Alabama’s decision to execute death row inmate Kenneth Smith using nitrogen gas has sparked controversy. Smith is scheduled for execution on 25 January, marking the state’s first use of this experimental method.

The proposed procedure involves strapping Smith to a gurney, placing a respirator mask on his face, and exposing him to pure nitrogen to induce oxygen deprivation, leading to death. However, the use of nitrogen gas for human execution lacks comprehensive scrutiny. Limited data are available beyond reports of workplace accidents involving nitrogen.

Veterinary scientists have conducted laboratory studies on animals, generally rejecting the use of nitrogen for euthanasia due to ethical concerns. Veterinary guidelines in the US and Europe advise against using nitrogen hypoxia, the proposed execution method, for euthanasia in most mammals, except for pigs. For larger mammals, sedation is recommended before applying the gas, a step absent in Alabama’s execution protocol.

Despite the absence of an initial sedative, a federal judge in Alabama, Austin Huffaker, approved Kenneth Smith’s execution using nitrogen gas. He dismissed the inmate’s claim of an intolerable risk of harm.

The UN High Commissioner for Human Rights in Geneva described Smith’s proposed execution as suffocation by nitrogen gas. The UN body suggests that this method may amount to torture or cruel, inhuman, or degrading treatment prohibited by international law.

The American Veterinary Medical Association (AVMA) recommends sedation for large animals euthanised with nitrogen, but Alabama’s execution protocol does not include provisions for sedation in human executions using nitrogen.

Kenneth Smith was sentenced to death in 1988 for the murder-for-hire of Elizabeth Sennett, a pastor’s wife. Charles Sennett, her husband, paid Smith and another man for the killing before taking his own life when suspicions turned toward him.

A jury voted 11 to 1 in favour of giving Kenneth Smith a life sentence. However, the trial judge overturned the decision to send him to death row. Comparisons between human and animal deaths are complicated due to significant differences, including the fact that humans can be conscious of the process. In Smith’s case, he experienced a failed execution in November 2022, enduring hours on the gurney while a vein for lethal drug injection was unsuccessfully sought.

Following the failed execution, Smith exhibited symptoms of profound trauma, with reported sleeplessness, migraines, depression, and anxiety. While acknowledging differences between species, evidence from animal experiments suggests potential issues with using nitrogen as a killing method.

The American Veterinary Medical Association (AVMA) declined to comment on Kenneth Smith’s pending execution, stating that their guidelines apply only to animals. Similar experiments conducted by the European Commission yielded almost identical findings and recommendations. Dogs and cats displayed convulsions and gasping after exposure to nitrogen, leading the scientists to conclude that this method is unacceptable unless the animal is anesthetised.

The European Commission’s paper mentioned that kittens and puppies are resistant to nitrogen. They fall unconscious but fail to die, hence an unacceptable method. The euthanasia of birds was also considered unacceptable unless the animals were unconscious.

David Morton, a professor emeritus of biomedical science and ethics at the University of Birmingham, part of the commission’s panel, highlighted the unsatisfactory nature of nitrogen hypoxia as a euthanasia method for animals due to the potential for severe distress before unconsciousness and death.

Morton expressed uncertainty about the species variation and potential outcomes in humans. He noted a paradox in Alabama’s approach. Professor Morton argued that while animal experiments are typically used as proxies for humans, the ultimate test is conducted using a human being.