Cryogenic liquids, or Cryogens, are liquefied gases that are kept in their liquefied state at very low temperatures.  Typically, cryogenic liquids have boiling points below -51 ℃ (-60℉ or 222K). All cryogenic liquids are extremely cold and small amounts of liquid may expand into very large volumes of gases when heated, even when exposed to room temperatures.

Cryogenic liquids are generally divided into three categories:

• Inert Gases: Cryogenic liquids consisting of inert gases generally do not burn or support combustion, and have little or no toxic effects.  However, they can be extreme cold hazards and they may displace oxygen as they evaporate, leading to asphyxiation.  Examples include nitrogen, helium, neon, argon, and krypton.
• Flammable Gases:  These are cryogenic liquids that produce a gas that can burn in air.  Common examples include hydrogen, methane, and liquefied natural gases.
• Oxygen: In addition to being an extreme cold hazard, liquid oxygen is a very concentrated oxygen source.  Many normally non-combustible materials may burn in the presence of liquid oxygen.  Organic materials may even explosively react on contact with liquid oxygen.

Always wear appropriate personal protection equipment, including loose fitting insulated gloves made for cryogenic work, face shield used in combination with splash goggles or safety glasses, and appropriate apron, lab coat, or coveralls. Appropriate laboratory attire must be worn while handling cryogenic liquids (long pants, closed top toed/top shoes).

Cryogenic liquids must be stored in well ventilated areas. EH&S may require oxygen level detectors in certain situation due to the gas expansion ratio of cryogenic liquids.

Review the Chemical Hygiene Plan or Laboratory Safety Manual for a detailed discussion on the proper use and handling of cryogenic liquids. In addition, EH&S developed a standard operating procedure for handling cryogenic liquids.