[null and void]

NASA Ames lost a technician who was testing a mask that was supposed to be hooked up to air instead of pure nitrogen. It was so quick he didn’t even have time to remove the mask.

[pierrem15]

You’ll feel a little dizzy, pass out after about 2 1/2 minutes, cardiac arrest 2-3 minutes afterwards. About as painless as you can get.

[Vigilanteman]

The theory behind the execution method is that changing the composition of the air to 100% nitrogen would cause the inmate to pass out and then die from lack of oxygen. …

It isn't a theory. It is fact. Not only the incident you mentioned, but farming accidents where the victim inhales too high of a concentration of nitrogen. Manure pits, spreading NH4 when the wind is blowing the wrong way and other occupational dangers of agriculture involving nitrogen abound.