Document KJwgkLQrDk2kVN5r1NRner0Xr

572 IRVING HARTMANN 3. Coal pneumatic cleaning plants (No. 653)' 4. Plastics industry .(No. 654) ; 5. Flour and feed mills (No. 610 j 6. Pulverized-fuel systems (No. 60) j 7. Confectionery plants (No. 657) ! 8. Spice-grinding plants (No. 656) I 9. Starch factories (No. 61A) j 10. Sugar- and cocoa-pulverizing systems (No. 62) j 11. Sulfur dust (No. 655) 12. Terminal grain elevators (No. 61B) i 13. Suggested good practices for the application of suction and venting for the jcontr<5|| of dust in grain elevators and storage units (No. 661) 14. Country grain elevators (No. 64) 16. Wood-flour manufacturing establishments (No. 662) 16. Woodworking plants (No. 663) 17. Aluminum processing and finishing (No. 65) Other pertinent NFPA standards and pamphlets are: 1. Standard for fire and explosion prevention by inerting (No. 69) 2. Pamphlets on combustible metals 3. Guide for explosion venting (No. 68) 4.Pamphlet on static electricity 5. National electrical code Important recommendations in these codes include: 1. All possible ignition sources should be eliminated from equipment contaiS ing flammable dust and from areas surrounding such equipment. This means] prohibiting"open"flames"'or'lightH"an.d_smaking;''avoidin'g_the"use"of''el'e'ctrtt^% gas cutting or welding equipment for repair work, unless dust-producing machirf ery in that part of the plant is shut down and the vicinity is entirely dust-frlffl grounding all machinery capable of producing static electrical sparks; providing conduits^for electric wiring and locating switches and motors outside, or: usinj dustproof types; adhering strictly, in installing wiring and electrical equipmen. to the rules of the National Electrical Qode pertaining to hazardous location^ using magnetic separators to prevent entrance of hazardous materials to1 dug! grinding mills; using nonferrous blades in fans through which dust passes; an) avoiding the use of high-speed shafting and belts wherever possible. 2. Buildings should be constructed to avoid the collection of dust pn be ledgesj-and;Tq.theq;suj,fa;ces,-;particularly'overhead--Good-'housekeeiJing-is-arpff esscsntialjnj.pr^vepting dust accumulation and dissemination. In .removal , qf|m from exposed surfaces, vacuum cleaning is preferable, although soft push broofi| may be used, without serious hazard; for highly flammable dusts industrial vacuu:^ cleaners--.of.*approved. design. are recommended....Use of. compressed., air, for-adus) removal is highly dangerous. Buildings in which flammable dusts are produce stored should be detached units pf incombustible construction, including itisiM partitions; and hazardous areas within buildings should be separated by su] stantial fire walls. 3. Equipment wherein dust clouds may be produced, such as grinders,' C<||| veyors, elevators, or collectors, should be as dust-tight as possible; it should Ms . HAZARDS OF COMBUSTIBLE DUST 573 he smallest practical interior volume; and it should be constructed strong enough ^withstand explosion pressures from dust. 4. Properly designed and proportioned and properly distributed vents, in the [form of unrestricted openings if possible; hinged windows, panels, or light wall construction in rooms; and the use of release diaphragms or other vent closures ^.equipment will release explosion pressures without damage. In recent years much work on venting has been performed by the Bureau of Stines18"20 in explosion galleries of several sizes. The pressure-release requirements M, various dusts have been determined with unrestricted vents (Figure 8), and the fillative effectiveness of numerous diaphragms was studied.18 Many of the data RATIO OF RELIEF AREA TO VOLUME OF ENCLOSURE, SQ. FT. PER 100 CU. FT. Hlgure 8. Effect of unrestricted relief vents on pressures developed by dust explosions, in 1 cubic foot test gallery. (Courtesy Bureau of Mines, U. S. Department of the Interior.) ^^ventihg through ducts of various shapes and sizes, effects of bends in ducts, Secondary vents in ducts, flame speeds in ducts, quenching of explosions in ducts, land quenching during the incipient stages of ignitions have not been published yet, ffd'the research is in fact still being continued. "1. Hartmann and J. Nagy, V. S. Bur. Mines Kept. Invest. No. 3924, 1946. ** I. Hartmann, Pressure release for dust explosions, Natl. Fire Protect. Assoc. Quart., 40, jH3 (July, 1946). " J. Nagy, J. E. Zeilinger, and I. Hartmann, U. S. Bur. Mines Repl. Invest. No. 4636, 1950. JS.also I. Hartmann, Chem. Eng. Progr., 53, 107M (1957); I. Hartmann and J. Nagy, Ind. mg. Chem., 49, 1734 (1957). "1 *.. . i-