Alabama began using nitrogen gas to execute death row inmates earlier this year. The process involves placing a respirator gas mask over the inmate’s face to replace breathable air with pure nitrogen gas. It kills the person by depriving them of oxygen.

Alabama is planning to carry out the nation’s third execution with nitrogen gas. The move comes as critics argue the method needs more scrutiny before it is used to put another person to death. Carey Dale Grayson,

A federal appeals court said Monday it will let the nation’s third execution with nitrogen gas go forward this week in Alabama, rejecting arguments that the new method causes unconstitutional levels of pain.