Next week, Alabama prison officials plan to escort Kenneth Eugene Smith from his cell, strap a mask to his face and replace his breathing air with nitrogen gas. It would likely be the first execution of its kind anywhere in the world.

How did we get here? Lethal injection has been the dominant method in the United States for decades, but around 2010, pharmaceutical companies began refusing to sell the necessary drugs to prison agencies. States turned to new suppliers and drug cocktails under the cover of new secrecy laws. But the disruptions led to more public scrutiny of the method as journalists gave reports of prisoners screaming, choking and being cut and stabbed in the search for veins.This article was published in partnership with AL.com.

Some states abandoned executions entirely, leading to an overall decline in recent years, while others considered alternatives. South Carolina built a firing squad chamber, while Arizona refurbished a gas chamber.

Alabama state officials have said the goal of “nitrogen hypoxia” is for the prisoner to quickly lose consciousness as oxygen leaves his or her body. But Smith lawyer’s are asking a series of federal courts to stop the execution, arguing that if something goes wrong, he might vomit, asphyxiate or be left in a persistent vegetative state. So far, they’ve been unsuccessful.

There were 11 gas executions in the U.S. between 1979 and 1999, according to the Death Penalty Information Center, a research group that tracks executions. Those involved filling a chamber with cyanide gas, leading to suffocation. By contrast, nitrogen has been proposed for euthanasia patients in Europe, and politicians who support it point to accidental deaths of pilots and scuba divers. Oklahoma legislators reportedly watched YouTube videos of teenagers passing out from a similar lack of oxygen after inhaling helium.

Smith was convicted of killing Elizabeth Sennett in 1988, after being hired by her husband, who was seeking a life insurance payout. Alabama attempted to execute Smith in 2022 using lethal injection, but gave up after spending four hours trying to insert an IV.

The copy of Alabama’s new nitrogen protocol that appears in court records is heavily redacted, but if Smith is executed on Jan. 25 as scheduled, other states could begin using nitrogen in similar ways. The Marshall Project spoke with Dr. Jeffrey Keller, president of the American College of Correctional Physicians, which trains and represents doctors who work behind bars, about this moment in the history of executions. Our conversation has been edited for length and clarity.

Maurice Chammah: What should the average person understand about an execution by nitrogen? What might happen if this method catches on nationally?

Jeffrey Keller: I don’t have much to say about how it’s going to work because nobody does. It’s entirely experimental. There is some concern that leaking nitrogen could affect bystanders, and I don’t know if that’s true, because nobody knows.

It’s also proposed to be painless, and I know that is wrong: The proponents refer to people who have become nitrogen-intoxicated during airplane flights, or scuba diving, and then woke up and reported they didn’t feel anything. But the incarcerated person knows exactly what’s going to happen.

If I told you, at 11 a.m. tomorrow, I’m going to place a plastic bag over your head and suffocate you to death, you’d have intense anxiety and fear and the release of stress hormones, up until the moment that it happens. Is that suffering? Of course. But how much they’ll feel when the nitrogen hits, I don’t know — because, again, nobody knows.

Source: Vomiting, Seizures, Stroke: What Could Happen in the First Nitrogen Execution in the U.S.