For the purpose of this subpart the term “liquefied petroleum gas” means any liquefied flammable gas which is composed predominantly of hydrocarbons or mixtures of hydrocarbons, such as propane, propylene, butane, butylene, or butadiene, and which has a Reid vapor pressure exceeding 40 pounds per square inch absolute at 100 °F as determined by ASTM D323 (incorporated by reference, see § 58.03-1).