Flashback arrestors

A flashback is where a gas flame moves ‘upstream’ into hoses, regulators and even gas bottles and cylinders. It can result in serious injury and equipment damage.

Workers most at risk of injury from flashback includes those who use portable and mobile oxy/fuel gas systems for welding, heating or cutting metal in industries such as plumbing, engineering, demolition, farming, lift installing, scrap metal, air conditioning and gas fitting.

A flashback means that you need to review your system including checking both equipment and the work procedure. Always make sure the cause of the flashback is discovered and repaired before workers attempt to relight. After any flashback incident, a competent person should remove and inspect flashback arrestors, gas hoses and fittings and, if necessary, discarded or repaired.

What causes a flashback?

A flashback begins when the flame moves back from the welding tip and into the blowpipe, usually with a loud bang or a hissing noise.

Most flashbacks are caused by faults in gas hose fittings. These faults can be caused by:

• wear and tear
• dirt
• excessive heat
• carbonising
• damage during transport or storage, or
• incorrect operating procedures.

Flashback can also happen when there is uneven gas pressure in two supply hoses and this may cause the blowpipe flame to move into whichever gas hose is under least pressure. A flashback always indicates that something is wrong, either with the equipment or the work procedure.

What is a flashback arrestor?

A flashback arrestor is designed to contain a flashback and prevent it from penetrating into upstream equipment (i.e. hoses, regulators and gas cylinders).

Flashback arrestors both quench the flame and close off the gas supply. Most flashback arrestors are fitted with a non-return valve, flame arrestor and thermal cut-off valve which closes if the arrestor becomes overheated.

You must ensure the flashback arrestor is compatible with the type of gas and equipment you are using and comply with AS4603-1999 Flashback arresters—Safety devices for use with fuel gases and oxygen or compressed air. Flashback arrestors should be inspected and tested by a competent person every 12 months.

Flashback happens at very high speeds (up to 13 metres per second); much faster than the time it takes for a worker to manually shut off the system.

Australian Standard AS4839-2001 The safe use of portable and mobile oxy-fuel gas systems for welding, cutting, heating and allied processes specifies that for optimum protection, flashback arrestors should be fitted to both the regulator and the touch for oxygen and fuel gas lines.

Working safely when welding, cutting and heating

Flashback arrestors are only one part of a safe system of work. Arrestors are not a substitute for safe work procedures, safe transport and storage, regular checks and maintenance, instruction, information, training, supervision for operators and following the manufacturer's safety guidelines.

You should have in place emergency plans and procedures and ensure that your workers are trained to recognise flashback should it occur.