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LOPALayerofProtectionAnalysisEr.SrinivasanPremkumarDirector&ChiefProcessSafetySpecialistALARPProcessSafetySolutionsLayerofProtectionAnalysis(LOPA)–IntroductionLOPADisclaimer•Thougheveryefforthasbeentakentoassuretheaccuracyandreliabilityofthecontent,nopartofthecontentshallconstituteastandard,oranendorsement,recommendationordefinitiveguidance.Thecontentisofferedasaguidefortheknowledgeandawarenessonthefundamentalsandfirstprinciples.Nothinginthecontentshallbedirectlyappliedwithoutanindependentprofessionaladvice.Neithertheauthornortheorganizationunderwhichtheauthorisemployedtakesresponsibilityforanyerrorsoromissions.2LOPABhopalIncident3Source:Bhopal.orgOn3December1984,aUnionCarbideplantinBhopal,Indialeakedthedeadlygasmethylisocyanate(MIC)Noneofthesafetysystemsdesignedtocontainsuchaleakwereoperational,allowingthegastospreadthroughoutthecityofBhopalLOPANormalOperation4AtmosphericVentMICInletMICOutletMICStorageTankRefrigerationSystemReliefVentHeaderScrubberKnockoutDrumFlareStackProcessVentHeaderNC(orBlinded)NaOHNaOHforTreatment-3MICstoragetanks-2forstorageand1onstandby-Maxoperatinglevelis50%LOPAOriginalDesignConsiderations5AtmosphericVentMICInletMICOutletMICStorageTankRefrigerationSystemReliefVentHeaderScrubberKnockoutDrumFlareStackProcessVentHeaderNC(orBlinded)NaOHNaOHforTreatmentLayer1(ProcessDesign&OperatingPhilosophy)Layer2(BPCS–TemperatureControl)Layer3(CriticalAlarms&Response)Layer4(Automation–SISorESD)–NoneLayer5(ReliefSystem)Layer6(Flare)Layer7(EmergencyResponse)LOPAWhathappened?6AtmosphericVentMICInletMICOutletMICStorageTankRefrigerationSystemReliefVentHeaderScrubberKnockoutDrumFlareStackProcessVentHeaderNaOHNaOHforTreatmentLOPAWhathappened?7AtmosphericVentMICInletMICOutletMICStorageTankRefrigerationSystemReliefVentHeaderScrubberKnockoutDrumFlareStackProcessVentHeaderNaOHNaOHforTreatmentLayer1(ProcessDesign&OperatingPhilosophy)Layer2(BPCS–TemperatureControl)Layer3(CriticalAlarms&Response)Layer4(Automation–SISorESD)–NoneLayer5(ReliefSystem)Layer6(Flare)Layer7(EmergencyResponse)LOPALayersofProtection–ProcessRelatedHazards8EmergencyResponsePhysicalProtection(post-release)e.g.dikePhysicalProtection(pre-release)e.g.pressurereliefvalveAutomaticShutdownSysteme.g.SIF,ESDCriticalAlarms&OperatorResponseBasicProcessControlSystemProcessDesignLOPAWhatisLOPA?•LOPAisasemi-quantitativeriskassessmenttoolforanalyzingandassessingtherisksofthescenarioswithhigherconsequenceofconcern(e.g.majoraccidentscenarios)–Theriskiscomparedagainstthecompany’srisktolerancecriteria–Iftheriskisatanunacceptablelevel,additionalprotectionlayers(i.e.controlmeasures)areidentifiedandsuggestedforimplementation•Riskisafunctionoflikelihoodandseverity(i.e.consequence)•TheLOPAusesorder-of-magnitudeestimatesfordeterminingthelikelihood•TheseverityistypicallyassessedqualitativelyinreferencetothecompanyRiskMatrixdefinitions–Alternatively,mathematicalconsequenceanalysisresultscanbeusedtoassesstheseverity(ifrequired)•LOPAisoneofthecommonlyappliedtoolsfordeterminingtherequiredSafetyIntegrityLevel(SIL)inaSafetyInstrumentedFunction(SIF)9LOPAScenario-BasedRiskAssessmentTool•LOPAisappliedtothescenario-basedriskassessments•LOPAisappliedtoasingleinitiatingeventandasingleconsequencepair•Thescenariostartswithaninitiatingevent,propagatesthroughthecascadingeventsandotherunfavorableconditionsandresultsinaconseque...