Pillar of fire from a Liquid Petroleum Gas (LPG) explosion. LPG fuel is a mixture of gases such as propane and butane obtained from natural gas or petroleum. These gases are liquefied by pressurising them in a bottle to make them convenient to transport. If the gas leaks, mixes with air and ignites, an explosion could result. Photographed during research conducted by the Health and Safety Laboratory in Britain. CROWN COPYRIGHT UNDER LICENCE FROM THE HEALTH & SAFETY LABORATORY & CONTROLLER OF HER MAJESTY'S STATIONERY OFFICE