"Cryogenic liquids are liquefied gases that are kept in their liquid state at very low temperatures. The word 'cryogenic' means 'producing, or related to, low temperatures,' and all cryogenic liquids are extremely cold. Cryogenic liquids are classified in the model codes as fluids with a boiling point lower than -130 F (-90 C) at an absolute pressure of 14.7 pounds per square inch (101.3 kilopascals). All cryogenic liquids are gases at normal temperatures and pressures. These gases must be cooled below room temperature before an increase in pressure can liquefy them. Different cryogens become liquids under different conditions of temperature and pressure, but all have two properties in common: They are extremely cold, and small amounts of liquid can expand into very large volumes of gas. Each cryogenic liquid has its own specific properties, but most cryogenic liquids can be placed into one of three groups."
Coffee Break Training - Fire Protection Series No. FP-2014-9
United States Fire Administration: http://www.usfa.fema.gov/