Safe Handling and Use of Liquid Nitrogen

GENERAL:

Liquid nitrogen is inert, colorless, odorless, noncorrosive, extremely cold (-320 Fahrenheit), and nonflammable.  Expansion from liquid to gas ratio is 1 to 694.


PERSONAL PROTECTIVE EQUIPMENT:

Chemical splash goggles, face shield, and gloves of impermeable material should be used.  Long sleeves and cuff-less trousers/slacks are also recommended during handling, transfer operations or whenever the possibility of exposure to liquid nitrogen spills exists.


SAFE HANDLING:

Impact resistant containers that can withstand the extremely low temperatures should be used.  Materials such as carbon steel, plastic and rubber become brittle at these temperatures.  USE ONLY APPROVED, UNSEALED CONTAINERS.  Never pour liquid nitrogen into a thermos.  Never seal liquid nitrogen in a container.  Vaporization could cause the container to build up enormous pressure and explode.


HAZARDS:

Liquid nitrogen may produce conditions for asphyxiation by displacement of the concentration of oxygen in air below levels necessary to support life.  Heat leaks are always present and vaporization takes place continuously.  Rate of evaporation varies, depending upon the design of the containers and the volume stored. In general, cryogenic containers have a built-in safety pressure release.

Liquid nitrogen should only be stored in well-ventilated areas.  A vapor cloud or plume, created by water vapor condensation, can be evidence of a release. As the gas warms up to room temperature, the vapor cloud may not be visible, but the danger may still be present.  DO NOT rely on the presence of a plume as evidence of nitrogen release.

Keep the dust cap on the dewar fill/drain outlet to prevent contamination (dewar flasks are vacuum jacketed, non-pressurized containers).  Check the caps to make sure they have not become sealed by frost accumulation.

Danger!  Vials immersed in liquid nitrogen may explode violently when removed!  Wear face and eye protection!   Plastic vials (even Nunc vials with silicon O-rings) used for storing cells in liquid nitrogen are designed to be used in the liquid nitrogen vapor phase.  When immersed in the liquid phase, the liquid nitrogen frequently enters vials around the cold O-ring.  When vials are removed to room temperature, the liquid nitrogen in the vial immediately begins to boil.  Usually it escapes harmlessly past the seal.  Occasionally (about 1 out of 1000 vials), the seal is too tight, and the pressure causes a violent rupturing of the vial, sending shards of sharp plastic rocketing in unpredictable directions with sufficient energy to lacerate the face and cause severe eye injury.  When removing vials from liquid nitrogen, it is mandatory that you wear full face shields, pulled in to touch your chin so that chards can't fly under the shield.  If they fit, wear goggles underneath the face shield.
(special thanks to Dr. Ray Frackelton for the above information)


EXPOSURE:

Exposure, which may be too brief to affect the skin of the face or hands, may damage delicate tissues.  Extensive tissue damage or burns can result from exposure to liquid nitrogen or cold nitrogen vapors.  Flush affected areas with large volumes of tepid water (105-115F) to reduce freezing.  Loosen clothing that may restrict circulation.  DO NOT APPLY HEAT.  Frozen tissues are painless and appear waxy with a pallid yellow color.  Persons suffering from a lack of oxygen should quickly be moved to areas with normal atmosphere. If the victim is not breathing, assisted ventilation should be initiated.

REMINDERS:

  1. Boiling and splashing always occur when filling a warm container with cryogenic liquid or when inserting objects into these liquids.
  2. Perform tasks slowly to minimize boiling and splashing.
  3. The container should be appropriately vented to prevent over pressurization.
  4. Do not store liquid nitrogen for long periods in an uncovered container.
  5. Never totally seal a container.
  6. Never dip a hollow tube into liquid nitrogen as it may spurt liquid.
  7. Only qualified, gas-supplier personnel should service or correct associated problems with cylinders.