Cryogenic liquids have boiling points less than -73ºC (-100ºF). Liquid nitrogen, liquid oxygen and carbon dioxide are the most common cryogenic materials used in the laboratory. Hazards may include fire, explosion, embrittlement, pressure buildup, frostbite and asphyxiation.

Many of the safety precautions observed for compressed gases also apply to cryogenic liquids. Two additional hazards are created from the unique properties of cryogenic liquids:

Extremely Low Temperatures

The cold boil-off vapor of cryogenic liquids rapidly freezes human tissue. Cold burns and frostbite caused by exposure to cryogenic liquids can result in extensive tissue damage.  Also, proper materials selection is important in cryogenic conditions.  Most metals become stronger upon exposure to cold temperatures, but materials such as carbon steel, plastics and rubber become brittle or even fracture under stress at these temperatures. Proper material selection is important. Cold burns and frostbite caused by cryogenic liquids can result in extensive tissue damage.

Vaporization

All cryogenic liquids produce large volumes of gas when they vaporize. Liquid nitrogen will expand 696 times as it vaporizes. The expansion ratio of argon is 1:847, hydrogen is 1:851, and oxygen is 1:862. If these liquids vaporize in a sealed container, they can produce enormous pressures that could rupture the vessel. For this reason, pressurized cryogenic containers are usually protected with multiple pressure relief devices. The expansion ratio of cryogenic liquids, (except oxygen) in an enclosed area can significantly reduce the percentage of oxygen in the area and cause asphyxiation. Vaporization of liquid oxygen can produce an oxygen-rich atmosphere, which will support and accelerate the combustion of other materials. Vaporization of liquid hydrogen can form an extremely flammable mixture with air.

[collapsed title=Properties of Common Cryogenic Materials]

Most cryogenic liquids are odorless, colorless, and tasteless when vaporized. When cryogenic liquids are exposed to the atmosphere, the cold boil-off gases condense the moisture in the air, creating a highly visible fog.

Always handle these liquids carefully to avoid skin burns and frostbite. Exposure that may be too brief to affect the skin of the face or hands may damage delicate tissues, such as the eyes.

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[collapsed title=General Rules Regarding Handling of Cryogenic Materials]

• Labs using cryogenic materials must have a lab specific Standard Operation Procedure (SOP) that covers not only how the material is to be used, but how the Dewars are to be transported to and from the building loading dock
• BEST PRACTICE WHEN TRANSPOTING A DEWAR IS TO AVOID TRAVELING WITH A DEWAR IN A PASSENGER ELEVATOR. Release of a material such as liquid nitrogen in the small space such as an elevator may pose an asphyxiation hazard. Employ the buddy system and have a fellow employee/student remain outside the elevator on the sending and receiving floors. Nitrogen does not have good warning properties and can displace oxygen to dangerously low levels
• Do not store Dewars in unventilated or poorly ventilated spaces
• Cryogenic materials shall not be used in a confined space with inadequate ventilation due to the potential for asphyxiation.  (This includes cold rooms and warm rooms)
• Cryogenic materials shall not be warmed in closed containers.
• Dewars shall be inspected daily for ice plug formation. 
• Cryogenic materials containers shall have relief devices that have been engineered into the containers or closed systems. 
• Tampering WITH or altering the pressure relief valve on a cryogenic material container is strictly forbidden
• Boiling and splashing always occur when charging or filling a warm container with cryogenic liquid or when inserting objects into these liquids. Perform these tasks slowly to minimize boiling and splashing. Use tongs to withdraw objects immersed in a cryogenic liquid.
• Ensure that whatever you are putting a cryogenic material into is suitable for the material. Glass Dewars should be wrapped in protective mesh or taped.
• Use extreme caution with cryotubes. An explosion hazard exists if liquid nitrogen has entered the tube through any defects or cracks and may expand rapidly causing an explosion/shrapnel hazard
• Never touch un-insulated pipes or vessels containing cryogenic liquids. Flesh will stick to extremely cold materials. Even nonmetallic materials are dangerous to  touch at low temperatures.
• Use wooden or rubber tongs to remove small items from cryogenic liquid baths. Cryogenic gloves are for indirect or splash protection only, they are not designed to protect against immersion into cryogenic liquids.
• Cylinders and dewars should not be filled to more than 80% of capacity, since expansion of gases during warming may cause excessive pressure buildup.
• Check cold baths frequently to ensure they are not plugged with frozen material.

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[collapsed title=Protective Clothing for Working with Cryogenic Materials]

• Face shields worn over safety glasses or chemical splash goggles and lab coat are required during transfer and handling of cryogenic liquids.
• Trousers (cuffless) should be worn on the outside of boots or work shoes.
• Wear loose fitting, dry, insulated cryogenic gloves when handling objects that come into contact with cryogenic liquids and vapor.

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[collapsed title=Cooling Baths and Dry Ice]

• Neither liquid nitrogen nor liquid air should be used to cool a flammable mixture in the presence of air, because oxygen can condense from the air, leading to an explosion hazard.
• Wear insulated, dry gloves and a face shield when handling dry ice.
• Add dry ice slowly to the liquid portion of the cooling bath to avoid foaming over. Do not lower your head into a dry ice chest, since suffocation can result from carbon dioxide buildup.

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[collapsed title=Liquid Nitrogen Cooled Traps]

Traps that open to the atmosphere condense liquid air rapidly. If you close the system, pressure builds up with enough force to shatter glass equipment. Therefore, only sealed or evacuated equipment should use liquid nitrogen cooled traps.

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[collapsed title=Emergencies Involving Cryogenic Materials]

• Anticipate emergency situations, have proper handling equipment in the lab and readily available for spills.
• Check the MSDS to determine what is appropriate.
• In the event of a spill or adverse reaction notify lab personnel immediately that an incident has occurred.
• Do not attempt to clean up a spilled cryogen. If a large volume of gas is released, leave the area immediately and call the Georgia Tech Police at 404-894-2500.
• If a flammable or oxidizing gas is involved, evacuate and pull the fire alarm.  If you can do so safety, turn off all ignition sources at the breaker box on your way out of the building.
• Remain on site to speak with First Responders.
• If skin comes in contact with a cryogen or dry ice, run the area of skin under lukewarm water for 15 minutes (do not use hot or cold water). Seek professional medical attention.
• If your finger is burned, do not place it in your mouth. This could burn your mouth. Do not rub the area — this can cause further tissue damage.

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