Flame arrester
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
The uses of a flame arrester include:
- Stopping the spread of an open fire
- Limiting the spread of an already occurred explosion
- Preventing potentially explosive mixtures from igniting
- Confining fire within a controlled location
- Stopping the propagation of a flame traveling at subsonic velocities
Some common objects that have flame arresters are:
- Fuel storage tank vents
- Fuel gas pipelines
- Safety storage cabinets for paint, aerosol cans, and other flammable mixtures
- The exhaust system of internal combustion engines
- The air intake of marine inboard engines
- Davy lamps in coal mining
- Overproof rum and other flammable liquors.[2]
- Portable plastic gasoline containers[4][5]
Principles
A flame arrester functions by absorbing the heat from a flame front traveling at subsonic 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.[6] 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 to 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.[7]
References
- ^ a b c Arpentinier, Philippe; Cavani, Fabrizio; Trifiro, Ferrucio (2001). The Technology of Catalytic Oxidations. Vol. 2. Paris: Editions TECHNIP. p. 748. ISBN 2-7108-0777-7.
- ^ a b McManus, Neil (1998). Safety and Health in Confined Spaces. CRC Press. p. 147. ISBN 1-56670-326-3.
- ^ 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" (PDF). The United States Chemical Safety and Hazard Investigation Board: 47. Archived from the original (PDF) on 2006-09-22. Retrieved 2007-11-19.
{{cite journal}}: Cite journal requires|journal=(help) - ^ Stevick, Glen (2011). "Failure Analysis and Prevention of Fires and Explosions with Plastic Gasoline Containers". Journal of Failure Analysis and Prevention. 75 (11): 455–465. doi:10.1007/s11668-011-9462-z.
"A flame arrester works by removing heat from a flame and keeping the temperature of the fuel on the other side of the arrester below its ignition point. The flame arrester mesh breaks the flame into many flamelets, and the heat of these flamelets is transferred to the walls of the mesh". (The link is to the abstract only: A free full-text link is on Google Scholar.)
- ^ ASTM F3326 Standard Specification for Flame Mitigation Devices on Portable Fuel Containers
- ^ 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
- ^ 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" (PDF). The United States Chemical Safety and Hazard Investigation Board: 29. Retrieved 2014-04-10.
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See also
