Cryogenic liquids are liquified gases that are kept in their liquid state at very low temperatures. Their boiling points are below -150°C (-238°F). All cryogenic liquids are gases at normal temperature and pressure. Their common characteristics are that they are extremely cold, and small amounts of liquid can expand into very large volumes of gas. Cryogenic liquids are used in food freezing and chilling, metal fabrication processes, biological sample preservation, vacuum pumping systems, cooling infrared detectors, cooling samples in electron microscopes, cryostats for low temperature research and superconducting magnet systems such as in magnetic resonance imaging equipment.
Health hazards associated with cryogenic liquids include injuries resulting from fire and explosion, injuries through contact, and asphyxiation.
Fire and explosion - Danger of fire and explosion exists with escaping cryogens such as oxygen and hydrogen. The danger is such that even materials normally non-combustible will ignite if allowed to become coated with an oxygen-rich condensate. Thermal shock to containers, or a gas pressure greater than the containers are designed to hold, may cause explosions. Implosions may result from pressures produced by "cryo-pumping" which are nearly equal to the existing atmospheric pressure on the equipment being used, unless this equipment is designed to withstand such pressure changes. Structural or other material coming into contact with cryogenic fluids may become combustible, explosive, or subject to failure from strain or impact due to altered physical characteristics.
Cold burns - Direct or indirect uninsulated contact with cryogenic fluids causes cold burns, (i.e., frostbite). Delicate tissue, such as eyes in particular, can be damaged by a brief exposure.
Asphyxiation - With the exception of oxygen, rapid expansion of cryogenic fluids results in an oxygen deficient atmosphere if the immediate environment is inadequately ventilated; this can lead to asphyxiation.
WHMIS regulatory agencies agreed that cryogenics is a workplace related issue and that temperature need not constitute the sole criterion for inclusion in WHMIS Class E - Corrosive Material; (e.g., see file for nitrogen, liquid, on "Substance-specific" page).