This method was used for the first time in Alabama last week. For at least two minutes, Kenneth Eugene Smith appeared to shake and writhe on the gurney
I honestly can't understand what is going on over there. Killing people with nitrogen is without question one of the best ways to kill a person. A grow box and a large N² tank are enough. How hard can that be?
I mean, people died by accident in nitrogen atmospheres while happily eating lunch.
The use of nitrogen is nothing more than biological suffocation whilst the person is awake. They will know only that horrible inability to breathe whilst at the same time resorting to panic and anxiety breathing. If you wanted to do execution badly, this is it. (Yes, I understand the mechanisms from gaseous exchange through to the pons medulla reflex)
Please read for yourself about the process in Switzerland. Come back when you have understanding of what happens there vs the nitrogen mask. Or alternatively provide your medical expertise to counter?