MASK OFF! oxygen - deficient - atmosphere!!

Oxygen-deficient atmospheres are the leading cause of confined space fatalities in the shipyard. While normal atmosphere contains between 20.8 and 21 percent oxygen, OSHA defines as oxygen deficient any atmosphere that contains less than 19.5 percent oxygen, and as oxygen enriched, any atmosphere that contains more than 22 percent.

Oxygen-deficient atmospheres may be created when oxygen is displaced by inerting gases, such as carbon dioxide, nitrogen, argon, or the ship's inert gas system or firefighting system. Oxygen can also be consumed by rusting metal, ripening fruits, drying paint, or coatings, combustion, or bacterial activities.

Oxygen-enriched atmospheres may be produced by certain chemical reactions, but in a shipyard they are typically caused by leaking oxygen hoses and torches. Oxygen enriched atmospheres present a significant fire and explosion risk.