Backfire Flashback and flame arrestors ~ Marine Notes

Backfire Flashback and flame arrestors Preventive measures

Flashback and flame arrestors

Summary

Backfire and flashback can happen. In oxy-fuel processes it is important to use safety devices to prevent mishaps in the equipment. This issue of “Safety Information” deals with the most frequently used safety devices for the prevention of backfire and flashback in oxy-fuel gas equipment. Oxygen and fuel gas may be hazardous if improperly used or handled. This type of equipment should not be used unless proper safety procedures have been understood and applied. The gas and equipment suppliers should place safety and product information at the disposal of the customer.

Backfire and flash back

In a backfire the flame burns back into the torch with a cracking sound. Either the flame is extinguished, or it is reignited at the nozzle opening. In a sustained backfire the flame continues back into the torch, often reaching the mixing point for oxygen and fuel gas. An initial crack is followed by a whistling sound.

Regarding the cause, general preventative measures and hazards of both backfire and sustained backfire, the

reader should refer to the basic guidelines for welders. This Safety Information will only deal with the specific

risk of flashback, and the safety devices that can prevent it.

In a flash back, the flame recedes through the torch back into one of the supply hoses. The hose can explode. In the worst case, the flame can continue into the regulator and into the cylinder.

Causes of flash back A gas mixture in one of the hoses in combination with a backfire when igniting a burner can cause a flashback. The gas mixture in the hose results from reverse flow, i.e. when gas at a high pressure flows into a hose with a lower pressure. If there is sufficient gas mixture in the hose the explosion can be so violent that the hose bursts.

Preventive measures (see References)

To prevent reverse flow and flashback, safety devices incorporating check valve and flashback arrestor must be mounted on the torch and/or regulators.

The different safety devices are discussed below. They are dealt with in different standards 1,2.

Check valves and flash back arrestors By using available safety devices the risk of flashback can in most cases be avoided. The most common safety devices are check valves and flashback arrestors. In some countries the use of check valve and/or flashback arrestors are mandatory, whereas in other countries the use of these are only recommendations.

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