Flashback arrestor: about 13 metres a second without one

• Fit a flashback arrestor to every torch set as recommended practice, and check that it is the type the manufacturer specifies.
• Check the hoses, fittings, regulators, gauges and torch valves before a set leaves the depot.
• Take any set with a known fault out of service.
• Re-check the set on site, since transport can cause damage.
• Keep a short written record of each check.

This post explains the flashback arrestor in plain terms. It is written for owners who buy and maintain torch sets and for dispatchers who decide which kit goes out with which tech. It is not legal advice, and it does not replace the rules that apply where you work. Check those rules, and the instructions that came with your equipment, before you act on anything here.

A flashback is when the flame moves back into the torch and, from there, into the hoses. In a normal set-up, the gas comes out of the torch tip and burns in front of it. The flame stays at the tip because the gas speed and the burn speed are balanced. When that balance breaks, the flame can run backwards.

Common triggers are easy to miss on a busy job. A tip that overheats after a long run of work can start to glow and ignite the gas inside it. A tip blocked by spatter or dirt can change the gas flow and let the flame slip back. A loose connection can let air into the gas line and create a mix that burns in the wrong place. A worn regulator or a poor seal can cause the same problem.

The key point for owners and dispatchers is that a flashback is not only a torch problem. It is a set-up problem. The torch, hoses, regulators, cylinders and fittings form one system. If one part lets the flame through, the rest of the system is exposed.

WorkSafe New Zealand, in its guidance on health and safety in welding, puts the speed in plain numbers. It says that if a flashback arrestor is not attached, the flame will travel about 13 metres a second up the gas supply hoses to the regulator and possibly into the gas cylinders, potentially causing them to explode. You can read the full guidance on the WorkSafe New Zealand health and safety in welding page.

A flame moving that fast does not give a person time to close a valve, step back, or think. By the time someone sees the fire at the torch, the flame may already be in the hose. That is why the flashback arrestor is not an optional extra, even for a job that is usually quick. The arrestor is there for the moment when everything else has already failed.

The manufacturer specifies where it sits in the line for your set. Its job is to stop a flame travelling back up the line. Different designs work in different ways, but the aim is the same: the flame should be stopped or cut off before it passes through the device and reaches the rest of the supply.

An arrestor is not a substitute for good practice. It will not fix a worn-out tip, a leaking regulator, or a torch that is left lit while the tech walks away. It is a last line of protection. For that reason, owners should treat it as a recommended part of the set, not as something a tech can leave off when the kit feels heavy or awkward.

When you buy or specify a set, check that the arrestor is part of the kit or is clearly listed as an accessory. Check that the parts fit each other. Mixing parts from different makers can cause leaks or stop the arrestor working as its maker intended. If you are not sure whether two parts are compatible, ask the manufacturer or supplier before the set goes out.

It helps to walk through a set from the cylinder to the tip and ask what could go wrong at each point.

At the cylinder, the main risks are damage to the valve or the cylinder itself, and any leak that lets gas collect where someone is working. Store and secure cylinders the way your site rules and the supplier's guidance require.

At the regulator, the risk is a fault in pressure control or a leak through a seal. A regulator that does not hold its setting can change the gas flow and make the flame unstable. Gauges should be read before and during use, and any sign of a fault should be dealt with before the set is used again.

In the hoses, the risks are wear, cuts, cracks and loose connections. Hoses are often dragged over sharp edges, run past hot work, or left in the sun. A hose that looks fine from the outside can still have a damaged inner layer, so if a hose has been hit, crushed or burned, take it out of service.

At the torch and tip, the risks are blockage, overheating and a bad seal at the joint. Tips should be kept clean and sized for the job. Torch bodies should be checked for cracks and for valves that do not close properly. A torch that will not stay shut is a warning sign, not a small inconvenience.

Dispatch is often the last chance to catch a fault before a tech is on site, so the check should be simple enough to do every time. A good pre-dispatch check covers these points:

• The flashback arrestor is fitted, is the right type for the set, and is not damaged.
• The hoses are whole, not cracked, not burned, and not patched with tape.
• The fittings and clamps are tight and not stripped.
• The regulators and gauges work and show sensible readings when the set is connected.
• The torch valves close fully, and the tips are clean and the right size.
• The cylinders are secured for transport, and their valves are closed when not in use.

If any item fails, the set should not go out until it is fixed or replaced. A dispatcher who sends a set with a known fault is making a decision on the tech's behalf, and that is an unfair decision to place on someone working alone on a site.

Keep the check short and written down. A tick sheet or a simple digital form is enough. The point is that a fault found at the depot is cheap to fix, while the same fault found at a live job can be very costly.

A depot readies 5 torch sets for a day of work. On the check, 2 sets fail: one has no arrestor fitted and one has a cracked hose. Both are tagged, taken out of service and held back, and their jobs move to another day.

Techs should check the set again on site, because damage can happen in transport. Before lighting anything, look at the hoses, check the connections, and make sure the arrestor is fitted the way the manufacturer intended. If something is wrong, stop, tag the set, and report it. Working with a known fault because the job is waiting is the kind of shortcut that causes accidents.

When lighting a torch, set the gas flows as the manufacturer's instructions describe, and open and close the valves in the correct sequence. If the flame starts to behave badly, shut the torch off in the correct order. Do not try to fix it while it is still burning. Investigate once the set is safe.

After use, close the cylinder valves, release the pressure in the hoses as the instructions describe, and then store the set. Do not leave a torch lit in a box, under a bench or on a hot surface. Do not leave hoses coiled near heat or sparks. These are simple habits, and they are the ones most often missed when people are tired or in a hurry.

The flashback arrestor is one part of a larger set of controls. WorkSafe New Zealand's welding guidance covers other health and safety risks in welding and points readers to a section on reviewing control measures, which is worth reading for any owner or dispatcher who runs a team. For ventilation, see welding ventilation rules.

The same guidance also refers readers to outside material, including a Weld Australia technical note. Owners who work across borders should check which rules apply in each place, because the details can differ.

Fire is also part of the picture. The Canadian Centre for Occupational Health and Safety describes fire protection as methods of control that minimize the damage from fires when they do occur. That idea fits torch work well. You cannot promise that a flashback will never happen, so you plan for it. The arrestor is one of those plans. The others include a clean work area, a fire extinguisher suited to the work, a clear way out, and a tech who knows what to do if a flame goes wrong. The CCOHS page on fire protection sets out the general approach. For related checks, see fire safety checks before dispatch.

Owners set the standard for what goes on the truck. That means a few clear decisions, written down and applied to every set.

First, decide that a flashback arrestor is part of every torch set you own or hire. Do not make it optional for particular jobs or particular techs.

Second, decide how sets are inspected, who does the inspection, and how often. Pick a method that suits your team, and make sure it is followed. The check does not need to be complicated, but it does need to happen.

Third, decide what happens to a damaged set. Damaged hoses, faulty regulators and missing arrestors should be taken out of service and labelled. They should not be left in a van or a shed where someone might grab them in a hurry.

Fourth, decide who is responsible for each part of the check. In a small business, that may be the owner. In a larger one, it may be a workshop lead or a dispatcher. Whoever holds the role should know exactly what to check and what to do when a set fails.

Dispatchers sit at the point where kit meets people. They know which tech is going to which job, and they can see whether the right set is being sent. They do not need to be torch experts, but they do need a simple rule and the authority to enforce it.

Make the rule clear: no arrestor, no set. If a tech asks for a set that has not been checked, check it first. If a set has a visible fault, pull it and send a different one. If a job needs a set that is not available, reschedule the job or send it to someone with the right kit.

Keep a note of which sets go to which techs. If a fault is found later, the record shows where the set has been and who used it. That helps with investigation and with the next check. For a handoff format, see the field service work order checklist.

If you are the tech using the set, you are the last person who can see the flame. Your job is to check the set before you light it, watch the flame while you work, and stop the moment something looks wrong.

Before you start, look at the hoses and connections. Make sure the arrestor is fitted and that nothing is hanging loose. If you find a fault, do not work around it. Report it, tag the set, and ask for a replacement. A short delay is far cheaper than a fire.

While you work, keep the torch pointed away from people, hoses and flammable material. Keep the hoses clear of hot work and sparks. Watch for signs of a flashback, such as a popping or squealing sound, a flame that moves into the torch body, or a torch that becomes very hot. If you see any of these, shut the torch off in the correct order and get clear of the area.

After you finish, close the valves, store the set safely, and report anything that did not work as it should. Techs often notice small faults first, and a short report can stop a bigger problem later.

A simple record for each torch set should show when it was last checked, who checked it, what was found, and what was done. If a set is repaired or replaced, note that too. Over time, the record shows patterns. A certain hose may wear out quickly, or a certain regulator may keep failing.

Keep records for each set, not just for the team as a whole. That way, if a fault appears, you can trace it back to the set and the last check. Review the records from time to time and ask whether the checks are happening and whether the same problems keep returning. If they do, the answer may be a different hose, a different regulator, or a different way of working.

If you are unsure about a particular set or rule, check the manufacturer's instructions and the official guidance that applies where you work. Ask a qualified person if the question stays open. A short question at the depot is always better than a long recovery after a fire.

Pick one torch set today and run the pre-dispatch checks above on it, starting with the flashback arrestor. Write down what you find, and do not send the set out if any item fails.

Is a flashback arrestor needed on every set?

Yes, this post recommends one on every set, because WorkSafe New Zealand's guidance describes what happens when no arrestor is attached.

What should you check first on a torch set?

Check the flashback arrestor first: confirm it is fitted, is the right type for the set, and is not damaged. Then check the hoses, fittings, regulators, gauges and torch valves.