Propane Safety program provides basic knowledge of proper cylinder refueling operations by vehicle operators with an emphasis on safety. Liquefied petroleum gas, commonly called LPG or LP gas is a mixture of several hydrocarbon gases. Propane and butane, used separately or in mixtures, are the principal LP gases. Propane is a vapor at normal temperatures and atmospheric pressure. Your gas supplier converts propane to a liquid which greatly reduces space requirements. Moderate pressure holds the propane in liquid form until needed.