Controlled-atmosphere killing
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Inert gas asphyxiation is a form of asphyxiation which results from breathing a physiologically inert gas in the absence of oxygen, or a low amount of oxygen, rather than
atmospheric air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Gravity of Earth, Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating Atmo ...
(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, helium, nitrogen and methane. The term "physiologically inert" is used to indicate a gas which 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 oxygen concentration in inspired gas and blood to dangerously low levels, thereby eventually depriving all cells in the body of oxygen. According to the
U.S. Chemical Safety and Hazard Investigation Board The U.S. Chemical Safety and Hazard Investigation Board (USCSB), generally referred to as the Chemical Safety Board or CSB, is an independent U.S. federal agency charged with investigating industrial chemical accidents. Headquartered in Washing ...
, 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. Hazards with inert gases and the risks of asphyxiation are well established. An occasional cause of accidental death in humans, inert gas asphyxia with gases including helium, nitrogen, methane and argon has been used as a suicide method. Inert gas asphyxia has been advocated by proponents of
euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different eut ...
, using a gas-retaining plastic hood device colloquially referred to as a
suicide bag A suicide bag, also known as an exit bag or hood, is part of a euthanasia device consisting of a large plastic bag with a drawcord used to commit suicide through inert gas asphyxiation. It is usually used in conjunction with a flow of an inert g ...
. Nitrogen asphyxiation has been approved in some places as a method of capital punishment, but has not yet been used for this purpose.


Process

When humans breathe in an asphyxiant gas, such as pure nitrogen, helium,
neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypton ...
, argon, methane, or any other physiologically inert gas(es), they exhale carbon dioxide without re-supplying oxygen. Physiologically inert gases (those that have no toxic effect, but merely dilute 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 Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
, which in humans arises mostly from carbon dioxide levels rising), or the side effects of poisoning. In scuba diving rebreather accidents, there is often little sensation, however, a slow decrease in oxygen breathing gas content has effects which are quite variable. 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. Some animal species are better equipped than humans to detect hypoxia, and these species are more uncomfortable in low-oxygen environments that result from inert gas exposure; however, the experience is still less aversive than CO2 exposure.


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 (tidal volume + functional residual capacity) 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 Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...
, when arterial oxygen saturation is less than 60%. "At oxygen concentrations
n air N, or n, is the fourteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''en'' (pronounced ), plural ''ens''. History ...
of 4 to 6%, there is loss of consciousness in 40 seconds and death within a few minutes". At an altitude over , 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. The US Air Force trains air crews to recognize their individual subjective signs of approaching hypoxia. Some individuals experience headache, dizziness, fatigue, nausea and euphoria, and some become unconscious without warning. Loss of consciousness may be accompanied by convulsions and is followed by
cyanosis Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...
and cardiac arrest. About seven minutes of oxygen deprivation causes death of the
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
. In a 1963 study by RAF Institute of Aviation Medicine, subjects were asked to hyperventilate in a nitrogen atmosphere. Among the results: The study did not report how much discomfort the subjects felt.


Animal slaughter


Relation to controlled atmosphere killing

''Controlled atmosphere killing'' (''CAK'') or ''controlled atmosphere stunning'' (''CAS'') is a method for slaughtering animals such as chickens or
cane toads The cane toad (''Rhinella marina''), also known as the giant neotropical toad or marine toad, is a large, terrestrial true toad native to South and mainland Central America, but which has been introduced to various islands throughout Oceania ...
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 Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
, and for this reason many consider some types of controlled atmosphere killing more humane than other methods of killing. However, "stunning" is often done using carbon dioxide. 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. 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 concentration of carbon dioxide.


Euthanasia of animals

Diving animals such as
rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...
s and
mink Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...
s and burrowing animals are sensitive to low-oxygen atmospheres and (unlike humans) will avoid them, making purely hypoxic techniques possibly inhumane for them. For this reason, the use of inert gas (hypoxic) atmospheres (without CO2) for
euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different eut ...
is also species-specific.


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, 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 Orbiter aft compartment. 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. During a pool party in Mexico in 2013, eight party-goers were rendered unconscious and one 21-year-old male was put into a coma after liquid nitrogen was poured into the pool. Occasional deaths are reported from recreational inhalation of helium, but these are very rare from direct inhalation from small balloons. The inhalation from larger helium balloons has been reportedly fatal. 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. In 2015, a technician at a health spa was asphyxiated while conducting unsupervised cryotherapy using nitrogen. In 2021, six people died of asphyxiation and 11 more were hospitalized following a liquid nitrogen leak at a poultry plant in Gainesville, Georgia.


Suicide

Use of inert gas for suicide was first proposed by a Canadian, Dr Bruce Dunn. Dunn commented that, "...the acquisition of a compressed gas cylinder, an appropriate pressure reducing regulator, and suitable administration equipment... asnot inaccessible to a determined individual, but relatively difficult for a member of the public to acquire casually or quickly." Dunn collaborated with other researchers, notably the Canadian campaigner, John Hofsess, who in 1997 formed the group "NuTech" with Derek Humphry and Philip Nitschke. Two years later, NuTech had streamlined Dunn's work by using readily-available party balloon cylinders of helium. The method of suicide based on self-administration of helium in a bag, a colloquial name being the "exit bag" or
suicide bag A suicide bag, also known as an exit bag or hood, is part of a euthanasia device consisting of a large plastic bag with a drawcord used to commit suicide through inert gas asphyxiation. It is usually used in conjunction with a flow of an inert g ...
, has been referenced by some medical euthanasia advocacy groups. 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. After attempts were made by authorities to control helium sales in Australia, a new method was introduced that instead uses nitrogen. 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. 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 ndtotally legal" manner. Nitschke said that nitrogen is "undetectable even by autopsy, which was important to some people". Nitschke produced a
3D printed 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
pod, " Sarco", 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.


Capital punishment

Execution by nitrogen asphyxiation was discussed briefly in print as a theoretical method of capital punishment in a 1995 '' National Review'' article. The idea was then proposed by Lawrence J. Gist II, an attorney at law, under the title, International Humanitarian Hypoxia Project. 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. In April 2015, Governor Mary Fallin of
Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...
signed a bill allowing nitrogen asphyxiation as an alternative execution method. Three years later, in March 2018, Oklahoma announced that, due to the difficulty in procuring lethal injection drugs, nitrogen gas will be used to carry out executions. 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. In March 2018, Alabama became the third state (after Oklahoma and Mississippi), to authorize the use of nitrogen asphyxiation as a method of execution. In the case ''
Bucklew v. Precythe ''Bucklew v. Precythe'', 587 U.S. ___ (2019), was a United States Supreme Court case regarding the standards for challenging methods of capital punishment under the Eighth Amendment to the United States Constitution. In a 5–4 decision, the Cour ...
'', decided 1 April 2019, the U.S. Supreme Court ruled that a Missouri
death row Death row, also known as condemned row, is a place in a prison that houses inmates awaiting Capital punishment, execution after being convicted of a capital crime and sentenced to death. The term is also used figuratively to describe the state of ...
inmate could not avoid death by lethal injection and choose inert gas asphyxiation using nitrogen, since it has never been used in any execution in the world.


See also

* * * *


Notes

{{reflist, refs= {{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 rolonged or acute hypoxiathere 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 {{cite web, url=http://www.charlydmiller.com/LIB/forensicpathasphyxia.html, title=Forensic Pathology 2e, Chapter 8: Asphyxia, work=charlydmiller.com PETA's Animal Times, UK, Autumn 2005 {{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 {{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 {{cite news , url=http://www.csb.gov/safety_publications/docs/SB-Nitrogen-6-11-03.pdf , title=Hazards of Nitrogen Asphyxiation , publisher=U.S. Chemical Safety and Hazard Investigation Board , date=2003-06-11 , access-date=2007-02-15 , 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 , url-status=dead {{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 Creque, S.A. "Killing with kindness – capital punishment by nitrogen asphyxiation" National Review. 1995-9-11. {{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 "Argon, hydrogen, helium, and nitrogen are inert gases that cause asphyxiation if present in high enough concentration to dilute O2 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 O2 in the inspired air to levels at which the SaO2 and PaO2 fall, resulting in inadequate O2 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. 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, se

{{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
{{cite journal , pmid = 21361949 , doi=10.1111/j.1556-4029.2011.01723.x , volume=56 , title=Recent trends in suicides utilizing helium , date=May 2011 , vauthors=Austin A, Winskog C, van den Heuvel C, Byard RW , journal=J. Forensic Sci. , issue=3 , pages=649–51, s2cid=30521706 {{cite journal, url=https://web.archive.org/web/20141204230210/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


External links


NIOSH respirator fact sheet

U.S. Chemical Safety and Hazard Investigation Board

Restraint asphyxia


Humane Society of the United States comparison of controlled-atmosphere killing (CAK) to electrical water-bath stunning
Controlled Atmosphere Killing
People for the Ethical Treatment of Animals

by Michael P. Copeland, J.D., Thom Parr, M.S., and Christine Pappas, J.D., Ph.D.
''Execution by Nitrogen Hypoxia: Search for Scientific Consensus''
by Kevin M. Morrow, J.D. Animal welfare Causes of death Execution methods Meat industry Nitrogen Poultry farming Slaughter methods Toxicology Asphyxia