UL 644

These requirements cover aboveground, underground, and interchangeable (aboveground or underground) stationary container assemblies for liquefied petroleum gases which include any material having a vapor pressure not exceeding that allowed for commercial propane composed predominately of the following hydrocarbons, either by themselves or as mixtures: propane, propylene, butane (normal butane or isobutane), and butylenes. These container assemblies are provided with tanks constructed under the appropriate provisions of the current edition of the Boiler and Pressure Vessel Code of the American Society of Mechanical Engineers (ASME).

Container assemblies covered by these requirements are those using fuel storage tanks having a water capacity of 2000 gallons (7.57 m3) or less and designed for delivery of fuel in the gaseous phase, but they may also incorporate a liquid take-off in addition to a vapor take-off.

Container assembly installations are intended to be made in accordance with the Liquefied Petroleum Gas Code (National Fire Codes, Vol. 2), NFPA 58. They are not intended for use in chemical, petrochemical, petroleum, or utility power plants; nor pipeline or marine terminals; nor related storage facilities at such plants or terminals.