Witness Reverend Jeff Hood told reporters he saw a man ‘struggling for their life’ for 22 minutes as Smith became the first US death row inmate executed by nitrogen asphyxia
“Kenny just began to gasp for air repeatedly and the execution took about 25 minutes total.”
As someone well versed in inhaling Nitrous Oxide, why not not just use Nitrous Oxide? That'd be a quick way out, and it's cheap, you can buy enough to kill a person on Amazon for like $30. Even if you fuck it up, they're unconscious and feeling nothing.
There's functionally no difference. The way that they messed this up would have still created suffering because they weren't letting carbon dioxide escape.
The suffocation feeling comes from CO2 buildup, not lack of oxygen. The same issue can happen with nitrous oxide if you don't let the CO2 escape.
Also, and keep in mind I have never killed myself using this method, so I don't know first hand, but, nitrogen is lighter than carbon dioxide, so if the person had 100% pure nitrogen to breathe, and no carbon dioxide, and is maintained with their head near the top of the pod, they would have died fast and allegedly without feeling it.
However, I am absolutely convinced that the people responsible for this execution did research on how to make this method as painful as possible (done right, it is apparently euphoric, and there is NO WAY they would even remotely take the risk of this happening), so they probably went out of their way to have a nitrogen-oxygen mix (like our atmosphere), but with lower amounts of oxygen, and forced the person to stay in a position that would guarantee they would die from CO2 asphyxiation rather than nitrogen.
It is even more inhumane than just using CO2 (as is done in meat "production"), because it prolongs the suffering quite a lot... The whole point of using CO2 on animals is to expedite the process... at the expense of their suffering.
Nitrogen is undetectable with human senses, whereas you'll instantly know if you enter an area with a high CO2 concentration. CO2 is also heavier than air, so it tends to stay in the "pit" they lower the animals into.
I'm going to take a wild guess here and say no one knows. The folks who put the mask on the dude are probably not any sort of experts in masks, gas, or not being an ass, and everyone in this thread is speculating.