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{{Short description|Sealed room into which gas is pumped in, causing death by poisoning or asphyxiation}}
{{Other uses}}
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{{Use dmy dates|date=July 2022}}

[[File:2013 KL Majdanek Baths and Gas Chamber - 30.jpg|thumb|Gas chamber at [[Majdanek concentration camp]] near [[Lublin]]]]

A '''gas chamber''' is an apparatus for killing humans or animals with gas, consisting of a sealed chamber into which a [[poison]]ous or [[asphyxiant gas]] is introduced. Poisonous agents used include [[hydrogen cyanide]] and [[carbon monoxide]]. High concentration [[carbon dioxide]] is typically used in gas chambers for animals.

==History==

In America, the utilization of a gas chamber was first proposed by [[Allan McLane Hamilton]] to the state of Nevada.<ref name="Sinclair Sinclair Prejean 2011 p. 27">{{cite book |last1=Sinclair |first1=B.W. |last2=Sinclair |first2=J. |last3=Prejean |first3=H. |title=Capital Punishment: An Indictment by a Death-Row Survivor |publisher=Skyhorse Publishing |year=2011 |isbn=978-1-62872-134-8 |url=https://books.google.com/books?id=FlmCDwAAQBAJ&pg=PT27 |access-date=2022-10-12 |page=27}}</ref><ref name="Engel 2016 p. 160">{{cite book |last=Engel |first=H. |title=Lord High Executioner: An Unashamed Look at Hangmen, Headsmen, and Their Kind |publisher=Open Road Media |year=2016 |isbn=978-1-5040-3149-3 |url=https://books.google.com/books?id=KDBeCwAAQBAJ&pg=PT160 |access-date=2022-10-12 |page=160}}</ref><ref name="Hansen Hansen 2022 p. 435">{{cite book |last1=Hansen |first1=L.L. |last2=Hansen |first2=L.P. |title=Intro Penology & Corrections - 1E |publisher=Aspen Publishing |series=Aspen Paralegal Series |year=2022 |isbn=978-1-5438-4635-5 |url=https://books.google.com/books?id=lEeJEAAAQBAJ&pg=PA435 |access-date=2022-10-12 |page=435}}</ref><ref name="Riddle Loyd Branham Thomas 2012 p. 63">{{cite book |last1=Riddle |first1=J.E. |last2=Loyd |first2=S.M. |last3=Branham |first3=S.L. |last4=Thomas |first4=C. |title=Nevada State Prison |publisher=Arcadia Publishing |series=Images of America |year=2012 |isbn=978-0-7385-8545-1 |url=https://books.google.com/books?id=6dbCOgM2nHQC&pg=PA63 |language=et |access-date=2022-10-12 |page=63}}</ref> Since then, gas chambers have been used as a method of execution of condemned prisoners in the United States and continue to be a legal execution method in three states, seeing [[nitrogen asphyxiation|legislated reintroduction with inert N<sub>2</sub>]], although redundant in practice since the early 1990s.<ref>{{cite web |url=http://www.deathpenaltyinfo.org/methods-execution |title=Methods of Execution |publisher=Death Penalty Information Center |url-status=live |archive-url=https://web.archive.org/web/20110225054450/http://www.deathpenaltyinfo.org/methods-execution |archive-date=2011-02-25}}</ref> [[Lithuania]] used gas chambers for civilian, penal use in the 1930s, with the last known execution carried out in 1940. None of these saw mass use, however, and were strictly for "criminal" purposes.

Most notably, during [[the Holocaust]] large-scale gas chambers designed for mass killing were used by [[Nazi Germany]] from the late 1930s, as part of the ''[[Aktion T4]]'', and later for its [[genocide]] program.

More recently, escapees from [[North Korea]] have alleged executions to have been performed by gas chamber in prison camps, often combined with [[medical experimentation]].<ref>{{cite news |url=https://www.theguardian.com/world/2004/feb/01/northkorea|title=Revealed: The gas chamber horror of North Korea's gulag|website=[[The Guardian]]|date=February 2004|access-date=2022-01-25|archive-date=2018-03-14|archive-url=https://archive.today/20180314200443/https://www.theguardian.com/world/2004/feb/01/northkorea|url-status=live}}</ref>

==Nazi Germany==
{{See also|Extermination camp#Gassings|The Holocaust#Extermination camps|Evidence and documentation for the Holocaust#Use of gas chambers}}
<!-- This section is linked from [[Bergen-Belsen concentration camp]] -->
[[File:Majdanek Komora Gazowa.JPG|thumb|Interior of Majdanek gas chamber, showing [[Prussian blue]] residue]]

[[Nazi Germany]] made extensive use of various types of gas chambers for mass-murder during [[the Holocaust]].

Beginning in 1939, gas chambers were used as part of ''[[Aktion T4]]'', an "[[involuntary euthanasia]]" program under which the Nazis murdered people with physical and intellectual disabilities, whom the Nazis considered [[Life unworthy of life|"unworthy of life"]]. Experiments in the gassing of patients were conducted in October 1939 in occupied [[Poznań]] in Poland. Hundreds of prisoners were murdered by [[carbon monoxide poisoning]] in an improvised gas chamber.<ref name="browning">{{cite book |title=The Origins of the Final Solution: The Evolution of Nazi Jewish Policy, September 1939 – March 1942 |publisher=Arrow |last=Browning |first=Christopher |year=2005 |isbn=978-0-8032-5979-9}}</ref> In 1940, gas chambers using bottled pure carbon monoxide were established at six killing centres in Germany.<ref name="USHMM-HE">{{cite web |url=https://www.ushmm.org/wlc/en/article.php?ModuleId=10005220 |title=Gassing Operations |website=Holocaust Encyclopedia |publisher=United States Holocaust Memorial Museum |access-date=30 November 2017 |url-status=live |archive-url=https://web.archive.org/web/20171203210358/https://www.ushmm.org/wlc/en/article.php?ModuleId=10005220 |archive-date=3 December 2017}}</ref> In addition to persons with disabilities, these centres were also used during [[Action 14f13]] to murder prisoners transferred from concentration camps in Germany, Austria, and Poland. Concentration camp inmates continued to be murdered even after the euthanasia program was officially shut down in 1941.<ref name="klee">{{cite book |title=Euthanasie im NS-Staat. Die Vernichtung lebensunwerten Lebens |trans-title=Euthanasia in the NS State: The Destruction of Life Unworthy of Life |language=de |last=Klee |first=Ernst |year=1983 |publisher=Fischer Taschenbuch Verlag |location=Frankfurt am Main |isbn=978-3-596-24326-6}}</ref>

During the [[Operation Barbarossa|invasion of the Soviet Union]], mass executions by [[exhaust gas]] were performed by ''[[Einsatzgruppen]]'' using [[gas van]]s, trucks modified to divert engine exhaust into a sealed interior gas chamber.<ref name="USHMM-HE" />

Starting in 1941, gas chambers were used at [[extermination camp]]s in Poland for the mass-murder of [[Jews]], [[Romani people|Roma]], and other victims of [[the Holocaust]]. Gas vans were used at the [[Chełmno extermination camp]]. The [[Operation Reinhard]] extermination camps at [[Belzec extermination camp|Belzec]], [[Sobibor extermination camp|Sobibor]], and [[Treblinka extermination camp|Treblinka]] used exhaust fumes from stationary [[diesel engine]]s.<ref name="USHMM-HE" />
[[File:Auschwitz-crematorium-II-openings-1943.jpg|thumb|350x350px|The openings through which Zyklon B was poured into the gas chamber of crematorium II at [[Auschwitz Birkenau]] are visible in this February 1943 photo, taken by SS Dietrich Kammann.<ref>{{Cite book |last=Pressac |first=Jean-Claude |url=https://archive.org/details/JCPAuschwitzTechniqueAndOperationOfTheGasChambers/mode/1up |title=Auschwitz: Technique and operation of the gas chambers |date=1989 |publisher=The Beate Klarsfeld Foundation |page=340 |url-access=limited |via=Internet Archive}}</ref> Poles Ludwik Lawin and Taduesz Kubik, who worked in the camp photography studio, stole a number of Kammann's [[Negative (photography)|negatives]] and buried them.<ref>{{Cite web |last=www.auschwitz.org |title=Pictures taken by the SS / Informing the world / History / Auschwitz-Birkenau |url=https://www.auschwitz.org/en/history/informing-the-world/pictures-taken-by-the-ss |url-status=live |archive-url=https://web.archive.org/web/20250525023422/https://www.auschwitz.org/en/history/informing-the-world/pictures-taken-by-the-ss |archive-date=2025-05-25 |access-date=2025-06-10 |website=Auschwitz-Birkenau Museum |language=en}}</ref>]]
In search of more efficient killing methods, the Nazis experimented with using the [[hydrogen cyanide]]-based [[fumigation|fumigant]] [[Zyklon B]] at the [[Auschwitz concentration camp]]. This method was adopted for mass-murder at the Auschwitz and [[Majdanek concentration camp|Majdanek]] camps. Up to 6,000 victims were gassed with Zyklon B each day at Auschwitz.<ref name="USHMM-HE" />

Most extermination camp gas chambers were dismantled or destroyed in the last months of [[World War II]] as [[Soviet Union|Soviet]] troops approached, except for those at [[Dachau concentration camp|Dachau]], [[Sachsenhausen concentration camp|Sachsenhausen]] and Majdanek. One destroyed gas chamber at Auschwitz was reconstructed after the war to stand as a memorial.

==North Korea==
Kwon Hyok, a former head of security at [[Camp 22]], described laboratories equipped with gas chambers for [[Asphyxiant gas|suffocation gas]] experiments, in which three or four people, normally a family, are the experimental subjects.<ref>{{cite news |url=https://www.theguardian.com/korea/article/0,2763,1136483,00.html |title=Revealed: the gas chamber horror of North Korea's gulag |first=Antony |last=Barnett |date=31 January 2004 |newspaper=The Guardian |access-date=14 December 2016 |archive-date=24 May 2020 |archive-url=https://web.archive.org/web/20200524153555/https://www.theguardian.com/world/2004/feb/01/northkorea |url-status=live}}</ref><ref>[http://freekorea.us/2007/02/18/holocaust-now-looking-down-into-hell-at-camp-22/ Video testimonials by former guards and prisoners at Camp 22] {{webarchive|url=https://web.archive.org/web/20071024121846/http://freekorea.us/2007/02/18/holocaust-now-looking-down-into-hell-at-camp-22/ |date=2007-10-24}}, where the experiments are said to have occurred, with Google Earth images Camp 22 and other camps</ref> After the chambers are sealed and poison is injected through a tube, while scientists observe from above through glass. In a report reminiscent of an earlier account of a family of seven, Kwon claims to have watched one family of two parents, a son and a daughter die from suffocating gas, with the parents trying to save the children using [[mouth-to-mouth resuscitation]] for as long as they had the strength. Kwon's testimony was supported by documents from Camp 22 describing the transfer of prisoners designated for the experiments. The documents were identified as genuine by Kim Sang Hun, a London-based expert on Korea and human rights activist.<ref name="bbc01">{{cite news |url=https://news.bbc.co.uk/2/hi/programmes/this_world/3440771.stm |title=Within prison walls |access-date=2009-12-15 |author=Olenka Frenkiel |date=January 30, 2004 |publisher=BBC News |url-status=live |archive-url=https://web.archive.org/web/20090623201644/http://news.bbc.co.uk/2/hi/programmes/this_world/3440771.stm |archive-date=June 23, 2009}}</ref>

==Lithuania==
In 1937–1940, [[Lithuania]] operated a gas chamber in [[Aleksotas]] within the First Fort of the [[Kaunas Fortress]].<ref name="cernevic" /> Previous executions were carried out by hanging or by shooting. However, these methods were viewed as brutal and in January 1937, the criminal code was amended to provide execution by gas which at the time was viewed as more civilized and humane. Lithuania considered and rejected execution by poison. Unlike the American or German model the Lithuanian gas chamber, built out of bricks, worked by inputting compressed lethal gas from an external storage cylinder (Černevičiūtė 2014). The first execution was carried on July 27, 1937: Bronius Pogužinskas, age 37, convicted of murder of five people from a Jewish family.<ref name="cernevic" /> Historian Sigita Černevičiūtė counted at least nine executions in the gas chamber, though records are incomplete and fragmentary. Of the nine, eight were convicted of murder. One of these, Aleksandras Maurušaitis, was also convicted of anti-government actions during the [[1935 Suvalkija strike]]. The last known execution took place on May 19, 1940, for robbery. The fate of the gas chamber after the [[Occupation of Lithuania by Soviet Union 1940|occupation by the Soviet Union]] in June 1940 is unclear.<ref name="cernevic">{{cite news |first=Sigita |last=Černevičiūtė |title=Dujų kamera prieškario Lietuvoje 1937–1940 metais |newspaper=15Min.lt |date=April 8, 2014 |url=http://www.15min.lt/naujiena/aktualu/istorija/duju-kamera-prieskario-lietuvoje-1937-1940-metais-582-418225 |publisher=15 min (republished from Naujasis Židinys-Aidai) |language=lt |access-date=2016-11-26 |url-status=live |archive-url=https://web.archive.org/web/20161127154408/http://www.15min.lt/naujiena/aktualu/istorija/duju-kamera-prieskario-lietuvoje-1937-1940-metais-582-418225 |archive-date=November 27, 2016}}</ref>

==Soviet Union==
{{main|Gas van}}
As historian [[Robert Gellately]] pointed out, "the Soviets sometimes used a gas van (''dushegubka''), as in Moscow during the 1930s [...], but had no gas chambers."<ref>Robert Gellately: ''Lenin, Stalin, and Hitler: The Age of Social Catastrophe''. New York: Knopf, 2007, p. 367.</ref> In interrogations in the late 1930s, [[NKVD]] officers had testified that special trucks called "soul takers" (''dushegubki'') were supposed to carry prisoners to their executions but instead gassed them on their way by channeling exhaust fumes into the compartment where the prisoners were held.<ref name="H463">Igal Halfin: ''Stalinist Confessions: Messianism and Terror at the Leningrad Communist University''. Pittsburgh: Univ. of Pittsburgh Press, 2009, p. 463.</ref> Author [[Tomasz Kizny]] assumes that they were in use while NKVD officer Isai Berg oversaw the executions at [[Butovo firing range|Butovo]] (October 1937 to 4 August 1938).<ref>Tomasz Kizny, Dominique Roynette: ''La grande terreur en URSS 1937–1938''. Lausanne: Éd. Noir sur Blanc, 2013, p. 236.</ref>
Berg is quoted that "there was no other way to execute so many people". According to yet another contemporary this was only a precautionary method aimed at preventing riots. Historian [[Igal Halfin]] notes, that execution by gas is never mentioned in other Soviet sources, and it contradicts the Soviet practice of individualized executions.<ref name="H463" />

==United States==
[[File:Map of US gas chamber usage.svg|thumb|left|Gas chamber usage in the United States.{{legend|#FFFF33|'''Secondary''' method only}} {{legend|#7fff00|'''Previously''' used, but '''not presently'''}} {{legend|#0099CC|'''Never''' used}}]]
[[File:PostFurmanUSGasChamber.gif|thumb|left|Post-[[Furman v. Georgia|''Furman'']] uses by state and numbers]]

Gas chambers have been used for [[capital punishment in the United States]] to execute [[List of United States death row inmates|death row inmates]]. The first person to be executed in the United States by lethal gas was [[Gee Jon]], on February 8, 1924. An unsuccessful attempt to pump poison gas directly into his cell at [[Nevada State Prison]] led to the development of the first makeshift gas chamber to carry out Jon's death sentence.<ref name="DPIC-Descriptions">{{cite web |url=http://www.deathpenaltyinfo.org/descriptions-execution-methods#gas |title=Descriptions of Execution Methods: Gas Chamber |publisher=[[Death Penalty Information Center]] |year=2010 |access-date=November 3, 2010 |url-status=live |archive-url=https://web.archive.org/web/20101112105603/http://www.deathpenaltyinfo.org/descriptions-execution-methods#gas |archive-date=November 12, 2010}}</ref>

On December 3, 1948, [[Miran Edgar Thompson|Miran Thompson]] and [[Sam Shockley]] were executed in the gas chamber at [[San Quentin State Prison]] for their role in the [[Battle of Alcatraz]].

In 1957, [[Burton Abbott]] was executed as the governor of California, [[Goodwin J. Knight]], was on the telephone to stay the execution.<ref>{{cite news |date=March 25, 1957 |url=http://www.time.com/time/magazine/article/0,9171,809259,00.html |title=Race in the Death House |magazine=[[Time (magazine)|Time]] |access-date=2007-11-14 |archive-url=https://web.archive.org/web/20080330000547/http://www.time.com/time/magazine/article/0,9171,809259,00.html |archive-date=March 30, 2008}}</ref>

Since the restoration of the death penalty in the United States in 1976, 11 executions by gas chamber have been conducted. Four were conducted in [[List of people executed in Mississippi|Mississippi]], 2 in [[List of people executed in Arizona|Arizona]], 2 in [[List of people executed in California|California]], 2 in [[List of people executed in North Carolina|North Carolina]], and 1 in [[List of people executed in Nevada|Nevada]]. The first execution via gas chamber since the restoration of the death penalty was in Nevada in 1979, when [[Jesse Bishop]] was executed for murder. The most recent execution via gas chamber was in 1999.<ref>{{cite web|url=https://deathpenaltyinfo.org/executions/execution-database?filters%5Bmethod%5D=Gas|title=Execution Database &#124; Death Penalty Information Center|publisher=[[Death Penalty Information Center]]|access-date=September 4, 2021|archive-date=September 4, 2021|archive-url=https://web.archive.org/web/20210904220226/https://deathpenaltyinfo.org/executions/execution-database?filters%5Bmethod%5D=Gas|url-status=live}}</ref> By the 1980s, reports of suffering during gas chamber executions had led to controversy over the use of this method.<ref name="CNN">{{cite news |title=German executed in Arizona, legal challenge fails |publisher=CNN |date=March 4, 1999 |url=http://www.cnn.com/US/9903/04/arizona.execution.01/ |archive-url=https://web.archive.org/web/20081011002515/http://www.cnn.com/US/9903/04/arizona.execution.01/ |archive-date=October 11, 2008}}</ref>

At the September 2, 1983, execution of [[Jimmy Lee Gray]] in [[Mississippi]], officials cleared the viewing room after 8 minutes while Gray was still alive and gasping for air. The decision to clear the room while he was still alive was criticized by his [[Attorneys in the United States|attorney]]. In 2007, [[David Bruck]], an attorney specializing in death penalty cases, said, "Jimmy Lee Gray died banging his head against a steel pole in the gas chamber while reporters counted his moans."<ref>{{cite news |title=Some examples of post-Furman botched executions |publisher=Death Penalty Information Center |date=May 24, 2007 |url=http://www.deathpenaltyinfo.org/article.php?scid=8&did=478 |url-status=live |archive-url=https://web.archive.org/web/20071122180900/http://www.deathpenaltyinfo.org/article.php?scid=8&did=478 |archive-date=November 22, 2007}}</ref>

During the April 6, 1992, execution of [[Donald Harding|Donald Eugene Harding]] in [[Arizona]], it took 11 minutes for death to occur. The prison warden stated that he would quit if required to conduct another gas chamber execution.<ref>{{Cite news |last=Weil |first=Elizabeth |title=The needle and the damage done |newspaper=The New York Times |date=February 11, 2007 |url=https://www.nytimes.com/2007/02/11/magazine/11injection.t.html?_r=1&pagewanted=1&oref=slogin |url-status=live |archive-url=https://web.archive.org/web/20170421134244/http://www.nytimes.com/2007/02/11/magazine/11injection.t.html?_r=1&pagewanted=1&oref=slogin |archive-date=April 21, 2017}}</ref> Following Harding's execution, Arizona voted that all persons condemned to death after November 1992 would be executed by [[lethal injection]].<ref name="CNN" />

Following the execution of [[Robert Alton Harris]] in 1992, a federal court declared that "execution by lethal gas under the California protocol is unconstitutionally [[cruel and unusual punishment|cruel and unusual]]."<ref>{{cite court |litigants=Fierro, Ruiz, Harris v. Gomez |vol=77 |reporter=f.3d |opinion=301 |pinpoint=309 |court=U.S. 9th Circuit |year=1996 |url=https://scholar.google.com/scholar_case?case=26906922262871934}}</ref> However, this decision was vacated after California amended its statute to allow death row inmates to choose between lethal injection and the gas chamber.<ref>{{Cite web |title=Fierro v. Terhune, 147 F.3d 1158 {{!}} Casetext Search + Citator |url=https://casetext.com/case/fierro-v-terhune |archive-url=https://web.archive.org/web/20200630011042/https://casetext.com/case/fierro-v-terhune |archive-date=30 June 2020 |access-date=2024-02-09 |website=casetext.com}}</ref> By the late 20th century, most states had switched to methods considered to be more humane, such as lethal injection. California's gas chamber at San Quentin State Prison was converted to an execution chamber for lethal injection.{{When|date=December 2024|reason=when exactly was it converted}}

As of 2020, the last person to be executed in the gas chamber was German national [[LaGrand case#Background|Walter LaGrand]], sentenced to death before 1992, who was executed in [[Arizona]] on March 3, 1999. The [[U.S. Court of Appeals for the Ninth Circuit]] had ruled that he could not be executed by gas chamber, but the decision was overturned by the [[Supreme Court of the United States|United States Supreme Court]].<ref name="CNN" /> The gas chamber was formerly used in [[Colorado]], [[Maryland]], [[Nevada]], [[New Mexico]], [[North Carolina]] and [[Oregon]]. Seven states (Alabama, Arizona, California, Mississippi, [[Missouri]], Oklahoma, and [[Wyoming]]) authorize lethal gas if lethal injection cannot be administered, the condemned committed their crime before a certain date, or the condemned chooses to die in the gas chamber.<ref>{{Cite web |title=Methods of Execution |url=https://deathpenaltyinfo.org/executions/methods-of-execution?scid=8&did=245 |access-date=2024-02-06 |publisher=Death Penalty Information Center}}</ref> Alabama, Mississippi, and Oklahoma specify the nitrogen hypoxia method, Arizona specifies the hydrogen cyanide method, and the other states do not specify the type of gas.<ref>{{Cite web |title=State-by-State Execution Protocols |url=https://deathpenaltyinfo.org/executions/methods-of-execution/state-by-state-execution-protocols |access-date=2024-02-06 |publisher=Death Penalty Information Center}}</ref> In October 2010, [[Governor of New York]] [[David Paterson]] signed a bill rendering gas chambers illegal for use by [[humane society|humane societies]] and other animal shelters.<ref name="humaneanimal">{{cite web |url=http://public.leginfo.state.ny.us/LAWSSEAF.cgi?QUERYTYPE=LAWS+&QUERYDATA=$AGM374$@TXAGM0374+&LIST=SEA17+&BROWSER=BROWSER+&TOKEN=26623049+&TARGET=VIEW |title=Agriculture and Markets Law § 374 |access-date=January 31, 2012 |archive-date=December 10, 2019 |archive-url=https://web.archive.org/web/20191210230501/http://public.leginfo.state.ny.us/LAWSSEAF.cgi?QUERYTYPE=LAWS+&QUERYDATA=$AGM374$@TXAGM0374+&LIST=SEA17+&BROWSER=BROWSER+&TOKEN=26623049+&TARGET=VIEW |url-status=live}}</ref>

== Animal slaughter ==
Gas chambers are used in the slaughter process of animals, particularly pigs and chickens. They are used on groups of animals reducing the need to handle each animal individually, and is relatively inexpensive when applied at scale.<ref>{{Cite journal |last1=Steiner |first1=Aline R. |last2=Flammer |first2=Shannon Axiak |last3=Beausoleil |first3=Ngaio J. |last4=Berg |first4=Charlotte |last5=Bettschart-Wolfensberger |first5=Regula |last6=Pinillos |first6=Rebeca García |last7=Golledge |first7=Huw D. W. |last8=Marahrens |first8=Michael |last9=Meyer |first9=Robert |last10=Schnitzer |first10=Tobias |last11=Toscano |first11=Michael J. |last12=Turner |first12=Patricia V. |last13=Weary |first13=Daniel M. |last14=Gent |first14=Thomas C. |date=2019-11-02 |title=Humanely Ending the Life of Animals: Research Priorities to Identify Alternatives to Carbon Dioxide |journal=Animals: An Open Access Journal from MDPI |volume=9 |issue=11 |page=911 |doi=10.3390/ani9110911 |doi-access=free |issn=2076-2615 |pmc=6912382 |pmid=31684044}}</ref>

In slaughterhouses in the UK, pigs must be killed by the gas in the chamber.<ref>{{Cite web |title=Slaughter |url=https://www.hsa.org.uk/faqs/slaughter |access-date=2025-11-12 |website=www.hsa.org.uk |language=en}}</ref> In other countries, pigs may be stunned using the gas chamber first. While unconscious, the pigs are then killed with a sharp knife outside of the gas chamber.<ref>{{Cite web |title=Stages of pork production {{!}} Australian Pork |url=https://australianpork.com.au/about-pig-farming/stages-pork-production |access-date=2025-11-12 |website=australianpork.com.au}}</ref> 

In 2024 in England and Wales, 90% of pigs killed in a slaughterhouse were stunned with this high concentration CO2 method. Chickens, both broiler (77%) and spent egg laying hens (99%), are also frequently stunned in slaughterhouse gas chambers, with a lower CO2 mixture.<ref>{{Cite web |date=2025-03-03 |title=Farm animals: slaughter sector survey 2024 |url=https://www.gov.uk/government/publications/farm-animals-slaughter-sector-survey-2024 |access-date=2025-11-12 |website=GOV.UK |language=en}}</ref>

=== Animal welfare concerns ===
The high concentration [[Carbon dioxide|CO2]] gas typically used is highly aversive and painful to pigs, and still takes at 47-60 seconds on average to stun them in test conditions. The pain and distress of high CO2 concentrations is caused by irritation mucous membranes such as the eyes, mouth and airways, distress, and causes pigs to show aversive behaviours such as gasping, vocalization, and trying to escape. For these reasons, the [[European Food Safety Authority]] concluded that CO<sub>2</sub> stunning is not optimal from an animal welfare perspective.<ref>{{Cite journal |last1=Sindhøj |first1=E. |last2=Lindahl |first2=C. |last3=Bark |first3=L. |date=2021-03-01 |title=Review: Potential alternatives to high-concentration carbon dioxide stunning of pigs at slaughter |url=https://www.sciencedirect.com/science/article/pii/S175173112030166X |journal=Animal |volume=15 |issue=3 |article-number=100164 |doi=10.1016/j.animal.2020.100164 |pmid=33461892 |bibcode=2021Anim...1500164S |issn=1751-7311}}</ref>

Alternatives using inert gas instead of high concentration gas have been successfully tested. Argon was found to be most promising, as the pigs' aversion to the gas was strongly reduced, retrofitting existing gas chambers is possible, and relatively quick. However this method takes longer, raising costs per pig 2-3 fold compared to high concentration CO2, and meat quality differed between trial, having higher numbers of blood spots.<ref>{{Cite web |last=Driver |first=Alistair |date=2025-05-05 |title=The search for alternative methods to slaughter pigs |url=https://www.pig-world.co.uk/features/welfare-features/the-search-for-alternative-methods-to-slaughter-pigs.html |access-date=2025-11-19 |website=Pig World |language=en-US}}</ref><ref>{{Cite journal |last1=Mace |first1=Jenny L. |last2=Knight |first2=Andrew |date=2025-03-13 |title=Pig welfare and ethical considerations during abattoir stunning: CO2 vs. alternative methods such as argon gas |journal=Frontiers in Veterinary Science |language=English |volume=12 |article-number=1542798 |doi=10.3389/fvets.2025.1542798 |pmid=40151566 |pmc=11948533 |doi-access=free |issn=2297-1769}}</ref> 

==Method of use==
===Using hydrogen cyanide===
[[File:Santa Fe gas chamber.jpg|thumb|left|The former gas chamber at [[New Mexico State Penitentiary]], used only once in 1960 and later replaced by [[lethal injection]].]]
[[File:gaschamber.jpg|frame|upright|Executions in California were carried out in the gas chamber at [[San Quentin State Prison]]. It was modified for the use of [[lethal injection]], but has been returned to its original designated purpose,{{explain|date=August 2021}} with the creation of a new chamber specifically for lethal injection.]]

The hydrogen cyanide gas chamber is considered to be the most dangerous, most complicated, most time-consuming and most expensive method of administering the death penalty.<ref>''Handbook of Death and Dying'' by Clifton D. Bryant – Page 499</ref><ref>{{cite web |url=http://swordandscale.com/the-death-penaltys-future-2/ |title=The Death Penalty's Future? |work=Sword and Scale |date=31 March 2015 |access-date=2015-07-09 |url-status=live |archive-url=https://web.archive.org/web/20150710022827/http://swordandscale.com/the-death-penaltys-future-2/ |archive-date=2015-07-10}} fourth paragraph</ref><ref>[http://www.history.com/shows/modern-marvels/videos/gas-chamber "The History Channel" – ''Modern Marvels'' (gas chamber)] {{webarchive|url=https://web.archive.org/web/20150709171925/http://www.history.com/shows/modern-marvels/videos/gas-chamber |date=2015-07-09}}</ref> It is also notoriously impossible to halt once initiated, which has occurred in the case of stays, such as in the case of [[Burton Abbott]].<ref>{{cite web |url=https://www.crimeandinvestigation.co.uk/this-day-in-crime/15-march/reprieve-telephone-call-comes-as-burton-abbott-is-executed |title=Reprieve telephone call comes as Burton Abbott is executed}}</ref><ref>{{cite web |url=https://gizmodo.com/in-1957-he-was-executed-for-murder-but-was-he-a-victim-1722087551 |title=In 1957, He Was Executed for Murder—But Was He a Victim of Circumstance? |date=4 August 2015}}</ref><ref>{{cite magazine |url=http://www.time.com/time/magazine/article/0,9171,809259,00.html |title=Race in the Death House |magazine=[[Time (magazine)|Time]] |date=March 25, 1957 |archive-url=https://web.archive.org/web/20080330000547/http://www.time.com/time/magazine/article/0,9171,809259,00.html |access-date=2022-08-04|archive-date=30 March 2008}}</ref> The same event supposedly occurred in the final, completed execution of [[Caryl Chessman]] in 1960.<ref>{{cite news |url=https://apnews.com/article/e2c1ca99a5a96e0a538b184726d66a68 |title=Followimng moved for Wednesday PMS and is now available for AMs TODay's TOPIC: Ninth Reprieve |publisher=[[Associated Press]]}}</ref> The condemned person is strapped into a chair within an airtight chamber, which is then sealed. The executioner activates a mechanism which drops [[potassium cyanide]] (or [[sodium cyanide]])<ref>{{cite web |url=https://www.britannica.com/topic/gas-chamber |title=Gas chamber &#124; execution device |access-date=2015-07-03 |url-status=live |archive-url=https://web.archive.org/web/20150628133911/https://www.britannica.com/topic/gas-chamber |archive-date=2015-06-28}} second paragraph</ref><ref>{{cite news |url=https://www.baltimoresun.com/1997/06/22/execution-by-gas-in-md-to-end-next-week-killer-hunts-death-will-be-last-by-method/ |title=Execution by gas in Md. to end next week Killer Hunt's death will be last by method |work=The Baltimore Sun |date=22 June 1997 |url-status=live |archive-url=https://web.archive.org/web/20150705032705/http://articles.baltimoresun.com/1997-06-22/news/1997173051_1_gas-chamber-hunt-lethal-injection |archive-date=2015-07-05}}</ref> pellets into a bath of [[sulfuric acid]] beneath the chair; the ensuing chemical reaction generates lethal [[hydrogen cyanide]] gas.

:{{chem2 | H2SO4 + 2 XCN -> 2 HCN + X2SO4 }} (X is an [[alkali metal]] ion)

The condemned is advised to take several deep breaths to speed unconsciousness. Nonetheless, the condemned person often convulses and drools and may also urinate, defecate, and vomit.<ref>''Encyclopedia of Capital Punishment in the United States'', 2d ed.&nbsp;&nbsp;by Louis J. Palmer, Jr.&nbsp;&nbsp;(page 319)</ref><ref>''The Death Penalty As Cruel Treatment And Torture''&nbsp;&nbsp;by William Schabas&nbsp;&nbsp;(page 194)</ref>

Following the execution the chamber is purged with air, and any remnant gas is neutralized with [[Ammonia|anhydrous ammonia]], after which the body can be removed (with great caution, as pockets of gas can be trapped in the victim's clothing).<ref name="HCN">{{cite web |url=http://www.deathpenaltyinfo.org/descriptions-execution-methods#gas |title=Descriptions of Execution Methods |publisher=Death Penalty Information Center |access-date=2 February 2015 |url-status=live |archive-url=https://web.archive.org/web/20150202105345/http://www.deathpenaltyinfo.org/descriptions-execution-methods#gas |archive-date=2 February 2015}}</ref>

===Excluding all oxygen===
{{main|Inert gas asphyxiation}}

Nitrogen gas or oxygen-depleted air has been considered for human execution, as it can induce [[nitrogen asphyxiation]]. The victim detects little abnormal sensation as the oxygen level falls. This leads to [[asphyxia]]tion (death from lack of oxygen) without the painful and traumatic feeling of suffocation, or the side effects of poisoning.<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>

In April 2015, [[Governor of Oklahoma|Oklahoma Governor]] [[Mary Fallin]] approved a bill allowing nitrogen asphyxiation as an execution method.<ref name="newsok.com">{{cite web |url=http://newsok.com/oklahoma-gov.-mary-fallin-signs-bill-allowing-nitrogen-asphyxiation-as-alternative-execution-method/article/5411181 |title=Oklahoma Gov. Mary Fallin signs bill allowing nitrogen asphyxiation as alternative execution method |website=NewsOK.com |url-status=live |archive-url=https://web.archive.org/web/20160329185215/http://newsok.com/oklahoma-gov.-mary-fallin-signs-bill-allowing-nitrogen-asphyxiation-as-alternative-execution-method/article/5411181 |archive-date=2016-03-29}}</ref> On March 14, 2018, Oklahoma Attorney General [[Michael J. Hunter|Mike Hunter]] and Corrections Director [[Joe Allbaugh|Joe M. Allbaugh]] announced a switch to nitrogen gas as the state's primary method of execution.<ref>{{cite news|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|title=Oklahoma says it will begin using nitrogen for all executions in an unprecedented move|date=March 18, 2018|author=Mark Berman|newspaper=The 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 struggling for years to design a nitrogen execution protocol, the State of Oklahoma announced in February 2020 that it was abandoning the project after finding a reliable source of drugs to carry out the lethal injection executions.<ref>{{cite news|title=Oklahoma Attorney general says state will resume executions|url=https://nypost.com/2020/02/13/oklahoma-attorney-general-says-state-will-resume-executions/|newspaper=[[New York Post]]|access-date=March 22, 2020|archive-date=March 9, 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 2018, Alabama approved nitrogen asphyxiation as an execution method and allowed death row inmates a choice of method. In September 2022, a court stayed the [[execution of Alan Eugene Miller]], who was set to be executed by lethal injection. Miller asserted that he had chosen nitrogen hypoxia as his method of execution, as permitted by Alabama law, but the form documenting his choice had been lost. The court decided to stay the execution to allow for further investigation into his claim.<ref>{{Cite web |last= |first= |date=2022-09-20 |title=Alabama inmate Alan Eugene Miller granted stay of execution |url=https://www.al.com/news/birmingham/2022/09/judge-grants-stay-for-alabama-inmate-alan-miller-ahead-of-thursday-execution.html |access-date=2022-10-06 |website=AL.com |language=en}}</ref> On January 25, 2024, [[Execution of Kenneth Eugene Smith|Kenneth Eugene Smith]] became the first person to be executed by nitrogen asphyxiation.<ref>{{Cite news |last1=Betts |first1=Anna |last2=Bogel-Burroughs |first2=Nicholas |date=2024-01-25 |title=The Alabama Execution Case: What We Know |url=https://www.nytimes.com/2024/01/25/us/execution-alabama-kenneth-smith.html |access-date=2024-01-26 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>

==Further reading==
*[[Scott Christianson|Christianson, Scott]] (2010). ''The Last Gasp: The rise and fall of the American gas chamber'' (Kindle edition). Berkeley: [[University of California Press]], {{ISBN|978-0-520-25562-3}}

==References==
{{Reflist|30em}}

== External links ==

* {{Wikiquote-inline|Gas chamber}}
{{capital punishment}}

{{DEFAULTSORT:Gas Chamber}}
[[Category:1803 introductions]]
[[Category:Infrastructure of the Holocaust]]
[[Category:Execution methods]]
[[Category:Execution equipment]]
[[Category:Toxicology]]
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