The above is my version of title from April 17, 2015 by The Guardian.
I missed this story from April 2015.
Oklahoma is the only state with nitrogen hypoxia as a method of execution. They also have the firing squad as another method.
South Carolina considered nirogen hypoxia in 2016 but it never got to the floor for a vote.
I would assume that other states with capital punishment would go to nitrogen hypoxia as an alternative method of execution as the left has lethal injections tied up in court.