HAZARDS ASSOCIATED WITH CRYOGENIC GAS / MATERIALS
Cryogenic liquids are liquids that exist between -66°C and -266°C.
Cryogens Can Present One or More of the Following Hazards
- A. Physiological Hazards – Severe cold “burns” or frostbite may be inflicted if the human body comes in contact with cryogenic fluids, boiled-off vapor, or surfaces cooled by cryogenic fluids. The evolution of large volumes of gases associated with evaporation of cryogenic liquid spills can result in asphyxiation.
For instance, nitrogen expands approximately 700 times in volume, going from liquid to gas at ambient temperature. Asphyxiation and chemical toxicity are hazards encountered when entering a cryogenic vessel that has been used to store cryogenic liquids if proper ventilation/purging techniques are not employed.
- Material and Construction Hazards – The selection of materials calls for consideration of the effects of low temperatures on the properties of those materials.
Some materials become brittle at low temperatures. Brittle fracture can occur very rapidly resulting in almost instantaneous failure.
Low temperature equipment can also fail due to thermal stresses caused by differential thermal contraction of the materials.
Over pressurization of cryogenic equipment can occur due to the phase change from liquid to gas if not vented properly.
All cryogenic fluids produce large volumes of gas when they vaporize.
- Flammability and Explosion Hazards –
- High Pressure Gas Hazards – Potential hazards exist in highly compressed gases because of the stored energy. In cryogenic systems high pressures are obtained by gas compression during refrigeration, by pumping of liquids to high pressures followed by rapid evaporation, and by confinement of cryogenic fluids with subsequent evaporation. If this confined fluid is suddenly released through a rupture or break in a line, a significant thrust may be experienced.