A federal judge ruled Wednesday that Alabama can proceed with its first execution by asphyxiation by nitrogen gas later this month, saying it was unlikely that a convicted inmate would prove the new method was cruel or unusual punishment, AFP reported.

Kenneth Smith, convicted of contract killing in 1988, will be executed in Alabama on January 25 by a method in which executioners place a mask over his face connected to a nitrogen cylinder designed to deprive him of oxygen.

It has become increasingly difficult for US states to obtain barbiturates used in lethal injection protocols, in part because of a European ban that prevents drug companies from selling the drug for use in executions.

As a result, some states tried to revive old methods such as firing squad, while Alabama, Mississippi and Oklahoma introduced new gas-based protocols.

A death row inmate has sued the Alabama Department of Corrections, alleging that the proposed method poses dangerous risks, including that the mask’s seal could break, allowing oxygen to enter, which could prevent the execution.

Such a scenario could trigger a stroke or leave Smith in a permanent vegetative state, he argued.

Last week, United Nations experts warned that what would be the world’s first case of execution by inert gas would likely violate the international treaty against torture and other cruel, inhuman or degrading punishment.

Judge R. Austin Huffaker of the U.S. District Court in Montgomery, Alabama, ruled against Smith, who requested a stay of execution to allow the trial to proceed.

“Smith is not guaranteed a painless death,” Huffaker wrote in his opinion, citing U.S. Supreme Court precedent. He wrote that Smith “has not demonstrated that the current protocol is dangerous or highly likely to cause a significant risk of serious injury or additional pain.”

Smith, 58, is one of only two people alive in the US to have survived an execution attempt since Alabama missed a previously scheduled execution by lethal injection last November when several attempts to insert a needle into a vein failed.

Robert Grass, an attorney representing Smith, said he plans to appeal the decision.

Kenneth Smith was convicted of murdering a preacher’s wife in 1988, a contract killing paid for by the preacher himself.