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Cryogenic and Compressed Gas Safety

Hazards of Cryogenic Liquefied Gases

1. Extreme Cold

  • Causes rapid frost burn on skin exposed to cold surfaces, gases and liquid. Extreme exposure may cause injuries equivalent to third degree burns.
  • Causes fragility in materials, examples are carbon steel, plastics and latex tubing. These materials will shatter when struck or stressed.
  • Materials shrink when cold, this causes additional stress and parts that no longer fit properly, can result in leaks.

2. Asphyxiation

  • Asphyxiation due to oxygen displacement. A liquefied gas will displace large quantities of air as it evaporates. For example evaporating liquid nitrogen will displace 697 times its liquid volume.
    Except for liquid oxygen gases will not support life when they evaporate. Oxygen deficiency cannot be sensed readily by the victim.
    Highly deficient atmospheres can cause rapid physical collapse and death.
    Self contained breathing apparatus is required in areas of less than 19.5% oxygen.

3. Over Pressurization

  • A container with inadequate pressure relief will accumulate pressure until a portion of the container ruptures, thereby causing risk of injury.

Hazard Prevention

1. Ventilation

  • Don’t use large quantities of cryogens without proper ventilation. In the event of a liquid helium “quench” or large spill evacuate the area, post “Do Not Enter” signs and inform your supervisor.
  • Wait for the air to be replenished by the building ventilation system before re-entering the room.

2. Safety Equipment

  • Familiarize yourself with the safety equipment in your area, on your equipment and in the transfer area (room 063). Use gloves and goggles to transfer cryogens

3. Cryogenic Systems

  • Never enclose a cryogenic liquid without a vent device. Always put a relief device between any points that might isolate a portion of a cryogenic system.
  • Vacuum insulation that is failing will show sweat, cold spots or entirely frost over a dewar or cryostat. This could cause relief valves and burst disks to fail, resulting in catastrophic failure.
    Monitor the physical state of your system.

Hazards of Compressed Gas Cylinders and Systems

1. Asphyxiation by Oxygen Displacement

2. Fire and Explosion

  • Ignition can be caused by static, heat sources or electric spark.
  • Fuel sources must be removed from cylinder locations.
  • Oxygen cylinders should be stored at least 20 feet from flammable gas cylinders.

3. Chemical Reactions

  • Gases may react with materials they are exposed to, including flesh.
  • The regulator must be matched to the application, a greased regulator cannot be used with oxygen.

4. Poisoning

  • Many gases are poisonous, example Carbon Monoxide.

5. High Pressure

  • Equipment will burst if it is not strong enough to contain the pressure it is exposed to.
  • Pressure will increase in systems and cylinders exposed to high temperatures and may cause a rupture to occur.

6. Improper Cylinder Handling

  • Cylinders are inherently unwieldy given their long shape, high centre of mass and heavy weight.
  • Falling cylinders are a hazard on two counts, they can cause damage or injury merely by falling over and striking other objects or people, or they may be damaged themselves thereby causing the cylinder to rupture explosively or the valve could break off causing the cylinder to accelerate rapidly.

Precautions for Compressed Gas Cylinders and Systems

  1. Read MSDS sheets for all gases used in your lab, these should be present in the MSDS file.
  2. Open valves slowly to control pressure surges and heat of compression.
  3. Keep supplier emergency numbers in a convenient location.
  4. Use a four wheeled cart to move a gas cylinder, the cap must be on and wear safety shoes. The cap should be on when the cylinder is not in use.
  5. Secure cylinders to stationary objects like walls or heavy benches.
  6. If the cap will not come off do not insert anything into the vent holes. A strap wrench is available in room 063 or contact Serge in Stores.
  7. Use safety goggles when attaching regulators and opening the cylinder for the first time.
  8. Keep oxidizing gases separate from combustible gases and away from sources of fuel.
  9. Keep cylinders away from heat sources, this will cause the internal pressure to rise.
  10. Do not allow cylinders to be struck by an electrical spark, this will weaken the metal structure of the cylinder.
  11. Keep grease and oil away from oxygen, be sure that regulators and all equipment has been cleaned for oxygen service.
  12. Be sure the regulator is approved for the type of gas and for the required pressure. The CGA fitting is specific for the gas type . Do not change the fitting, members of the Dept. have done this in the past so check regulators before use.
  13. Use proper certified relief valves and burst disks to protect your equipment and yourself.
  14. Insure adequate ventilation and isolate hazardous gases.
  15. The Technical Standards and Safety Authority, TSSA is responsible within the province of Ontario for enforcing regulations concerning pressurized vessels and piping systems. They require under provincial law that all pressurized equipment must be manufactured to ASME specifications and that only certified components be used. Also that all new pressurized systems must be certified by the TSSA. (Applies to non air systems over 15psi)

Emergency Response

Cryogens

Minor Spills: 20 to 50 litres.
Evacuate the area.
Inform people in the immediate vicinity.
Post “Do Not Enter” signs
Seek 1st Aid if required.
Allow time for liquid to evaporate, for gas to dissipate and for the ventilation system to replace the room’s air before re-entering the room.

Major Spills: > 50 litres or a damaged or tipped liquid cylinder.
Evacuate the area.
Inform people in the immediate vicinity.
Call the Safety Committee Co-Chairs:  Phil Scolieri at 978-2957 or Peter Hurley at 978-1726
Call Robert Henderson at 978-8510
Call your Supervisor.
In extreme cases call the Campus Police 978-2222
Seek 1st Aid if required.

Compressed Gas Leaks

If possible to do safely close valve on gas cylinder attached to a leaking system.
If you are not trained to handle the problem or it is beyond your control:

Evacuate the area.
Alert others in the vicinity.
Call the Safety Committee Co-Chairs:  Phil Scolieri at 978-2957 or Peter Hurley at 978-1726
Call Robert Henderson at 978-8510
Call your Supervisor.
In extreme cases call the Campus Police 978-2222
Seek 1st Aid if required and remove clothing contaminated with hazardous gases.

For additional information regarding safety please contact:
             Robert Henderson at 978-8510 hender@physics.utoronto.ca