Cryogenic safety

The University has two major documents outlining the safety guidelines for using cryogenic materials within the University.

Safe methods of use for cryogenic liquids


The University of Auckland’s Safe Methods of Use for Cryogenic Liquids are outlined below.

Burns

Cryogenic liquids are, by definition, extremely cold. Contact between cryogenic liquids and exposed skin can produce a painful burn. A splash of cryogenic liquid to the eye can cause loss of vision.

Personal Protective Equipment

  • Face shield.
  • Loose fitting Thermal Mittens or Gloves (that can be easily shaken off).
  • Closed Shoes or boots.
  • If pouring cryogenic fluids ensure pants material is not tucked into boot.

Emergency Treatment for Burns

  • Attempt to raise the burnt area to room temperature reasonably quickly.
  • Do not use warm water.
  • Do not remove clothing around burn as it may lift frost bitten skin.

Asphyxiation

Cryogenic liquids will expand many times their origin volume when they convert to gas at room temperature.

If vented into a closed space, cryogenic liquids such as helium, argon and nitrogen will displace oxygen when they become gaseous and have the potential to create oxygen deficient environments in a closed room.

Because of the nature of the gases involved, the victim will have no warning that they are in or entering an oxygen-deficient environment.

For this reason, container of cryogenic liquid must never be stored in small enclosed rooms.

Liquid nitrogen and argon (where the gas is heavier than air) must never be stored or used in basement areas or pits where gas can accumulate and develop an oxygen deficient atmosphere.

Other hazards associated with cryogenic liquids

1. Pressure buildup
Boiling of liquefied gases within a closed system increases pressure. Users must make certain that cryogenic liquids are never contained in a closed system. Cold fingers and similar devices have exploded when either an ice dam is formed within the apparatus or when users create a closed system by shutting off all valves. Users should also tape exposed glass parts to minimize the hazard of flying glass shards in the event of an explosion.

2. Oxygen enrichment
Liquid nitrogen and liquid helium may fractionally distill air, causing liquid oxygen to collect in the cryogenic container.
Liquid oxygen increases the combustibility of many materials, creating potentially explosive conditions. Make sure to provide adequate venting when working with cryogenic liquids in a closed system or enclosed space.

3. Embrittlement
Do not dispose of cryogenic liquids down the drain! Ordinary materials such as metal or polyvinylchoride (PVC) piping in laboratory sinks may not be able to withstand cryogenic temperatures.
Allow cryogenic liquids to evaporate in a fume hood or other well-ventilated area. Materials exposed to cryogenic temperatures for long periods or materials that have undergone periodic warming and freezing must be examined regularly for cracks and warping.

4. Cryotube Explosions
Cryotubes used to contain samples stored under liquid nitrogen may explode without warning when warmed. Tube explosions are caused by liquid nitrogen entering the tube through minute cracks and then expanding rapidly as the tube thaws. Cryotubes may be thawed behind shields or in fume hoods where the glass sash can provide shielding. When thawing cryotubes in the open, take the following protective steps:

  • wear a face shield, or at least safety goggles, whenever handling cryogenic liquids
  • wear heavy gloves.

5. Transporting Liquid Nitrogen in Lifts

  • Liquid nitrogen must travel unaccompanied in the lift.
  • If a general service lift is being used it is important that this task takes place at a time when the lifts are not being used; outside of peak times.
  • Two people must work together to transport liquid nitrogen via the lift. One person must be stationed on the relevant floor to receive the liquid nitrogen when the lift arrives.
  • The second person places the approved liquid nitrogen container in the lift, places the WARNING SIGN (A-frame, kept in designated area such as a loading dock) immediately behind the lift door so it will bar entry to the lift, and then selects the floor/level and exits the lift before the doors close.
  • The first person removes the liquid nitrogen and the sign when it arrives.
  • The warning sign must be returned to the designated area, e.g. loading dock, immediately; before further work commences.
  • Liquid Nitrogen must not be carried up and down stairwells.

 

 Safe Method of Use Updated 9th May 2012

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SMOU 18 Cryogenic Liquids
(22.2 kB, PDF)
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Safety guidelines for cryogenic materials


The University’s Safety Guidelines for Cryogenic Materials provides more thorough information about the use of cryogenic materials within University laboratories. All staff who work with cryogenic materials should be familiar with these guidelines.

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