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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 in the opposite direction, usually leading to a loud explosion. If not stopped, it can travel back through the torch into hoses, regulators, and even gas cylinders.
Several factors can trigger a flashback, including worn-out or poorly maintained equipment, operator mistakes, incorrect monitoring of cylinder pressures, and more!
The results of a flashback can range from minor equipment damage to a catastrophic gas cylinder explosion that could cause serious injuries, fatalities, or extensive property damage. Since it’s impossible to predict how severe these effects might be, protecting yourself from flashbacks is crucial.
A flashback arrestor is specifically designed to contain a flashback and stop it from reaching upstream equipment like hoses, regulators, and gas cylinders.
Let’s break down the main components of a **WELDCLASS**® Flashback Arrestor and their functions:
1. **Non-Return Valve**: Prevents the reverse flow of gas.
2. **Sintered Flame Filter**: Blocks the flame from traveling backward.
3. **Thermal Activated Cut-Off Valve**: Found in regulator-mounted models, this valve closes automatically if there’s a continuous flashback or backfire, stopping gas flow in any direction.
The Australian standard AS4839-2001 ("Safe Use of Portable and Mobile Oxy-Fuel Gas Systems...") mandates the use of flashback arrestors (as per Clause 7.3). Due to this standard, flashback arrestors are legally required by health and safety authorities in all Australian states and territories.
Think about it: Can you really afford not to install flashback arrestors? If you haven’t installed them on your oxy equipment, you’re exposing yourself to multiple risks, including:
- Physical consequences such as equipment and property damage, or even injury or death.
- Violation of OH&S/WHS regulations.
- Potential legal and financial consequences like lawsuits or loss of insurance coverage.
Check out this photo to see the kind of destruction that can result from an explosion involving gas cylinders.
Australian Standard AS4839-2001 specifies that for maximum protection, flashback arrestors should be installed on both the regulator and the torch, as well as on both the oxygen and fuel gas (acetylene or LPG) lines. For detailed instructions, refer to AS4839-2001, Clause 7.3.
Flashbacks can happen with any oxy-fuel system, whether you’re using oxy-acetylene or oxy-LPG (oxy-propane). They can occur on either the oxygen or fuel gas line, which is why FBAs should be installed on each gas line.
Even though the risk of a flashback with LPG/propane-only torches is very low, some work sites may still require FBAs to be installed on all gas/flame equipment, even if oxygen isn’t being used.
Not all flashback arrestors are created equal! To ensure the ones you choose will protect you effectively, here’s what you should look for:
AS4839-2001 specifies that all flashback arrestors must be manufactured according to the Standard AS4603. This is critical because non-compliant arrestors might not stop a flashback!
Always check the labels of your flashback arrestors to confirm compliance with AS4603. If you’re unsure, dispose of them and get compliant ones instead.
AS4603 requires that FBAs be independently tested by a qualified third party. Compliance is usually indicated on the label or packaging.
Weldclass Flashback Arrestors are independently tested by the Apragaz laboratory in Europe, and this certification is clearly marked on the packaging and the FBA itself.
An essential safety feature, not all FBAs come with a thermal cut-off valve. This valve closes if the internal temperature becomes unsafe during a sustained flashback or backfire, preventing further gas flow. Without this feature, there’s a risk of the FBA failing.
AS4839-2001 recommends that regulator-mounted FBAs include a thermal cut-off valve, which is often indicated by a [TV] symbol on the label. If you don’t see any mention of a thermal valve, it likely doesn’t have this feature.
Weldclass regulator-mounted FBAs include a thermal cut-off valve.
Since gas has to pass through flame filters and other components, every FBA reduces gas flow to some extent. Be mindful of the flow rating for the FBAs you use to ensure they support the tasks you’re performing.
Standard model FBAs typically have low flow ratings and work well for light cutting or brazing but aren’t ideal for medium-to-high flow tasks like oxy heating, heavy cutting, or gouging.
Weldclass Flashback Arrestors have medium flow ratings, with up to 35% higher flow capacity than some standard models. This makes them suitable for a broader range of applications, including cutting, brazing, gouging, and medium-to-heavy heating.
**Key Features:**
- Complies with AS4603 and EN ISO 5175-1 (formerly EN730).
- Independently certified by Apragaz laboratory in Belgium, Europe.
If you’ve installed flashback arrestors, remember that AS4603 and AS4839 require regular testing or replacement at least every 12 months, and after every flashback incident. Testing should be done by qualified repairers.
AS4839 also specifies that FBAs must be replaced at least every 5 years.
Many operators now opt to replace rather than test, especially since FBA costs have decreased in recent years. The cost of testing, along with downtime for dismantling equipment and waiting for tests, often outweighs the cost of replacement units. Additionally, some FBAs may fail due to normal wear and tear, adding extra costs to the testing process.
Please note that while we’ve made every effort to ensure accuracy, this information is general in nature and shouldn’t replace professional advice. Always consult applicable standards, industry guidelines, and regulations.
*Disclaimer: While all care has been taken to ensure the information provided is accurate, Weldclass assumes no responsibility for any errors or omissions. This content is intended for educational purposes only and should not be considered a comprehensive guide.*
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