Liquid Nitrogen Safety

1. General precautions for all use of Liquid Nitrogen

• Liquid Nitrogen can cause terrible burns. Hand protection and goggles (not safety glasses) are to be worn at all times when handling liquid nitrogen. When handling large quantities, a full length apron will minimize the chance of a spill going into your shoes, where it might distroy some cubic centimeters of flesh before you can get your shoes and socks off. Persons using a tipper to dispense liquid nitrogen must wear a full face shield over goggles, cryo-gloves, full length trousers/pants or a full length apron, and footwear that covers the entire foot.

• Guard against pressure build-up by using a pressure relief vessel or a venting lid.

• Remove metal jewelry/watches on hand and wrists.

• Glass Dewars must be taped solidly around the outside. The plastic mesh with which some small thermoses are sold protects the Dewar itself to an extent, but does not protect against injury from glass shards resulting from implosion.

• Asphyxiation -- Nitrogen is not poisonous; the air is already about 78% nitrogen (oxygen makes up about 21%, and trace gases the remaining 1%). However, if sufficient liquid nitrogen is vaporized into a poorly ventilated space so as to reduce the oxygen percentage to below 20%, the people in that space are close to real bad trouble from oxygen deprivation. Rapid venting can cause rapid displacement of normal air, leading to a local concentration of nearly 100% nitrogen.

• Use only vessels designed for extreme cold. Not all Dewars are rated for liquid nitrogen!

• Do not carry liquid nitrogen in an open Dewar on any of the elevators.

• Cryotubes containing samples stored under liquid nitrogen may explode without warning. Tube explosions are thought to be caused by liquid nitrogen entering the tube through minute cracks and then expanding rapidly as the tube thaws. Serious accidents have occurred around the country due to tube failures.

2. Dispensing Liquid Nitrogen

• It is to be dispensed only into smaller Dewars which either have carrying handles or are on wheels, 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 Dewars should wear full length trousers/pants or full length apron, and footwear that covers the entire foot, along with goggles or face shield and cryo-gloves.

• Persons filling must be in constant attendance to the filling operation.

3. Transporting by hand or cart through a building or between buildings.

• Large mobile Dewars or liquid nitrogen refrigerators (or the trolleys carrying these) used for transporting cryogens within a building or between building should be equipped with a braking mechanism. Do not use feet to brake wheels. Take care to avoid crushing hands or fingers between the vessel and walls or door frames.

• Outside transport of wheeled vessels containing any cryogen should be undertaken by no less than two persons, and care must be taken to stay completely clear of sewer grates, large cracks in the pavement, or any other hazards which could catch the wheels and cause tipping.

• Inside buildings, from room to room, the best transport is by Dewars shich either have carrying handles or are on wheels, 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".)

• For short distances in hallways it is acceptable to hand-carry a quart or smaller Dewar of nitrogen which has no handles, IF

  • the Dewar is your only load (no books, no coffee, no other items), and

  • the vessel has a venting lid (a cork or loose stopper is fine), and

  • you are carefully watching for people who will run into you, and

  • the vessel is carried with both hands and as far away from your face as comfortably possible.