The process of putting someone to death is already traumatic to the guards that have to make it happen. It makes them question whether they can find salvation - even though their job made them do it.
Now you’re asking them to experiment on people? At the very least let’s use surefire methods & people who are already murderers for this profession
Nitrogen asphyxiation IS a surefire method. People die from it all the time and it's a big hazard among people who work with nitrogen because your body is literally incapable of telling you there is anything wrong.
The only experimentation is social. We know for a fact that nitrogen asphyxiation is quick and painless.
I don't support the death penalty, but if you're going to do it, nitrogen is the way to go.