When a flammable mixture of fuel gas and air or oxygen is present in a gas line upstream of a welding or cutting blowpipe, flame can flashback into the gas line, and there is the possibility of a serious accident.
The flame arrestor usually contains an element which may consist of narrow passages through a wire mesh or metal foam. When a flame enters the element, it is quickly cooled by the cold surface of the element and the flame is extinguished. The flame arrestor may contain a pressure or temperature actuated cut-off valve, and may then be known as a flashback arrestor.
It is strongly recommended that arrestors with cut-off valves are fitted to the pressure regulator outlet of all acetylene cylinders and acetylene distribution systems. It is highly advisable to fit them to the oxygen outlet, and other fuel gas outlets. They can be fitted to the blowpipe, but this offers no protection from a fire arising from a leaking hose.