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Using Nitrogen Gas For Executions Is Untested and Poorly Understood. Three States Plan to Do It Anyway.

Oklahoma, Mississippi, and Alabama have all authorized the practice in capital punishment. So what happens now?

Photo illustration by Elizabeth Brown. Photo from Getty Images.

In April 2015, Oklahoma became the first state to authorize the use of nitrogen gas to execute prisoners on death row after a botched execution called the state’s use of lethal injection into question. With the Supreme Court considering the constitutionality of the procedure, and the state facing a shortage in the necessary drugs, Mike Christian, a Republican state representative, proposed nitrogen instead. 

“The process is fast and painless,” Christian told reporters at the time. “It’s foolproof.”

The method, known as nitrogen hypoxia, involves depriving the body of oxygen by replacing the air with nitrogen, and has never been used to kill death row prisoners. 

Mississippi and Alabama followed Oklahoma in 2017 and 2018 in approving nitrogen for executions. But none of the states has actually come up with a way to use it. That comes as a relief to opponents who say there’s no way to predict whether it will be painless.

There is a limited body of scientific research on the use of nitrogen to kill humans. Most information on the subject comes from industrial accidents, suicides, and euthanasia on small animals

Though the suicides and accidental deaths involving nitrogen are sometimes described as peaceful, some doctors say the conditions present in an execution are very different.

This theoretical situation would be difficult to create in real life,” Dr. John Ard, a neuroanesthesiologist and professor at New York University, wrote in an email. “The prisoner would be in a state of panic. Even if the system was perfect, the prisoner could hold out for minutes by breath holding.”

Nitrogen could be administered through either a gas chamber or mask, and experts say the quality of the nitrogen will be important. A 2013 handbook from the American Veterinary Medical Association on euthanizing animals advises that nitrogen gas “must be supplied in a precisely regulated and purified form.”

States have used gas to execute prisoners before; Nevada was the first state to employ hydrogen cyanide in 1924. The method failed so horribly—prisoners thrashed in distress during long, agonizing executions—that California’s federal courts ruled that it amounted to cruel and unusual punishment. 

When today’s primary method, lethal injection, was proposed, officials believed it would be more humane than the electric chair. As with nitrogen, Oklahoma was a pioneer, adopting a protocol recommended by a forensic pathologist who acknowledged that he was “an expert in dead bodies but not an expert in getting them that way.” Since its introduction, lethal injection has been responsible for the highest rate of botched executions: Something goes wrong roughly seven out of 100 times. 

I think that Oklahoma adopted [nitrogen hypoxia] with the same lack of scientific rigor that it adopted the previous method,” Robert Dunham, executive director of the Death Penalty Information Center, told The Appeal. “And the fact that you were the first to make a blunder and you blunder your way through choosing the next method doesn’t make you a leader; it makes [one] question the judgment of other people who follow you.”

The Oklahoma Department of Corrections did not respond to a request for comment on its approval of nitrogen for executions. “We are still working with the Attorney General’s office on developing a method and protocol that meets with legal and constitutional requirements,” Matthew Elliott, a spokesperson for the department, told The Appeal via email. 

But Deborah Denno, a Fordham University law professor who is an expert in the history of capital punishment, sees nitrogen as the latest in a string of poorly chosen execution methods. “History has shown they only get worse. They only get sloppier, they only get riskier,” she said. “There will come a time when people can’t believe that we did this.”


Christian, the Oklahoma representative, introduced nitrogen hypoxia to the state legislature after watching “How to Kill a Human Being,” a BBC documentary. In the program, British conservative politician turned journalist Michael Portillo deems a nitrogen mask “the perfect killing machine.”  

At the time, Oklahoma had put executions on hold. The state had just botched its execution of Clayton Lockett—he died of a heart attack after writhing and convulsing on the gurney—and was awaiting a U.S. Supreme Court decision on the constitutionality of its new procedure for lethal injection. Authorizing nitrogen to kill prisoners would give the state an alternative way to kill prisoners should it not pass the test. 

Inspired by the documentary, Christian enlisted three people to study whether Oklahoma should start using nitrogen gas to execute people. None of them had careers in science or medicine. They put together a 14-page report without any evidence of original research, instead citing sources such as a National Review article and a 1963 study on the effects of breathing in nitrogen through a mask. 

The trio recommended that Oklahoma start using nitrogen gas, writing that the method would be a humane and simple way to carry out death sentences. 

The Supreme Court ultimately decided that Oklahoma could move forward with lethal injection, but in 2018, state officials announced that they were struggling to secure lethal injection drugs and would be pivoting to using nitrogen for executions instead. The method, they said, would allow the state to start executing people again; its last execution was in 2015.

Yet the change has proved difficult to carry out because the agency has had trouble securing a device to deliver the nitrogen to prisoners. In February emails to The Appeal, Oklahoma DOC spokesperson Elliott wrote that once it has the device, the state will begin working on the protocol for carrying out executions. “We’ve determined some things that will likely work,” he wrote. “The issue is companies/manufacturers won’t sell us the appropriate technology out of fear of backlash from anti-death penalty activists.” 

In March, Attorney General Mike Hunter said that the state would most likely recruit an in-state manufacturer and hoped to have the method submitted for court review by the end of the year. 

Apart from obtaining the device, the state would also need to procure nitrogen gas. In February, Elliott told The Appeal that the department had a “reliable supply” of the gas, but this month he said that although it has maintained that supply, it does not have “a specific supplier for executions via hypoxia.” 

Oklahoma’s contracted gas supplier, Airgas USA, which sells industrial, medical, and specialty gases to the state at a discount, told The Appeal that it would not supply the state with gas for executions. In an email, company spokesperson Kimberly Menard wrote: “Notwithstanding the philosophical and intellectual debate of the death penalty itself, supplying nitrogen for the purpose of human execution is not consistent with our company values. … Airgas’ contact with the State of Oklahoma has been notified of this position.”

Under a 2015 agreement, Oklahoma cannot seek an execution date sooner than five months after the protocol is published by the Department of Corrections. “Just getting a copy of the protocol will not be enough,” Dale Baich, a federal public defender who represents Oklahoma death row prisoners, told The Appeal. “What the state will have to do is be very forthcoming about who it talked to, what are the qualifications of the people who came up with the plan?”


Alabama will follow Oklahoma’s lead in carrying out nitrogen executions, state Senator Cam Ward, chairperson of the Senate Judiciary Committee, told The Appeal. “What I keep hearing is that the new states that have looked at doing this are kind of waiting to see how Oklahoma implements theirs first before just cutting new ground,” he said in a phone interview. “In other words, copy somebody else that’s already done it. I think we’re on hold until that happens.” 

A spokesperson for the Alabama Department of Corrections, Samantha Banks, did not answer specific questions from The Appeal about the state’s plan. In an email, Banks wrote that the department is “taking a deliberate approach in developing the protocol for carrying out executions by nitrogen hypoxia. Until the protocol is developed, there is no additional information we can provide at this time.”

In July, Attorney General Steve Marshall’s office entered into a $25,000 contract with workplace safety consultant company FDR Safety to “research process methods, support process, conduct task-based risk assessment, develop job instructions including safety requirements and conduct hazard communication training.” 

Senator Greg Albritton, chairperson of the committee in charge of reviewing contracts, told that the contract was related to the creation of the nitrogen gas execution method. The consultant contracted, Joseph Wolfsberger, specializes in occupational and industrial safety, according to FDR Safety’s website. The company declined to comment on its contract with Alabama. Wolfsberger did not respond to an email from The Appeal. 

Marshall’s office would not provide the state’s contract with FDR Safety to, citing an open records law exception for documents connected to safety and public interest. A spokesperson for Marshall did not respond to requests for a copy of the contract from The Appeal or answer questions about the creation of the execution protocol. 

Ward, however, says the contract, which is being paid with taxpayer dollars, should be made public. “Once the contract has been signed, I’ve always felt it should be transparent, public information,” he said.

Unlike in Oklahoma, where all death row prisoners could potentially be executed with nitrogen gas, Alabama prisoners who preferred the method were required to inform the prison warden of their choice over a 30-day period in June 2018. But prisoners and attorneys told the Montgomery Advertiser that no one informed them they had to make a choice until five days before the deadline, when there was not enough time to properly gather information about its use as a killing agent. The state has denied this allegation.

Ultimately, 51 Alabama death row prisoners elected to be executed by nitrogen gas. Their executions are on hold until the state figures out a method to carry them out. 

John Palombi, a federal public defender for the Middle District of Alabama, told The Appeal that some of the people he has represented experienced grisly deaths by lethal injection. He advised his clients—39 of whom opted in—to choose to be killed by nitrogen last year because “it would guarantee that they were not executed by a torturous method and protect their right to challenge any new protocol.”


Nitrogen gas will only be used in Mississippi if lethal injection is ruled unconstitutional or is “otherwise unavailable,” according to the 2017 law authorizing the method. The state does not specify the conditions that would need to be met for that to happen. 

There has not been an execution in the state for seven years because of challenges to its three-drug lethal injection protocol. In a federal lawsuit filed in 2015, attorneys for death row prisoners argued that using a single large dose of pentobarbital approved by the Food and Drug Administration was safer than using three drugs in succession, citing experts who say it will pose a lower risk of a painful execution. In filings, the state said that it cannot find FDA-approved pentobarbital to use in executions. 

As part of that lawsuit, Attorney General Jim Hood wrote in a June 2017 filing that the state had made no efforts to develop a way to kill prisoners with nitrogen hypoxia or to obtain equipment to do so. 

The lawsuit was delayed while awaiting a U.S. Supreme Court decision on lethal injection and became active again this month, according to a spokesperson for Hood. Attorneys are scheduled to meet with the judge in November to discuss the case, she said. 

Grace Fisher, a spokesperson for the Mississippi Department of Corrections, declined to comment on the status of the nitrogen hypoxia protocol, citing the ongoing litigation. She added, “Under state law, the identity of the supplier of lethal injection chemicals is exempt from disclosure.”