Alabama is set to carry out the first-ever execution by nitrogen hypoxia on death row inmate Kenneth Eugene Smith on Thursday.

The planned execution raises heated questions about the ethics of using the untried method to execute Smith, who has been through one previous execution attempt before.

If carried out, nitrogen hypoxia will be the first new method of execution since 1982 when the lethal injection was introduced.

What is nitrogen hypoxia?

Nitrogen hypoxia is a form of execution in which an inmate is deprived of oxygen until they only breath nitrogen, causing asphyxiation.

Nitrogen, a colorless, odorless gas, makes up around 80% of the air we breathe. It isn't deadly until it is separated from oxygen.

"What is known is that nitrogen gas, under certain circumstances, can cause death," said Joel Zivot, an associate professor in anesthesiology at Emory University's School of Medicine. "But the terms of how it's going to exactly work is still unclear."

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What are the ethical questions surrounding nitrogen hypoxia?

Former Alabama State Sen. Tripp Pittman, who introduced the bill to allow the use of nitrogen hypoxia in 2018, called it a "more humane method" of execution, a characterization that Zivot challenged.

Even if it does work, Zivot said, Smith could suffer an intensely painful death. "This will not be a death that will be discreet," he said. "It may be prolonged. I think that there will be a good chance there will be some suffering."

The nitrogen gas could induce a seizure in Smith, Zivot said. If the gas is administered through a mask, it could induce Smith to vomit, causing him to choke to death, he added.

If a mask is not secured well, Zivot said, the gas could leak out, posing a danger to the execution team in the room with Smith.

Zivot said Rev. Jeff Hood, Smith's spiritual adviser, was even asked to sign a waiver before entering the execution room.

"It would be akin to having a firing squad and having all the witnesses lined up next to the person you're going to shoot," Zivot said.

Zivot submitted a complaint about the use of nitrogen hypoxia to the United Nations Human Rights Council.

"The law requires that this execution not be cruel," Zivot said. "From what has been described to me, what I know about nitrogen gas and how it may work, this to me feels well within the definition of cruelty."

In response, a group of U.N. experts issued a press release in early January echoing his alarm.

“We are concerned that nitrogen hypoxia would result in a painful and humiliating death,” the four special rapporteurs wrote.

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How did Smith's previous execution fail?

The planned execution of Smith on Thursday comes more than a year after the first attempt to execute Smith by lethal injection in Nov. 2022 failed when executioners couldn't find one of Smith's veins.

Smith was strapped to a gurney for hours after the 11th Circuit Court of Appeals stayed his execution, only for the U.S. Supreme Court to rule it could proceed. Once it did, the execution team poked Smith with needles for hours without being able to access a vein.

It marked the second failed execution in the state in two months after an execution team also failed to find a vein to lethally inject death row inmate Alan Eugene Miller the same month. The same issues plagued the execution of Joe Nathan James Jr., who finally died during his execution in July 2022 after the team searched for a vein for three hours.

The failed executions prompted Gov. Kay Ivey to suspend all capital punishment pending a "top-to-bottom review" of the state's execution system.

The state resumed capital punishment in July 2023 with the execution of James Barber by lethal injection.

Who is Kenneth Eugene Smith?

Kenneth Eugene Smith was convicted in the 1988 murder of 45-year-old Elizabeth Sennett and sentenced to death in 1996.

Although the jury voted 11 to 1 to sentence Smith to life imprisonment without the possibility of parole, a trial judge overruled the jury's recommendation and sentenced him to death, according to court documents.

Sennett's husband Rev. Charles Sennett, who was deeply in debt, paid Smith and 42-year-old John Forrest Parker $1,000 each in a scheme to collect insurance on his wife's death.

Smith and Parker stabbed Sennett eight times in the chest and once on each side of her neck, according to court documents. A week later, Charles Sennett died by suicide after learning he was suspected in the murder.

Parker was also convicted and sentenced to death in the killing. He was executed by lethal injection in 2010.

What are the legal challenges to the execution?

Smith has filed two separate legal challenges to prevent the execution from moving forward on Thursday.

One case filed with the 11th Circuit Court of Appeals argues that Alabama's plan to execute Smith could subject him to a painful or prolonged death.

Smith's attorney Robert Grass told the court in arguments on Friday that the state's use of "untested methods" to execute Smith could cause him extreme suffering or even leave him alive, but in a vegetative state.

“This is the first time this will ever be attempted," Grass said. "There is no data on exactly what’s going to happen and how this will go forward."

In his response, Alabama Solicitor General Edmund LaCour argued that Smith would lose consciousness quickly and feel no pain during the execution, calling nitrogen hypoxia "the most painless and humane method of execution known to man."

The Alabama Supreme Court earlier this month rejected a second appeal filed by Smith that argued a second execution attempt after the previous failed attempt by lethal injection would constitute cruel and unusual punishment.

Smith's lawyers filed a request with the U.S. Supreme Court to halt the execution until it can take up the case.

Contributing: Associated Press

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at [email protected]. Follow her on X @CybeleMO.