Improve Safety with Flashback Arrestors

Oxy-Fuel Welding and Cutting Safety

Oxy-fuel welding involves two different compressed flammable gases (oxygen and acetylene), rubber hoses, gas regulators, and a torch head with either a heating torch tip or cutting tip. The shape and temperature of the flame is controlled by regulating the pressure of the flammable gases being burned at the torch tip.

Flashback arrestors are safety devices similar to check valves, which are installed in-line between the gas supply hoses and the torch head to prevent the flame from burning back into the torch head (flashback) or from exploding (backfire). These conditions can occur when a loss of pressure in one of the gases causes an imbalance of pressure in the torch head, such as when a compressed cylinder becomes empty or if gas valves are not opened/closed properly during torch start-up/shutdown. It can also be caused if the torch tip becomes clogged with molten metal or is held too close to the object being worked.

What Causes a Backfire During Welding?

A backfire during welding or cutting is a momentary backward movement of the flame into the torch tip. It is usually accompanied by a loud pop or bang as the flame extinguishes and reignites quickly. In the case of a severe backfire, the flame may burn back into the hose.

Occasionally, backfire flames can burn through the hoses (especially oxygen hoses) and cause severe injury. This momentary regression of the flame into the tip or torch can cause serious damage to the equipment and potentially cause an explosion in the cylinder regulators.

What Causes a Flashback During Welding?

A flashback is initiated by a backfire. It is usually recognized by a whistling or squealing sound. A flashback is a potentially hazardous situation because it results in very rapid internal heating and possible destruction of the equipment.

The equipment will heat up rapidly and sparks may begin flowing from the tip. It is important to understand any shutdown sequence before an incident occurs and to get both valves closed quickly when there is a flashback. Some manufacturers recommend shutting off either the fuel or oxygen first. Check your specific manufacturer’s recommendations for the proper valve shutdown sequence.

Flashback Arrestors for Welding Safety

To reduce backfires and flashbacks, use flashback arrestors and purge hose lines before lighting the oxy-fuel gas torch. Purging flushes out any combustible oxygen-fuel gas or air-fuel gas mixtures in the hoses. Caution should be taken when purging the hoses; never point the torch at an ignition source or purge the hoses in a confined space.

To protect operators and equipment, it is recommended that all oxyacetylene welding equipment be protected by installing flashback arrestors. Arrestors are inexpensive protection for gas welding equipment and the operators who use them and are available through welding supply companies.

Once a flashback starts, an arrestor is the only device that will stop a hose fire. Flashback arrestors provide protection in three ways:

• A filter that stops the flame from traveling back to the regulator
• A check valve that stops the reverse flow of gases
• A cutoff valve that stops the flow of gases

For maximum protection, install flashback arrestors at the end of the hose, next to the regulators.