2. Cryogenic storage: Because of its extremely cold temperature, liq uid nitrogen can be ha zardous if im properly used. When handling liq uid nitrogen, take precau tions to protect your eyes, face, and skin from exposure to the liq uid. Wear protec tive clothing, incl uding a laboratory coat, gloves designed for handling material at cryogenic tem peratures, and a face shield. To red uce your exposure to cryogenic temperatures, design inventory systems for storing frozen specimens that allow for easy retrieval a nd that minimize the ti me req uired to look for speci mens. Prolonged exposure to cryogenic tem peratures can lead to a loss of sensation i n the hands that can only be recovered after vvarmi ng. This loss of sensation can lead to a false sense of security regarding damage to tissues by the low temperatures. When the tem perature in a liq u id nitrogen unit becomes tolerable and work in g in the unit is no longer uncomfortable, the operator has reached a point where dam age from the cryogenic temperatures is likely. When liquid nitrogen is used i n confined and inadeq uately ventilated areas, the nitrogen can quickly displace the room air. Liq uid nitro gen freezers should be located in well -ven ti l ated areas, and special precautions should be tak en during fill operations. In facilities with several liq uid nitrogen freezers, an oxygen mon itor should be installed to warn occupants of any deterioration in the air q uality due to the nitrogen gas. Plastic screw-capped vials can present a ha zard if stored directly in l iq uid nitrogen. Vials with an inadeq uate seal between the cap and the vial can fill wit h liquid nitrogen. Upon retrieval to warmer
150 Kumar, Kashyap, Singh, and Srivastava
temperatures the vials may explode violently or may spray liq uid, potentially disseminating the contents of the vial. Like wise when opening plastic vials after thawing some dissemina tion of the contents may occur. Therefore, material in plastic ampoules should be stored in the vapor above the liquid nitrogen.