Nitrogen gas inhalation doesn’t hurt at all.
Human lungs evolved to be highly sensitive to
concentrations of carbon dioxide which then
regulates breathing. And since nitrogen comprises
most of the air, we evolved to not notice it, as
it doesn’t reach high concentrations on its own.
So the ‘user’ on pure nitrogen feels no need to
breathe, since there is no carbon dioxide, and when
he does breathe he pulls in a gas the feels normal.
Starved for oxygen, his mind drifts away and he’s gone.
I’ve favored N2 inhalation for the death penalty for years.
Nitrogen gas is cheap, plentiful, and bungled executions using needles, sedating the felon, or shortage of fatal
injectibles cease to be a problem.