A US district judge has given the green light for the first-ever execution by nitrogen gas asphyxiation to go ahead. The ruling means that Alabama inmate Kenneth Eugene Smith is currently scheduled to be put to death using the new method on January 25, although his attorney has launched an appeal against the decision.

Smith’s legal team argue that he is being used as a guinea pig for an experimental procedure, and that the proposed execution amounts to cruel and unusual punishment, thus rendering it unconstitutional. Under plans put forward by the state of Alabama, a respirator is to be placed over the prisoner’s nose and mouth in order to replace all breathable air with nitrogen gas, ultimately leading to suffocation.

At a court hearing in December, the state attorney general’s office said that the method would “cause unconsciousness within seconds, and cause death within minutes,” the Associated Press reports. In response, Smith’s lawyers have pointed out that the American Veterinary Medical Association advises against nitrogen hypoxia as a form of euthanasia for all mammals except pigs as the procedure is too “distressing”.

However, at a hearing earlier this week, federal judge R. Austin Huffaker ruled that Smith can be executed using the new method. In his report, Huffaker conceded that his decision means that “Smith is not guaranteed a painless death,” but ultimately found that the inmate “has not shown, and the court cannot conclude, the Protocol inflicts both cruel and unusual punishment rendering it constitutionally infirm under the prevailing legal framework.”

Smith was sentenced to death for the 1988 murder of Elizabeth Dorlene Sennett, for which he was paid $1,000 by the victim’s husband. In November 2022, he was the subject of a botched execution attempt, when prison staff spent 100 minutes trying to administer a lethal injection but could not find a vein before the midnight deadline for the capital punishment to be carried out.

Failed executions have become increasingly common in the US since 2010, when the companies that manufacture sodium thiopental stopped supplying the chemical for use in lethal injections. This has led numerous states to seek out new ways of putting prisoners to death, with some turning to the sedative midazolam.

However, the use of midazolam has proved highly controversial and has been blamed for some prisoners appearing to suffer convulsions several minutes after being injected. Seeking out a more effective execution method, the state of Oklahoma became the first to approve nitrogen asphyxiation in 2015.

Mississippi and Alabama soon followed suit, although no prisoner has yet been executed using the method. Unless Smith’s appeal is successful, he will be the first.