(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 .