Flame arrester

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A flame arrester being tested
A flame arrester made for 36 inch pipe that weighed 10 tons.

A flame arrester (also spelled arrestor), deflagration arrester,[1] or flame trap[2] is a device that stops fuel combustion by extinguishing the flame.[3]

Usage and applications

Flame arresters are used:

  • to stop the spread of an open fire
  • to limit the spread of an explosive event that has occurred
  • to protect potentially explosive mixtures from igniting
  • to confine fire within an enclosed, controlled, or regulated location
  • to stop the propagation of a flame traveling at sub-sonic velocities

They are commonly used on:

Principles

A flame arrester (also called a deflagration arrester) functions by absorbing the heat from a flame front traveling at sub-sonic velocities, thus dropping the burning gas/air mixture below its auto-ignition temperature: consequently, the flame cannot survive. The heat is absorbed through channels (passages) designed into an element. These channels are chosen and measured as the mesg (maximum Experimental Safe Gap) of the gas for a particular installation. These passages can be regular, like crimped metal ribbon or wire mesh or a sheet metal plate with punched holes, or irregular, such as those in random packing.[1]

The required size of the channels needed to stop the flame front can vary significantly, depending on the flammability of the fuel mixture. The large openings on a chain link fence are capable of slowing the spread of a small, slow-burning grass fire, but fast-burning grass fires will penetrate the fence unless the holes are very small.[4] In a coal mine containing highly explosive coal dust or methane, the wire mesh of a Davy lamp must be very tightly spaced.

For flame arresters used as a safety device, the mesh must be protected from damage due being dropped or struck by another object, and the mesh must be capable of rigidly retaining its shape during the propagation of a flame front. Any shifting of the individual wires that make up the mesh can create an opening large enough to allow the flame to penetrate and spread beyond the barrier.

On a fuel storage vent, flame arresters also serve a secondary purpose of allowing air pressure to equalize inside the tank when fuel is added or removed, while also preventing insects from flying or crawling into the vent piping and fouling the fuel in the tanks and pipes.

Safety

Flame arresters should be used only in the gas group and conditions they have been designed and tested for. Since the depth on an arrester is specified for certain conditions, changes in the temperature, pressure, or composition of the gases entering the arrester can cause the flame spatial velocity to increase, making the design of the arrester insufficient to stop the flame front ("propagation"). The deflagration may continue downstream of the arrester.[1]

Flame arresters should be periodically inspected to make sure they are free of dirt, insects using it as a nest, or corrosion. The U.S. Chemical Safety and Hazard Investigation Board concluded that an uninspected and badly corroded flame arrester failed to prevent a 2006 explosion at a wastewater treatment plant in Daytona Beach, Florida.[5]

References

  1. ↑ 1.0 1.1 1.2 Arpentinier, Philippe; Cavani, Fabrizio; Trifiro, Ferrucio (2001). The Technology of Catalytic Oxidations 2. Paris: Editions TECHNIP. p. 748. ISBN 2-7108-0777-7. Retrieved November 19, 2007 
  2. ↑ 2.0 2.1 McManus, Neil (1998). Safety and Health in Confined Spaces. CRC Press. p. 147. ISBN 1-56670-326-3. Retrieved November 19, 2007 
  3. ↑ The United States Chemical Safety and Hazard Investigation Board (2005). Investigation Report: Aluminum Dust Explosion, Hayes Lemmerz International-Huntington, Inc, Huntington, Indiana, October 29, 2003. The United States Chemical Safety and Hazard Investigation Board. p. 47. Archived from the original on 2007-10-24. Retrieved 2007-11-19. 
  4. ↑ Do Wire Fences Stop Ground Fires?, JAMES L. MURPHY AND HARRY E. SCHIMKE, U.S. Forest Service Research Note PSW-70, Pacific southwest forest and range experiment station, Berkeley, CA, 1965, http://www.fs.fed.us/psw/publications/documents/psw_rn070/psw_rn070.pdf
  5. ↑ The United States Chemical Safety and Hazard Investigation Board (2007). Investigation Report: Methanol Tank Explosion and Fire, Bethune Point Wastewater Treatment Plant, City of Daytona Beach, Florida, January 11, 2006. The United States Chemical Safety and Hazard Investigation Board. p. 29. Retrieved 2010-02-13. 

See also

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