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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?

Oxy-Fuel Systems:

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.

LPG / Propane only systems (without oxygen):

The risk of a flashback when using LPG/propane-only torches & equipment is extremely low, and using FBAs is not currently required in / by any Australian-standard.  However, some work sites may still require FBAs to be fitted to all gas/flame equipment, regardless of whether or not oxygen is being used.

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 regulator-mounted Flashback Arrestors include a thermal cut-off valve.

Flow-Rating

Becuase the gas has to pass through a flame filter and other components, every Flashback Arrestor will restrict gas flow to some extent.  This means you need to be aware of the flow rating for the FBAs you are using, to ensure they will allow sufficient gas flow for the work your are doing. 

Many 'standard' model FBAs have a Low flow rating and can be used for light cutting / brazing etc, but are not suitable for tasks that require medium-to-high flow rates such as oxy heating, heavy cutting/gouging, etc.

Weldclass Flashback Arrestors are Medium flow-rated, with up to 35% higher flow capacity than some other standard model FBAs. This makes them suitable for wider range of applications, including cutting, brazing, gouging and medium-to-heavy heating.

WELDCLASS^® Flashback Arrestors

• Conform to AS4603 and EN ISO 5175-1 (formerly EN730)

• Independantly certified by Apragaz laboratory, Belgium, Europe

• Each FBA is individually flame, flow and leak tested for peace of mind
  
  
• Medium flow rating, up to 35% higher flow capacity vs some other standard model arrestors & suitable for wider range of applications

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.

AS4839 also specifies that flashback arrestors must be replaced at least every 5 years.

Many operators are now choosing to replace rather than test – especially given that flashback arrestor costs have generally reduced in recent years. In addition to the cost of testing itself, the disruption and downtime cost involved in dismantling equipment (and waiting for testing to be completed before it can be used again) is often significant and outweighs the cost of replacement units. Also, it is not uncommon for a % of units to fail due to normal 'wear and tear' and require replacement, which then incurs further costs in addition to testing.

While all care has been taken to ensure the information presented is accurate, Weldclass accepts no responsibility for any errors or omissions in this article. The information given is of a general nature only intended to provide readers with a basic overview of the topics presented, does not take into account the specific circumstances of any individual application or situation, may be simplified and/or abbreviated, will not be a complete or exhaustive resource, and should not be used as a substitute for professional advice. All applicable standards (including Australian standards), industry guidelines and regulations should be consulted and followed. E.& O.E.