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

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7-76 Combustible Dust Explosion Page 4 FM Global Property Loss Prevention Data Sheets b) Locate dust producing operations in areas separated from different hazard occupancies by construction (dust-tight and explosion-resistant barriers) or distance. c) Minimize chances for dust accumulation by arranging building elements and equipment to reduce the likelihood of dust accumulations. Employ features such as smooth, easily cleaned walls, boxed in or covered horizontal surfaces (beams, joists, etc.), and surfaces sloped a minimum of 60° from the horizontal. d) Where fugitive dust release and accumulation exist in buildings, design the structure to safely vent the potential explosion using damage-limiting construction. e) Locate dust collection and transfer equipment outside, away from important buildings and utilities. f) Construct equipment that processes or transfers combustible particles to contain or safely vent a potential explosion. g) Where explosion venting or containment in equipment is not possible, eliminate the oxygen in the system by inerting, or install an explosion-suppression system. 2.1.6 Practice effective maintenance of production and protection equipment. An effective maintenance program will: a) Identify and eliminate fugitive dust sources continually. b) Test and maintain spark detection and extinguishing systems, explosion isolation devices, and relief vents to ensure they are in working order per manufacturer’s guidelines, or at least monthly. c) Test and maintain metal and non-metal detection and extraction equipment to ensure they are in working order, at least quarterly. d) Check belts and rotating equipment for alignment at least quarterly to prevent these becoming a source of friction heating. e) Lubricate bearings and rotating equipment (fans, blowers, size-reduction equipment) in accordance with manufacturer’s guidelines, or at least quarterly f) Remove accumulated dust on rotating equipment bearings and components to insure free movement and prevent friction heating, at least quarterly. g) Assign accountability and keep accurate records. 2.1.7 Ensure a comprehensive dust fire and explosion awareness program exists at all sites where combustible dust exists either within closed processing systems or as fugitive dust within buildings. Include the following: a) Basic education to promote awareness and understanding of the hazards of combustible dusts b) Instruction of new employees on the particular hazards and on precautions relevant to their departments c) A minimum of annual instruction, drill, and familiarization of the local public fire service and/or internal firefighting teams d) Periodic refresher training for all facility personnel 2.1.8 Strictly control potential dust ignition sources where combustible dusts may be present. a) Ensure all electrical equipment is rated Class II, Division 1 or 2, or Zone 20, 21, or 22 per NFPA 70, the National Electric Code, Articles 500, 502, and 506, as appropriate, or international equivalent. (Refer to Data Sheet 5-1, Electrical Equipment in Hazardous Locations, for additional details regarding area classification and equipment selection.) b) Use a hot work permit system to manage all hot work operations. (See DS 10-3, Hot Work Management, and Hot Work Management Kit, P9601) c) Prohibit smoking and open flames. d) Provide grounding and bonding of metal components with a resistance of less than 1 x 10 6 ohms to ground. (See DS 5-8, Static Electricity.) At least annually, check for continuity of the metal components and security of any bonding connections. ©2008 Factory Mutual Insurance Company. All rights reserved.
Combustible Dust Explosion 7-76 FM Global Property Loss Prevention Data Sheets Page 5 e) Subject all electrical equipment to an initial infrared (IR) scan and then at a frequency as dictated by results and DS 5-20, Electrical Testing. 2.1.9 Prohibit recycling of air material separator exhaust to buildings or rooms, except where either “a” or all of “b through h” apply: a) The return air duct discharges into an area that does not contain fugitive dust, combustible equipment or storage, combustible construction, high-value equipment, or equipment that is critical to production, OR b) Install a filter downstream of the dust air separators that prevents return of dust to the enclosure with a minimum efficiency of 99.9% at 10 microns AND c) Install a device to measure pressure-drop across the filter with an alarm to indicate when the filter needs to be cleaned or replaced AND d) Provide support for the filter with a wire mesh screen or other method that allows the filter to withstand a pressure equal to or exceeding the value of P red for the piece of equipment directly upstream from it AND e) Provide explosion isolation between the building and the last dust collector in the system (the one furthest downstream) AND f) On explosion-isolation system activation, shut down any connected dust- collection equipment AND g) Ignitable vapors, gases, or hybrid mixtures are not involved AND h) The dust-collection system meets the protection requirements in other sections of this data sheet. Where these features are present, the recycling of air material separator exhaust would not cause the building/room to require explosion protection features such as venting, etc. (other factors present in the building/room could create that need, however). 2.2 Room/Building Explosion Hazards 2.2.1 Construction and Location Isolate areas handling combustible dusts from other less hazardous occupancies by separation with construction or distance to minimize damage from the potential explosion or fire. Areas needing isolation would be where fugitive dust is not readily controlled for example, grinding, sanding, sawing, open conveying, filing open bins, etc. Excluded would be for example, rooms containing properly vented dust collectors, spray dryers, fluid bed dryers, etc. In new construction where some fugitive dust is likely, maximizing explosion venting beyond that calculated by DustCalc, can provide future flexibility for process or material changes, and often can be done with little additional cost. 2.2.1.1 Isolate areas handling combustible dusts using the methods listed below in order of preference (also see Figure 1, Table 1): a) Detached outside location at least 50 ft (15 m) away from an important building or facility (Fig. 1, Location 1) b) Along an exterior wall of an important building, preferably at a corner to limit exposure (Fig. 1, Location 2) c) Inside an important building on the first floor, either at an exterior corner or along an exterior wall. Avoid locations on upper floors of multistory buildings. Where above-grade locations are unavoidable, ensure the floor and ceiling of the room have the same pressure resistance as the walls. (Fig. 1, Locations 3 and 4) Where confirmed using DustCalc software, the spacing can be reduced to less than recommended in ″a″ above or Distance X in Table 1. ©2008 Factory Mutual Insurance Company. All rights reserved.
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