It would be a bit less terrible a method if it actually worked that way. Still depraved, but slightly less.
But it doesn't. Took 30 minutes for the guy to die, supposedly.
Vets swore off using this technique a while ago because of how clearly-distressed animals were when it was performed on them.
There's a big difference between the kind of freak industrial accident you're describing and intentional administration via a mask. And either way, we literally do not know if it is peace or torture.