MONTGOMERY, Ala. (AP) — A federal judge on Thursday refused to stop an upcoming nitrogen gas execution in Alabama saying the inmate was unlikely to prevail on claims that the method, which has been used multiple times, is unconstitutionally cruel.

Chief U.S District Judge Emily Marks declined a request from Anthony Boyd to block his scheduled Oct. 23 execution. Marks said Boyd had not met the legal burden for the “extraordinary remedy of a preliminary injunction.” Boyd’s legal team is appealing the decision.

Alabama began using nitrogen gas last year to carry out some executions. The method uses a gas mask to replace breathable air with pure nitrogen gas, causing the inmate to die from lack of oxygen.

Boyd, 53, argued the method violates the Eighth Amendment because inmates are subjected to “conscious suffocation” and feel the pain and terror of being deprived of oxygen. He had suggested a firing squad or taking an oral mixture of fatal drugs prepared by a medical professional as better alternatives.

“The Court does not doubt that a person consciously deprived of oxygen even for two minutes under the Protocol experiences discomfort, panic, and emotional distress,” Marks wrote.

But she added that the U.S. Constitution “does not guarantee Boyd a painless death” and that the fear of impending death is part of every execution.

The ruling came after a hearing last month in which testimony focused on estimates of how long an inmate is awake during a nitrogen execution and the reasons for the shaking and gasping movements exhibited by inmates executed with the gas.

The protocol requires prison officials to keep the nitrogen flowing for at least 15 minutes or five minutes after monitoring shows the inmate no longer has a heartbeat. The state indicated in court records that the first five inmates executed by nitrogen gas died at times ranging from 16 to 23 minutes after the nitrogen gas began flowing, Marks wrote.

A jury convicted Boyd of capital murder for his role in the 1993 killing of Gregory Huguley in Talladega. Prosecutors said Huguley was burned to death after he failed to pay for $200 worth of cocaine.

A prosecution witness testified as part of a plea deal that Boyd taped the victim’s feet before another man doused him with gasoline and set Huguley on fire.

Boyd has maintained he did not commit the 1993 murder. His supporters have launched a billboard campaign urging the state to halt the execution.