1、NFPA68 Standard on Explosion Protection by Deflagration Venting 2013 Edition NFPA, 1 Batterymarch Park, Quincy, MA 02169-7471 An International Codes and Standards Organization IMPORTANT NOTICES AND DISCLAIMERS CONCERNING NFPADOCUMENTSNOTICE AND DISCLAIMER OF LIABILITY CONCERNING THE USE OF NFPA DOCU
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29、Protection by Deflagration Venting2013 EditionThis edition of NFPA 68, Standard on Explosion Protection by Deflagration Venting, was pre-pared by the Technical Committee on Explosion Protection Systems. It was issued by theStandards Council on November 27, 2012, with an effective date of December 17
30、, 2012, andsupersedes all previous editions.This edition of NFPA 68 was approved as an American National Standard on Decem-ber 17, 2012.Origin and Development of NFPA 68NFPA 68, Standard on Explosion Protection by Deflagration Venting, started out as a tentative stan-dard in 1945, titled NFPA 68T, E
31、xplosion Venting Standard. In 1954, the temporary standard wasreplaced with NFPA 68, Guide for Explosion Venting, which brought together all the best availableinformation on the fundamentals and parameters of explosions, the data developed by small-scaletests, the interpretation of the results of th
32、ose tests, and the use of vents and vent closures thatwere current at the time. The information was then related to “rules of thumb” vent ratio recom-mendations, which were used for many years. Some of the vents that were designed using thoserules of thumb functioned well, while others were never pu
33、t to the test.Beginning in 1954, extensive experimentation was carried out in Great Britain and Ger-many and added to the existing information. The U.S. Bureau of Mines also did some work inthis area. However, the work was not completed because the group involved was reassigned todifferent programs.
34、In 1974, NFPA 68 was revised, and the work done in Great Britain and Germany wasincluded with the hope that the new information would provide a means for calculating ventratios with a greater degree of accuracy than that provided by the rules of thumb. The 1978revision included substantial data that
35、 were more valuable in designing explosion relief vents.In 1979, the committee began a major effort to rewrite the guide in order to incorporatethe results of the test work done in Germany. In addition, the 1988 edition, titled Guide forVenting of Deflagrations, contained rewritten text that more cl
36、early explained the various pa-rameters that affect the venting of deflagrations.The 1994 edition of NFPA 68 was completely rewritten to more clearly explain the prin-ciples of venting deflagrations. Revisions to each chapter improved the organization of infor-mation within the document without chan
37、ging the venting methodology. The thrust of thisrevision was to improve the user friendliness and adoptability of the guide and to clarify thiscomplex technology.The 1998 edition introduced updated terminology to be consistent with current industrialpractice. New information was added on the effects
38、 of vent ducts, calculation methods for evalu-ating those effects, and the effects of vent discharge. The revision also incorporated the “weakroof-to-shell” joint design as a means of venting silos and bins and provided new information onexplosions in elongated vessels. It also clarified the provisi
39、ons for securing restraint panels.The 2002 edition represented a complete revision of the guide and included updated andenhanced treatment for deflagration venting design for dusts and hybrid mixtures. The revi-sion also included new vent design equations based upon the methodology developed byFacto
40、ry Mutual Research Corporation. In addition to the generalized correlation for dustswere new methods to evaluate the effects of vent ducts, partial volumes, vent panel inertia,and initially elevated pressures. All design guidelines for gas mixtures were combined into asingle chapter, and the documen
41、t was revised in accordance with the NFPA Manual of Style.681NFPA and National Fire Protection Association are registered trademarks of the National Fire Protection Association, Quincy, Massachusetts 02169.The 2007 edition represented a complete revision, including a change from guide to standard. T
42、he new standard,titled Standard on Explosion Protection by Deflagration Venting, provided mandatory requirements for the design, location,installation, maintenance, and use of devices and systems to vent combustion gases and pressures from deflagrations.The Committee incorporated a new chapter on pe
43、rformance-based design that enabled users to present alternativedesign methods to satisfy the requirements for gas and mist mixtures, for dusts, and for hybrid mixtures. The Commit-tee also revised the generalized correlation for dusts on the basis of a review of additional experimental data. Thatre
44、view enabled the Committee to support revisions to the basic equation, along with changes to the equations forlow-inertia vent closures, panel inertia, partial volume, initially elevated pressures, and vent ducts. The Committee alsoadded a new chapter on inspection and maintenance.The 2013 edition i
45、ntroduces a revised calculation method for venting of deflagrations of gas mixtures. The chapteron venting of deflagrations in dust mixtures has been revised to address differences between translating vent panelsand hinged vent panels, to permit subatmospheric initial pressures, and to incorporate n
46、ew research on the entrain-ment of accumulated dust in a building. New sections address bucket elevators and grain silos, and new annex materialprovides guidance on designing vent ducts and estimating the fundamental burning velocity of a fuel.682 EXPLOSION PROTECTION BY DEFLAGRATION VENTING2013 Edi
47、tionTechnical Committee on Explosion Protection SystemsSamuel A. Rodgers, ChairHoneywell, Inc., VA ULuke S. Morrison, SecretaryProfessional Loss Control Inc., Canada SEMichael Davies, PROTEGO, Germany MTodd A. Dillon, XL Global Asset Protection Services,OH IAlexi I. Dimopoulos, ExxonMobil Corporatio
48、n,VA URep. American Petroleum InstituteHenry L. Febo, Jr., FM Global, MA IRobert J. Feldkamp, Nordson Corporation, OH MLarry D. Floyd, BASF/Ciba Specialty ChemicalsCorporation, AL UJoseph P. Gillis, Westboro, MA SEJohn E. Going, Fike Corporation, MO MStanley S. Grossel, Process Safety used synonymou
49、slywith the term vapor.3.3.18* Hydraulic Diameter. A diameter for noncircular crosssections that is determined by 4(A/p), where A is the cross-sectional area normal to the longitudinal axis of the space and pis the perimeter of the cross section.3.3.19* KG. The deflagration index of a gas cloud.3.3.20* KSt. The deflagration index of a dust cloud.3.3.21 Maximum Pressure (Pmax). See 3.3.27.1.3.3.22 Minimum Explosible Concentration (MEC). The mini-mum concentration of a combustible dust cloud that is capableof propagating a deflagration through a uniform mixture
