Cryogenic liquids are materials with a boiling point below –100°F (-73°C); common examples include liquid nitrogen, helium and argon, and dry ice/alcohol slurries. The cryogenic liquid undergoes large volume expansion when it transitions to the gas phase. For example, one volume of liquid nitrogen vaporizes into 694 volumes of nitrogen. Therefore, the heating of the cryogenic liquid in the sealed container generates a high pressure, which can rupture the container.
The hazards of cryogenic liquids include fire (in the case of flammable or oxidizing substances), pressure build-up, explosion, and severe frostbite (contact with the skin) and suffocation (due to the consumption of available oxygen). In addition, the boiling point of cryogenic liquids such as liquid nitrogen is lower than that of oxygen, and can condense oxygen in the atmosphere, thereby forming a local oxygen-rich environment by forming liquid oxygen. The combination of liquid oxygen with many organic (oxidizable) materials can cause violent reactions. A system equipped with a liquid nitrogen trap must not be open to the atmosphere until it is removed from the coolant.
Compressed gases are considered more dangerous than liquids or solids because of the high pressures involved and the ability of the gas to diffuse rapidly when released. In addition, many compressed gases are flammable, toxic or corrosive.
As a national facility, UNR is protected by International Fire Protection Regulations (IFC). The International Finance Corporation specifies the maximum amount of dangerous compressed gas allowed in each designated fire control area. The fire zone usually consists of multiple laboratories, so it is difficult to assign the maximum allowable number to each room. NFPA 45, “Laboratory Fire Standards Using Chemicals”, is also applicable to UNR in management. The standard provides guidelines for the maximum number of compressed gas or liquefied gas cylinders (500 square feet or less) in each laboratory, as shown below. Please contact the university CHO for more specific guidance.
Additional information about the safe handling and use of compressed gas can be obtained from the Compressed Gas Association, Matheson Tri-Gas, and the Air Liquide Design and Safety Manual.