I'm sorry about your coworker.There seems to be a lot of nonsense here. Nitrogen is not a toxic gas. 78% of the air we breathe is nitrogen. If you breathe 100%. Nitrogen you rapidly pass out from lack of oxygen. You do not feel breathless or suffocated, as it is rising CO2 content of your blood that triggers that sensation. If you breathe nitrogen your CO2 level stays normal.
I‘m aware of this because a shift supervisor I knew at a refinery where I worked was found dead with his head in the inspection hatch of a column that was being purged with nitrogen. He would have felt nothing and just passed out. Terrible accident.
Like most civilised people I am strongly opposed to the death penalty, but it does nobody any favours when silly scare stories about gas leaking from the mask etc. are put about by journalists.
That incident illustrates what could happen, though: a hose/mask setup, delivering enough nitrogen to suffocate the condemned, could potentially leak, causing the nitrogen to displace enough of the air in the room to cause a dangerously low oxygen concentration.