Flame Arrester Functions and Terminology

We have created Glossary of Flame arrester Terms with the most commonly used terminology for the flame arrester components of the vapor control business. These should help you in learning more about our arresters.
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Glossary of Terms

Components of A Detonation Flame Arrester
  • Flame Arrester Element (matrix) - The portion of a deflagration arrester or detonation arrester comprised of parallel spaced plates, packed ceramic or steel bed, stacked or rolled expanded metal or crimped metal windings. The element provides the heat sink and mechanical barrier to flame passage. The flame arrester element is mounted within the flame arrester element housing.
  • Flame Arrester Element Housing - The portion of a deflagration arrester or detonation arrester that houses the arrester element (matrix) and that provides sealing surface between the flame arrester element assembly and the flame arrester end sections.
  • Flame Arrester Element Retainer – Is a mechanism for retaining and sealing the flame arrester matrix within the flame arrester element housing.
  • Flame Arrester Element Assembly – The flame arrester element housing containing the flame arrester matrix and retaining mechanism.
  • Flame Arrester End Section - The Flanges that mate to the pipe that the Arrester is designed to fit and are usually attached to a transition section that attaches to a larger interior flange. The Arrester housing assembly is commonly sandwiched between two flame arrester end sections and held together by an array of studs nuts & washers.
Critical Physical Measurements
  • MESG (Maximum Experimental Safe Gap) - Measurement taken by moving two equatorial flanges until the space between them will not allow the combustion to propagate. MESG is dependent on gas composition.
  • HD (Hydraulic Diameter) - Measurement of all sides of a channel that would be exposed to a flame.
  • End-of-Line Flame Arrester- A flame arrester that is mounted at the end of a pipe (flanged or threaded inlet connection) and which vents directly to the atmosphere. The end of line flame arrester functions to stop unconfined deflagrations.
Flames/Flame-front profile/behavior
  • Flame Propagation - The spread of flame from the ignition source through a flammable mixture.
  • Deflagration - Combustion wave that propagates at subsonic velocities by the transfer of heat and active chemical species to the unburned gas ahead of the flame front.
  • Deflagration (Unconfined)- Deflagration in which the expanding combustion products are not confined by any means.
  • Deflagration (Confined)- Deflagration in which the expanding combustion products are confined by physical means.
  • Detonation - A type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations occur in both conventional solid and liquid explosives, as well as in reactive gases.
  • Over-driven Detonation – Sometimes called an Un-stable detonation is a reaction in a combustion wave propagating at supersonic velocity (at or beyond the speed of sound). In a piping system this phenomenon occurs for a relatively short distance after which it will transition into a “stable detonation”, assuming that the piping has not been breached as an explosion.
  • Explosion - a violent and destructive shattering or blowing apart of something due to a sudden increase in pressure as is caused by a detonation or deflagration.
  • Stable Detonation - Flame front propagating through a flammable gas mixture at a velocity greater than the speed of sound and generating a very high differential pressure front and occurs only after an Over-driven detonation has occurred. A stable detonation can theoretically go on for infinity if the enclosure containing did also or never exploded. A stable detonation can never become an over-driven detonation, but an over-driven detonation can become a stable detonation.
  • Flame Stabilization (also called an endurance burn) – If conditions are optimal (gas stream velocity/flame velocity), a flame in a piping system such a flair on top of a stack can migrate to the unprotected side of a flame arrester and stabilize on the face of the arrester element. This will eventually heat the element to the point that the differential temperature of the matrix is no longer sufficient and the flame will pass through (fail).
  • Flame Stabilization Testing - The most recognized flame stabilization testing standard was developed by the US Coast Guard. It is published in the U.S. Code of Federal Regulations, 33 CFR Part 154.Type I and Type II Flame Stabilization Testing. The Detonation Flame Arrestor is subjected to a stabilized flame (also called endurance burn) on the surface of the arrest element until the highest obtainable temperature is reached on the ignited side or until the temperature on the side which is not ignited (protected side) rises 100 Centigrade. The endurance burn is continued using the most severe conditions of flammable mixtures (stoichiometric mixture) and flow rate, for a period of time. And is rated as follows;
    • Type I Detonation Flame Arrestor - Flame passage shall not occur during a two-hour test period.
    • Type II Detonation Flame Arrestor - Flame passage shall not occur for a 15-minute test period.
Gas Groupings
  • The National Electric Code (NEC) groups gases into A, B, C, and D categories depending on how hot the gas burns and the MESG value of the gas.
  • International Electric Code (IEC) groups gases into IIC, IIB, & IIA.
Vapor control
  •  Detonation Flame Arrester products were created in response to environmental regulations (such as The Clean Air Act) which required liquid product storage terminals and hydrocarbon processing plants to control evaporative hydrocarbon emissions from loading and storage operations. This process is called vapor control. Two types of recognized vapor control technologies are commonly used; carbon adsorption vapor recovery and vapor destruction or combustion. Vapor destruction systems include elevated flare systems, enclosed flare systems, burner and catalytic incineration systems, and waste gas boilers. Both systems require flame or detonation flame arresters to maximize safety.
Vapor Compositions
  • Lower Explosive Limit (LEL) - The minimum concentration of gas vapor in air or oxygen below which flame propagation will not occur.
  • Upper Explosive Limit (UEL) - The maximum concentration of gas vapor in air or oxygen above which flame propagation will not occur.
  • Explosive Range (Ignitability Limit)- Concentration of gas vapor in air or oxygen that will ignite and sustain flame propagation.
  • Stoichiometric - Mixture Concentration of gas vapor in air or oxygen which results in complete combustion of all products producing maximum energy for a quantity of vapor. This is considered the worst-case condition for potential ignition, flame intensity, and propagation. All testing is done at stoichiometric air/gas concentrations.
  • Flashpoint - The minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid.