Examples of physiologically inert gases, which have caused accidental or deliberate death by this mechanism, are argon, helium, nitrogen and methane.
[citation needed] 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.
Inert gas asphyxia has been advocated by proponents of euthanasia, using a gas-retaining plastic hood device colloquially referred to as a suicide bag.
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.
[8] 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.
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.
[32] 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".
[33] Dunn collaborated with other researchers, notably the Canadian campaigner, John Hofsess, who in 1997 formed the group "NuTech" with Derek Humphry and Philip Nitschke.
[39] 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.
[41] Nitschke produced a 3D printed 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.
[42][43] Execution by nitrogen asphyxiation was discussed briefly in print as a theoretical method of capital punishment in a 1995 National Review article.
[45] 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.
[46] In April 2015, Governor Mary Fallin of Oklahoma signed a bill allowing nitrogen asphyxiation as an alternative execution method.
[47][48] 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.
[52] 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.
[60] 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.