Explainer | Alabama to carry out first nitrogen gas execution. How will it work and what are the risks?

Alabama is preparing to use a new method of execution: nitrogen gas.

Kenneth Eugene Smith, who survived the state’s previous attempt to put him to death by lethal injection in 2022, is scheduled to be put to death on Thursday by nitrogen hypoxia. If carried out, it would the first new method of execution since lethal injection was introduced in 1982.

The state maintains that nitrogen gas will cause unconsciousness quickly but critics have likened the never-used method of execution to human experimentation.

What is nitrogen hypoxia?

Nitrogen hypoxia execution would cause death by forcing the inmate to breathe pure nitrogen, depriving him or her of the oxygen needed to maintain bodily functions.

Has it ever been used?

No state has used nitrogen hypoxia to carry out a death sentence. In 2018, Alabama became the third state – along with Oklahoma and Mississippi – to authorise the use of nitrogen gas to execute prisoners.

Some states are looking for new ways to execute inmates because the drugs used in lethal injections, the most common execution method in the United States, are increasingly difficult to find.

How is it supposed to work?

Nitrogen, a colourless, odourless gas, makes up 78 per cent of the air inhaled by humans and is harmless when breathed with proper levels of oxygen.

The theory behind nitrogen hypoxia is that changing the composition of the air to 100 per cent nitrogen will cause Smith to lose consciousness and then die from lack of oxygen.