Cryogenic liquid

In the GHS these are refrigerated liquefied gases. They are kept in insulated vessels that are not fully sealed, because the liquid constantly boils off slowly as heat enters. Sealing such a vessel completely would let pressure build until it fails, so relief devices are essential and should never be blocked.

Contact with the liquid or very cold vapor, or with chilled pipes and surfaces, can cause frostbite-like burns within moments. Eyes are especially vulnerable. Clothing that traps liquid against the skin makes it worse, so loose, non-absorbent gloves, face protection and cuffless trousers worn over footwear are typical advice.

The expansion ratio from liquid to gas is large, so a small spill in a small room can displace oxygen and create an asphyxiation hazard with little warning. Oxygen monitors and good ventilation are common controls. Liquid oxygen adds a fire hazard because it greatly intensifies combustion, and it can soak into clothing.

Cold embrittles many materials, including carbon steel, rubber and some plastics, so only equipment designed for cryogenic use should be used. Never put a cryogen in an ordinary container or vacuum flask not designed for it.