Guide
Flame arrestor or flashback arrestor: two devices two jobs, two standards
A flame arrestor is a passive element that quenches a flame front in a pipe, vent or generator line and lets the gas keep flowing. A flashback arrestor is the device on oxy-fuel equipment: a flame arrestor element plus a non-return valve and thermal cut-off, built to IS 11006:2011, fitted at regulator and torch.
- Flame arrestor
- Passive quenching element in a pipe
- Flashback arrestor
- Flame arrestor element + non-return valve + thermal cut-off
- Indian Standard, flashback arrestors
- IS 11006:2011
- Indian Standard, flame arresters
- IS 16485:2020
- Casing test under IS 11006
- 10 × maximum working pressure or 60 bar
Two devices that are often confused, and why it matters
The words get used interchangeably in tenders, on purchase orders and on supplier websites, and the confusion is not harmless. A buyer who specifies "flame arrestor" for a cutting outfit can be supplied a device with no non-return valve. A plant engineer who specifies "flashback arrestor" for a generator outlet can be quoted a torch-mount unit that cannot pass the flow.
The difference is not size or brand. It is function.
The difference in one table
| Flame arrestor | Flashback arrestor | |
|---|---|---|
| What it is | One element: a sintered metal, wire-mesh or crimped-ribbon insert | A complete device containing a flame arrestor element and more |
| What it does | Quenches a flame front by taking heat out of it faster than it can propagate; gas keeps flowing | Quenches the flame, blocks reverse flow, and shuts the line if it gets hot or sees reverse pressure |
| Elements | Flame-quenching element, sometimes a housing with a drain | Flame arrestor element, non-return valve, thermal cut-off; often a filter; sometimes a pressure-sensitive cut-off |
| Where it is used | Generator outlets and pipework in an acetylene plant, tank vents, process pipelines carrying flammable gas | Oxy-fuel equipment: at the regulator outlet and the torch inlet, on both gases |
| Reverse flow | Not addressed | Blocked by the non-return valve, before and after a flashback |
| After an event | Inspect and return to service if undamaged | Thermal cut-off is non-resettable; the device is replaced |
| Indian Standard | IS 16485:2020 — flame arresters, performance | IS 11006:2011 — flashback arrestors, wet and dry types |
| International | ISO flame-arrester standards for process plant | EN ISO 5175-1 for oxy-fuel equipment |
What a flame arrestor does
A flame front travels through a gas mixture at a speed set by the gas. Pass that front through a passage narrow enough and long enough, and the walls take heat out of the flame faster than combustion puts it in; the flame goes out while the gas keeps moving. That is the whole of a flame arrestor. The element can be sintered bronze or stainless, a stack of wire mesh, or crimped metal ribbon wound into a cartridge; the choice is set by the gas, the flow and the pressure drop the line can afford.
In an acetylene plant the classic form is the wet arrestor — a hydraulic back-pressure valve in which the gas bubbles through a water seal that a flame cannot cross. IS 11006 covers both wet and dry types.
Rules that matter
A flashback on a cutting torch is a flame travelling back from the nozzle, through the torch, into the hose and toward the regulator and cylinder. Quenching the flame is only half the job, because what caused it — reverse flow of one gas into the other's hose, usually from a blocked nozzle or a hose at the wrong pressure — is still there. So the device adds:
What a flashback arrestor adds
- a non-return valve, which stops reverse flow and must work both before and after the flashback test;
- a thermal cut-off, which closes the line if the device is heated by a sustained burn-back and does not reset;
- on some models a pressure-sensitive cut-off, which closes on reverse pressure and stays closed until reset by hand;
- a filter, which keeps particles out of the element.
IS 11006 Annex B gives the colour bands: red for fuel gases, blue for oxygen, black for other gases. The casing has to survive ten times its maximum working pressure or 60 bar, whichever is higher, for five minutes (cl 4.1). On an acetylene device rated 1.5 bar, the 60 bar floor governs.
Where each one goes on a real site
On a cutting or welding outfit: flashback arrestors, two per line — one at the regulator outlet, one at the torch inlet — on the fuel gas and on the oxygen. A device at only one end protects only that end; the hose between them is full of gas.
On an acetylene plant: a wet arrestor at the generator outlet and arrestors in the line to the compressor and the filling manifold. The device at a generator outlet has to pass the plant's full flow at a fraction of a bar, which a torch-mount unit cannot do, and it sits outside the scope of EN ISO 5175-1, which runs from the regulator outlet to the blowpipe. IS 11006 is the standard to certify it against.
On a fixed pipeline: arrestors at every take-off point as well as at the supply end, because every outlet is a possible source of a flashback. The acetylene pipeline rules cover the pressure and bore limits that go with them.
What to ask a supplier
Three questions separate the trade. Which standard is the device built to, by number and year? Is the claim a BIS licence, an independent type test, or the manufacturer's own declaration — only five BIS licences exist against IS 11006 nationally, so most "IS 11006" claims are one of the other two? And is the flow rating stated at the pressure you will run, in m³/h or LPH, so a regulator-mount device is not fitted where a manifold device is needed?
KIGL manufactures flame arrestors and flashback arrestors at the Kolkata works; the flashback arrestor page carries the models, mounts and working pressures by gas.
Flame arrestor or flashback arrestor — frequently asked questions
Is a flame arrestor the same as a flashback arrestor?
No. A flame arrestor is one element — a sintered, mesh or crimped-ribbon insert that takes heat out of a flame front faster than it can propagate. A flashback arrestor is a complete device for oxy-fuel equipment that contains a flame arrestor element and adds a non-return valve, a thermal cut-off and usually a filter. Every flashback arrestor contains a flame arrestor; a flame arrestor on its own is not a flashback arrestor.
Which one do I need on a cutting torch?
A flashback arrestor, at both ends of the hose and on both gases: at the regulator and at the torch, on acetylene (or LPG) and on oxygen. The non-return valve is what stops oxygen flowing back into the fuel hose, and a plain flame arrestor does not have one.
Where is a plain flame arrestor used?
On lines where the gas must keep flowing through the device and there is no reverse-flow question to answer: generator outlets and pipework in an acetylene plant, tank vents, and process pipelines carrying a flammable gas or vapour. In an acetylene plant the wet type — a hydraulic back-pressure valve — is the traditional form.
Which standards apply in India?
IS 11006:2011 for flashback arrestors on acetylene, LPG and oxygen lines, covering both wet and dry types; IS 16485:2020 for flame arresters, performance requirements and test methods. Internationally, EN ISO 5175-1 covers safety devices on oxy-fuel equipment from the regulator outlet to the blowpipe, and does not itself specify where the device must be fitted.
Does a flashback arrestor need replacing after it works?
Yes. The thermal cut-off in a device to IS 11006 is non-resettable: once it has tripped the device is scrap and must be replaced. A pressure-sensitive cut-off, where fitted, closes and stays closed until it is manually reset. Either way, an arrestor that has arrested a flashback has done its job and comes out of service.
Can a flame arrestor stop a flashback in a hose?
It can quench the flame, but it cannot stop the reverse flow that caused it, so the gases can mix again and the next flashback follows. That is why the hose-end device is a flashback arrestor with a non-return valve, not a flame arrestor on its own.
References
- Bureau of Indian Standards. (2011). Flash back arrestors (IS 11006:2011, First Revision). [specification (Public Resource mirror)]
Enquiries
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State the gas or equipment, the quantity or capacity, and your location. KIGL will confirm the grade, the cylinder or plant size, and whether the location can be served from Noonmati, or through the agent network.