Cryogenic Liquids - University of Houston
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Cryogenic Liquids

Cryogenic liquids, or cryogens, are liquids with a boiling point below –153 oC(-243 oF; 120 K). They include liquid oxygen, liquid argon, liquid nitrogen, liquid hydrogen, and liquid helium, with liquid nitrogen the most commonly used. Although nitrogen occurs naturally in the atmosphere, and under those conditions it is not hazardous, compressed or refrigerated nitrogen is classified as a hazardous chemical, due to its extremely low boiling point of –195.6 oC (can lead to cold burns, frostbites, and material embrittlement), and a very high expansion ratio of 696: 1 when it moves from liquid phase to gas phase (can lead to oxygen deficient environment, asphyxiation, or explosion). 

Be sure to take the online training EH30: Cryogenic Liquids Safety Awareness training before working with cryogenic liquids. Follow the Cryogenic Liquids Guideline while working with cryogenic liquids.

Cryogenic Liquids Storage

  • Cryogenic liquids shall only be stored in a room with sufficient ventilation.
  • Do Not store or use cryogenic liquids in a confined space, walk-in refrigerators, environmental chambers, or rooms without ventilation.
  • Dewar flasks, which are used for relatively small amounts of cryogenic liquids, should have a dust cap over the outlet to prevent moisture from condensing and plugging.
  • Do Not store a cryogenic liquid in a sealed, airtight container at a temperature above the boiling point of the cryogenic liquid.
  • If an appreciable quantity of cryogenic liquids have to be stored or dispensed in a small room, an oxygen sensor with alarms (permanent, wall-mounted, or portable, worn on personnel) is recommended to warn lab personnel of oxygen deficiency.

Cryogenic Liquids Handling

  • Use only materials suitable for cryogenic temperature, including metals such as the 300 series stainless steels, some aluminum alloys, and copper or brass. When in doubt, contact the manufacturer or vendor for material specifications.
  • Do Not use rubbers, plastics, or carbon steels for handling cryogenic liquids.
  • Ensure all parts of the Dewar (wheels, handles, pressure relief valves, etc.) are in proper functioning condition. When in doubt, contact the manufacturer or vendor.
  • Avoid pouring cryogenic liquids above chest level.
  • When submerging a tool or sample into cryogenic liquid, move slowly as the cryogen can boil violently and splash.
  • Handle objects that are in contact with or immersed in cryogenic liquids with thermally insulated hand tools such as tongs or potholders.
  • Do Not dispose of cryogenic liquids down the drains.
  • Do Not work alone when handling or transporting cryogenic liquids. Have a buddy system.

Cryogenic Liquids Transportation

  • Do Not store or transport a cryogenic liquid Dewar in the closed cabin or trunk of a vehicle, or on a bus or shuttle.
  • Cryogenic liquid cylinders and Dewars must be transported in the open bed of a truck, or appropriate dolly or cart.
  • Avoid riding in an elevator with a cryogenic liquid Dewar.

Personal Protective Equipment for Handling Cryogenic Liquids

  • Never handle a cryogenic liquid or touch uninsulated pipes or equipment with bare hands.
  • Cryogenic gloves (heat resistant gloves) are required for cryogen liquid handling or dispensing. Cryogenic gloves must be loose-fitting so that they can be readily removed if cryogenic liquid splashes onto them.
  • A face shield over the safety glasses/goggles is recommended if splash is possible.
  • Laboratory coat, long pants, and closed toe shoes are required for handling cryogenic liquids.