Nitrogen & Inert Gas Asphyxiation

Nitrogen, argon and helium aren’t toxic, and you can’t see or smell them. That’s what makes them deadly. When they push oxygen out of the air, a worker can pass out after a breath or two, with no warning at all. Would-be rescuers often die the same way.

• General Industry
• Welders
• Refineries & plants
• Labs

Why there’s no warning

• Your body senses rising carbon dioxide, not falling oxygen. In nitrogen or argon, you breathe normally and feel nothing until you collapse.
• Normal air is about 21% oxygen. Below 19.5% is oxygen-deficient. At very low levels, unconsciousness can come within seconds and death within minutes.

Where it happens

• Tanks, vessels and pipes purged with nitrogen
• Welding inside tanks or pipes with argon or other shielding gas
• Leaking cylinders or lines in small rooms, pits and trailers
• Liquid nitrogen in labs, food plants and medical settings (1 liter of liquid becomes about 700 liters of gas)
• Dry ice (solid CO₂) in vehicles, coolers and walk-ins; CO₂ is also toxic at high levels
• Fire suppression systems that flood rooms with gas
• Fermentation and decaying material in tanks and silos (CO₂)

Prevention

• Test the air for oxygen before entering any space where inert gas could be present, and monitor continuously. See Gas Detectors.
• Ventilate with fresh air, and keep inert gas lines disconnected or blanked during entry.
• Post warnings on spaces and openings where inert gas is used.
• Use fixed oxygen monitors with alarms in rooms where gases or liquid nitrogen are stored or used.
• Don’t put your head into a tank opening or manway that may contain inert gas.
• Follow confined space rules, including permits and attendants. See Confined Spaces.

Cylinders and liquid nitrogen

• Store gas cylinders upright, secured, capped and in ventilated areas.
• Use the right regulators and fittings; don’t adapt connections between gases.
• Handle liquid nitrogen with face shield and insulated gloves; it also causes severe frostbite.

Last updated: October 2, 2026