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1、FunctionalsafetyEngineering-LayersofProtectionLayersofProtectionAnalysisFaultPropagationContextEventTreeMethodLayersofProtectionDefinitionLOPAEventTreeInitiatingEvnentsandFailureRatesExampleofLayersofProtectionFaultPropagationmodellingAnalyzetheChainofeventsthatleadstoana
2、ccidentControlSystemFailsOperatordoesnotrespondproperlyMechanicalrelieffailedOverpressureEventInitiatingeventLayersofProtectionAnalysis-LOPAAvariantofEventTreeAnalysisMorestructuresLikeeventtreeanalysis,theinitiatingeventstartthechainofeventsBranchesarelayersofprotectionC
3、onsideronlytwooutcomeAccidentNoEventLOPAVersionofEventTreePL2,failsPL1,failsPL3,failsAccidentQuantifyusingmultiplications;alllogicalANDsEx,ColumnRuptureLOPADrawtheLOPAdiagramforfollowingsituationsConsequenceoftheaccident=>fireduetodistillationcolumnrupturehasarootcauseofl
4、ossofcoolingwaterLayersofprotectionOperatorrespondtoalarmsandstopstheprocessProcessgenerallydesignedtowithstandlossofcoolingwaterThecolumnhasapressurereliefvalveSourceofignitionarecontrolledintheprocessareaEx:ColumnruptureLOPALOPACalculationsProceedaswitheventtree,butonly
5、needtocalculatethefrequencyofaccidentResultingaccidentfrequencyisinitiatingeventfrequencymultipliedbyPFDofallprotectionlayersExampleCoolingwaterfailurefrequencyis0,5/yearProtectionlayersOperatorresponsefailurePFD=0,15Reliefvalvefailure–PFD=0,07Processdesigninadequate–PFD=
6、0,01Ignitionsourcecontacted–PFD=0,3Ex:ColumnRupture,LOPAF=0,5/y*0,15*0,01*0,07*0,3=1,58E-5peryearFailureRateQuantificationHistoricalreliabilitydataspecifictoyourinstallationisbest,butoftendifficulttogetPlantmaintenanceandSISfunctiontestdatabyequipmenttypeIndustryaverageda
7、tagroupedbyequipmenttypeSomeexpertjudgmentisstillinevitableUsingMaintenanceandFunctionTestDataCompaniesusuallykeepmaintenancelogsIEC61511requiresfunctiontestinganddocumentationofresultsFunctiontestdatausedtoapproximatefailurerate:SimpleEquationforpointestimateoffailurerat
8、e:λ=#Failures/TotalUnitofOperationλ=FailureratePFDfromFailureRatePFDdependsonfailurerate,failure
