Cryogenic Liquid Safety

See rules from Oak Ridge rules   OMRL   NOAO

A cryogenic liquid is one having a temperature of -150 °C (-−238 °F or 123 K) or lower.  The most commonly encountered cryogens are liquid nitrogen, liquid oxygen, liquid argon, and liquid helium.  The safe handling of all of these is very similar, and any significant differences will be noted.

1. General precautions for all use of cryogenic liquids
  • At all times, HAVE A PLAN of what you will do if....
    • a pressurized Dewar spontaneously vents?
    • you freeze your watchband or wedding band to your finger?
    • the funnel (which you should not be using) freezes and spews liquid nitrogen upward into your face?
    • 160 L of LN2 for whatever reason falls onto its side?  (It happens.  It's scary and unpleasant and could easily be quite disastrous.)
  • Liquid cryogens can cause terrible "burns."  (Death of living tissue caused by the extreme cold.)  Streams of super cooled gasses and metal objects cooled to liquid nitrogen temperatures can be even more dangerous than the liquid.  Severe and permanent eye damage can occur from exposure to liquid cryogens or super cooled gasses.  Hand protection and goggles (not safety glasses) should be worn when dispensing and handling liquid cryogens.  When handling large quantities, a full length apron will minimize the chance of a spill going into your shoes, where it might destroy some cubic centimeters of flesh before you can get your shoes and socks off.  Persons using a tipper to dispense LN2 should wear a full face shield over goggles, cryo-gloves, full length cuffless trousers which completely cover the tops of the shoes (or a full length apron), and shoes which will not permit liquefied gas to enter them in case of a spill, and which are also quickly removable in case they do (allow liquid to enter). The correct PPE required for your application should be spelled out on the hazard assessment for your area.
  • Do not use a funnel unless it is specifically designed for use with liquid cryogens.  Appropriate funnels are vented to prevent buildup of gas beneath the funnel, and the top is partially covered to minimize splashing out of the top of the funnel.
 
  • Asphyxiation -- argon, helium, and nitrogen are not poisonous; the air is already about 78% nitrogen (oxygen makes up about 21%, and trace gases the remaining 1%).  However, if sufficient liquid cryogen is vaporized so as to reduce the oxygen percentage to below 19.5%, you are at risk of oxygen deprivation.  Rapid venting can cause near-total displacement of normal air, leading to a local concentration of about 100% of the cryogenic gas.  Simple asphyxiants such as argon, helium, and nitrogen do not have good warning properties!   (You might not feel "light-headed," you may simply pass out without any warning whatsoever.  And then die without regaining consciousness.)
  • Do not store container(s) of liquid cryogens in a cold room or any other location where a person could physically enter an anoxic (low oxygen) atmosphere.  (Cold rooms have no air changes and a person entering a room with elevated nitrogen in the air can quickly pass out and then die within several minutes of entering.
 

calculate how much LN2 is necessary to displace all your air.