Gas explosion

A gas explosion is an explosion resulting from mixing a gas, typically from a gas leak, with air in the presence of an ignition source. In household accidents, the principal explosive gases are those used for heating or cooking purposes such as natural gas, methane, propane, butane. In industrial explosions many other gases, like hydrogen, as well as evaporated (gaseous) gasoline (American English)/petrol (British English) or ethanol play an important role. Industrial gas explosions can be prevented with the use of intrinsic safety barriers to prevent ignition.
Lower and upper explosive limits.
Whether a mixture of air and gas is combustible depends on the air-to-fuel ratio. For each fuel, ignition occurs only within a certain range of concentration, known as the upper and lower flammability limits. For example, for methane and gasoline vapor, this range is 5-15% and 1.4-7.6% gas to air, respectively. An explosion can only occur when fuel concentration is within these limits.