Cryogenic Safety
What is a cryogen?
A cryogen is a supercooled gas that has been condensed into either liquid or solid form. Some common examples include liquid nitrogen and dry ice. These can be stored at anywhere from -109°F to -452°F.
Liquid Nitrogen: As cold as 77K or -195.8C, LN2 is one of the most common cryogens used. When pouring from an open container, always pour carefully and at a safe height to minimize splashing the liquid nitrogen. Be wary of air exposure, as moisture in the air can freeze in the presence of liquid nitrogen and damage valves on containers.
Liquid Helium: Do not let liquid helium come into contact with air. Moisture in the air can solidify if in contact with liquid helium. Ensure there are no heat leaks, as helium has a very low heat of vaporization and can take gaseous form quickly, rapidly increasing pressure.
Liquid Argon: LAr exists at -186C/303F and aside from the cryogen hazards, it is also heavier than air. It can settle in low areas and create oxygen deficient environments. O2 sensors in areas where liquid argon is used.
Liquid Hydrogen: The use of liquid hydrogen requires prior approval from EH&S. Because of its flammability, be sure to isolate equipment that uses liquid hydrogen, ensure ventilation of the environment, remove ignition sources, ground the system to eliminate static buildup, purge the system using helium, monitor for any hydrogen leakage, and limit the amount of hydrogen used to minimal amounts.
Your responsibilities
It is your responsibility to ensure the safe handling of cryogens in your lab. This includes storing cryogens in containers appropriate for the temperatures and materials being handled, working in a well ventilated environment, including pressure relief valves in systems that use cryogens, and wearing appropriate PPE for the cryogen(s) in use.
Tanks
Cryogens are stored in insulated tanks called dewars, which contain an outer protective vessel, an inner vessel which stores the cryogen, and a vacuum space in between. The dewar contains a pressure gauge, pressure relief valve, a liquid level gauge, a liquid (out) valve, and a gas (out) valve. The dewar also will have an intended way of transport. This can be found in either a ring around the top of the tank, wheels, and/or being located on a cart. All of these indicate the tank is intended to be pushed to its destination. Conversely, handles on the side of the tank indicate the tank is intended to be lifted. Do not try to lift a tank from its ring around the top of the tank.
Personal Protective Equipment
Face/Eye Protection
Splash goggles are the best option when working with liquid cryogens. Safety glasses do not offer the same protection against splashes. Look for “ANSI Z87” on the side of the goggles to confirm splash protection.
A face shield is required over the goggles when handling cryogens to protect from liquid splashes. This face shield should provide optical clarity through a plastic shield, but does not need to be specialized to any ANSI standards.
Hand Protection
Gauntlet-style gloves are required when handling cryogens. These gloves should be insulated to protect from any splashes on the outside of the gloves; loose fitting and easily removable in case of any liquid making contact with the skin; and made of a natural cloth like leather rather than polymers or rubber because these can harden when exposed to such low temperatures.
Body Protection
It is best practice to wear a sturdy lab coat and normal lab attire when handling cryogens. This includes long pants that cover shoes, closed toed shoes made from non-absorbent materials like leather or another non-woven material, and a lab coat that overlaps with glove cuffs.
