1、68 Standard on Explosion Protection by Deflagration Venting 2018 See ALERT NFPAISBN: 978-145591896-6 (PDF) ISBN: 978-145591897-3 (eBook) IMPORTANT NOTICES AND DISCLAIMERS CONCERNING NFPA STANDARDS NOTICE AND DISCLAIMER OF LIABILITY CONCERNING THE USE OF NFPA STANDARDS NFPA codes, standards, recommen
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31、t at www.nfpa.org/docinfo.68-1 NFPA and National Fire Protection Association are registered trademarks of the National Fire Protection Association, Quincy, Massachusetts 02169. Copyright 2017 National Fire Protection Association . All Rights Reserved. NFPA 68 Standard on Explosion Protection by Deag
32、ration Venting 2018 Edition This edition of NFPA 68, Standard on Explosion Protection by Deagration Venting, was prepared by the Technical Committee on Explosion Protection Systems. It was issued by the Standards Council on November 10, 2017, with an effective date of November 30, 2017, and supersed
33、es all previous editions. This document has been amended by one or more Tentative Interim Amendments (TIAs) and/or Errata. See “Codes & Standards“ at www.nfpa.org for more information. This edition of NFPA 68 was approved as an American National Standard on November 30, 2017. Origin and Development
34、of NFPA 68 NFPA 68, Standard on Explosion Protection by Deagration Venting, started out as a tentative standard in 1945, titled NFPA 68T, Explosion Venting Standard. In 1954, the temporary standard was replaced with NFPA 68, Guide for Explosion Venting, which brought together all the best available
35、information on the fundamentals and parameters of explosions, the data developed by small-scale tests, the interpretation of the results of those tests, and the use of vents and vent closures that were current at the time. The information was then related to “rules of thumb” vent ratio recommendatio
36、ns, which were used for many years. Some of the vents that were designed using those rules of thumb functioned well, while others were never put to the test. Beginning in 1954, extensive experimentation was carried out in Great Britain and Germany and added to the existing information. The U.S. Bure
37、au of Mines also did some work in this area. However, the work was not completed because the group involved was reassigned to different programs. In 1974, NFPA 68 was revised, and the work done in Great Britain and Germany was included with the hope that the new information would provide a means for
38、 calculating vent ratios with a greater degree of accuracy than that provided by the rules of thumb. The 1978 revision included substantial data that were more valuable in designing explosion relief vents. In 1979, the committee began a major effort to rewrite the guide in order to incorporate the r
39、esults of the test work done in Germany. In addition, the 1988 edition, titled Guide for Venting of Deagrations , contained rewritten text that more clearly explained the various parameters that affect the venting of deagrations. The 1994 edition of NFPA 68 was completely rewritten to more clearly e
40、xplain the principles of venting deagrations. Revisions to each chapter improved the organization of information within the document without changing the venting methodology. The thrust of this revision was to improve the user friendliness and adoptability of the guide and to clarify this complex te
41、chnology. The 1998 edition introduced updated terminology to be consistent with current industrial practice. New information was added on the effects of vent ducts, calculation methods for evaluating those effects, and the effects of vent discharge. The revision also incorporated the “weak roof-to-
42、shell” joint design as a means of venting silos and bins and provided new information on explosions in elongated vessels. It also claried the provisions for securing restraint panels. The 2002 edition represented a complete revision of the guide and included updated and enhanced treatment for deagra
43、tion venting design for dusts and hybrid mixtures. The revision also included new vent design equations based upon the methodology developed by Factory Mutual Research Corporation. In addition to the generalized correlation for dusts were new methods to evaluate the effects of vent ducts, partial vo
44、lumes, vent panel inertia, and initially elevated pressures.EXPLOSION PROTECTION BY DEFLAGRATION VENTING 68-2 2018 Edition All design guidelines for gas mixtures were combined into a single chapter, and the document was revised in accordance with the NFPA Manual of Style for NFPA Technical Committee
45、 Documents. The 2007 edition represented a complete revision, including a change from guide to standard. The new standard, titled Standard on Explosion Protection by Deagration Venting, provided mandatory requirements for the design, location, installation, maintenance, and use of devices and system
46、s to vent combustion gases and pressures from deagrations. The Committee incorporated a new chapter on performance-based design that enabled users to present alternative design methods to satisfy the requirements for gas and mist mixtures, for dusts, and for hybrid mixtures. The Committee also revis
47、ed the generalized correlation for dusts on the basis of a review of additional experimental data. That review enabled the Committee to support revisions to the basic equation, along with changes to the equations for low-inertia vent closures, panel inertia, partial volume, initially elevated pressu
48、res, and vent ducts. The Committee also added a new chapter on inspection and maintenance. The 2013 edition introduced a revised calculation method for venting of deagrations of gas mixtures. The chapter on venting of deagrations in dust mixtures was revised to address differences between translatin
49、g vent panels and hinged vent panels, to permit sub atmospheric initial pressures, and to incorporate new research on the entrainment of accumulated dust in a building. New sections addressed bucket elevators and grain silos, and new annex material provided guidance on designing vent ducts and estimating the fundamental burning velocity of a fuel. In the 2018 edition, a requirement has been added to adjust the K Stvalues for certain metal dusts if the K Stvalue was obtained in a vessel smaller than 1 m 3 , and an equation has been added to determine the hyd
