LOPAArticlesThefollowingwerethetwodefinitivepapersonthetopicofLayerofProtectionAnalysis(LOPA).TheCCPStextbookandourcoursenotebookprovidethemostup-to-dateexplanationonLOPA,butthesetwoarticlesareexcellentstartingpoints.1997CCPSConferenceandWorkshopProceedingsLayerofProtectionAnalysis:ANewPHAToolAfterHAZOP,BeforeFaultTreeAnalysisCopyright1997AmericanInstituteofChemicalEngineers3ParkAvenueNewYork,NewYork10016-5991Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recording,orotherwisewithoutthepriorpermissionofthecopyrightowner.AIChEandCCPSaretrademarksownedbytheAmericanInstituteofChemicalEngineers.ThesetrademarksmaynotbeusedwithoutthepriorexpresswrittenconsentoftheAmericanInstituteofChemicalEngineers.TheuseofthisproductinwholeorinpartforcommercialuseisprohibitedwithoutpriorexpresswrittenconsentoftheAmericanInstituteofChemicalEngineers.ToobtainappropriatelicenseandpermissionforsuchusecontactScottBerger,212-591-7237,scotb@AIChE.org.Itissincerelyhopedthattheinformationpresentedinthisvolumewillleadtoanevenmoreimpressivesafetyrecordfortheentireindustry;however,theAmericanInstituteofChemicalEngineers,itsconsultants,CCPSSubcommitteemembers,theiremployers,andtheiremployersofficersanddirectorsdisclaimmakingorgivinganywarrantiesorrepresentations,expressorimplied,includingwithrespecttofitness,intendedpurpose,useormerchantabilityand/orcorrectnessoraccuracyofthecontentoftheinformationpresentedinthisdocument.Asbetween(1)AmericanInstituteofChemicalEngineers,itsconsultants,CCPSSubcommitteemembers,theiremployers,theiremployersofficersanddirectorsand(2)theuserofthisdocument,theuseracceptsanylegalliabilityorresponsibilitywhatsoeverfortheconsequencesofitsuseormisuse.AIChECopyright1967-2006LayerofProtectionAnalysis:ANewPHAToolAfterHazop,BeforeFaultTreeAnalysisArthurM.(Art)Dowell,IIISeniorTechnicalFellow,HazardAnalysis,RohmandHaasCompany,POBox1915,DeerPark,TX77536-1915E-Mail:chedowe@rohmhaas.com(firstpublishedin“InternationalConferenceandWorkshoponRiskAnalysisinProcessSafety”,1997,CCPS/AIChE)ABSTRACTHowdoyouknowhowmanysafeguardsareenoughtopreventormitigateachemicalprocessimpactevent?WhatintegritylevelshouldbechosenforaSafetyInstrumented(interlock)System(SIS)?BuildingontheCCPS(CenterforChemicalProcessSafety)GuidelinesforSafeAutomationofChemicalProcesses,thispaperdescribesanewPHA(ProcessHazardAnalysis)toolcalledLayerofProtectionAnalysis(LOPA).StartingwithdatadevelopedintheHAZOP(HAZardandOPerabilityanalysis),andsuggestedscreeningvalues,themethodologyaccountsfortheriskreductionofeachsafeguard.Themitigatedriskforanimpacteventcanbecomparedwiththecorporation'scriteriaforunacceptablerisk.Additionalsafeguardsorindependentprotectionlayerscanbeadded.TherequiredintegritylevelforanySISsafeguardscanbedetermined.LOPAfocusestheriskreductioneffortstowardtheimpacteventswiththehighestrisks.Itprovidesarationalbasistoallocateriskreductionresourcesefficiently.LOPAcanbeeasilyappliedaftertheHAZOP,butbeforefaulttreeanalysis.IntroductionIntheSafetyLifeCycleoutlinedinISA-S84.01-1996(ISA,1996),stepsareincludedtodetermineifaSIS(SafetyInstrumentedSystem)isneededandtodeterminethetargetSIL(SafetyIntegrityLevel)fortheSIS.TheSILisdefinedbythePFD(ProbabilityofFailureonDemand)oftheSIS(1).S84.01givesguidanceonbuildinganSIStomeeta...
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