Nitrogen Suffocation

What to Know

• Alabama—the state with the worst record for botched executions—carried out the first execution in the world using nitrogen gas in 2024
• Despite graphic witness accounts demonstrating the 2024 execution of Kenny Smith did not go according to their own plan, Alabama officials told the public the execution was a success and offered to help other states suffocate people to death using nitrogen gas
• There is no scientific evidence on using nitrogen to execute people but it is generally not used to euthanize animals because it causes panic and distress
• Risks include feelings of suffocation and choking to death on one’s own vomit, as well as brain damage, a stroke, or a persistent vegetative state instead of death
• A mishap with odorless, colorless nitrogen could kill prison staff within minutes

Without Scientific Evidence, States Adopted Never-Before-Used Method

In 2015, Oklahoma became the first state to adopt a measure allowing prison staff to use nitrogen gas to execute people after the botched lethal injection execution of Clayton Lockett in 2014 led to a halt in executions.

Prior to Alabama’s execution of Kenny Smith in 2024, no execution had been carried out anywhere in the world using asphyxiation with an inert gas like nitrogen.

Despite the absence of scientific evidence on executing people using nitrogen suffocation, Mississippi passed a similar law in 2017, and on March 22, 2018, Alabama Gov. Kay Ivey signed legislation making Alabama the third state in the country to allow executions by nitrogen gas. Louisiana added nitrogen suffocation in March 2024.

Risk of Botched Nitrogen Execution

Alabama’s protocol calls for delivering nitrogen gas to the condemned person through a mask, which experts say creates a substantial risk that oxygen will infiltrate the mask.

According to experts, exposure to less than 100% pure nitrogen gas can cause severe and permanent injuries short of death—which could leave the person in a persistent vegetative state, causing him to have a stroke, or to experience the painful sensation of suffocation.

Vomiting is also a known side effect of oxygen deprivation. Using a mask that covers the nose and mouth creates a risk that the person will asphyxiate on his own vomit, especially where, as here, prison staff will not intervene to check or clear the person’s airway if he vomits after nitrogen has begun to flow.

United Nations experts have expressed alarm over the use of nitrogen gas, which they described as “an untested method of execution which may subject [the condemned person] to cruel, inhuman or degrading treatment or even torture.”

Warning that experimental executions by nitrogen gas asphyxiation likely violate international bans on torture and other cruel, inhuman, or degrading punishment, the experts said in a statement, “We are concerned that nitrogen hypoxia would result in a painful and humiliating death.”

The U.N. Human Rights Office also expressed serious concerns that execution by nitrogen gas could violate U.S. treaty obligations prohibiting torture, noting that Alabama’s protocol does not provide for a sedative prior to administration of the lethal gas.

Prison Employees May Face Risk of Asphyxiation or Injury

Nitrogen has killed people in industrial and medical accidents. A recent report into a nitrogen leak that killed six workers at a Georgia poultry plant underscored the extreme risks that nitrogen poses to workers’ lives, even in industries and facilities where the hazardous chemical has long been widely and regularly used.

Because nitrogen gas is odorless and colorless, correctional officers, prison staff, and observers at any execution face the risk of asphyxiation in the event of a leak. The Chemical Safety Board warns that “breathing an oxygen-deficient atmosphere can have serious and immediate effects, including unconsciousness after only one or two breaths. The exposed person has no warning and cannot sense that the oxygen level is too low.”

If nitrogen leaks—because the execution mask is not properly sealed or if a valve detaches—prison staff in the execution chamber may be at risk of injury or death. The Alabama Department of Corrections acknowledged in court that nitrogen gas presents “the dangers of inert-gas asphyxiation to employees.”

Nitrogen Inappropriate for Euthanizing Animals

The American Veterinary Medical Association has declared that nitrogen gas is inappropriate for euthanizing most animals. Its guidelines provide, “Current evidence indicates this method is unacceptable because animals may experience distressing side effects before loss of consciousness.”

“Veterinarians have generally stopped using nitrogen to euthanize animals, who showed severe signs of distress,” The New York Times reports.

Despite a History of Botched Executions, Alabama Continues to Experiment with Nitrogen Gas

On August 25, 2023, less than 10 months after the State of Alabama failed in its torturous attempt to execute Kenny Smith by lethal injection, the attorney general asked the Alabama Supreme Court to allow a second attempt to put Mr. Smith to death, this time using the unproven, untested method of nitrogen gas. The motion did not provide any details about how a nitrogen gas execution would be carried out.

With its long history of “failed and flawed executions and execution attempts,” EJI senior attorney Angie Setzer told the Associated Press, “Alabama is in no position to experiment with a completely unproven and unused method for executing someone.”

On November 1, 2023, the Alabama Supreme Court nonetheless granted the attorney general’s motion in a divided order signed by six justices. A week later, Alabama Gov. Kay Ivey set the execution for January 25, 2024.

State officials assured the courts and the public that Kenny Smith would lose consciousness “almost immediately” and die within a few minutes. 

Mr. Smith did not die within minutes as the State promised. The execution began at 7:53 pm but Mr. Smith was not pronounced dead until 8:25 pm.

Alabama officials said they do not know when the nitrogen gas started to flow into the mask that completely covered Mr. Smith’s face. But witnesses reported that at 7:57 pm, he began writhing in pain and his body started “thrashing against the straps” binding him to the gurney, “his whole body and head violently jerking back and forth for several minutes,” followed by “heaving and retching inside the mask.”

Mr. Smith clenched his fists and his legs shook. As Mr. Smith gasped for air, his body lifted against the restraints. Witnesses observed fluid inside of the mask. 

Despite witnesses reporting clear signs of distress and suffering, Alabama did not explain why the execution did not go as planned.

Federal Court Finds Nitrogen Protocol Is Unconstitutional

In 2025, Jeffery Lee filed a federal lawsuit challenging nitrogen suffocation as cruel and unusual punishment because it “causes inmates to experience prolonged air hunger and feelings of suffocation, which evoke severe anxiety, fear, and physiological distress.” The suit claimed the method cruelly superadds pain in violation of the Eighth Amendment because it triggers the person’s survival instincts to breathe oxygen while also preventing them from doing so.

Alabama’s use of the experimental method has raised serious concerns that it causes significant and lengthy suffering. Forcing a person to breathe nitrogen gas through a facemask until they die from lack of oxygen, Justice Sonia Sotomayor recognized, inflicts the “unnecessary psychological terror” of “conscious, excruciating suffocation” and “severe emotional suffering” while “consciously experiencing the ‘primal urge to breath.’”

After a bench trial, U.S. District Court Judge Emily Marks ruled on May 28, 2026, that death by nitrogen hypoxia does involve “some suffering” because people executed by nitrogen suffocation “likely experience severe air hunger,” which “results in profound physiological discomfort and distress, as well as anxiety, fear, and dread” and “can be worse than pain.” Despite these findings, the court held this suffering was not unconstitutional because people being executed lose consciousness “in not significantly more than one to three minutes” after nitrogen begins to flow into the mask.

Mr. Lee appealed, and the Eleventh Circuit Court of Appeals reversed the district court, finding that one to three minutes of suffering “presents a substantial risk of serious harm over and above death itself” in violation of the Eighth Amendment.

“Counting to 60 or 180 seconds is not a quick exercise,” the court wrote, “and constitutionally speaking, that timeframe is intolerable given the suffering that would likely take place under Alabama’s nitrogen hypoxia protocol.”

Accordingly, the Eleventh Circuit remanded to the district court, which held that Alabama’s nitrogen suffocation protocol violates the Eighth Amendment. The court permanently blocked Alabama from using nitrogen suffocation to execute Mr. Lee.

The Eleventh Circuit denied Alabama’s request to overturn that ban, and the Supreme Court refused the State’s motion asking the Court to vacate the injunction and allow it to use nitrogen suffocation to put Mr. Lee to death.