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Flashback Arrestors - your questions answered

Your questions answered on Flashback Arrestors for Oxy, Acetylene and LPG/Propane equipment

1. What is a FLASHBACK and why is it dangerous?

When a flashback occurs, the flame burns rapidly ‘upstream’, generally causing a loud explosion. If un-checked it can continue through the torch into hoses, regulators and gas bottles/cylinders.

Causes that can trigger a flashback include: Worn or improperly maintained Equipment, Operator Error, improper monitoring of cylinder pressures, and many other causes!

The consequences of a flashback can vary from slight Equipment Damage through to a major gas cylinder explosion resulting in death, injury and/or extensive property damage.

There is no way of predicting just how severe the effects will be, which is why you need to protect yourself against a flashback.

2. What is a FLASHBACK ARRESTOR (FBA) and what does it do?

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

The main parts of a WELDCLASS^® Flashback Arrestor and their functions are;

1. Non-Return Valve: this stops the reverse flow (back surge) of gas
2. Sintered Flame Filter: this blocks the flame
3. Thermal Activated Cut-Off Valve: (fitted to regulator mounted models only). In case of a sustained (continuous) flashback or backfire, this valve will close and stop the flow of gas in any direction.  

3. What are the current safety requirements?

The Australian standard AS4839-2001 (“The safe use of portable and mobile oxy-fuel gas systems….”) calls for the use of flashback arrestors (see Clause 7.3). Because of this standard, flashback arrestors are a mandatory requirement according to Health and Safety Authorities in Australian states and territories.

4. So….Why should I fit flashback arrestors?

Ask yourself “can I afford not to fit flashback arrestors?”. If you don’t have flashback arrestors fitted to your oxy equipment, you are exposing yourself many risks, including;

1. The potential ‘physical’ consequences of a flashback: Equipment and property damage and injury to persons and/or death
2. Breach of OH&S / WHS regulations and requirements
3. Potential legal and financial consequences of a flashback; litigation, insurance cover ‘disqualification’, etc 

5. Don’t fool yourself…. It can and does happen!

This photo demonstrates the damage that can occur from an explosion involving gas cylinders.

6. So, how many flashback arrestors do I need, and where should I fit them?

Australian Standard AS4839-2001 (“The safe use of portable and mobile oxy-fuel gas systems….”) specifies that for “optimum” protection, Flashback Arrestors should be fitted to:

• Both the regulator and the torch

• Both the oxygen line and fuel gas (Acetylene or LPG) line

For full details refer to AS4839-2001, Clause 7.3

7. What gases require flashback arrestors?

There is potential for flashback to occur with any oxy-fuel system, whether you use oxy-acetylene or oxy-LPG (oxy-propane).

The flashback can occur on either the oxy or the fuel gas line, which is why FBAs should be fitted to each gas line.

8. Are all Flashback Arrestors the same?

No! 

Here's what you need to look out for to ensure that the flashback arrestors you choose will protect you and perform when you need them to;

Compliance with AS4603

AS4839-2001 (“The safe use of portable and mobile oxy-fuel gas systems….”) also specifies that all Flashback Arrestors must be manufactured according to the Standard AS4603. This is very important, because if an arrestor does not comply to this standard, there is no guarantee that it will stop flashback!

If you are purchasing flashback arrestors, or if you already have them fitted to your equipment, always check the labels to make sure they comply to Australian Standards AS4603. If you own flashback arrestors, and you cannot determine that they comply with AS4603, do yourself a favour: Dispose of them and fit Arrestors that do comply.

Independently Tested / Certified

AS4603 states that to be compliant, FBAs must be tested by an independant qualified 3rd party. If the FBA has been independantly tested, normally this will be indicated on the label or packaging. 

Weldclass Flashback Arrestors are independantly tested / certified by Apragaz laboratory (Europe), and this is clearly indicated on the packaging and on the FBA itself. 

Thermal Cut-Off Valve

This is an important safety feature, however not all FBAs have a Thermal cut-off valve. In case of a sustained (continuous) flashback or backfire, if the internal temperature of the FBA reaches an unsafe level this valve will close and stop the flow of gas in any direction. Without this feature, if a sustained flashback occurs there is a risk that the FBA will fail. 

AS4839-2001 also specifies that for optimum protection, regulator-mounted Flashback Arrestors should have a thermal cut-off valve. The label on the FBA will indicate if it has a thermal cut-off valve. Sometimes this is shown via a "[TV]" symbol.
If you cannot see any reference to a thermal valve (on the regulator-mount FBA) on the label, then you can assume that it does not have this safety feature.

WELDCLASS^® Flashback Arrestors

• Conform to AS4603 and EN730

• Independantly certified by Apragaz laboratory, Belgium, Europe

• Each FBA is individually flame, flow and leak tested for peace of mind

Periodic Testing or Replacement

If you have flashback arrestors fitted, you should also be aware that Australian Standards AS4603 and AS4839 specify that all flashback arrestors must be tested (or replaced) at least every 12 months, and in the event of a flashback. Testing should be conducted by qualified repairers.

Disclaimer: While all care has been taken, Weldclass accepts no responsibility for any inaccuracies, errors or omissions in the content of this webpage or in any attachments. The information given is of a general nature only and does not take into account the specific circumstances of any individual person or organisation. Some information given may reflect the personal opinion of an individual. All product specifications are subject to change without notice. Any comments regarding the intended or suggested application for any product is for general description and identification purposes only. It is the sole responsibility of the user and/or owner and/or purchaser to select the appropriate product for their intended purpose and to ensure that the product selected is capable of performing correctly and safely in the intended application. E.&O.E.