Cryogenic Liquids & Dry Ice
Cryogenic liquids like liquid nitrogen, argon and oxygen are extremely cold gases kept as liquids. They’re used in labs, food freezing, metal work and medical supply. The cold is the obvious danger, but the bigger killer is invisible: the liquid turns into a huge amount of gas that can push the oxygen out of a room.
- General Industry
- Labs
- Food Processing
Common cryogens
| Material | Temperature | Main extra hazard |
|---|---|---|
| Liquid nitrogen | About −320°F (−196°C) | Oxygen-deficient air |
| Liquid argon | About −303°F (−186°C) | Oxygen-deficient air; heavier than air, collects in low spots |
| Liquid oxygen | About −297°F (−183°C) | Makes materials burn violently |
| Dry ice (solid CO2) | About −109°F (−78°C) | Carbon dioxide buildup in closed spaces |
The hazards
- Cold burns and frostbite: brief contact can freeze skin and eyes. Touching cold metal pipes or containers can make skin stick and tear.
- Asphyxiation: one liter of liquid nitrogen becomes roughly 700 liters of gas. In a small room, walk-in cooler or vehicle, it can lower oxygen to deadly levels with no warning. You can’t smell it, and the first breath of very low-oxygen air can make you collapse. See Inert Gas Asphyxiation.
- Pressure: cryogens boil constantly. A sealed container will build pressure until it bursts. Never put dry ice or liquid nitrogen in a tightly sealed bottle or cooler.
- Oxygen enrichment: liquid oxygen, and even very cold surfaces that condense oxygen from the air, can make clothing, grease and asphalt burn explosively. See Oxygen Hazards.
- Brittle materials: ordinary plastic and carbon steel can crack when they get this cold.
PPE
- Face shield over safety glasses or goggles when pouring or transferring
- Loose-fitting insulated cryogenic gloves that can be thrown off quickly
- Long sleeves and pants worn outside shoes, with no cuffs that can catch liquid
- Closed-toe shoes; no open shoes or sandals
Safe handling
- Use only containers made for cryogens, such as vented dewars, and keep pressure relief devices clear.
- Work in well-ventilated areas. Rooms where large amounts are stored or used should have oxygen monitors with alarms. See Gas Detectors.
- If the oxygen alarm sounds, leave and don’t go back until it’s safe. Never go in after someone who collapsed. Call for trained rescuers with air supply.
- Pour slowly to reduce splashing and boiling, and use a phase separator or funnel made for cryogens.
- Don’t ride in an elevator with a large dewar. Send it alone and meet it at the other floor.
- Secure large tanks and cylinders so they can’t tip. See Compressed Gas Cylinders.
Dry ice
- Handle with insulated gloves or tongs, never bare hands.
- Store it in a ventilated area in a container that lets gas escape.
- In a car or truck, keep it in a vented cooler, keep windows cracked or the fresh-air setting on, and don’t keep it in the cab for long trips.
First aid for cold burns
Remove clothing that isn’t frozen to the skin, warm the area gently in lukewarm (not hot) water, don’t rub it, and get medical care. For eye contact, flush with lukewarm water and call 911.
Standards & references
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