The University of Iowa

SAFETYmatters - Liquid Nitrogen Inventory

To assist EHS in the review of large LN2 storage/use areas, we are asking that individuals with LN2 ensure that the details are listed properly in your EHSA chemical inventory. Please ensure your inventories are up to date, specifically the following:

  • compressed gas cylinders of nitrogen gas (ft3) are not listed as liquid nitrogen;
  • amounts (Qty per Unit);
  • volume/size;
  • physical state;
  • number of units; and
  • location, room/building.

Liquid nitrogen is a cryogenic liquid commonly used in research labs.  As “cryogenic” means related to very low temperature, it is an extremely cold material.  The vapor of liquid nitrogen can rapidly freeze skin tissue and eye fluid, resulting in cold burns, frostbite, and permanent eye damage even with brief exposures.

Liquid nitrogen (LN2) is liquefied under high pressure and expands approximately 695 times in volume when it vaporizes. As a result, one liter of liquid can expand into 695 liters of gas.  If sufficient liquid nitrogen is vaporized, the oxygen percentage may be reduced below 19.5%, resulting in an oxygen deficient atmosphere. This may cause increased breathing and confusion and if the oxygen level is low enough, unconsciousness or death.  A ten-liter Dewar of LN2 spilled in a lab is often enough to reduce the oxygen content of the room to potentially dangerous levels. When LN2 vaporizes, there are no associated warning properties such as odor or color. To prevent asphyxiation hazards, handlers must make sure that the room is well ventilated when using cryogens indoors.

Larger containers of LN2, such as tanks used to fill Dewars, specimen storage units or equipment cooled by LN2, have more than enough LN2 to reduce oxygen to life threatening levels if a spill or leak occurs. Areas of heavy use or storage of LN2 may benefit from the placement of oxygen monitors.  Contact Justin Newnum or Rick Byrum with questions on the placement/use of an oxygen monitor.