From what I’ve read, it’s due to the fact that they’re strapping a mask to their faces. The exhaled gasses have nowhere to go, it mixes with the inert gas, and doesn’t cause a loss of consciousness as quickly as intended.

They would need to place the condemned in a chamber that fills with the inert, heavier than air, gas quickly, with a relief valve at the highest point to release breathable oxygen. If they flood the chamber quickly enough, the victim will barely be conscious long enough to wonder why the air is a little colder before they black out.

I think they should use a helmet, and give the condemned a choice between motorcycle, astronaut, or old timey diving helm. Make the execution a little more fun, ya know?

It makes more sense when you realize that the cruelty is the point.

There is a lot of room for error, but I’d still rather take the 5% chance of a botched death by a shot to the back of the head than the much more stress inducing process of being put into a guillotine.