Flame arresters protect systems subject to explosion hazards. They sit at the opening of an enclosure or on the connecting pipe of a system of enclosures. Their job is simple, which is to allow flow but prevent the transmission of flame.

Potentially explosive gas / air mixtures can form around tanks and processing equipment. They could ignite. Protective devices are required for safe handling in dangerous atmospheres across industrial applications.

In modern process plants, vapours need to be disposed of in an environmentally friendly manner. They are incinerated according to air pollution control regulations, and explosive mixtures are sent to an ignition source during operation. These are particular hazards that must be countered with special measures.

Early flame protection used gravel pots on fuel tanks. The gravel stopped explosions from entering storage tanks or connected lines. However, it had two serious drawbacks: non-reproducible flame-arresting capability and high pressure losses.

In 1929, a new development replaced loose gravel with wound corrugated metal strips. Combined with a patented shock absorber, this design stopped detonative combustion processes in the pipe with the lowest possible pressure loss. This became the PROTEGO® Detonation Detonation Explosion, die sich mit Überschallgeschwindigkeit fortpflanzt, gekennzeichnet durch eine Stoßwelle. Flame Arrester, developed by Robert Leinemann. He went on to found Braunschweiger Flammenfilter GmbH in 1954.

PROTEGO® Flame Arresters operate on the principle of flame quenching in narrow gaps.
When a mixture ignites in a gap between two walls, the flame spreads towards the non-combusted mixture. The expansion in volume of the combusted mixture pre-compresses the non-combusted mixture and accelerates the flame. Heat is then dissipated in the boundary layer and transferred to the large surface of the gap length compared to the gap width. By cooling the product below its ignition temperature, the flame is extinguished.

The gap width and gap length of the flame arrester element determine its extinguishing ability:

• The narrower and longer the gap, the greater the extinguishing effectiveness
• The wider and shorter the gap, the lower the pressure loss

PROTEGO® designs balance these two conditions. Special design features such as the patented Shock Wave Guide Tube Effect (SWGTE) and the shock absorber enable superior flow with minimum pressure loss.
 

Deflagration is an explosion that propagates at subsonic velocity. Three types exist:

• Atmospheric deflagration: occurs in open air without a noticeable increase in pressure
• Pre-volume deflagration: occurs in a confined space, such as within a vessel, initiated by an internal ignition source
• In-line deflagration: an accelerated explosion within a pipe, moving along its axis below the speed of sound

Stabilised burning is the even, steady burning of a flame stabilised at or close to the flame arrester element. Short-time burning lasts for a specific period. Endurance burning continues for an unlimited period.

The position of the deflagration-to-detonation transition (DDT) zone depends on several factors. These include operating pressure, operating temperature, pipe diameter, pipe configuration, test gas, and explosion group. It must be predetermined by experiments in each case.

Flame Arresters are categorised by combustion process and installation type:
 

• Static dry flame arresters are based on the FLAMEFILTER® principle of flame quenching in narrow gaps, using wound corrugated metal strips.

• Static liquid seal flame arresters use liquid barriers to stop incoming deflagrations or detonations from entering protected components. Two types exist. The liquid product flame arrester uses the product itself to form the seal. The hydraulic flame arrester breaks the flow of an explosive mixture into small bubbles flowing through water.

   

The location of installation determines the protective task:

Explosion Groups and MESG

Different gases have different flame propagation capacities. They are categorised into explosion groups according to their hazard level. The standard for this is the MESG, or Maximum Experimental Safe Gap. It is a characteristic number measured in the laboratory for the flame propagation ability of the product. Explosion groups use reference substances including methane, propane, ethene, and hydrogen.

Flame arresters tested under standard conditions are approved for use at temperatures up to 60°C (140°F) and a pressure of 1.1 bar (15.9 psi). Higher operating temperatures or pressures require special examination.