What Is a Flame Arrestor? Standards Guide
A flame arrestor (also spelled flame arrester) is a passive safety device that allows gas to pass through but stops flame propagation. It works by absorbing heat from the flame front through a matrix of narrow channels, cooling the gas below its auto-ignition temperature and quenching the combustion reaction. Flame arrestors are installed on storage tank vents, flare lines, and process piping to prevent external ignition sources from reaching flammable atmospheres inside equipment.
Working Principle
The flame arrestor element consists of tightly packed metal plates, crimped ribbons, or wire mesh that create hundreds of small passages. When a flame enters these passages, the large surface area of the metal absorbs heat from the combustion gases. If the channel diameter is smaller than the maximum experimental safe gap (MESG) for the gas, the flame cannot sustain itself and extinguishes.
| Gas Group (IEC 60079-20-1) | MESG (mm) | Example Gases |
|---|---|---|
| IIA | > 0.90 | Methane, propane, butane |
| IIB | 0.50 - 0.90 | Ethylene, hydrogen sulfide |
| IIC | < 0.50 | Hydrogen, acetylene |
The arrestor element must be rated for the specific gas group. A Group IIA arrestor will not stop a hydrogen (Group IIC) flame.
Types of Flame Arrestors
| Type | Location | Protection Against | Standard |
|---|---|---|---|
| End-of-line (deflagration) | At tank vent opening | Atmospheric ignition traveling into the tank | API 2028, ISO 16852 |
| In-line deflagration | In piping, close to ignition source | Deflagration (subsonic flame) in piping | ISO 16852 |
| In-line detonation | In piping, any distance | Detonation (supersonic flame) and deflagration | ISO 16852 |
| Pre-volume detonation | Between pipe and vessel | Detonation transitioning from pipe to volume | ISO 16852, EN 12874 |
Selection Criteria
| Parameter | Requirement |
|---|---|
| Gas group | Must match or exceed the gas group of the process fluid |
| Flame type | Deflagration only, or deflagration + detonation |
| Installation distance | End-of-line: at vent; In-line: L/D ratio determines deflagration vs. detonation rating |
| Pressure drop | Clean element: typically 0.5-5 mbar; fouled element: significantly higher |
| Temperature rating | Must withstand sustained burn (endurance burn) without element failure |
| Pipe size | Matched to piping; typically 2” to 24” |
| Material | Body: carbon steel or stainless steel; Element: SS 316, Hastelloy |
Maintenance
The narrow channels in flame arrestor elements are prone to fouling from condensate, polymerization products, corrosion, or particulate. A fouled element increases pressure drop and may impair venting capacity, leading to tank over-pressure or vacuum collapse. Regular inspection and cleaning (or element replacement) are required.
| Maintenance Item | Frequency |
|---|---|
| Pressure drop monitoring | Continuous (differential pressure transmitter) or monthly manual check |
| Visual inspection | Every 6-12 months (sooner in fouling services) |
| Element cleaning/replacement | When pressure drop exceeds manufacturer limits |
| Endurance burn testing | Per manufacturer recommendation after sustained fire event |
Flame arrestors work in conjunction with pressure/vacuum relief valves on storage tanks. The relief valve protects against over-pressure; the flame arrestor prevents flame ingress through the vent opening. Both must be sized for the same venting capacity per API 2000.
Understanding the LEL and UEL of process gases is critical when specifying flame arrestors, as the device must be effective across the entire flammable range.
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