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Nitrogen hypoxia

Death caused by breathing pure nitrogen through a mask, depriving the body of oxygen. First used by Alabama in 2024; ruled unconstitutional by a federal court in 2026.

  1. Mask fittedA respirator mask is secured over the nose and mouth
  2. Nitrogen flowsPure nitrogen replaces the air the prisoner breathes
  3. No oxygenWithout oxygen, unconsciousness and then death follow

How this method works, stage by stage. Illustration by DeathRowStats.

This article explains how the method works at the level reported in court records and the news. It does not include doses or technical instructions.

Overview

Nitrogen hypoxia is an execution method in which the prisoner breathes pure nitrogen gas through a mask, which deprives the body of oxygen. Alabama became the first place in the world to use it, executing Kenneth Smith in January 2024. By mid-2026 it had been used in eight executions in the United States: seven in Alabama and one in Louisiana.

How it works

Air is mostly nitrogen already; what keeps us alive is the oxygen mixed with it. When a person breathes only nitrogen, their blood stops receiving oxygen, leading to unconsciousness and then death. States introduced it partly because lethal injection drugs have become hard to obtain.

How it is administered

The prisoner is strapped to a gurney, and a respirator-style mask is fitted over the nose and mouth. Nitrogen is then delivered through the mask in place of air. Alabama's protocol says the prisoner should lose consciousness within seconds and die within about 15 minutes.

What the prisoner may experience

Witnesses at several Alabama nitrogen executions reported prisoners shaking, pulling against their restraints and breathing heavily for several minutes. Alabama has said some of this was caused by prisoners holding their breath.

In May 2026, after a trial, a federal judge found that people executed this way likely experience "severe air hunger", with distress, anxiety and fear, for one to three minutes before losing consciousness. Veterinary guidelines do not recommend nitrogen for euthanising most animals.

How long it takes

Longer than lethal injection in most reported cases. Kenneth Smith was pronounced dead 32 minutes after the gas was first administered. In Anthony Boyd's execution in 2025, about 30 minutes passed between him first showing signs of the gas's effects and the curtain being closed.

Cost

The states using it have not published the full cost of their nitrogen systems or the gas.

Availability

Unlike lethal injection drugs, nitrogen is a widely available industrial gas, which is one reason states adopted it. The limits on its use now are legal rather than practical.

Where it is used

It has been used by Alabama and Louisiana, and is also authorised in Mississippi, Oklahoma and Arkansas. In June 2026, a federal appeals court upheld a ruling that Alabama's nitrogen protocol is unconstitutional, and the US Supreme Court refused to let the state use it in the case before it. Alabama has since turned to lethal injection for scheduled executions, including that of Michael Taylor, whose warrant was originally obtained for nitrogen.

Sources

  1. PBS NewsHour / AP: Supreme Court refuses Alabama nitrogen request (June 2026)
  2. CBS News: Alabama nitrogen executions ruled cruel and unusual
  3. Alabama Reflector: appeals court upholds ruling
  4. SCOTUSblog: Court denies Alabama request
  5. Courthouse News: Supreme Court and the Anthony Boyd execution
  6. UPI: Alabama's first nitrogen execution
  7. Equal Justice Initiative: nitrogen suffocation (advocacy group)