Liquefied Petroleum Gas, commonly known as LPG, is generally used as a fuel in heating appliances, in vehicles, as well as a refrigerant and an aerosol propellant. It has rapidly replaced CFC's or Chlorofluorocarbons to reduce the damage to the ozone layer. LPG is essentially a mixture of Butane and Propane, and the most commonly marketed ratio is 40:60. This ratio varies from season to season, as in winter more Propane is used and in summer more Butane is used. A powerful odourant called Ethanethiol is added in minor amounts to LPG to help in easy detection of any leakage.

LPG is primarily derived from fossil fuels. The maximum amount of LPG is extracted during the refinement of crude oil and the next most common source is oil and gas streams, as and when they emerge from the earth. LPG evaporates at normal room temperature and pressure. To prevent this, LPG is supplied in pressurised cylinders and steel bottles. These bottles are never filled completely so as to accommodate thermal expansion. Normally, they are filled to 80- 85 % of their capacity. The ratio of the liquefied gas to vaporised gas also varies depending upon the pressure, temperature and composition. It is typically around 1:250.

Vapour pressure for a substance is the pressure at which it becomes liquid and it varies depending upon composition, pressure and temperature. LPG is heavier than air and if leaked tends to flow along the floor and settles in low spots like basements. This causes ignition and suffocation hazards if not properly dealt with - and hence the odourant.

So why use LPG at all? LPG is the lowest carbon emitting fuel available. It is not dangerous to the health of the users, as it burns cleanly leaving no soot and minute quantities of sulphur emissions. It does not pose any water or ground pollution hazards either. This, plus the fact that huge quantities of LPG could be stored in bulk tanks and stored underground or underwater if required, tends to make it the number one cooking fuel in some countries. It is also referred to as auto gas when it is used in automobiles, or to fuel internal combustion engines. It is also used as an alternative fuel for sparking ignition engines. It is non corrosive, non toxic and does not contain any lead additives. It also has a very high octane rating (108 RON). It has a specific calorific value of 46.1 MJ/kg, which is better than both petrol and diesel.

LPG constituents Propane and Isobutane, at high purity, are used to make hydrocarbon refrigerants. This is done because hydrocarbons tend to be more efficient and are generally cheaper as they are byproducts of fuel production. Millions of households worldwide use LPG as cooking fuel, and in some countries like Brazil the government also gives special discounts on LPG prices to people below the poverty line. LPG is definitely worth a try, especially when the entire world seems to be concerned about carbon footprints and green living.