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 flash back into the gas line, and there is the possibility of a serious accident.
A flame or flashback arrestor is a safety device designed to stop a flame in its tracks. It is therefore used to prevent flashback into cylinders or pipework.
A flashback arrestor should not be confused with a non-return valve, which has no particular flame stopping properties. A non-return valve can reduce the probability of a flashback, as it serves to prevent reverse flow of oxygen into fuel lines and fuel into oxygen lines.
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.
- UK: The Safe Use of Compressed Gases in Welding, Flame Cutting and Allied Processes, HSG139 (HSE Books)
- Flame Arrestors HSG158 (HSE Books)
- USA: Compressed Gas Association Inc Publication TB-3