It's also the reason people pass out and die in high-nitrogen or helium environments. Your body can still exchange out CO2 (and O2 in really high concentrations

It's also the reason people pass out and die in high-nitrogen or helium environments. Your body can still exchange out CO2 (and O2 in really high concentrations) and you just carry on until you... Stop. A couple of refrigeration engineers died near us at a poultry processing plant after it was found that the on-site liquid nitrogen tanks had a small leak. CCTV showed them just happily working in a room without ventilation and they just died. Was all very sad.