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CRYOGENIC LIQUIDS
The information provided in this document is intended to inform University personnel of the dangers of and the safe use of cryogenic materials. As with any hazardous material, the user must be aware of the hazards the materials present, utilize appropriate engineering controls and work place practices, and use personal protective equipment to prevent exposures. Additional information on the safe use of cryogenic liquids is available from the Compressed Gas Association.
Should you have a question about a hazardous material, contact your supervisor or EH&S.
PROPERTIES AND SAFETY ISSUES
A cryogenic liquid includes any liquid with a boiling point less than -1500C. The most common cryogenic liquids at the University include oxygen and nitrogen. Should cryogenic liquids such as argon, hydrogen, helium, neon, krypton and xenon be present, contact EH&S for an evaluation.
Cryogenic materials are utilized at the University because they are compact and supply a much greater volume of gas per volume than a gas cylinder. Also, some of the applications, such as medical care, require the cryogenic material.
Many of the safety precautions used for the handling of compressed gases apply to the same gas in the liquid state. However, the following properties require appropriate precautions:
Extreme Cold: All cryogenic liquids are extremely cold. The liquids and the “boil-off” vapors can freeze human tissue very rapidly. Materials such as carbon steel, plastic and rubber become very brittle and can fracture.
High Liquid-to-Gas Expansion Rations: When cryogenic materials vaporize, large volumes of gas are generated. For example, one liter of liquid nitrogen will generate 700 liters of gas at atmospheric pressures. Use these materials in a well ventilated area.
Fogging and Leak Detection: Most cryogenic liquids generate odorless, colorless, and tasteless gases. However, the boil-off gases condense the moisture in the air, thus creating a highly visible fog.
Other Properties: All cryogenic gases, other than oxygen, can displace breathable air in an enclosed space and creating an asphyxiation hazard.
GENERAL SAFETY PRACTICES
This section will list freezing hazards and general safety practices for handling, transporting and using cryogenic liquids:
Skin/Eye Frostbite: Because of their extremely low temperatures, cryogenic liquids can produce frostbite on skin and exposed eye tissue in a short period of time. The vapors from the liquids are extremely cold and can damage tissue as well.
Boiling and Splashing: When filling a warm container, boiling and splashing actions take place. Always perform these filling operations slowly to minimize boiling/splashing. If the vapors or liquids contact the eyes or skin, follow first aid measures.
Flesh Tearing & Material Embrittlement: Never allow exposed skin to make contact with uninsulated pipes or vessels containing cryogenic materials. The frozen metal will cause the flesh to stick immediately. Should one try to pull skin away from the surface, the flesh may tear off. Materials such as rubber, plastics become hard and brittle at extremely low temperatures. Even carbon steal become brittle and can fracture at the low temperatures.
Containers and Storage Systems
Only equipment and containers designed for the intended product and service pressure and temperature are to be used with cryogenic liquids. Containers must be clean, especially those to be used to hold oxygen. Cryogenic containers must be made from materials suitable for cryogenic temperatures.
Transfer of cryogenic liquids into warm lines or containers should be done slowly to prevent thermal shock to the piping or container and possible excessive pressure buildup. When transferring cryogenic liquids from one container to another, the receiving container should be cooled gradually to prevent thermal shock and to avoid splashing. Escaping gas should be vented to a safe location to prevent a build up in an enclosed space.
Three type of portable cryogenic liquid storage vessels are generally used:
- Liquid Dewards: These containers are open-mouthed, non-pressurized, vacuum-jacketed vessels. Prevent the accumulation of ice in the neck or the mouth of the opening to prevent a blockage and pressure buildup in the dewer.
- Lab Dewards: Most of these containers are made of metal but some smaller units are made of glass. The units have wide-mouth openings without permanent tops. Often a lid or cover may be used to extend the holding time of the contents.
- Liquid Cylinders: Liquid cylinders are pressurized containers designed and fabricated in accordance with DOT-4L specifications. There are three major types of liquid cylinders; one for dispensing liquid or gas, one for dispensing gas only, and one for liquid withdrawal only.
Personal Protection
Safety equipment is to be used to prevent cryogenic material from making contact with the skin. The equipment is to include:
- Safety Glasses: Safety glasses must be worn during transfers and other handling of cryogenic liquids. If activities might cause spraying or splashing, a face shield or chemical goggles should be worn.
- Insulated Gloves: Insulated gloves should always be worn when handling anything that comes into contact with the cryogenic liquid or the vapors released. Gloves should be loose fitting for quick removal should liquids be spilled into them.
- Clothing: Considerations must be made to prevent cryogenic material from contacting skin. Clothing provides a partial barrier but may also result in additional exposures. For example, cuffs on pants may allow the accumulation of cryogenic liquid that results in extended exposures.
First Aid for Cold-Contact Burns
If properly handled, employees should never experience contact with a cryogenic material. Should an exposure occur with the liquid or cold gas, the following emergency treatment is recommended:
- Remove any clothing that may restrict circulation to the frozen area. Do not rub frozen parts. Obtain medical assistance through the Emergency Department as soon as possible.
- Place the affected body part in a warm water bath (less than 1050F). The victim should also be kept warm. Supportive treatment for shock should be provided.
- Frozen tissues are painless and appear waxy. Thawing may require 15 to 60 minutes and should continue until the skin turns pink or red.
Special Precautions for Oxygen
Although nonflammable, oxygen accelerates and supports combustion. Flammable gas mixtures will burn at lower ranges because of the enriched oxygen atmosphere. Therefore, keep organic materials away from oxygen storage/use locations. The same is true for oxygen-saturated clothing.
Special Precautions for Nitrogen
All gas use and storage should be done in a well-ventilated area. High concentrations of inert gases in an enclosed space could result in the breathable oxygen in the air to fall below a safe level.
Asphyxia develops slowly as the oxygen content in the air falls below 20.9%. When the oxygen content falls to about 15-16%, the flame from the combustion of ordinary combustible materials will be extinguished. An individual breathing this concentration will start to experience physiological symptoms including sleepiness, fatigue, loss of coordination, errors in judgment. Should the concentration fall below this level and approach 12% or lower, brain damage or death may occur.
Because many inert cryogenic materials do not have odors, storage and use locations must first be evaluated. Contact EH&S for this evaluation. In some cases, a special area monitor may be required.
Recommended Site Specific Safety Training
Because cryogenic materials are used in certain locations, it is up to the supervisor to provide proper training for personnel under their supervision. Any site specific training provided to an employee is to be documented and the training record retained by the PI/supervisor. Training is to include:
- Information on the nature and properties of cryogenic liquid in both the liquid and the gaseous phase.
- Specific instructions on the equipment to be used.
- Approved materials that are compatible with cryogenic liquids.
- Use and care of protective equipment and clothing.
- Safety, first-aid and the availability of medical assistance through Strong ED.
- Handling emergency situations such as fire, leaks, and spills.
- Good housekeeping practices.
- Having access to Material Safety Data Sheets as required by OSHA’s Hazard Communication Standard or OSHA’s Laboratory Standard.
QUESTIONS? Contact EH&S Industrial Hygiene Unit at (585) 275-3241 or e-mail EH&S Questions.
This page last updated 11/8/04. Disclaimer
