Liquid Nitrogen and Frozen Biological Material

1. Storage and retrieval of frozen biological material from liquid nitrogen requires appropriate personal protective equipment (PPE). The major risks associated with liquid nitrogen (-196 degrees C) are frostbite, asphyxiation, exposure, and the samples exploding. Gloves thick enough to insulate but flexible enough to allow ampoule manipulation should be worn. When liquid nitrogen boils off during routine use, regular ventilation is sufficient to remove the excess, but when nitrogen is being dispensed, or a lot of material is being inserted into the freezer, extra ventilation is necessary.

When ampoules are submerged in nitrogen, the pressure difference between the outside and inside of the ampoule is high; if it is not perfectly sealed, liquid nitrogen will enter, so that when thawed the ampoule will explode violently. Ensure that ampoules are perfectly sealed, but in any event always wear eye protection and a face shield. Thawing from storage under liquid nitrogen must always be allowed to occur in a container with a lid, such as a plastic bucket, and eye protection and a face shield must be worn.

2. Liquid Nitrogen and dry ice must never be used or stored in walk-in refrigerators or freezers. These areas have inadequate ventilation which will cause the liquid nitrogen and dry ice (CO2) to displace the oxygen content to dangerous levels.