5_定量火灾风险评估

5.1OverviewInthischapter,quantitativefireriskassessmentisintroduced.Thetermquantitativefireriskassessmentreferstoanassessmentinvolvingnumericalquantificationsnotonlyoftheprobabilityafirehazard,orfirescenariooccurring,butalsotheconsequencesofthatfirehazardorfirescenario.Bymultiplyingthenumericalvaluesofprobabilityandconsequenceeachfirescenarioisgivenanumericalfireriskvalue.Byaccumulatingthesumoftheriskvaluesfromallprobablefirescenarioswecanobtainanoverallfireriskvalue.Theoverallfireriskvaluecanbeusedforcomparisonswiththoseofalternativeorcode-compliantfiresafetydesigns.Ingeneraltherearetwowaystoperformsystematicquantitativefireriskassessmentsasfollows:1.byusingachecklisttogothroughalistofpotentialfirehazardsandthequantitativeassessmentoftheirfirerisks;2.byusinganeventtreetogothroughasetofpotentialfirescenariosandthequantitativeassessmentoftheirfirerisks.Inboththesemethods,thevaluesfortheprobabilityandconsequenceparametersareobtainedfromstatisticaldata,iftheyareavailable,orfromsubjectivejudgment,ifsuchdataarenotavailable.(仅在我们本课程的讲解中，采用了统计或主观估计的方式，火灾的结果还可以通过确定性的分析计算获得)5.2ChecklistMethodAswasdiscussedinChapter4,thechecklistmethodemploysthecreationofachecklistofpotentialfirehazardsandtheconsiderationoffireprotectionmeasures,eitherinplaceortobeadded,toarriveatanassessmentofthefirerisks.Thecreationofachecklistofpotentialfirehazardsallowsasystematiccheckofpotentialfirehazardsthatareinplace.Thelistingoffireprotectionmeasuresalongsidewiththepotentialfirehazardsallowsaquickcheckofanysafetydeficienciesandanyneedtoprovideadditionalfireprotectionmeasurestominimizetherisk.Thechecklistmethod,therefore,isanenumerationofpotentialfirehazards,fireprotectionmeasures,eitherinplaceortobeadded,andtheassessmentoftheresidualfirerisks.Itisusedtoidentifyanydeficienciesandanycorrectivemeasuresneededtominimizethefirerisks.Itdoesnotinclude,however,theconsiderationofthelogicaldevelopmentoffireevents,whichwillbediscussedinSection5.3usinganeventtree.AnexampleofachecklistmethodemployingquantitativefireriskassessmentisshowninTable5.2.ThisisthesameexamplethatwasusedinChapter4,exceptthatquantitativeassessmentisemployedhereratherthanqualitativeassessment.Thisexamplelooksatapotentialfirehazardinthelivingroomofahouseandtheconsiderationofanumberofadditionalfireprotectionmeasurestominimizetherisk.Obviously,therecouldbemanypotentialfirehazardsinahouse.Acompletefireriskassessmentwouldinvolvetheidentificationofallpotentialfirehazardsandtheconsiderationofvariousfireprotectionmeasurestominimizetherisk.Atypicalhouseusuallyhassomefireprotectionmeasures,suchassmokealarms.Additionalfireprotectionmeasureswouldlowertheriskfurther.SimilartotheexampleinChapter4,thisexampleconsiderssixdifferentcombinationsofthreeadditionalfireprotectionmeasures.Thethreeadditionalfireprotectionmeasuresare:(1)nosmokingmaterial(suchascigarettes)inthelivingroom,(2)sprinklers(3)regularevacuationdrills.Eachofthethreefireprotectionmeasureshasanimpactoneithertheprobabilityoffireoccurrenceortheconsequenceofafireoccurrence.Forexample,themeasureof‘nosmokingmaterialinthelivingroom’wouldhaveanimpactonloweringtheprobabilityoffireoccurrence;whereasthemeasuresof‘sprinklers’and‘regularevacuationdrills’wouldhaveanimpactonloweringtheconsequenceofafireoccurrencebysuppressingorcontrollingthefireorbyallowingtheoccupantstoevacuatemorequickly.Itshouldbeemphasizedthatthisisjustanexampletoshowhowquantitativefireriskassessmentcanbecarriedoutusingachecklistmethod.Therearenostandardchecklistmethodsinfireriskassessment.InTable5.2,theinherentfireriskvalues(withoutthehelpofanyfireprotectionmeasures)wereobtainedpreviouslyinChapter3.Table3.2inChapter3showsthattheprobabilityoffireoccurrenceinCanadianhouseswas1.75×10−3fires/house/yearin1996andthepercentageofthesehousefiresthatoccurredinthemainlivingareawas8.5%.Usingthesefigures,theprobabilityoffireoccurrenceinthemainlivingareainCanadianhousesin1996was,therefore,1.75×10−3×8.5%or1.49×10−4fires/house/year.Table3.2inChapter3alsoshowsthattheconsequenceoffiresoriginatinginthemainlivingareain1996was43.2×10−3deaths/fire,andtheresultantrisktolifefromthesefireswas6.43×10−6deaths/house/year.ThesepreviouslyobtainedinherentriskvaluesareusedinthepresentexampleandareshowninTable5.2.TheinherentriskvaluesinTable5.2werebasedonfirestatisticswhichincludedsomefireprotectionmeasures,suchassmokealarms,thatwererequiredbyregulations.Ifadditionalfireprotectionmeasuresareputinplace,theinherentfireriskswouldbefurtherreduced.InTable5.2,theimpactofeachofthesixfireprotectioncombinationsisassessedusingaresidualmultiplicationfactoroftheinherentvaluesoftheprobabilityortheconsequence.Thisallowsthefireprotectionengineersandtheregulatorstoassesstheimpactofthesefireprotectionmeasuresbasedontheirassessmentsofthereductionoftheinherentvalues.Onewaytoassesstheimpactoffireprotectionmeasuresisthroughtheuseofstatisticalinformation,iftheyareavailable.Unfortunately,suchinformationisnotalwaysavailable.Theinformationmaybeinthedatabasesofcollectionagencies,butnotnecessarily