Alabama is seeking to become the first state to execute a prisoner by making him breathe pure nitrogen.

The Alabama attorney general’s office on Friday asked the state Supreme Court to set an execution date for death row inmate Kenneth Eugene Smith, 58. The court filing indicated Alabama plans to put him to death by nitrogen hypoxia, an execution method that is authorized in three states but has never been used.

Nitrogen hypoxia is caused by forcing the inmate to breathe only nitrogen, depriving them of oxygen and causing them to die. Nitrogen makes up 78% of the air inhaled by humans and is harmless when inhaled with oxygen. While proponents of the new method have theorized it would be painless, opponents have likened it to human experimentation.