What Is a Flashback Arrestor and How Does It Work?

The short answer

A flashback arrestor shuts off gas flow and extinguishes a flame before it can travel back through a hose or pipeline to your gas source. Inside a long pipe, a returning flame can accelerate to detonation velocity, so the arrestor has to act in a fraction of a second. IIGAS builds arrestors for every point in the system — for fuel gases (acetylene, LPG, hydrogen, natural gas) and for oxygen alike — to BIS 11006 and EN ISO 5175-1.

How a flashback arrestor works: three safety elements

A good arrestor is triple-safe — it combines three elements so that even if a flame starts back up the line, it is stopped and the gas is cut off:

• ✓Non-return valve — a spring-loaded valve that blocks reverse gas flow back into the hose or line
• ✓Flame-arrestor filter — a sintered stainless-steel element that cools and quenches the flame in a fraction of a second
• ✓Thermal cut-off valve — a fusible seal that melts and shuts off the gas before dangerous temperatures build

On bulk acetylene lines, a fourth element — a water-seal chamber — absorbs the flame front as well.

Dry vs water-seal (wet) arrestors

The two broad families are dry arrestors and water-seal (wet) arrestors:

• ✓Dry arrestors use a sintered flame-arrestor element and a non-return valve. Compact and maintenance-light, they fit torch hoses, manifolds and pipelines.
• ✓Water-seal (wet) arrestors pass the gas through water and a distributor disc that quench the flashback, with a non-return valve below and a relief valve on top. They protect bulk and plant acetylene lines.

On every IIGAS acetylene plant, a wet-type water-seal arrestor sits at the generator outlet as the first line of defence, and a dry-type arrestor with uniflow valves guards the cylinder-charging manifold.

What causes a flashback?

• ✓Lines not purged before lighting, or wrong working pressures
• ✓A hot refractory or workpiece igniting the mixture
• ✓Sparks — including static and debris strikes in ducting
• ✓Nozzle blockage folding the flame back into the torch
• ✓Leaks anywhere in the gas-management system

The IIGAS (KIGL-FBA) range

IIGAS builds four model families so there is an arrestor for every gas, pressure and connection, from DN6 to DN150, threaded or flanged:

Where to fit a flashback arrestor

Fit an arrestor as close to the flame as possible — and on both the fuel-gas and the oxygen line. Where that is not practical, protect the main pipeline, the gas bank or manifold, and the cylinder itself. Every arrestor should be tested for gas tightness and gas return at least once a year by a qualified person.