Alabama is preparing to execute a death row inmate using nitrogen gas, an experimental method that veterinarians in the US and across Europe have deemed unacceptable as a form of euthanasia for most animals.
Barring last-minute appeals, Kenneth Smith, 58, is scheduled to be judicially killed on 25 January using a previously untested technique. Alabama’s department of corrections is proposing to strap him to a gurney, apply a respirator mask to his face, then force him to breathe pure nitrogen which would cause oxygen deprivation and death.
The method has not been subjected to scrutiny for humans other than reports of workplace accidents in which people became unintentionally trapped in a nitrogen-rich environment and died. Veterinary scientists, however, have carried out laboratory studies on animals and have largely ruled it out for ethical reasons.
Guidelines produced by veterinary authorities in the US and Europe advise that nitrogen hypoxia, as the method is known, is unacceptable for the euthanasia of most mammals other than pigs. Larger mammals, the recommendations say, should be sedated to render them unconscious before the gas is applied.
Alabama’s protocol does not include an initial sedative.
Last week, a federal judge gave the green light for Smith’s execution to go ahead using nitrogen gas. Austin Huffaker, from US district court in Alabama, said he had been unpersuaded by the prisoner’s claim that the untested procedure posed him an “intolerable risk of harm”.
International pressure is mounting, however. On Tuesday, the UN high commissioner for human rights in Geneva expressed alarm that Smith’s proposed execution, which it described as “suffocation by nitrogen gas”, could amount to torture or cruel, inhuman or degrading treatment banned under international law.
The UN body noted that the American Veterinary Medical Association (AVMA) “recommends giving even large animals a sedative when being euthanized in this manner, while Alabama’s protocol for execution by nitrogen asphyxiation makes no provision for sedation of human beings prior to execution”.
Smith was sentenced to death for the 1988 murder-for-hire of a pastor’s wife, Elizabeth Sennett. Her husband, Charles Sennett, paid Smith and another man $1,000 each for the killing, then took his own life after suspicions turned to him.
A jury voted by 11 to 1 to give Smith a life sentence, but the trial judge overturned their decision and sent him to death row.
Direct comparisons between human and animal deaths are fraught given the obvious differences, not least that humans can have prior consciousness of what is happening to them. That is especially true in Smith’s case, as he was subjected to a failed execution in November 2022 in which he was placed on the gurney for hours in an unsuccessful search for a vein through which to inject lethal drugs into him.
In the wake of that failed execution, Smith has displayed symptoms of profound trauma. His own prison doctors have reported that he suffers sleeplessness, migraines, depression and anxiety.
Despite the differences, evidence from animal experiments does point to potential issues in the use of nitrogen as a killing method. The AVMA’s guidelines record that rats showed signs of panic and distress when given the gas, including open-mouthed breathing and seizure-like behavior.
Similar aversion and distress was found with mice and mink. The association concluded that euthanasia by nitrogen was acceptable with conditions for chickens, turkeys and pigs, but that it should be avoided for other species.
“Use of nitrogen is unacceptable for other mammals,” the guidelines state.
The Guardian invited the AVMA to comment on Smith’s pending execution, but it declined. “Our document applies only to animals,” a spokesman said.
Similar laboratory experiments have been carried out by the European Commission with almost identical findings and recommendations. A team of scientists reported that dogs and cats displayed convulsions and gasping after being given nitrogen, concluding that this “is not an acceptable [euthanasia] method unless the animal is anaesthetised”.
The European commission paper said that “kittens and puppies are resistant – they fall unconscious but fail to die – this is not an acceptable method”. It added that “euthanasia of birds is not considered acceptable unless unconscious” and warned that the responses of the birds “may be objectionable to personnel”.
David Morton, professor emeritus of biomedical science and ethics at the University of Birmingham in the UK, was part of the panel that drew up the commission’s guidelines. Though he has not himself conducted animal experiments using nitrogen, he said that the group found that nitrogen hypoxia was an unsatisfactory euthanasia method for animals for welfare reasons.
“It is effective, but it can cause severe distress before unconsciousness and death ensue. In effect it is a suffocation method. It is likely also that there will be considerable species variation, and we are not sure what will happen in humans.”
Morton also noted a paradox in the way Alabama was approaching Smith’s pending execution. “Animal experiments are usually used as a proxy for humans, but not so in this case it seems – the ultimate test is being carried out using a human being.”
Another member of the European Commission panel, a biologist and medical scientist with a background in animal euthanasia, Clifford Warwick, told the Guardian that he was concerned that Smith might suffer during the procedure. “Wherever strong concentrations of singular or greatly dominant gases are used, such as nitrogen, in nowhere near their normal relevant balance to oxygen, then I suspect that the animal’s/person’s body will dramatically sense the difference and process it as an emergency insult leading to acute distress.”