( CNN ) Oklahoma Gov . Mary Fallin signed a bill on Friday that would allow the state to perform executions with nitrogen gas if lethal injection is ruled unconstitutional or becomes unavailable . Nitrogen causes a quick loss of consciousness and then death from lack of oxygen , Fallin 's office said in a press release . CNN affiliate KFOR says it 's never been used in an execution in the United States . `` The person will become unconscious within eight to 10 seconds and death a few minutes later . In other words , a humane , quick and painless death , '' said Rep. Mike Christian , one of the bill 's authors , according to KFOR . Robert Dunham , executive director of the Death Penalty Information Center , told the Washington Post that the same `` painless '' argument had been used to advance the use of lethal injections . `` The hasty manner in which this bill sped into law reflects the same lack of care with which Oklahoma has managed its execution process historically , '' he said . Oklahoma 's executions have been put on hold while the U.S. Supreme Court reviews its use of lethal injections . Last year , the state came under scrutiny when it took 43 minutes to kill convicted killer Clayton Lockett . Fallin reaffirmed her support for the death penalty . `` Oklahoma executes murderers whose crimes are especially heinous , '' Fallin said . `` I support that policy , and I believe capital punishment must be performed effectively and without cruelty . The bill I signed today gives the state of Oklahoma another death penalty option that meets that standard . '' The governor 's office said the first alternative for execution is lethal injection , followed by nitrogen gas , the electric chair and the firing squad .
Nitrogen gas causes a quick loss of consciousness and then death from lack of oxygen , Oklahoma says . The state 's executions are on hold while the U.S. Supreme Court reviews the state 's use of lethal injections .