Liquid Petroleum Gas (LPG or LP Gas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing fluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer. The gases are a mix of propane and butane usually with propylene and butylenes present in small concentration. A powerful oderant, ethyl mercaptan, is added to these so that leaks can be detected easily. LPG is manufactured during the refining crude oil, or extracted from oil or gas streams as they emerge from the ground.
It becomes liquid at room temperarture under pressure, so is supplied in pressurised steel bottles. These are usually filled to 85% of their capacity with the liquified gas to provide room for the liquid to expand if the bottle gets hot. The liquified gas has an expansion ratio of about 250:1.
LPG was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed in the United States.
