Cryogenic Materials Safety
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:
||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.|
||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.|
||Wear closed-toe shoes that cover the top of the foot or boots with trouser legs extended over the top of the boot.|
||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.|
||Ear plugs or earmuffs may be required where excessive noise levels occur near filling and venting operations.|
Procedures for Frostbite Injuries
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.