He can’t have a last meal due to the danger of him throwing up in the air tight mask ??
The whole business seems contrived to me.
Why the need for an air tight mask - a small room filled with nitrogen would asphysxiate in seconds.
The room wouldn't even need to be that well sealed.
LN2 isn't expensive, although investment needs to be made to handle it.
LN2, expands into a gas 700x greater in volume - a small Dewar could provide 17'500l of Nitrogen - hence the dangers of asphyxia and explosive expansion.
If capital punishment were necessary (and I don't believe it is); this all seems to provide a simple means to kill.
So why the air tight mask etc.
Why not just wait until the prisoner was asleep and pump nitrogen into the room?
It seems that death in itself, is not the entire goal.
A macabre device with a mask, jeopardy over whether this will work and observing fear in the prisoner, all appear to be part of the 'spectacle'.
Could it be that nitrogen hasn't been used before, because it would be too straightforward?
This is one reason why I can never agree with capital punishment - it has always been about the exhibition (and may unwittingly make the prisoner, a star) - would you catch the underground to go and see a hanging?
https://londonist.com/london/undergroundtoapublichanging
This is a part of humanity that I've never been comfortable with.