Nitrogen, which cannot be detected by smell, is frequently used for purging tanks because it has inert (non-reactive, non-flammable) properties.
However, in high concentrations, nitrogen can belethal because it displaces oxygen in the body.
When oxygen levels in the body decrease, the brain triggers the breathing rate to increase. This causes a further build-up of nitrogen in the body.
When oxygen levels fall to 4-6 percent, the victims fall into a coma in less than 40 seconds. Once this happens, chances of survival are minimal.