Environmental Health & Safety

CRYOGENIC LIQUIDS GUIDELINES

Purpose: The information provided in this document is intended to inform University personnel of the dangers of and the safe use of cryogenic materials.

Scope: As with any hazardous material, the user must be aware of the hazards the materials present, utilize appropriate engineering controls, implement 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 PI/supervisor or the Laboratory Safety Unit at ext. 5-3241 (275-3241).

Guidelines:

1. 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, carbon dioxide, hydrogen, helium, neon, krypton and xenon be present, contact the Laboratory Safety Unit 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 traditional gas cylinder.  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. 
   • 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. Materials such as rubber or plastics become hard and brittle and can fracture at the low temperatures.
   • Boiling and Splashing: When filling a warm (even room temperature) Dewar, boiling and splashing actions take place. Always perform these filling operations slowly to minimize boiling/splashing. If the vapors or liquids contact the eye or skin, follow first aid measures.
   • 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 645 liters of gas at atmospheric pressures.  Use, store and dispense these materials in a well ventilated area. In addition, if a cryogenic material is placed into a container and the container is sealed and left at room temperature (even for a few minutes), the container can over-pressurize and "explode".
   • 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, creating an asphyxiation hazard. Should cryogenic oxygen be released, the oxygen level can become elevated and enhance any combustion present.
2. CONTAINERS AND STORAGE SYSTEMS
   
   Only equipment and containers designed for the intended product, 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 handling 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 Dewar:  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 Dewar:  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.
3. PERSONAL PROTECTION
   
   A Job Hazard Assessment needs to be completed by the PI/supervisor to identify actions that could result in exposures to the cryogenic materials. The assessment will help determine the most appropriate personal protective equipment (PPE) needs to be utilized when handling cryogenic liquids. Such equipment includes:
   • >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 must be worn with safety glasses/goggles.
   • Insulated Gloves:  Cryogenic rated insulated gloves should always be worn when dispensing cryogenic liquids, handling anything that comes into contact with the cryogenic liquid, or where there is a potential for spill with a cryogenic liquid. 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 resulting in extended exposures. Protective clothing can include aprons, sleeve covers, foot covers or boots.
4. FIRST AID FOR COLD-CONTACT BURNS
   
   Employees should never experience contact with a cryogenic material if proper handling techniques are utilized. Should a prolonged exposure occur with the liquid or cold gas, seek medical attention/advice immediately. Immediate first aid measures include:
   • Remove any clothing that may restrict circulation to the frozen area.  Do not rub frozen parts.  Obtain medical assistance through Occupational Medicine, UHS and/or the SMH 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.  Immediate medical attention is needed since thawing may require 15 to 60 minutes, should continue until the skin turns pink or red, and needs to be completed under medical attention.
5. SPECIAL PRECAUTIONS FOR CRYOGENIC OXYGEN
   
   Although nonflammable, oxygen accelerates and supports combustion.  Flammable gas mixtures will burn at lower temperatures because of the enriched oxygen atmosphere.  Therefore, keep organic materials, combustible materials, or spark generating equipment away from oxygen storage/use locations.  The same is true for oxygen-saturated clothing.
6. SPECIAL PRECAUTIONS FOR CRYOGENIC NITROGEN
   
   All cryogenic nitrogen use and storage locations must be well-ventilated.  The sudden release of large quantities of nitrogen in an enclosed space could result in the breathable oxygen concentration in the air falling below a safe level. Asphyxia develops slowly as the oxygen content in the air falls below 19.5%. 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, and/or errors in judgment.  Should the concentration fall below this level and approach 12% or lower, brain damage or death may occur.
   
   The following is an example of the oxygen level should a 160 liter container of liquid were to be released quickly into a 24’ long, 20’ wide and 10’ high room (assuming the room had very little ventilation):
   
   Initial oxygen level of room = 20.9%
   Volume of room = 24’x20’x10’ = 4800 cuft
   
   160 liters liquid nitrogen releases the following volume of gaseous nitrogen:
   (160 L liquid N₂) x (645 L of N₂ gas/liter liquid N₂) = 103,200 L of N₂ gas
   
   Given 1 cuft = 28.32 L, converting to cuft:
   (103,200 L of N₂) ÷ 28.32 L/cuft = 3644 cuft
   
   Final possible oxygen level (assuming little ventilation in room):
   (20.8%)(4800 cuft-3644 cuft) ÷ 4800 cuft = 5.0% oxygen
   
   This value would be potentially life threatening!
   
   Because liquid nitrogen and many other inert cryogenic materials do not have an odor, taste, and are invisible, their storage and use locations must be evaluated before use. Contact Laboratory Safety Unit for this evaluation. In some cases, a special area oxygen monitor may be required.

Administration:

Because cryogenic materials are used in certain locations, it is up to the PI/ supervisor to conduct a Job Hazard Assessment, provide and ensure the use of any needed PPE, and 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 (PPE) and clothing.
• Safety, first-aid and the availability of medical assistance through Strong ED, Occupational Medicine and UHS.
• Handling emergency situations such as fire, leaks, and spills.
• Good housekeeping practices.
• Having access to Safety Data Sheets as required by OSHA’s Hazard Communication Standard or OSHA’s Laboratory Standard.

---

QUESTIONS or COMMENTS?
Contact EH&S at (585) 275-3241 or e-mail EH&S Questions.

This page last updated 12/4/2015. Disclaimer.