Liquid nitrogen is commonly used in biorepositories for the storage of cells and tissue samples. However, liquid nitrogen handling is associated with risks of serious accidents, including cold burns, asphyxiation, and explosions. These concerns have recently been brought to the limelight by a fatal nitrogen gas leak that occurred at a Georgia poultry plant in January 2021. Strict precautions should be taken while working with liquid nitrogen, including the use of personal protective equipment and compliance with safe handling procedures.
Liquid nitrogen properties
Nitrogen is an odorless, colorless, and tasteless gas that is liquified under high-pressure conditions. Liquid nitrogen is liquefied nitrogen gas with a boiling point of approximately -196°C (-320°F). It undergoes spontaneous gas conversion with a rate depending on the specific conditions, which decreases the amount of liquid nitrogen.1 Notably, liquid nitrogen can expand into large gas volumes.
Liquid nitrogen has found applications in many areas of human life, including in medicine (for removal of certain skin lesions), as a computer coolant, in cryogenics (the production and effects of very low temperatures), and in the storage of biospecimens.
Significance of liquid nitrogen in biorepositories
Liquid nitrogen plays an important role in the storage of both cells and tissue samples in biorepositories. It preserves biospecimens at a very low storage temperature that halts biological activity – a major advantage of liquid nitrogen as a cryopreserving agent. The exact mode of liquid nitrogen handling in biorepositories varies with the scale and type of tissue storage conditions. Facilities with multiple cryofreezers opt for bulk tank storage of the liquid nitrogen outside the storage facilities. Vacuum-jacketed piping will be installed to distribute the liquid nitrogen to individual freezers. Such a set-up is much safer, since the bulk of liquid nitrogen placed outside the enclosed areas of biorepositories. Biorepositores with a limited number of cryofreezers opt for smaller, portable dewar systems to hook up to individual cryofreezer. It is critical to secure the dewars to prevent them from rolling off and causing tipping hazards. In any of these use cases, working with liquid nitrogen is always associated with clear risks that require strict precautions.
A recent example of a fatal accident occurred at a poultry plant in Georgia2 clearly illustrates the risks associated with liquid nitrogen use and significance of addressing this issue diligently. During unplanned maintenance work on a processing and freezing line, a nitrogen gas leak took place that caused six fatalities and 12 hospitalizations.
Risk of accidents associated with liquid nitrogen use1,3
Handling liquid nitrogen is associated with an increased risk of accidents, including asphyxiation, cold burns, and explosions. In case of a liquid nitrogen-related accident, medical attention should be sought immediately.
Risk of asphyxiation
Liquid nitrogen can expand into large volumes of gas, which can lead to oxygen displacement and risk of asphyxiation.3 Therefore, in cases of large liquid nitrogen spills, the personnel should be evacuated. Moreover, if people working with liquid nitrogen become dizzy, they should be immediately evacuated to a well-ventilated area.
Risk of cold burns, frost bites, and eye damage
The very low temperature of liquid nitrogen leads to another important hazard: risk of cold burns, frost bites, or eye damage after contact with liquid nitrogen due to instant freezing.3 If a person’s skin has been exposed to liquid nitrogen or cold nitrogen gas, the normal body temperature should be restored by flashing the affected area with large volumes of tepid water, and the tissue should be protected from further damage and infection. However, the frozen body part should not be rubbed to prevent further tissue damage, and heat should not be applied.
Risk of explosion due to pressure buildup or due to liquid oxygen
When liquid nitrogen expands into gas in an enclosed environment, risk of explosion arises. Liquid nitrogen should not be stored in sealed containers because sealed containers may not be able to contain the pressure caused by its gas expansion. A pressure relief vessel or a venting lid should be used to protect against pressure buildup.