The Supreme Court has ruled in favor of Alabama's planned execution of Kenneth Eugene Smith by nitrogen hypoxia, a method that has raised concerns among legal experts and garnered criticism from the United Nations. Smith is set to become the first person in the United States to be put to death using nitrogen gas.

Smith's lawyers had argued that it would be unconstitutional for the state to proceed with a second execution attempt after a failed lethal injection in 2022. However, the justices rejected these arguments, clearing the way for the execution to take place.

In addition to the Supreme Court ruling, Smith's legal team has also asked the 11th U.S. Circuit Court of Appeals to block the execution, but a ruling from this court is still pending.

The use of nitrogen gas as a method of capital punishment has been widely criticized by medical professionals, including veterinarians who oppose its use on animals. The American Veterinary Medical Association has advised against the use of nitrogen gas for euthanizing most mammals, considering it distressing. The use of nitrogen gas in animal euthanasia is limited to specific cases, such as with chickens.

Experts have repeatedly warned about the potential for unnecessary suffering and the threat to the health of those present during nitrogen hypoxia executions. The process involves inhaling pure nitrogen gas or nitrogen gas at lethal concentrations, leading to asphyxiation.

While lethal gas is authorized as an execution method in seven states, Alabama, Mississippi, and Oklahoma are the only ones that have specified the use of nitrogen for this purpose. Alabama is the only state that has released a formal execution protocol for nitrogen hypoxia, albeit heavily redacted.

Alabama officials have defended the use of the gas, stating that breathing nitrogen through a mask would cause the person to lose consciousness before oxygen deprivation leads to death. Smith's legal team, however, has accused the state of using him as a "test subject" for an unproven and potentially cruel method of execution.

The United Nations' human rights office has called on Alabama to halt the execution, highlighting the lack of scientific evidence to prove that nitrogen inhalation will not result in grave suffering.

During the execution, Smith will be strapped to a gurney and forced to breathe nitrogen through a gas mask until his body is depleted entirely of oxygen. While nitrogen inhalation has never been used before in the death chamber, cases of accidental overexposure to nitrogen in industrial settings have shown the harmful effects. When oxygen in the air is reduced to less than 10% due to excessive nitrogen, it can cause loss of consciousness, convulsions, and death.

The Supreme Court's ruling allows Alabama to proceed with the controversial use of nitrogen hypoxia as an execution method, despite ongoing concerns and opposition from various groups.