Cryogenic Liquid Safety

 

5. Dispensing from stationary bulk storage tank (outside, at loading dock of PHYS) into large mobile dispensing Dewar.
  • This operation is to be performed only by trained university stores staff.  

 

6. Dispensing from large (~160 L) dispensing Dewar at various locations within the Physics Building.  
  • Nitrogen is to be dispensed only into smaller Dewars which either (a) have carrying handles or (b) are on wheels or (c) are 500 mL or smaller, and which have pressure relief valves or pressure venting lids.  A wide-base Dewar which is stable on a wheeled cart qualifies as "on wheels."
  • Persons filling must be in constant attendance to the filling operation.
  • The fill tube should be equipped with a phase separator.
  • The receiving vessel should be placed so that the delivery is immediately at the mouth of the receiving vessel.  (i.e., do not allow the liquid nitrogen to fall through a distance to reach the receiving vessel.)  The receiving vessel must be supported in some stable way while it is being filled (holding it in position by hand is not a good idea).
  • Do not hold the vessel with unprotected hands while filling.
  • Persons filling Dewars should wear full length non-cuffed trousers (covering tops of shoes) or full length apron, and shoes which will not admit spilled cryogen and which are easy to remove quickly.  Also wear goggles and cryo-gloves.   The specific PPE required should be specified in the hazard assessment for the area.
  • Large dewars should have brakes set when parked or when connected to equipment.  Some dewars have brakes on the caster like many common items.  Others have the brake shown to the right.  Step on the apply brake control firmly to set the brake, or stem on the release brake control to remove the brakes.  The controls are positioned as shown to the right.  If the dewar doesn't have brakes, wheel chocks can be used.