Under certain conditions, otherwise harmless gases can kill. Inert gases such as argon, helium, carbon dioxide, and nitrogen can asphyxiate a person.

Welders have died inside the hold of a ship or inside a tank because the triggers of their gas metal-arc welding guns were left slightly depressed over a weekend and the shielding gas was not turned off. When they returned to work the following Monday, the shielding gas inside the enclosed space had pushed out all the air and they were asphyxiated.

Asphyxiation occurs rapidly and without warning. All possible precautions should be taken to ensure than an adequate oxygen supply is available. Neither respirators nor gas masks supply oxygen. They only filter or purify. If asphyxiation is possible, workers should be equipped with supplied air masks, or the area should be well ventilated to assure the availability of air suitable for breathing.