NFPA68Standard on Explosion Protection by Deflagration Venting 2023 NFPA
IMPORTANTNOTICESANDDISCLAIMERSCONCERNINGNFPASTANDARDS NFPA codes standards remended practices and guides (NFPA Standards) of which the document contained hereinis one are devloped through aconsensus standards development proces approedby he American National Standards Institute.This proces brings together volunteers representing varied viewpoints and interests to achieve consensus onfire and other safety issues.While the FPAadministers the proces and establishes rules to promote fairness n the development of consensus it does not independently test evaluate or verify the accuracy of any information or the soundness of any judgments contained in NFPA Standards. The FPA dilaimsliability forany ersonal injury propert oroher amage of aynature whatsee whetherpcialiniretconsquental rpenatordrectlrindireclyreultingfrom thepblication of or reliance on FPA StandardsThe FPA also makes no guaranty or warranty as to the accuracy or pleteness of any information published herein. In issuing and making FPA Standards available the NFPA is not undertaking to render professonal or ther person or entity to someone else.Anyone using this document should rely on his or her own independent judgmentor as appropriate seek the acice of a petent professional indetermining the exercise of reasonable care in any given circumstances. TheFPAhasnopowernordoeitundertaketopoliceornforcepliance withthe contentsofPA Standards. Nor does the FPA list certify tes or inspect products designs or installations for pliance with this documentAny certification or other statement of pliance with the requirements of this document shall not be atributable to the NFPA and is solely the responsibility of the certifier or maker of the statement. REMINDER:UPDATINGOFNFPASTANDARDS Users of NFPA codes standards remended practices and guides (*NFPA Standards") should be aware thatthee documentmaybesupereded ataytimebythissuance f aewdiionma amended with the issuance of Tentative Interim Amendments (TlAs) or be corrected by Errata. It is intended that throughregularrevisionsandamendmentsparticipans in theNFPA standards development proces consider the then-current and available information on incidents materials technologies innowations and methods as these develop over time and that NFPA Standards reflect this consideration.Therefore any previous edition of this document no longer represents the current NFPA Standard onthe subjectmatter adressed.FPA encourages the use of themost current edition of any NFPA Standard [as it may be amended by TIA(s) or Errata] to take adtvantage of current experience and understanding. An official NFPA Standard at any point in time consists of the current edition of the document including any issued TIAs and Errata then in effect. To determine whether an NFPA Standard has been amended through the issuance of TIAs or corrected by Errata visit the *Codes & Standards* section at ww.nfpa.org CoyrihFPAFxlsnPAFrclaordsbiingring nosb
ADDITIONALIMPORTANTNOTICESANDDISCLAIMERSCONCERNINGNFPASTANDARDS Updating of NFPA Standards Users of FPA cods stanards remnd practices and guides (NFPA Stanards) should be amare that e docuenmaybe upesededat anytme by the ssance faneweitionmaybe anedith t iance oTentati paticipanintheFPAstandardsdlopment procesconiderthe thenurrent andailableinfomatio nnidens Interim Amendments (TIAs) or be corrected by Erata. It is intended that through regular revisons and amendments matrialchlitnanhdstlpran hatPAal considerationhrfore an preiou ditin ofthisdcumtolongerrprents thcurentFPAStandardnh sitmattraFArgthrdianyPASadasitmayan bTA(s）rEatato takaantage fct exprinandstadingAnicialFPAaatanypoitin time consists of the current edition of the document including any isd TIAs and Erata then in effect. "Codes & Stancards” scction at .nfpa.org. To determine whether an NFPA Standard has been amended through the issuance of TLAs or corrected by Errata visit the Interpretations of NFPA Standards A statement writn or oral that is not pocced n accordance with Section 6f the Regulatons Gweing th Development o NPA Standars shall not be considered the official position of NFPA or any of is Committees and shall ot be considered to be nor be relied upon as a Formal Interpretation. Patents The FPA does not ake an position with resectto the alidity of any patnt rights refrenced in relatd t or aserted n connection with an NFPA StandardTheusers ofNFPA Sandands bear thesole responsibility for etemining the validit of any sach paten rights as wellas the risk of infringementf such righs and the NFPA disclaimsliabilty for th infringement of any patent resulting from the use of or reliance on NFPA Standlards. NFPA ahersto thepoliy othAmericanationalStana Iti (ANS)regaingteincsinof patn American National Standards (the ANSI Patent Policy) and hereby gives the folowing notice puruant to that polic: NOTICE: The user's attention is called to the posibility that pliance with an NFPA Standard may reqire use of an inention covered by patent rights. NFPA takesno position as to thealidity of anysuch patnt rights or as towhcther such patentrighcostitinential patclaer thAPatnoliIfinconetinwiththANSIPat Policy a patent holderhasfiled a stamt of willinges to grat lienss under these rights n reasonabl and noniscriminatory tms andconditons toapplicants dsiring toobinsach a licnc copisf such fledsatments canb obained on requst from NFPA For further infomation contact the NFPA at the adres listed helo. Law and Regulations appliable lams and these documens may not be constraed as doing so. puliat icode ar rcmmdd pactices and gide nten tuge ationthat i nt ince ith Copyrights hthnlasdlni tn NFPA does not waive any rights in copright to these documents practices andmthodB makig these ocment aailal fr and adptinby publicathorits and prkate urs th Lse ofNFPA Sanars forregulatory puposesshould e accolishe through aloptionbreferenTh te “adoptin by referencc mcans the citing of title edition and publishing information only. Any dletions additions and changes deired by theadopting authority shoul be noted separat in the aopting nrmt Inorder to asist NFPA in folloing thusesmad ofisdoumentsadoping authorities arerequested tonotiy theFPA Aention:Scrtary Standards Coucil) in writing of such use. For technical asistance and questions concerning acloption of NFPA Standards contact NFPA at the address belowc. For Further Information goeingiscodeandstandelopmnt proccninginatin nthpcresfrreutingFomal All questions or other munications relating to FPA Standlards and all requests for infomation on NFPA procedures InerprttsfpringimntsanfpingisintAain Batterymarch Park PO. Box 9101 Quincy SA 02269-9101; email:sds_adinf@enfpa.org. renlmoPAaae tthattnt thecretartanard CilPA For more infomation about NFPA visit the NFPA wehsite at wwnfpaorg AlI NFPA codes and standards can be vieed at no cost at .nfpa.org/docinfo. Copyrighi C NFPAFor excluse use on NFPA Free Access platlorm Not for distribution downioading. or printing. For inquiries contact custservnipa.org. To reporr unauthorized use contacl legal@nlpa.org.
68-1 Copsright O 2022 National Fire Protection Association°. All Rights Reserved. NFPA°68 Standard on ExplosionProtection byDeflagrationVenting 2023 Edition This citinoNFPA ndExplsiPrtiobDtiingwaspreparedby te Technical Comittee onExploionProttionSstemIwsisd by theStandarlsCocil on Noxember 29 2022 with an effective date of December 19 2022 and supersedes all previous editions. This ecdition of NFPA 68 was approwed as an American National Stanard on December 19 2022. Origin and Development of NFPA 68 in1945iPA8TES954maranwsla NFPA 6S ExPt bDefVig statdtastna staa with NFPA 68Gide fo Exple ting hich brought together all thebest available information on the fnlamentals and paramters of cxplosioms the lata developed by smallscal tts the inteprtati thrultsf those testsand theusefvents anentcuresthatwerecurentat the timc.Th infomaionwasthnrelated orleofthmbveraiorecolatonshich were u frmanyasSmef tvens thatwere degneduing thos lof thm functioned well while others were never put to the test. Beginning in 1954 extensive cxperimentation was carried out in Great Britain and Germany and adled to the existing information.The US. Brcan of Mines also did some work in thisarea. However the work was not pleted bccause the group invoed was reassigned to diferent programs. In 1974 NFPA 68 was revised and the work done in Great Britain and Gemany was incladed with thehopethatthfmaind idamansfrcalatingentrtiswithagreat degr ofaccrac than that prwided btherleofthmh.h1978reisnncldd sutantal data that were more valuable in dlesigning explosion relief vents. In 1979 the miee began a major efforto rewrite te guide in rder to incorporate the results of the test work donc in Gcrmany. In addition the 1988 cdition titled Guide for liting Defgtiontineri txtthatmorelearxplained thearis paramt that aft the venting of deflagrations. The 1994 edition of NFPA 68 was pletely rewriten to more clearly explain the principles of document without changing the venting methodology.The thnast of this revision was to improwe the venting deflagrations. Revisions to cach chapter improwed the organization of information within the The1998cdiionincedupattilgytoheconsstenwithurret ital practi.wfmtinasanthfsftdtsallatnmhfr those ffcts and the effects of vent discharge. The reision alo incorporated the weak roof-o- she joint design as a mcans of venting silos and bins and prwidled new information on cxplosions in clongated vesels. It also clarified the prwisions for securing restraint panels. Thc 2002 cdiion represented a lete reison of the guide and incldedupat and enhanced treamentfrdeflagratinventing deigfrsts andhridmtureThrevisinalo incldnwvent igqutinhaseuponthemethoolgy deelopedbyFactory ul ResearchCorratinnadiionotgneralizecorrlatin for dstsrnemethod All desiggilieframixerembindiingehptand tedt was cahatetheffets fvent dutspartallmesvent panlneriand initiall leated re. revised in accordance with the NFPA Menl f Syle for NFPA Tchniral Committe Decmms. NFPA and Ntial Fie Ptecti Aciati are rgistd ademr ofte National Fie Pectio Aciatin Qcy Maache 0210. Copyrighi NFPAFor excluse use n NFPA Free Access platlormNot for distribution，downicading.or prining For inquiries contact custservnpaorg.To repor unauthorized use conacl legal@nlp.rg.
68-2 EXPLOSION PROTECTION BYDEFLAGRATION VENTING Tc 2007ditin rrentd alete isoncling a change fromgud stanad.T wtand id StdExlPtbeftnpiandryqirmnthigcatall maintenanc and use of devices and sstems to vent bustion gases an presures from deflagrations. The Comitee incorporated aew chapter on erformancbased desig thatenabed uss to presentaltmatie lsign methoairqifoasandistrsranfrixTCtteai Comittppisttcqnngithchgtqisflla the gencralized correlation for dusts on the hasis of a resview of additional experimental data. That resiew cnabled the inetia patiam nill atd prs an vent duts T Comie al add aw chapt nptin ad maintenance. Thc 201dition intocdreisd calculatnmthodfrventing of deflagratsfgasmtresTechaptn venting of deflagrations in dust mixtures was revised to adres differences between translating vent panels and hinged vent panels to permit sub atmospheric initial presures and to incorporate new rescarch on the entrainment of accumulated dust in a bilding ew scctions adresed bucket leators and grain silos and new annex material prowided guidance on designing vent ducts and estimating the funcamental burning velocity of a fuel. In te2018iineqirmntwasadathalsfrcrtinmtldsthKalwasinna eemller than1mAnatwasad o ti thraic diamteforrectanglarcloeThchap on venting gas mixture and mist deflagrations was reorganized to clarify the order and applicahility af the various afjustments andcorrectionstoreqiredventarcaAnewanex was added toimplementthequations and calulation procedures inclding partia ffcsThereqiremen for detrmining wererelaced with reqirment for detmining P and the cquations to determine the turbulent flame enhancement factor were revised. Thc chapern vening dst and hyrid mixe lgratios was also reorganizd in ordr ofintnde executin.The cqtionrtiningthventareafrlatdrashc rasreedndanmleallatias tmodinglfllinrf filter was ardedl. Requirements for the use of plastic buckets in bucket elevators were mowed from the annex to the body of the standard. For the2023 ition tefirhallan azard istancereqirmens forgaseand duss haebnbinedandmd intoChaptfconisteinaplicaionTh paal lecalasfrbthassandshabenrevis accot frsolid jctsrecingthopnair ailablfrmixingnd tccoutfr psbldstconcetatins belo theorstcase concentratinshfunametalbminglcityastheanex haebeenupaedhaedn current anailable cata and an annex on vent sizing for hydrogen mistures has been added. 2023 Edition CoyrihNFPAFoxlusenFPAFrecs plaotrdstbiningr priing For inquiries contact custservnipa.org.To reporr unauthorized use contacl legal@nlpa.org.