Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities
Acetylene is the only fuel gas recommended for underground working conditions because it is lighter than air. It is also the only fuel gas, for instance, which can be used to weld steel.In cutting, oxy-acetylene gives the fastest preheating and piercing times of any fuel gas combination.