Search About Newsletters Donate
Death Sentences

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

A doctor on what’s new — and what isn’t — about the latest death penalty experiment.

A photograph shows barbed wire and a prison tower at Holman Prison at sunset.
Holman Prison in Atmore, Alabama, is where the state’s executions take place.

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

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.

MC: Veterinarians have shied away from using nitrogen for animal euthanasia, finding the gas causes distress in some mammals. Alabama proposes to fit a mask over Smith’s face — similar to how an anesthesiologist would for surgery — and says there is little risk. But other medical experts say that in a hospital, you can usually assume the patient will be cooperative.

JK: This is no different from lethal injection, in that sense. Just as if you don’t hold your arm still, it’s harder to start an IV line, if you don’t hold your head still, it’s harder to get a seal. Regardless of the cooperation, we’re not using medical experts, having an anesthesiologist fit the mask or titrate the nitrogen, someone who has done this hundreds and hundreds of times. This is why they’ve had botched lethal injections, and the lack of expertise will be no different now in terms of risk. The line you get from the prisons is that it will be peaceful and calm. But is the patient always going to be willing and have a beatific visage as they’re doing this? No.

MC: Robert Jason Yong, an expert enlisted by Smith’s defense team, warned that there could be vomiting or seizures, or even that the execution could fail, causing the person to go into a persistent vegetative state. What would a doctor do in that situation?

JK: If it happened in an operating room, they’d take off the mask and the whole thing would stop, and you get a medical evaluation to see how bad the vomiting was. Did they aspirate? Did any of it get into their lungs? But whoever is at the execution may not be trained to do that, and certainly won’t be practiced at it. What percentage of people we’re going to do this to will vomit? I don’t know. Some. It’s not going to be zero, I’ll tell you. The assumption is often that this is going to go perfectly. But as with lethal injection, as more of these are done, everything that can go wrong will eventually.

MC: What else could go wrong with the mask?

JK: EMTs in ambulances will find someone with hollow cheeks, or who has taken their false teeth out, will have trouble forming a seal with a mask. Or talk to firefighters. If they’re going to run into a burning building, they have to have their masks perfectly fitted, and it’s not one-size-fits-all. A firefighter who gains or loses 50 pounds needs to get a new mask. They are not allowed to have facial hair because it interferes with the seal. So are we going to make sure the death row inmate gets a shave right before? Has anyone thought of that?

Alabama’s protocol does not mention shaving, but in a court filing, a lawyer for the state wrote that if Smith is concerned about this, he can choose to shave himself. Smith’s lawyers point out that if he prays aloud, his mask might slip.

MC: Why don’t doctors play more of a role in executions? Your own organization has a code of ethics stating doctors should “not be involved in any aspect” of carrying them out.

JK: It goes back to the Hippocratic Oath that all physicians in the U.S. take when they graduate. Our job is to make people better. Executions are the antithesis of what being a medical professional is all about. And in medical ethics, one of the principles is that you don’t do medical experiments on incarcerated people. This is an experiment being done on an incarcerated person.

MC: NPR reported that Alabama asked Smith’s spiritual advisor to sign a waiver, acknowledging gas could leak from the mask and harm him. This is also true for the correctional officers, but what about the psychological risks they face with the new method?

JK: That’s probably no different from lethal injection, or before that the electric chair, or cyanide, or even hangings or beheadings in the Middle Ages. Witnessing someone being killed will have profound psychological effects on some people, and nitrogen isn’t going to make that better. It’ll be no different from before.

Maurice Chammah Twitter Email is a staff writer and host of the podcast “Just Say You're Sorry,” as well as the author of “Let the Lord Sort Them: The Rise and Fall of the Death Penalty.” He writes narrative features on a range of criminal justice subjects, including the death penalty, forensics and art and music by incarcerated people.