Investigator Exposed to Infectious Material in Cryotube Explosion

Key Instruction Points

  • Be aware of the potential for pressurization when working with cryogenic liquids.

  • A researcher at a university reported that a vial of potentially infectious materials "exploded" when she removed it from liquid nitrogen.

  • As you may have guessed, the "explosion" occurred when the liquid N2 that has leaked into a vial expands when removed from the cold. This used to be a fairly common problem with heat-sealed glass ampules, because it was difficult to obtain perfectly fused glass with no microscopic holes. This problem was largely resolved with laboratories began using plastic cryovials with a silicone seal. Nunc* makes a sleeve called CryoFlex that slips over the vial and then is heat-sealed to keep the liquid out. However, even with this type of product an explosion infrequently occurs.

Several Ways to Prevent this from Happening  

  • Cryogenic storage vials are designed for VAPOR PHASE STORAGE in liquid nitrogen freezers. This means that they are designed to sit in the cloud of extremely cold nitrogen gas that sits just above a small reservoir of liquid nitrogen in the bottom of the freezer. Leakage of liquid nitrogen into the vial occurs with the freezer is overfilled and the vials are immersed in liquid nitrogen. This problem can be avoided by not overfilling the freezers with liquid nitrogen.

  • Visually check each cryovial prior to filling to ensure there are no defects around the rim. Cryovials should never be re-used.

  • When removing samples, pause for a moment in the neck of the dewar before bringing them into the room atmosphere - if one is going to pop, it will usually do so early in the warm-up process.

  • The importance of gloves and face shield can not be overemphasized. Tubes stored in liquid phase dewars, where the ampules are in canes is especially hazardous. Since nitrogen freezers tend to be located separate from the labs, full face shields and gloves should be available near the nitrogen freezers so no one is tempted to pull a vial without protection because they forgot to bring a shield with them.