Liquid nitrogen is one of the cryogenic liquids commonly used in research labs. As “cryogenic” means related to very low temperature, it is an extremely cold material. It is liquefied under high pressure condition and can expand to a very large volume of gas. The major hazards of liquid nitrogen are associated with the properties of extreme cold and evaporation. Additional information about hazards of liquid nitrogen is described below:
Extreme Cold
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.
Asphyxiation
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.
Oxygen Enrichment
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.
Transportation /Handling
Container
Storage
Eye/face protection
A full face shield over safety glasses or chemical splash goggles are recommended during transfer and handling of cryogenic liquids to minimize injuries associated with splash or explosion.
Skin protection
Loose-fitting thermal insulated or leather gloves, long sleeve shirts, and trousers with cuffs should be worn while handling liquid nitrogen. Safety shoes are also recommended while handling containers.
A special note on insulated gloves: Gloves should be loose-fitting so they are able to be quickly removed if cryogenic liquid is spilled on them. Insulated gloves are not made to permit the hands to be put into a cryogenic liquid. They will only provide short-term protection from accidental contact with the liquid.