Cryogenic Materials

Because of the inherent danger, only knowledgeable personnel should handle cryogenic materials, fluid piping systems, and related equipment. A variety of physical hazards are associated with this class of material:

• Serious burns to the skin can result from direct contact with a cryogen or related equipment.
• Permanent damage to the eyes can result from contact with liquid cryogen.
• Liquid cryogens warmed above their critical temperature will generate high pressures that can cause a confining vessel to rupture or even explode. Fully containing a cryogenic fluid as a liquid at room temperature is usually not feasible. For example, the pressure required to maintain liquid nitrogen at room temperature is 43,000 psi.
• Cryogens have significant potential for creating oxygen deficiency because they have large liquid-to-gas expansion ratios, generally greater than 700 to 1. A small spill produces a large volume of gas that can displace air in a confined space, creating a serious oxygen deficiency.
• In addition to being a physical hazard and an asphyxiant, cryogenic material may also be corrosive, flammable, or reactive. Storage dewars and process vessels must be labeled with the common name of the contents written in English. Material Safety Data Sheets (or comparable safety information) and emergency leak or spill procedures for each cryogen must be available in the immediate area where these materials are stored or used.

Safe handling practices must be observed whenever working with or around cryogens. Do not use cryogens in unventilated spaces such as closets or transport in vehicles without adequate ventilation. When transferring cryogen from pressurized dewars with hoses or tubing, be sure to verify that there are pressure relief devices between all valves. Cryogens can be trapped in the transfer hose or in the tube between two valves, which may cause the hose to rupture and whip around out of control.

Cryogenic liquids present special fire and explosion hazards. A flammable mixture cooled in the presence of air with liquid nitrogen or liquid oxygen can cause oxygen to condense and thereby create an explosive mixture. Keep these mixtures away from ignition sources. Transport fragile cryogenic containers with caution-use a hand truck. Cushion glassware in a protective covering to prevent injury caused by flying glass in the event of implosion/explosion.

Eye, hand, and body protection must be worn to prevent contact of liquid cryogens with the eyes or exposed skin. A hazard evaluation performed on each cryogenic operation will determine the specific personal protective equipment (PPE) required. The following are the minimum PPE requirements for cryogenic operations:

Eyes

When pouring liquid nitrogen from a dewar, use non-vented chemical goggles or safety glasses with side shields. When working with liquid nitrogen in an open container or when transferring liquid nitrogen from a pressurized device, use safety glasses and a full-face shield.

Hands

When working on piping systems with exposed components at cryogenic temperatures, wear loose-fitting gloves made for cryogenic work (or leather welding type without gauntlets) to assure that skin will not freeze to cold pipes or metal parts. Loose-fitting gloves can be thrown off readily if cryogen is spilled into them. Small spills of liquid nitrogen, if not trapped against the skin, will usually evaporate without causing damage.

Feet

Wear closed-toe shoes that cover the top of the foot or boots with trouser legs extended over the top of the boot.

Body

Wear long-sleeved clothing made of non-absorbent material, cuff-less long trousers worn outside boots or over shoes, and an apron made of leather (or other appropriate material) when handling large quantities of cryogens.

Ears

Ear plugs or earmuffs may be required where excessive noise levels occur near filling and venting operations.

The most likely cause of frostbite to the hands and body is contact with cold metal surfaces. Frostbite can be instantaneous if the skin is moist. Immediate treatment is vital. Report promptly to a medical care facility or call 911 and follow these suggestions:

• Warm the affected area rapidly by immersion in water (not to exceed 105° F), body heat, or exposure to warm air.
• Calm the victim and avoid aggravating the injury. People with frostbitten feet should not walk on them. Do not rub or massage the affected parts of the body.
• If the eyes are affected, flush them with water for least 15 minutes.
• Always seek medical attention for frostbite injuries.