DS 7-76 Prevention and Mitigation of Combustible Dust ... - FM Global

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7-76 Combustible Dust Explosion Page 16 FM Global Property Loss Prevention Data Sheets 2.3.3.3.6 Flame Front Diverter or Explosion Diverter a) Do not install this device upstream of an air-moving fan because an explosion originating upstream of the diverter will propagate past the diverter. b) Do not use explosion diverters in air streams that have a significant loading of abrasive dust that would eventually erode through the pressure-relieving diverter cover. c) Do not use explosion diverters for hybrid mixtures where the flammable vapors exceed the LEL. d) Flame-front diverters built commercially or inhouse according to design guidelines in Figure 6 are acceptable. e) Ensure a prefabricated rupture disk used for the pressure-venting opening has a release pressure equal to or less than 0.1 barg (1.5 psig). f) Where the diverter is constructed in house and a prefabricated rupture disk is not used, ensure the device meets the following criteria: 1. When providing a solid cover, ensure it will quickly and easily release during an explosion. 2. When providing a rupture membrane, use a weak weather-resistant material, such as aluminum foil or tar paper. 3. Confirm the rupture pressure is at or below 0.1 barg (1.5 psig) by calculations or pressure testing. Base this calculation on the ultimate tensile strength of the material. 2.3.3.3.7 High Speed Abort Gate Fig. 6. Acceptable design parameters for explosion diverters a) Actuate the high-speed abort gate by either pressure detection or infrared explosion detection in the upstream vessel expected to experience the explosion. b) Ensure the detection system and abort-gate responses are fast enough to completely close the abort gate before the dust flame front reaches it. (See Section 3.1.15 for how to estimate the flame front travel time.) ©2008 Factory Mutual Insurance Company. All rights reserved.
Combustible Dust Explosion 7-76 FM Global Property Loss Prevention Data Sheets Page 17 Fig. 7. Explosion diverter Fig. 8. Indoor installation of explosion diverter c) Ensure the abort-gate reset is manual. Automatic reset is not acceptable. 2.3.3.3.8 Double-Dump Valve Provide an interlock to ensure both valves do not open simultaneously. 2.3.3.3.9 Back-Blast Damper Fig. 9. High-speed abort gate This is essentially a check valve that is effective in stopping explosion propagation in the opposite direction of normal flow. Ensure the device is provided with an explosion vent downstream from the normal flow in the system. ©2008 Factory Mutual Insurance Company. All rights reserved.
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DS 7-76 Prevention and Mitigation of Combustible Dust ... - FM Global

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