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Your Questions Answered About Flashback Arrestors for Oxy, Acetylene, and LPG/Propane Equipment
When a flashback happens, the flame burns quickly 'upstream', usually causing a loud explosion. If left unchecked, it can keep going through the torch into hoses, regulators, and even gas cylinders.
Things that can cause a flashback include worn-out or poorly maintained equipment, operator mistakes, improper monitoring of cylinder pressures, and other factors!
The results of a flashback can range from minor equipment damage to a big gas cylinder explosion leading to serious injuries, fatalities, and extensive property damage. It’s impossible to predict how severe these effects will be, so protecting yourself against flashbacks is crucial.
A flashback arrestor is specifically designed to hold back a flashback and prevent it from reaching upstream equipment like hoses, regulators, and gas cylinders.
The main components of a WELDCLASS® Flashback Arrestor and their functions are:
1. Non-Return Valve: Prevents the reverse flow of gas.
2. Sintered Flame Filter: Blocks the flame.
3. Thermal Activated Cut-Off Valve: (Only on models mounted on regulators). In case of a continuous flashback or backfire, this valve will shut off and stop gas flow in any direction.
This picture shows what a flashback arrestor looks like for oxy, acetylene, and LPG (propane) equipment.
Australian Standard AS4839-2001 ("The safe use of portable and mobile oxy-fuel gas systems...") requires the use of flashback arrestors (Clause 7.3). Due to this standard, flashback arrestors are legally required by health and safety authorities in Australian states and territories.
Ask yourself, "Can I really afford not to install flashback arrestors?" If you don't have them fitted to your oxy equipment, you're putting yourself at risk of several dangers, including:
1. Physical consequences of a flashback: Equipment and property damage, and possible injury or death.
2. Violation of OH&S/WHS regulations.
3. Potential legal and financial consequences of a flashback: lawsuits, loss of insurance coverage, etc.
This image shows the kind of damage that can happen from an explosion involving gas cylinders.
Australian Standard AS4839-2001 ("The safe use of portable and mobile oxy-fuel gas systems...") recommends that for maximum protection, flashback arrestors should be installed on:
- Both the regulator and the torch
- Both the oxygen line and the fuel gas (acetylene or LPG) line
For more details, refer to AS4839-2001, Clause 7.3.
There’s always a risk of flashback with any oxy-fuel system, whether you’re using oxy-acetylene or oxy-LPG (oxy-propane). A flashback can happen on either the oxygen or the fuel gas line, which is why FBAs should be fitted to each gas line.
The risk of a flashback when using LPG/propane-only torches and equipment is very low, and there’s no current requirement for FBAs in any Australian standard. However, some work sites might still demand FBAs on all gas/flame equipment, regardless of whether oxygen is being used.
No!
Here’s what you should look for to ensure the flashback arrestors you choose will protect you and function when needed:
AS4839-2001 ("The safe use of portable and mobile oxy-fuel gas systems...") also specifies that all flashback arrestors must be manufactured according to Standard AS4603. This is critical because if an arrestor doesn’t comply with this standard, there’s no guarantee it will stop a flashback!
If you’re buying flashback arrestors or already have them fitted to your equipment, always check the labels to confirm they comply with Australian Standards AS4603. If you own flashback arrestors and can’t verify they comply with AS4603, do yourself a favor: Dispose of them and get ones that do comply.
AS4603 states that to be compliant, FBAs must be independently tested by a qualified third party. If the FBA has been independently tested, this will usually be indicated on the label or packaging.
Weldclass Flashback Arrestors are independently tested/certified by Apragaz laboratory (Europe), and this is clearly marked on the packaging and on the FBA itself.
This is an important safety feature, though not all FBAs come with a Thermal cut-off valve. In the case of a sustained flashback or backfire, if the internal temperature of the FBA reaches an unsafe level, this valve will close and stop gas flow in any direction. Without this feature, a sustained flashback could potentially cause the FBA to fail.
AS4839-2001 also specifies that for optimal 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 don’t see any mention of a thermal valve (on the regulator-mounted FBA) on the label, you can assume it doesn’t have this safety feature.
Weldclass regulator-mounted Flashback Arrestors include a thermal cut-off valve.
Because gas has to pass through a flame filter and other components, every Flashback Arrestor will limit gas flow to some degree. You need to know the flow rating of the FBAs you’re using to ensure they’ll provide enough gas flow for your work.
Many 'standard' model FBAs have a low flow rating and are suitable for light cutting/brazing, but they aren’t ideal for tasks requiring medium-to-high flow rates like 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 a broader range of applications, including cutting, brazing, gouging, and medium-to-heavy heating.
Comply with AS4603 and EN ISO 5175-1 (formerly EN730)
Independently certified by Apragaz laboratory, Belgium, Europe
If you have flashback arrestors installed, 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 after a flashback incident. Testing should be done 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 since flashback arrestor costs have generally decreased in recent years. Besides the cost of testing itself, the downtime involved in dismantling equipment (and waiting for testing to be completed) can be significant and outweigh the cost of replacement units. Additionally, it’s not uncommon for a percentage of units to fail due to normal wear and tear and require replacement, adding further costs beyond 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.
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