Flame arresters: how they work and when they are required

Flame arresters are passive safety devices whose mission is to prevent a flame or detonation propagating through a pipe from reaching a vessel, a process or a potentially explosive atmosphere. In applications handling flammable vapours or combustible gases, their correct selection and sizing are as critical as those of any safety valve.

Operating principle

A flame arrester extinguishes the flame by dissipating its heat through a matrix of narrow channels —typically a corrugated stainless steel ribbon element— whose hydraulic diameter is smaller than the MESG (Maximum Experimental Safe Gap) of the gas. As the flame crosses these channels, it loses energy by conduction and radiation faster than combustion can sustain it. The result: the flame is extinguished before it can pass to the other side.

Types according to EN ISO 16852

The harmonised European standard EN ISO 16852 classifies flame arresters according to the type of combustion they must stop and their position in the system:

• In-line deflagration: protect against subsonic flame fronts. They are installed at a limited distance from the ignition source.
• Stable and unstable detonation: capable of stopping supersonic flame fronts. Essential in long lines where deflagration can transition to detonation.
• End-of-line: protect atmospheric vents where an external source (lightning, spark) could ignite the mixture.
• Flame arresters for endurance burning: withstand a stable flame on their surface for a defined time without failing.

When is it mandatory to install one?

Within the European framework, the ATEX 2014/34/EU directive requires flame-propagation protection measures in any equipment intended for areas with explosive atmospheres. In practice, a flame arrester is mandatory on:

• Vents of atmospheric tanks storing flammable liquids (class I and II) connected to atmosphere.
• Vapour recovery lines at loading and unloading bays.
• Flares and acid-gas collection systems in refineries.
• Blowers and gasholders in biogas plants and landfills.
• Vent lines of anaerobic digesters and biomethane storage vessels.

Common mistakes in selection

The most common cause of failure is not an equipment defect but inadequate selection. Before specifying a flame arrester, it is advisable to verify:

• The gas explosion group (IIA, IIB1, IIB2, IIB3, IIC) and its actual MESG, not the standard group's.
• The operating temperature and the product's flash point.
• The allowable pressure drop: an undersized flame arrester can prevent venting during an overpressure event.
• Accessibility for periodic inspection of the flame-arresting element —mandatory under ATEX—.

A properly selected and maintained flame arrester turns an external ignition incident into a non-event for the process.

Conclusion

The flame arrester is one of the few passive barriers that simultaneously protects personnel, the environment and the production asset. Its cost is marginal compared to the risk it mitigates, but it demands technical rigour from selection through to inspection. At Tecnovent we offer flame arresters certified to EN ISO 16852 and ATEX, sized specifically for each application.