE Media LLC |date=2014-07-04 |access-date=2015-04-11 |archive-date=2015-02-26 |archive-url=https://web.archive.org/web/20150226074129/http://www.vice.com/video/death-in-a-can-australias-euthanasia-loophole |url-status=live }}</ref> Nitschke stated that the gas cylinders can be used for both brewing and, if required, to end life at a later stage in a "peaceful, reliable [and] totally legal" manner.<ref>{{cite news |url=http://www.abc.net.au/7.30/content/2012/s3657550.htm |title=Euthanasia campaigner under scrutiny |author=Sexton, Mike |date=18 December 2012 |work=ABC |access-date=6 May 2013 |archive-date=7 July 2013 |archive-url=https://web.archive.org/web/20130707143023/http://www.abc.net.au/7.30/content/2012/s3657550.htm |url-status=live }}</ref> Nitschke said that nitrogen is "undetectable even by autopsy, which was important to some people".<ref>{{cite news |url=http://www.watoday.com.au/wa-news/euthanasia-group-to-show-west-aussies-how-to-die-well-20130503-2ixgd.html |title=Euthanasia group to show West Aussies how to die 'well' |author=Orr, Aleisha |date=3 May 2013 |work=WAToday |access-date=8 May 2013 |archive-date=7 May 2013 |archive-url=https://web.archive.org/web/20130507052456/http://www.watoday.com.au/wa-news/euthanasia-group-to-show-west-aussies-how-to-die-well-20130503-2ixgd.html |url-status=live }}</ref> Nitschke used 3D printing to build a "Sarco pod" device that fills with nitrogen at the push of a button, claiming to cause its user to become unconscious within a minute and then die of oxygen deprivation.<ref name="WashPost_20211209">{{cite news |last1=Mark |first1=Julian |title=In the works for years, a suicide machine will soon be tested in Switzerland |url=https://www.washingtonpost.com/nation/2021/12/09/switzerland-suicide-machine-pod/ |newspaper=The Washington Post |date=December 9, 2021 |archive-url=https://web.archive.org/web/20211209184451/https://www.washingtonpost.com/nation/2021/12/09/switzerland-suicide-machine-pod/ |archive-date=December 9, 2021 |url-status=live }}</ref><ref>{{Cite web|url=https://www.thetimes.com/world/europe/article/suicide-pod-boss-detained-amid-strangulation-mark-claims-r23n0zrq9|title=Suicide pod boss detained amid 'strangulation mark' claims|first=Adam Sage|last=Paris|date=29 October 2024|website=www.thetimes.com}}</ref>
== Capital punishment == === History === Execution by nitrogen asphyxiation was discussed briefly in print as a theoretical method of capital punishment in a 1995 ''National Review'' article.<ref name="Creque"/> The idea was then proposed by Lawrence J. Gist II, an attorney at law, under the title, International Humanitarian Hypoxia Project.<ref>[https://web.archive.org/web/20101122222859/http://www.gistprobono.org/ihhp/index.html International Humanitarian Hypoxia Project]. gistprobono.org.</ref> In a televised documentary in 2007, the British political commentator and former MP Michael Portillo examined execution techniques in use around the world and found them unsatisfactory; his conclusion was that nitrogen asphyxiation would be the best method.<ref name="videosift" />
In April 2015, Governor Mary Fallin of Oklahoma signed a bill allowing nitrogen asphyxiation as an alternative execution method.<ref name="newsok.com">{{cite web|title=Oklahoma Gov. Mary Fallin signs bill allowing nitrogen asphyxiation as alternative execution method|url=http://newsok.com/oklahoma-gov.-mary-fallin-signs-bill-allowing-nitrogen-asphyxiation-as-alternative-execution-method/article/5411181|work=NewsOK.com|access-date=2015-04-18|archive-date=2018-04-23|archive-url=https://web.archive.org/web/20180423120222/http://newsok.com/oklahoma-gov.-mary-fallin-signs-bill-allowing-nitrogen-asphyxiation-as-alternative-execution-method/article/5411181|url-status=live}}</ref><ref>{{cite web|date=18 April 2015|title=Oklahoma governor signs 'foolproof' nitrogen gas execution method|url=https://www.theguardian.com/us-news/2015/apr/17/oklahoma-nitrogen-execution-method-death-penalty|work=The Guardian|agency=Associated Press|access-date=12 January 2018|archive-date=6 May 2021|archive-url=https://web.archive.org/web/20210506123914/https://www.theguardian.com/us-news/2015/apr/17/oklahoma-nitrogen-execution-method-death-penalty|url-status=live}}</ref> Three years later, in March 2018, Oklahoma announced that, due to the difficulty in procuring lethal injection drugs, nitrogen gas would be used to carry out executions.<ref>{{cite web|url=https://www.livescience.com/62037-oklahoma-executions-nitrogen.html|title=Oklahoma Turns to Nitrogen Gas for Executions|website=Live Science|date=15 March 2018|access-date=17 March 2018|archive-date=17 March 2018|archive-url=https://web.archive.org/web/20180317231840/https://www.livescience.com/62037-oklahoma-executions-nitrogen.html|url-status=live}}</ref><ref>{{cite news|author=Mark Berman|date=March 18, 2018|title=Oklahoma says it will begin using nitrogen for all executions in an unprecedented move|url=https://www.washingtonpost.com/news/post-nation/wp/2018/03/14/oklahoma-says-it-will-begin-using-nitrogen-for-all-executions-in-an-unprecedented-move/?noredirect=on|newspaper=Washington Post|access-date=August 10, 2018|archive-date=May 31, 2020|archive-url=https://web.archive.org/web/20200531063903/https://www.washingtonpost.com/news/post-nation/wp/2018/03/14/oklahoma-says-it-will-begin-using-nitrogen-for-all-executions-in-an-unprecedented-move/?noredirect=on|url-status=live}}</ref> After making "good progress" in designing a nitrogen execution protocol, but not actually carrying out any executions, Oklahoma announced in February 2020 it had found a new reliable source of lethal injection drugs, but would continue working on nitrogen execution as a contingency method.<ref>{{cite web|title=Oklahoma Attorney general says state will resume executions|date=13 February 2020|url=https://nypost.com/2020/02/13/oklahoma-attorney-general-says-state-will-resume-executions/|access-date=March 22, 2020|publisher=nypost.com|archive-date=9 March 2021|archive-url=https://web.archive.org/web/20210309035317/https://nypost.com/2020/02/13/oklahoma-attorney-general-says-state-will-resume-executions/|url-status=live}}</ref>
In March 2018, Alabama became the third state (after Oklahoma and Mississippi), to authorize the use of nitrogen asphyxiation as a method of execution.<ref>{{cite web|url=https://apnews.com/9d8ea52c7fa242b7b98a060709380698|title=Alabama 3rd state to allow execution by nitrogen gas|website=Associated Press|date=22 March 2018|access-date=3 April 2018|archive-date=3 April 2018|archive-url=https://web.archive.org/web/20180403173433/https://apnews.com/9d8ea52c7fa242b7b98a060709380698|url-status=live}}</ref> In August 2023, the Alabama Department of Corrections released its protocol for nitrogen hypoxia executions, designating Kenneth Eugene Smith, convicted of murder for hire in 1996, as the first death row inmate to undergo this method.<ref>{{Cite news |last=Harcourt |first=Bernard E. |date=18 September 2023 |title=Alabama Has a Horrible New Way of Killing People on Death Row |work=The New York Times |url=https://www.nytimes.com/2023/09/18/opinion/alabama-executions-botched.html |access-date=19 September 2023 |archive-date=18 September 2023 |archive-url=https://web.archive.org/web/20230918213350/https://www.nytimes.com/2023/09/18/opinion/alabama-executions-botched.html |url-status=live }}</ref><ref>{{cite news |last1=Allen |first1=Jonathan |title=Alabama seeks to execute prisoner using nitrogen gas asphyxiation |url=https://www.reuters.com/legal/alabama-seeks-execute-prisoner-using-nitrogen-gas-asphyxiation-2023-09-22/ |access-date=29 November 2023 |work=Reuters |date=22 September 2023 |language=en |archive-date=15 December 2023 |archive-url=https://web.archive.org/web/20231215032723/https://www.reuters.com/legal/alabama-seeks-execute-prisoner-using-nitrogen-gas-asphyxiation-2023-09-22/ |url-status=live }}</ref><ref name="guardian-al">{{cite news |agency=Associated Press |title=Alabama court approves nitrogen gas as new method for executions |url=https://www.theguardian.com/us-news/2023/nov/02/alabama-court-approves-use-nitrogen-gas-execution |work=The Guardian |date=2 November 2023 |access-date=29 November 2023 |archive-date=29 November 2023 |archive-url=https://web.archive.org/web/20231129163311/https://www.theguardian.com/us-news/2023/nov/02/alabama-court-approves-use-nitrogen-gas-execution |url-status=live }}</ref> On November 1, the Supreme Court of Alabama authorized the execution to go ahead using the nitrogen hypoxia protocol.<ref name="guardian-al" /> On 25 January 2024, he became the first person to be executed by nitrogen hypoxia in the world.<ref name="BBC-Al">{{Cite web|date=January 25, 2024|title=Kenneth Eugene Smith: Alabama carries out first US nitrogen gas execution|url=https://www.bbc.com/news/world-us-canada-68085513|access-date=January 25, 2024|website=BBC|archive-date=January 26, 2024|archive-url=https://web.archive.org/web/20240126025112/https://www.bbc.com/news/world-us-canada-68085513|url-status=live}}</ref> Though the State Attorney General said afterward that Smith's execution showed that nitrogen hypoxia was an "effective and humane method of execution",<ref>{{cite news |title=Alabama executes a man with nitrogen gas, the first time the new method has been used |url=https://www.koreatimes.co.kr/www/world/2024/01/501_367670.html |work=The Korea Times |date=26 January 2024 |access-date=January 26, 2024 |archive-date=January 26, 2024 |archive-url=https://web.archive.org/web/20240126141948/https://www.koreatimes.co.kr/www/world/2024/01/501_367670.html |url-status=live }}</ref> several people watching the execution reported that Smith "thrashed violently on the gurney"<ref name="BBC-Al" /> for several minutes, with his death reportedly occurring 10 minutes after the nitrogen was administered to the chamber.<ref>{{cite news |last1=Roney |first1=Marty |title=Nitrogen gas execution: Kenneth Smith convulses for four minutes in Alabama death chamber |url=https://www.montgomeryadvertiser.com/story/news/local/alabama/2024/01/25/four-minutes-of-convulsions-kenneth-smith-executed-with-nitrogen-gas/72358038007/ |access-date=26 January 2024 |work=Montgomery Advertiser |date=26 January 2024 |archive-date=January 26, 2024 |archive-url=https://web.archive.org/web/20240126212205/https://www.montgomeryadvertiser.com/story/news/local/alabama/2024/01/25/four-minutes-of-convulsions-kenneth-smith-executed-with-nitrogen-gas/72358038007/ |url-status=live }}</ref><ref>{{Cite news|url=https://www.theguardian.com/us-news/2024/jan/26/what-is-nitrogen-gas-execution-risks|title=Nitrogen gas execution: how it works and why it's controversial|first=Gloria|last=Oladipo|date=26 January 2024|newspaper=The Guardian}}</ref> The United Nations High Commissioner for Human Rights condemned the use.<ref>{{cite web |title=Alabama execution: Statement by UN High Commissioner for Human Rights |url=https://www.ohchr.org/en/statements/2024/01/alabama-execution |publisher=OHCHR |access-date=27 January 2024 |date=26 January 2024 |archive-date=January 27, 2024 |archive-url=https://web.archive.org/web/20240127030343/https://www.ohchr.org/en/statements/2024/01/alabama-execution |url-status=live }}</ref>
On September 26, 2024, Alan Eugene Miller became the second convicted man put to death by way of nitrogen gas, in Alabama, followed by both Carey Dale Grayson and Demetrius Terrence Frazier on November 21, 2024, and February 6, 2025, respectively. Earlier on March 5, 2024, Louisiana Governor Jeff Landry signed a law allowing executions to be carried out via nitrogen gas.<ref>{{cite news|last=Finn|first=James|date=March 5, 2024|title=Jeff Landry signs bills to expand Louisiana death penalty, eliminate parole|work=The Times-Picayune/The New Orleans Advocate|url=https://www.nola.com/news/politics/legislature/jeff-landry-signs-bill-to-expand-louisiana-death-penalty/article_9b33b116-da5d-11ee-a325-3f26b93ed77e.html|access-date=March 6, 2024|archive-url=https://archive.today/20240306125537/https://www.nola.com/news/politics/legislature/jeff-landry-signs-bill-to-expand-louisiana-death-penalty/article_9b33b116-da5d-11ee-a325-3f26b93ed77e.html|archive-date=March 6, 2024|url-status=live}}</ref> A year after Louisiana approved the method, convicted rapist-killer Jessie Hoffman Jr. became the first inmate executed by nitrogen hypoxia in Louisiana on March 18, 2025, making Louisiana the second state to carry out nitrogen gas executions, while at the same time putting an end to the state of Louisiana's 15-year pause on executions.<ref name="The Guardian">{{Cite news |work=The Guardian |date=March 18, 2025 |title=Louisiana uses nitrogen gas for first time in death row execution|url=https://www.theguardian.com/us-news/2025/mar/18/louisiana-nitrogen-gas-execution-jessie-hoffman-jr }}</ref>
After Smith's execution, several other states became open to the possibility of legally carrying out nitrogen gas executions. Lawmakers from Ohio, where a moratorium is in effect since the state's last execution in 2018, were considering legalizing nitrogen gas as a new method of execution aside from lethal injection.<ref>{{cite news |last=Carr Smyth|first=Julie|title=After Alabama pioneers nitrogen gas execution, Ohio may be poised to follow |url=https://apnews.com/article/death-penalty-ohio-attorney-general-c47ea9e0ef7e96c8e0264f50e6c15566 |work=AP News |date=January 30, 2024 |access-date=January 31, 2024 |archive-date=January 31, 2024 |archive-url=https://web.archive.org/web/20240131004724/https://apnews.com/article/death-penalty-ohio-attorney-general-c47ea9e0ef7e96c8e0264f50e6c15566 |url-status=live }}</ref><ref>{{cite news |last1=Dailey|first1=Natasha|last2=Betts|first2=Anna|title=States Where the Death Penalty Has Stalled Look to Alabama |url=https://www.nytimes.com/2024/01/30/us/death-penalty-alabama-ohio.html |work=The New York Times |date=January 30, 2024 |access-date=January 31, 2024 |archive-date=January 31, 2024 |archive-url=https://web.archive.org/web/20240131003740/https://www.nytimes.com/2024/01/30/us/death-penalty-alabama-ohio.html |url-status=live }}</ref><ref>{{cite news |last=Nurse|first=Krystal|title=After Alabama execution, Ohio Republicans push to allow nitrogen gas for death penalty |url=https://www.usatoday.com/story/news/nation/2024/01/30/ohio-republicans-want-nitrogen-gas-executions/72406517007/ |work=USA Today |date=January 30, 2024 |access-date=January 31, 2024 |archive-date=January 31, 2024 |archive-url=https://web.archive.org/web/20240131004002/https://www.usatoday.com/story/news/nation/2024/01/30/ohio-republicans-want-nitrogen-gas-executions/72406517007/ |url-status=live }}</ref> In March 2025, the Arkansas Legislature voted for a bill that authorized the use of nitrogen asphyxiation as a method of execution.<ref>[https://www.kark.com/news/politics/arkansas-nitrogen-gas-execution-bill-clears-house-and-heads-for-senate/]</ref><ref>{{cite news|url=https://www.ualrpublicradio.org/local-regional-news/2025-03-11/arkansas-legislature-approves-executions-using-nitrogen-hypoxia|title=Arkansas Legislature approves executions using nitrogen hypoxia|date=March 12, 2025|work=}}</ref><ref>{{cite news|url=https://arkansasadvocate.com/2025/03/12/arkansas-lawmakers-approve-nitrogen-gas-execution-bill-await-governors-signature/|title=Arkansas lawmakers approve nitrogen gas execution bill, await governor's signature|date=March 12, 2025|work=}}</ref> Governor Sarah Huckabee Sanders signed the Bill into law on March 18, 2025.<ref>{{cite news|url=https://apnews.com/article/executions-arkansas-nitrogen-sarah-huckabee-sanders-4af9ebd60f272f65a09e266444bb0831|title=Arkansas governor signs legislation allowing executions by nitrogen gas|date=March 18, 2025|work=Associated Press}}</ref>
As of 2025, Alabama, Arkansas, Oklahoma, Mississippi and Louisiana are the only states that authorize the use of nitrogen asphyxiation as a method of execution. In the case ''Bucklew v. Precythe'' in 2019, the U.S. Supreme Court ruled that a Missouri death row inmate with cavernous hemangioma, a rare disorder that causes swelling of blood-filled cavities, could not avoid death by lethal injection and choose inert gas asphyxiation using nitrogen, since it had never been used in any execution in the world.<ref>{{cite news |title=US Supreme Court rules inmate has 'no right to painless death' |url=https://www.bbc.com/news/world-us-canada-47780123 |access-date=29 November 2023 |date=1 April 2019 |archive-date=12 April 2023 |archive-url=https://web.archive.org/web/20230412074030/https://www.bbc.com/news/world-us-canada-47780123 |url-status=live }}</ref>
===List of people executed by nitrogen hypoxia=== As of October 23, 2025, eight people, all male, were executed in the United States by nitrogen hypoxia. Seven in Alabama, and one in Louisiana. {| class="wikitable sortable" style="text-align:center;" |- ! scope="col" | {{Abbr|No.|Number}} ! scope="col" | Name ! scope="col" | Race ! scope="col" | Age ! scope="col" | Sex ! scope="col" data-sort-type="date" | Date of execution ! scope="col" | State ! scope="col" | Method ! {{Abbr|Ref.|Reference(s)}} |- ! scope="row" | 1 | Kenneth Eugene Smith | rowspan="3" |White | 58 | rowspan="8"|M | January 25, 2024 | rowspan="4"| Alabama | rowspan="8"| Nitrogen hypoxia | <ref>{{cite news |title=Alabama carries out nation's first known execution with nitrogen gas. Here's what we know |url=https://edition.cnn.com/2024/01/26/us/alabama-execution-nitrogen-what-we-know/index.html |publisher=CNN |date=January 26, 2024 |access-date=January 26, 2024 |archive-date=January 26, 2024 |archive-url=https://web.archive.org/web/20240126135148/https://edition.cnn.com/2024/01/26/us/alabama-execution-nitrogen-what-we-know/index.html |url-status=live}}</ref> |- ! scope="row" | 2 | Alan Eugene Miller | 59 | September 26, 2024 | <ref>{{Cite web |last=Roney |first=Jonathan Limehouse and Marty |title=Alan Eugene Miller becomes second inmate in US to be executed with nitrogen gas |url=https://www.usatoday.com/story/news/nation/2024/09/26/alan-eugene-miller/75398202007/ |access-date=September 26, 2024 |website=USA TODAY |language=en-US}}</ref> |- ! scope="row" | 3 | Carey Dale Grayson | 50 | November 21, 2024 | <ref>{{cite news|title='Society failed': Murder victim's daughter condemns execution |work=BBC|date= November 22, 2024|url=https://www.bbc.com/news/articles/c20gyy7d6gwo}}</ref> |- ! scope="row" | 4 | Demetrius Terrence Frazier | rowspan="2" | Black | 52 | February 6, 2025 | <ref>{{cite news|date=February 6, 2025 |work=Malay Mail |title=US executes serial rapist, murderer with nitrogen gas in controversial first; UN condemns method |url=https://www.malaymail.com/news/world/2025/02/07/us-executes-serial-rapist-murderer-with-nitrogen-gas-in-controversial-first-un-condemns-method/165822 }}</ref> |- ! scope="row" | 5 | Jessie Dean Hoffman Jr. | 46 | March 18, 2025 | Louisiana | <ref name="The Guardian"/> |- ! scope="row" | 6 | Gregory Hunt | rowspan="2" | White | 65 | June 10, 2025 | rowspan="3" | Alabama | <ref>{{Cite news |work=Associated Press |date=June 11, 2025 |title=Alabama executes a man by nitrogen gas for the beating death of a woman in 1988|url=https://apnews.com/article/execution-alabama-nitrogen-gas-1799b231099c2e260bee7f55b97fa31f }}</ref> |- ! scope="row" | 7 | Geoffrey Todd West | 50 | September 25, 2025 | <ref>{{Cite news | work=New York Times|date=September 25, 2025|title=He Couldn't Get Alabama to Spare His Mother's Killer, but Still Found Peace|url=https://www.nytimes.com/2025/09/25/us/alabama-execution-william-berry-geoffrey-west.html}}</ref> |- ! scope="row" | 8 | Anthony Todd Boyd | Black | 54 | October 23, 2025 | <ref>{{Cite news | work=RTE News|date=October 24, 2025|title=Alabama executes convicted murderer with nitrogen gas|url=https://www.rte.ie/news/us/2025/1024/1540316-us-execution/}}</ref> |}
== See also == * Gas chamber, a chamber for death by asphyxiation or poisoning
== References == <references> <ref name="Fisher">{{cite book|author1=Paul W. Fisher |title=USAF Flight Surgeon's Guide |publisher=USAF School of Aerospace Medicine |url=http://wwwsam.brooks.af.mil/af/files/fsguide/HTML/Chapter_02.html |access-date=5 March 2015 |archive-date=16 March 2007 |chapter=2 - High Altitude Respiratory Physiology |quote=With [prolonged or acute hypoxia] there may be convulsions and eventual failure of the respiratory center. |url-status=bot: unknown |archive-url=https://web.archive.org/web/20070316011544/http://wwwsam.brooks.af.mil/af/files/fsguide/HTML/Chapter_02.html }}</ref> <ref name="DiMaio">{{cite web|url=http://www.charlydmiller.com/LIB/forensicpathasphyxia.html|title=Forensic Pathology 2e, Chapter 8: Asphyxia|work=charlydmiller.com|access-date=2007-02-08|archive-date=2021-02-24|archive-url=https://web.archive.org/web/20210224154556/http://www.charlydmiller.com/LIB/forensicpathasphyxia.html|url-status=live}}</ref> <ref name="Auto40-1">PETA's Animal Times, UK, Autumn 2005</ref> <ref name="awfc">{{Cite web |last=Wepruk |first=Jacqueline |title=The Disposal of Spent Laying Hens |url=https://awfc.ca/english/works/pub/disposehens.htm |url-status=dead |archive-url=https://web.archive.org/web/20121204073853/https://awfc.ca/english/works/pub/disposehens.htm |archive-date=2012-12-04 |access-date=2012-12-06 |publisher=The Animal Welfare Foundation of Canada}}</ref> <ref name="Joanna-thesis">{{Cite web |url=http://www.landfood.ubc.ca/animalwelfare/publications/pdfs/theses/Joanna-thesis.pdf |title=ALTERNATIVES TO CARBON DIOXIDE EUTHANASIA FOR LABORATORY RATS |access-date=2012-02-07 |archive-url=https://web.archive.org/web/20130320052350/http://www.landfood.ubc.ca/animalwelfare/publications/pdfs/theses/Joanna-thesis.pdf |archive-date=2013-03-20 |url-status=dead }}</ref> <ref name="CSB">{{cite news |date=2003-06-11 |title=Hazards of Nitrogen Asphyxiation |url=http://www.csb.gov/safety_publications/docs/SB-Nitrogen-6-11-03.pdf |publisher=U.S. Chemical Safety and Hazard Investigation Board |access-date=2007-02-15 |url-status=dead |archive-url=https://web.archive.org/web/20070203150950/http://www.csb.gov/safety_publications/docs/SB-Nitrogen-6-11-03.pdf |archive-date=2007-02-03}}</ref> <ref name="Time">{{cite news |url=http://www.time.com/time/magazine/article/0,9171,922499,00.html |archive-url=https://web.archive.org/web/20080206123546/http://www.time.com/time/magazine/article/0,9171,922499,00.html |url-status=dead |archive-date=February 6, 2008 |title=Shuttle Tragedy |publisher=Time |date=30 March 1981|url-access=subscription }}</ref> <ref name="Creque">Creque, S.A. "Killing with kindness – capital punishment by nitrogen asphyxiation" National Review. 1995-9-11.</ref> <ref name="videosift">{{cite web|url=http://www.videosift.com/video/How-to-Kill-a-Human-Being-in-search-of-a-painless-death|title=How to Kill a Human Being – in search of a painless death|work=VideoSift|access-date=2009-05-23|archive-date=2009-02-25|archive-url=https://web.archive.org/web/20090225212040/http://www.videosift.com/video/How-to-Kill-a-Human-Being-in-search-of-a-painless-death|url-status=live}}</ref> <ref name="Wilkenfield">"Argon, hydrogen, helium, and nitrogen are inert gases that cause asphyxiation if present in high enough concentration to dilute O<sub>2</sub> in the inspired air to dangerous levels. ... Asphyxia, which is synonymous with respiratory failure, can be defined as insufficient oxygen at the cellular level. ... Simple asphyxiants are gases that are physiologically inert. They do not suppress cardiac output or alter the function of the hemoglobin. Rather, they cause asphyxiation only when present in high enough concentration to lower the concentration of O<sub>2</sub> in the inspired air to levels at which the SaO<sub>2</sub> and PaO<sub>2</sub> fall, resulting in inadequate O<sub>2</sub> delivery to tissues." Quoted from Simple Asphyxiants, Mark Wilkenfield, M.D. Chapter 34, pp. 556–7. in: ''Environmental and Occupational Medicine'', Editors William N. Rom, Steven B. Markawitz. 4th Edition, Publisher: Lippincott Williams & Wilkins, 2007. {{ISBN|0781762995}}, 9780781762991.</ref> <ref name="CSB.gov Safety Bulletin">[http://www.csb.gov/assets/1/19/SB-Nitrogen-6-11-031.pdf Chemical Safety Board Bulletin] {{Webarchive|url=https://web.archive.org/web/20160304190717/http://www.csb.gov/assets/1/19/SB-Nitrogen-6-11-031.pdf|date=2016-03-04}} This is a government summary of accidental 80 nitrogen inhalation deaths, mostly in occupational circumstances. For a presentation form with additional material, see [http://www.csb.gov/assets/1/19/Nitrogen_Asphyxiation_Bulletin_Training_Presentation.pdf] {{Webarchive|url=https://web.archive.org/web/20160304191159/http://www.csb.gov/assets/1/19/Nitrogen_Asphyxiation_Bulletin_Training_Presentation.pdf|date=2016-03-04}}</ref> <ref name="Austin">{{cite journal |vauthors=Austin A, Winskog C, van den Heuvel C, Byard RW |date=May 2011 |title=Recent trends in suicides utilizing helium |journal=J. Forensic Sci. |volume=56 |issue=3 |pages=649–51 |doi=10.1111/j.1556-4029.2011.01723.x |pmid=21361949 |s2cid=30521706}}</ref> <ref name="Hamilton">{{cite journal |url=http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/6041/SPUMS_V27N1_13.pdf?sequence=1 |title=Rebreather physiology review |first=RW (Bill) |last=Hamilton |journal=SPUMS Journal |volume=27 |issue=1 |date=March 1997 |access-date=2020-01-23 |archive-date=2014-12-04 |archive-url=https://web.archive.org/web/20141204230210/http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/6041/SPUMS_V27N1_13.pdf?sequence=1 |url-status=usurped }}</ref> </references>
== External links == * [https://www.cdc.gov/niosh/npptl/topics/respirators/factsheets/respfact.html NIOSH respirator fact sheet] * [http://www.csb.gov/ U.S. Chemical Safety and Hazard Investigation Board] * [http://www.charlydmiller.com/ Restraint asphyxia] * [https://web.archive.org/web/20130118234523/http://www.humanesociety.org/issues/slaughter/research/welfare_birds_slaughter.html The Welfare of Birds at Slaughter]: Humane Society of the United States comparison of controlled-atmosphere killing (CAK) to electrical water bath stunning * [http://www.peta.org/features/the-case-for-controlled-atmosphere-killing.aspx Controlled Atmosphere Killing] {{Webarchive|url=https://web.archive.org/web/20131028114821/http://www.peta.org/features/the-case-for-controlled-atmosphere-killing.aspx |date=2013-10-28 }}: People for the Ethical Treatment of Animals * [https://www.documentcloud.org/documents/4608553-East-Central-University-Draft-Report.html ''Nitrogen Induced Hypoxia as a Form of Capital Punishment''], by Michael P. Copeland, J.D., Thom Parr, M.S., and Christine Pappas, J.D., Ph.D. * [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3237947 ''Execution by Nitrogen Hypoxia: Search for Scientific Consensus''], by Kevin M. Morrow, J.D.
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Category:Animal welfare Category:Causes of death Category:Execution methods Category:Nitrogen Category:Poultry farming Category:Slaughter methods Category:Toxicology Category:Asphyxia Category:Suicide by suffocation