A flashback arrestor or flame arrestor is a device most commonly used in oxy-fuel welding and cutting to stop the flame from burning back up into the equipment and causing damage or explosions. The two main types are dry and wet. Each has its own advantages and disadvantages. Most oxy-fuel flashback arrestors are the dry type.
Dry flashback arrestors typically use a combination of methods to stop flashback. This is the type that is typically found on most workshops, home or portable oxy-fuel kits as they work just as effectively with any orientation, need very little maintenance, and are often small and light enough to be installed between the torch and hoses. They include:
Liquid seal flame arrestors are liquid barriers following the principle of a siphon where the liquid stops the entering deflagration and/or detonation and extinguishes the flame, they work by bubbling the gas through a non-flammable and ideally non-gas-absorbing liquid, which is typically water. They stop the flame by preventing it from reaching the submerged intake.
These devices are normally very effective at stopping flashbacks from reaching the protected side of the system. They have the disadvantages of only working in one orientation and tend to be much larger than dry type arrestors. This makes them mainly only suitable for large or fixed installations and the liquid level needs to be constantly checked.
On smaller units having a pressure release valve to prevent the unit from bursting under a severe flashback, the fluid level should be monitored to keep it always above the intake and not so high that the liquid could splash or overflow into the outlet.