16FTAconstructionDefinetheTOP event inaclearandunambiguousway.Shouldalwaysanswer:Whate.g.,"Fire"Wheree.g.,"intheprocessoxidationreactor"Whene.g.,"during normal operation"Whatarethe immediate,necessary,and sufficientevents and conditions causing theTOPevent?ConnectviaAND-orOR-gateProceedinthiswaytoanappropriatelevel(=basicevents)Appropriatelevel:IndependentbasiceventsEventsforwhichwehavefailuredataNTNU-TrondheimNorwegian University ofScienceand Technologywww.ntnu.edu
16 FTA construction Define the TOP event in a clear and unambiguous way. Should always answer: • What e.g., “Fire” Where e.g., “in the process oxidation reactor” • When e.g., “during normal operation” • What are the immediate, necessary, and sufficient events and conditions causing the TOP event? Connect via AND‐ or OR‐gate Proceed in this way to an appropriate level (= basic events) Appropriate level: • Independent basic events • Events for which we have failure data
17FTAsymbolsSymbolDescriptionLogic gatesOR-gateAThe on-gate indicates that the outputevent A occurs if any of the inputevents EroccurEEAND-gilteThe AND-gate indicates that the out-put event A occurs only when all theinput eveints Er occur at the sametimeE,EzEInput eventsBasic eventThe Basic event represents a ba-sic equipment failure that requiresno further development of failurecausesUndeveloped eventThe Undeveloped event representsan event that is not examined fur-ther because information is unavail-able or becatise its consequence isinsignificantDescriptionComment rectangleThe Comment rectangle is for sup-plementary informationTransfer symbolsTransfer-outThe Transfer-ouit symbol indicatesthat the fault tree is developed fur-ther at the occurrence of the corre-NTNU-Trondheimsponding Transfer-in symbol福Norwegian University ofTransfer-inScience and Technology公www.ntnu.edu
17 FTA symbols
18FTA constructionTOPevent=NowaterfromfirewatersystemValveCausesforTOPevent:VF=ValvefailureG1=NooutputfromanyofthefirepumpsG2=NowaterfromFP1Firepump1Firepump2G3=NowaterfromFP2EngineFP1FP2FP1=failureofFP1EF=Failure of engineFP2=FailureofFP2NTNU -Trondheim莎NorwegianUniversityofScience and Technologywww.ntnu.edu
18 FTA construction TOP event = No water from fire water system Causes for TOP event: VF = Valve failure G1 = No output from any of the fire pumps G2 = No water from FP1 G3 = No water from FP2 FP1 = failure of FP1 EF = Failure of engine FP2 = Failure of FP2
19FTAconstructionNowaterfromfirepumpsystemOValveblocked,orNowaterfromfailtoopenthetwopumpsNowaterfromNowaterfrompump1pump2FailureofFailureofFailureofFailureofpump1enginepump2engineFPFP2NTNU-TrondheimEF-Norwegian University ofScience and Technologywww.ntnu.edu
19 FTA construction
20FTAanalysisAcut setinafaulttree isa setofbasiceventswhose(simultaneous)occurrenceensuresthattheTOPeventoccursA cut set is said tobeminimal if the set cannotbereduced without loosing itsstatus asa cutsetTheMethodforObtainingCUtSets(MOCUS)canbeusedtoidentifyallminimalcutsetsinafaulttree.NTNU-TrondheimNorwegian University ofScienceandTechnologywww.ntnu.edu
20 FTA analysis A cut set in a fault tree is a set of basic events whose (simultaneous) occurrence ensures that the TOP event occurs A cut set is said to be minimal if the set cannot be reduced without loosing its status as a cut set The Method for Obtaining CUt Sets (MOCUS) can be used to identify all minimal cut sets in a fault tree