Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature. It is a colorless liquid with a density of 0.807 g/ml at its boiling point (−195.79 °C (77 K; −320 °F)) and a dielectric constant of 1.43. It is also referred to as dry ice or LN2.
Liquid nitrogen is a cryogenic liquid that can cause rapid freezing on contact with living tissue.
Hazards of liquid nitrogen
The vapor of liquid nitrogen can rapidly freeze skin tissue and eye fluid, resulting in cold burns, frostbite, and permanent eye damage even by brief exposure.
Liquid nitrogen expands 695 times in volume when it vaporizes and has no warning properties such as odor or color. Hence, if sufficient liquid nitrogen is vaporized so as to reduce the oxygen percentage to below 19.5%, there is a risk of oxygen deficiency which may cause unconsciousness. Death may result if oxygen deficiency is extreme. To prevent asphyxiation hazards, handlers have to make sure that the room is well ventilated when using cryogens indoors.
When transferring liquid nitrogen, oxygen in the air surrounding a cryogen containment system can dissolve and create an oxygen-enriched environment. Since the boiling point of nitrogen is lower than oxygen’s, liquid oxygen evaporates slower than nitrogen and may build up to levels which can increase the flammability of materials such as clothing near the system. Equipment containing cryogenic fluids must be kept clear of combustible materials in order to minimize the fire hazard potential. Condensed oxygen in a cold trap may combine with organic material in the trap to create an explosive mixture.
Pressure Buildup and Explosions
Without adequate venting or pressure-relief devices on the containers, enormous pressures can build upon cryogen evaporation. Users must make sure that cryogenic liquids are never contained in a closed system. Use a pressure relief vessel or a venting lid to protect against pressure build-up.
This liquid is dangerous, see BBC news about it here.
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Safe handling of liquid nitrogen
- Never allow any unprotected part of your body to touch objects cooled by liquid nitrogen
- Wear protective clothing: Protect your eyes with a face shield or safety goggles (safety glasses without side shields do not give adequate protection). Always wear cryo gloves when handling anything that is, or may have been, in immediate contact with liquid nitrogen. The gloves should fit loosely, so that they can be thrown off quickly if liquid should splash into them.
- Use only containers designed for low-temperature liquids: Do not ever cover or plug the entrance opening of any liquid nitrogen dewar. Do not use any stopper or other device that would interfere with venting of gas.
- Use proper transfer equipment: Use a phase separator or special filling funnel to prevent splashing and spilling when transferring liquid nitrogen into or from a dewar. The top of the funnel should be partly covered to reduce splashing. Use only small, easily handled dewars for pouring liquid. For the larger, heavier containers, use a cryogenic liquid withdrawal device to transfer liquid from one container to another.
- Do not overfill containers to avoid overflow and spillage of the liquid.
- Never use hollow rods or tubes as dipsticks: When a warm tube is inserted into liquid nitrogen, liquid will spout from the bottom of the tube due to gasification and rapid expansion of liquid inside the tube. Wooden or solid metal dipsticks are recommended; avoid using plastics that may become very brittle at cryogenic temperatures which then become prone to shatter like a fragile piece of glass.
General precautions when working with liquid nitrogen (Dry ice or LN2)
- Avoid eye or skin contact with these substances.
- Never handle dry ice or LN2 with bare hands.
- Use cryogenic gloves, which are designed specifically for
working in freezers below -80°C and for handling containers
or vials stored in these freezers.
- Cryogenic gloves need to be loose-fitting so that they can
be readily removed if LN2 splashes into them or a piece of
dry ice falls into them.
- Always use appropriate eye protection.
- Do not use or store dry ice or LN2 in confined areas, walk-in
refrigerators, environmental chambers or rooms without
ventilation. A leak in such an area could cause an
- Never place a cryogen on tile or laminated counters
because the adhesive will be destroyed.
- Never store a cryogen in a sealed, airtight container at a
temperature above the boiling point of the cryogen; the
pressure resulting from the production of gaseous carbon
dioxide or nitrogen may lead to an explosion.
- For more information about specific cryogens, read the
Material Safety Data Sheet for the substance in question.
First aid measures
- In case of exposure to cryogens or dry ice, remove any
clothing that is not frozen to the skin. Do NOT rub frozen
body parts because tissue damage may result. Obtain
medical assistance as soon as possible.
- Place the affected part of the body in a warm water bath
(not above 40°C). Never use dry heat.