The lower appeals court and US Supreme Court declined to block what Eugene Smith lawyers called a “cruel and unusual” death penalty.
Smith 58 was convicted in 1989 of murdering Elizabeth Senett. Opponents says nitrogen cause unnecessary suffering and leak could harm person present in the room. Alabama has 30 hours to carry out the execution which involves pumping nitrogen gas through a mask from Thursday at 6 00 GMT.
Smith would be the first person to put to death by this method in the US and according to the Dealth Penalty Information Center anywhere all over the globe.
Breathing pure nitrogen without oxygen cause the cells to break down and leads to death. Lawyers for the inmate who has been on death row since 1996.They were filing another appeal to the country top court in the hope for final minute reprieve.
Alabama and two other US states have approve the used of nitrogen hypoxia as alternative method of execution because the drugs used in injections have difficult to find contributing to a fall in the use of death penalty nationally.
The UN High Commissioner fro Human Rights has said gassing Smith could amount to torture or degrading treatment and called for a halt.
Alabama already try to execute the Smith by lethal injection 2 years ago but were unable to raise a vein before the state death warrnat expired.
Smith was one of two men convicted of murdering 45 year old Sennett in a $1000 killing for hire in March 1988. His legal team argue the nitrogen gas method is recently released and untested leaving him at danger of choking on his own vomit.
Smith spiritual adviser RJ Hood will be present in the room when the execution happens. He told BBC he believes he will be in risk if the nitrogen leaks.
Alabama has one of the highest per capita execution rates in the US and 165 people currently on death row. Smith peer hitman, John Forrest Parker was executed in 2010.