5-定量火灾评估

Chapter5

QuantitativeFireRiskAssessment5.1OverviewInthischapter,quantitativefireriskassessmentisintroduced.Thetermquantitativefireriskassessmentreferstoanassessmentinvolvingnumericalquantificationsnotonlyoftheprobabilityafirehazard,orfirescenariooccurring,butalsotheconsequencesofthatfirehazardorfirescenario.Bymultiplyingthenumericalvaluesofprobabilityandconsequenceeachfirescenarioisgivenanumericalfireriskvalue.Byaccumulatingthesumoftheriskvaluesfromallprobablefirescenarioswecanobtainanoverallfireriskvalue.Theoverallfireriskvaluecanbeusedforcomparisonswiththoseofalternativeorcode-compliantfiresafetydesigns.Ingeneraltherearetwowaystoperformsystematicquantitativefire

riskassessmentsasfollows: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)5.2ChecklistMethodAswasdiscussedinChapter4,thechecklistmethodemploysthecreationofachecklistofpotentialfirehazardsandtheconsiderationoffireprotectionmeasures,eitherinplaceortobeadded,toarriveatanassessmentofthefirerisks.Thecreationofachecklistofpotential

firehazardsallowsasystematiccheckofpotentialfirehazardsthatareinplace.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,butnotnecessarilyintheirpublishedreportswhichusuallyshowgeneralinformationandnotthespecificinformationthatisrequiredforfireriskassessment.Ifnosuchinformationisavailable,subjectivejudgmentmayberequired.Otherwise,theuseoffundamentalandrationalapproachtoquantificationisrequired,includingtheuseofmathematicalmodelingoffiredevelopmentandoccupantevacuation,whichwillbediscussedinlaterchapters.Forexample,thereissomestatisticalinformationonthebenefitsofrestrictingsmokingmaterialandofinstallingsprinklers,butnotmuchinformationonthebenefitsofimplementingregularevacuationdrills.NFPAstatisticsshowthatapproximately7%offiresinhomesarecausedbysmokingmaterials(NFPAFireStatistics,2006)andapproximately14%ofthesefiresoccurinthemainlivingarea(Hall,2006).Therefore,7×14%orapproximately1.0%offiresinhomesarefiresthatbothoriginateinthemainlivingareaandarecausedbysmokingmaterial.IfthesefirestatisticscanalsoapplytoCanadianhomes,thenrestrictingsmokingmaterialinthemainlivingareawouldreducethenumberoffireoccurrenceinthemainlivingareafrom8.5%(seeTable3.2inChapter3)to7.5%ofhousefires.Thereductionoffireoccurrencefrom8.5to7.5%is12%.Thecorrespondingresidualmultiplicationfactoroftheinherentprobabilityvaluebyrestrictingsmokingmaterialistherefore0.88,whichisshowninTable5.2.NFPAstatisticsalsoshowthat,basedon1989–1998data,thereductionindeathsinoneandtwofamilydwellingswithsprinklersis51%whencomparedwithsimilardwellingswithoutsprinklers(KimberlyandHall,2005).Thecorrespondingresidualmultiplicationfactoroftheinherentconsequencevaluebyinstallingsprinklersistherefore0.49,whichisshowninTable5.2.Withregardtothebenefitsofimplementingregularevacuationdrills,thereisnoinformationonthereductionofdeathratesthatiseasilyavailable.Forthisexample,wehavetomakeanassumption.Weknowthatifregularevacuationdrillsarecarriedout,therewillbefasterevacuationsandthereforelowerdeathrates.Forthisexample,letusassumeareductionofthedeathrateby60%.Theresidualmultiplicationfactoroftheinherentconsequencevaluebyimplementingregularevacuationdrillsistherefore0.40,whichisshowninTable5.2.Inactualfireriskassessments,thisvalueneedstobejudgedandagreeduponbetweenthefireprotectionengineersandregulators.Table5.2alsoshowsthattheimpactsontheconsequenceofinstallingsprinklersandofimplementingregularevacuationdrillsaremultipliedtogether.Thatis,thebenefitsofsprinklersandofregularevacuationdrillshaveacombinedresidualconsequencefactorof0.49×0.40or0.20.Themultiplicationoftheresidualfactorsisbasedontheargumentthateachfireprotectionmeasurereducestheresidualdeathratebyacertainpercentageinsuccession.Thedeathrateisfirstreducedbythesprinklerssuppressingtheseverityofthefires,andthenfurtherreducedbyfasterevacuationoftheoccupants.ThereductionoftheriskvaluesofthesixcombinationsofadditionalfireprotectionmeasuresisshowninTable5.2.Theresidualriskmultiplicationfactorsrangefrom0.88to0.20.Thequantificationoftheriskvaluesallowsnumericalcomparisonsofthevariousfireprotectionoptions.Thisisnotthecaseinqualitativefireriskassessment(Table4.4inChapter4).ItshouldbeemphasizedagainthatthevaluesinTable5.2areselectedasanexampletoshowhowsuchachecklistmethodcanbecarriedout.Thesevalueswereselectedfromavailablestatisticalinformationwithoutmuchin-depthsearch.Asmorestatisticalinformationbecomesavailable,moreextensivesearchanddetailedanalysisareneededtofindthecorrectvalues.Inactualfireriskassessments,thesevaluesneedtobecarefullyselectedandagreeduponbystakeholders.Inactualfireriskassessments,thesevaluesneedtobecarefullyselectedandagreeduponbystakeholders.Subjectivejudgmentoftheprobabilitiesandconsequencesprovidesaquickassessmentofthepotentialfirerisks.Morefundamentalandrationalapproachestoquantification,includingtheuseofmathematicalmodelingoffiredevelopmentandoccupantevacuation,willbediscussedinlaterchapters.5.4Event-TreeMethodAneventtreeisanotherwaytoidentifypotentialfirehazards,assesstheirprobabilitiesandconsequences,andarriveatriskvalues.Differentfromthechecklistmethod,aneventtreeshowsmorethanalistofpotentialfirehazardsandfireprotectionmeasuresfortheassessmentoftheprobabilities,consequencesandeventuallytheriskvalues.Theevent-treemethodinvolvestheconstructionofaneventtreeofvariousfirescenariossubsequenttotheinitiationofafirehazard,asdescribedinChapter2.Thefirescenariosprovidemorelogicalinformationforthejudgmentofprobability,consequenceandriskvalues.Anexampleofanevent-treemethodemployingquantitativefireriskassessmentisshowninFigure5.1.ThisisthesameexamplethatwasusedinChapter4,exceptthatquantitativeassessmentisemployedratherthanqualitativeassessment.InFigure5.1,thebranchingtodifferenteventsdependsonthesuccessorfailureofthefireprotectionmeasuresinplace.Thisexamplelooksatonefirehazardinanassumedapartmentbuildingandtheconsiderationofanumberofadditionalfireprotectionmeasurestominimizetherisk.Thesameeventtreecanbeconstructedformorehazardsandmorefireprotectionmeasures.Acompletefireriskassessmentwouldinvolvetheidentificationofallpotentialfirehazardsandtheconsiderationofvariousfireprotectionmeasurestominimizetherisk.Atypicalapartmentbuildingusuallyhassomefireprotectionmeasures,suchasfireresistantconstructionandfirealarms.Additionalfireprotectionmeasureswouldlowertheriskfurther.ThisexampleconsidersthesamesixdifferentcombinationsofthreeadditionalfireprotectionmeasureswhichwereconsideredinthechecklistmethodinSection5.3.Thethreeadditionalfireprotectionmeasuresare:(1)nosmokingmaterial(suchascigarettes)intheapartments,(2)sprinklersand(3)regularevacuationdrills.Eachofthethreefireprotectionmeasureshasanimpactoneithertheprobabilityoffireoccurrenceortheconsequenceofafireoccurrence.Forexample,themeasureof‘nosmokingmaterialintheapartment’wouldhaveanimpactonloweringtheprobabilityoffireoccurrence;whereasthemeasuresof‘sprinklersand‘regularevacuationdrills’wouldhaveanimpactonloweringtheconsequenceofafireoccurrencebysuppressingorcontrollingthefireorbyallowingtheoccupantstoevacuatemorequickly.Aswasinthediscussionofthechecklistmethod,theeventtreeinFigure5.1isonlyanexampletoshowhowaneventtreecanbeusedforquantitativefireriskassessment.Thedescriptionofeacheventisthejudgmentforthisexampleonly.Otherapplicationsmayhavedifferentdescriptions.Thedescriptionsallowmoretransparentdiscussionsandagreementsamongstakeholders.Inanevent-treemethod,theprobabilityofeachfirescenarioiscalculatedusingtheprobabilityvaluesofsuccessorfailureofimplementingthefireprotectionmeasuresthatareassociatedwiththescenario.Someoftheseprobabilityvaluescanbeobtainedfromstatistics,iftheyareavailable.Forexample,NFPAstatisticsshowthat,basedonthe1999–2002data,sprinklersinapartmentbuildingshaveareliabilityof96%ofactivatingandcontrollinglargefiresthatshouldactivatesprinklers(KimberlyandHall,2005).Notethatsmoulderingfiresandsmallfiresmaynotactivatesprinklers.Ifnosuchinformationisavailable,thensubjectivejudgmentmayberequired.Forexample,thereisnostatisticalinformationthatcanbeeasilyfoundontheprobabilityofsuccessorfailureofimplementinga‘nosmokingmaterial’plansothattherewillbealowerrateoffireoccurrence.Withoutsuchstatisticalinformation,wehavetomakeanassumption.Letusassumeforthisexamplethattheprobabilityofsuccessofimplementinga‘nosmokingmaterial’planis70%.Similarly,thereisnostatisticalinformationthatcanbeeasilyfoundontheprobabilityofsuccessorfailureofimplementinga‘regularevacuationdrills’planinapartmentbuildingssothattheoccupantswouldknowwhattodoincaseofafirealarmandwouldthereforeevacuatemorequicklythanwithoutsuchdrills.Letusassumeforthisexamplethattheprobabilityofsuccessofimplementinga‘regularevacuationdrills’planis80%.Inrealriskassessments,thesevaluesneedtobecarefullyanalysedandagreeduponbyfiresafetyengineersandregulators.Successisdefinedasthatthefireprotectionplanactuallyworks.ThescenarioprobabilitiesareshowninFigure5.1.Forexample,ScenarioAhasaprobabilityof2.40×10−03,whichistheproductof0.30(failureprobabilityofimplementinga‘nosmokingmaterial'plan)×0.04(failureprobabilityof‘sprinklersystem’)×0.20(failureprobabilityofimplementinga‘regularevacuationdrills’plan).Intheevent-treemethod,theprobabilityoffireoccurrenceforeachfirescenarioisassessedbasedontheinherentrateoffireoccurrenceandtheimpactofvariousfirepreventionmeasurestominimizethisinherentrateoffireoccurrence.InFigure5.1,theimpactofeachofthefireprotectionmeasuresontheinherentrateoffireoccurrenceisassessedusingaresidualprobabilitymultiplier.在事件树方法中，每一个火灾场景出现的可能性基于火灾发生的固有频率和各种火灾安全措施对降低火灾发生固有频率的影响来确定。如图5.1，每一种火灾保护措施对火灾发生固有频率的影响通过一个残余可能性因子来体现（residualprobabilitymultiplier）。Thisallowsthefireprotectionengineersandregulatorstoassesstheimpactofthesefireprotectionmeasuresbasedontheirassessmentsofthereductionoftheprobabilityoffireoccurrence.Someoftheseresidualprobabilitymultiplierscanbeobtainedfromstatistics,iftheyareavailable.Ifnosuchinformationisavailable,thensubjectivejudgmentmayberequired.火灾安全工程师基于火灾安全措施对火灾发生可能性的减缩情况来确定火灾安全措施的影响。某些残余可能性因子可由统计数据获得，如果没有可用的统计数据，则需要进行主观判断。比如没有“在公寓中使用阻燃材料”对减少火灾发生影响的统计数据。

我们只能对此进行假设，在本例中假设“在公寓中使用阻燃材料”与“在建筑中禁烟”对火灾发生可能性的影响相同，其残余可能性因子为0.88(见Table5.2)。即在“在公寓中使用阻燃材料”成功，其结果是将火灾发生的频率下降到其固有频率的0.88。Forexample,thereisnostatisticalinformationthatcanbeeasilyfoundonthereductionoffireoccurrenceofimplementinga‘nosmokingmaterial’planforapartmentbuildings.Withoutsuchstatisticalinformation,wehavetomakeanassumption.Letusassumeforthisexamplethattheresidualprobabilitymultiplierofa‘nosmokingmaterial’planinapartmentbuildingis0.88,thesameasthatforhousefires(seeTable5.2).Thatis,theconsequenceofasuccessful‘nosmokingmaterial’planisthereductionoftherateoffireoccurrenceto0.88ofitsinherentvalue.ThisresidualprobabilitymultiplierforeachfirescenarioisshowninFigure5.1.Forexample,ScenariosA,B,C,D,allwithafailureofimplementingthe‘nosmokingmaterial’plan,havearesidualprobabilitymultiplierof1(noreduction);whereasScenarioE,F,G,H,allwithasuccessofimplementingthe‘nosmokingmaterial’plan,havearesidualprobabilitymultiplierof0.88.每一个火灾场景的这个残余可能性因子在图5.1中显示出来。比如ScenariosA,B,C,D，“在公寓中使用阻燃材料”全部失败，残余可能性因子为1，意味着没有减少火灾的发生；而ScenarioE,F,G,H,“在公寓中使用阻燃材料”成功，具有的残余可能性因子为0.88，即火灾发生的可能性，降低到固有值的0.88。Thatis,theconsequenceofa‘nosmokingmaterial’planisthereductionoftherateoffireoccurrenceto0.88ofitsinherentvalue.Alsoinanevent-treemethod,theconsequenceofeachfirescenarioisassessedbasedontheinherentconsequenceofthefireandtheimpactofthevariousfireprotectionmeasurestominimizetheconsequence.InFigure5.1,theimpactofeachofthefireprotectionmeasuresontheconsequenceisassessedusingaresidualconsequencemultiplier.Thisallowsthefireprotectionengineersandregulatorstoassesstheimpactofthesefireprotectionmeasuresbasedontheirassessmentsofthereductionoftheconsequence.Someoftheseresidualconsequencemultiplierscanbeobtainedfromstatistics,iftheyareavailable.Forexample,NFPAstatisticsshowthat,basedonthe1989–1998data,thereductionindeathsinapartmentbuildingswithsprinklersis81%whencomparedwithsimilarbuildingswithoutsprinklers(KimberlyandHall,2005).Theresidualconsequencemultiplierofasprinklersystemthereforeis0.19.Thatis,theconsequenceofinstallingasprinklersystemisthereductionofthedeathrateperfireto0.19ofitsinherentvalue.Ifnosuchinformationisavailable,thensubjectivejudgmentmayberequired.Forexample,thereisnostatisticalinformationthatcanbeeasilyfoundonthedeathreductionbenefitofimplementinga‘regularevacuationdrills’plan.Withoutsuchstatisticalinformation,wehavetomakeanassumptionagain.Letusassumeforthisexamplethattheresidualconsequencemultiplierofa‘regularevacuationdrills’planis0.40.Thatis,theconsequenceofa‘regularevacuationdrills’planisthereductionofthedeathrateperfireto0.40ofitsinherentvalue.ThisresidualconsequencemultiplierforeachscenarioisshowninFigure5.1.Forexample,ScenarioBhasaresidualconsequencemultiplierof0.40,whichistheproductof1.00(residualconsequencemultiplierofafailedsprinklersystem)×0.40(residualconsequencemultiplierofasuccessful‘regularevacuationdrills’plan).Figure5.1showstheresidualriskvaluesofallthefirescenarioswhicharebasedonthesuccessorfailureofthreefireprotectionmeasures.Theprobabilityvalueofeachfirescenarioistheproductoftheindividualprobabilityvaluesofallthebranchesthatareassociatedwiththatscenario.Theresidualprobabilitymultiplierofeachscenarioistheproductoftheindividualprobabilitymultipliersofallthefireprotectionmeasuresthatareassociatedwiththatscenario.Theresidualconsequencemultiplierofeachscenarioistheproductoftheindividualconsequencemultipliersofallthefireprotectionmeasuresthatareassociatedwiththatscenario.

Finally,theresidualriskmultiplierforeachscenarioistheproductof(scenarioprobability)×(residualprobabilitymultiplier)×(residualconsequencemultiplier).Forexample,ScenarioEhasascenarioresidualriskmultiplierof4.93×10−03,whichistheproductof5.60×10−03(scenarioprobability)×0.88(residualprobabilitymultiplier)×1.00(residualconsequencemultiplier).InFigure5.1,themultiplicationoftheresidualmultipliersisbasedontheargument,asdiscussedinSection5.3,thateachfireprotectionmeasurereducestherateoffireoccurrence,ortheseverityofthefire,orthedeathrateperfire,insuccessionbyacertainpercentage.Itshouldbeemphasizedagainthatthevaluesintheexampleareselectedbytheauthorasanexampletoshowhowsuchevent-treemethodcanbecarriedout.Inrealriskassessments,thesevaluesneedtobecarefullyanalyzedandagreeduponbyfiresafetyengineersandregulators.Subjectivejudgmentoftheprobabilitiesandconsequencesprovidesaquickassessmentofthepotentialfirerisks.Morefundamentalandrationalapproachestoquantification,includingtheuseofmathematicalmodelingoffiredevelopmentandoccupantevacuation,willbediscussedinlaterchapters.Differentfromthechecklistmethod,theevent-treemethodallowsthesummationoftheriskvaluesofallthefirescenariosintoonesingleriskvalueforthewholesystem.Thisallowsdirectcomparisonsoftheriskvaluesofvariousfiresafetydesignoptions,includingcode-compliantdesigns.Figure5.1showsthecombinedresidualriskmultiplierofimplementingthesethreefireprotectionmeasuresis1.06×10−1.Thatis,theresidualriskisreducedto10.6%ofitsinherentvalueTheinherentfireriskvaluesofapartmentbuildingscanbeobtainedfromstatistics.Forexample,inCanada,the1996Canadianfirestatistics(CouncilofCanadianFireMarshalsandFireCommissioners,1996)showthatthetotalnumberoffiredeathsinapartmentbuildingsinthatyearwas88.Also,the1996Canadiancensusdata(StatisticsCanada,1996)showthatthetotalnumberofapartmentunitsunderthecategoryof‘apartment5ormorestoreys’was979470.Theriskofdyinginanapartmentunit,therefore,was88deathsdividedby979470apartmentsor8.98×10−5deaths/apartment/year.Comparethisriskvaluewiththatofhousefiresof1.94×10−5deaths/house/year(seeChapter3,Section3.3.3),theriskofapartmentfiresismuchhigher.Partoftheexplanationscouldbethatthefirerisksinahousearecausedbyfiresoriginatinginthesamehouse,whereasthefirerisksinanapartmentunitarecausedbyfiresoriginatingfromallapartmentunitsinabuilding.5.5SummaryQuantitativefireriskassessmentisanassessmentinvolvingnumericalquantificationsofboththeprobabilityofoccurrenceofafirehazard,orfirescenario,andtheconsequenceofthatfirehazardorfirescenario.Themultiplicationofthenumericalvaluesofprobabilityandconsequencegiveseachfirescenarioanumericalfireriskvalue.Thecumulativesumoftheriskvaluesfromallprobablefirescenariosgivesanoverallfireriskvalue.Theassessedriskcanberisktolife,lossofpropertyandsoon.Quantitativefireriskassessmentallowsanumericalcomparisonoftheoverallfireriskvaluesofdifferentfiresafetydesignsinabuilding.Italsoallowstheassessmentofequivalencybycomparingthefireriskofanalternativefiresafetydesignwiththatofacode-compliantdesign.Thereareingeneraltwowaysofconductingsystematicquantitativefireriskassessments:(1)usingachecklisttogothroughalistofpotentialfirehazardsandthequantitativeassessmentoftheirfirerisks;(2)usinganeventtreetogothroughasetofthepotentialfirescenariosandthequantitativeassessmentoftheirfirerisks.Withinthechecklistmethod,therearespecificmethodsthathavebeendevelopedbyvariousorganizationsfortheirownuse.Oneparticularoneiscalledtheriskindexingmethodwhichuseswell-definedschedules,ortables,toratetherisks.Inboththechecklistandevent-treemethods,theoutcomeisalistofpotentialfirehazards,orfirescenarios,andtheirassessedfireriskvalues.Summationofalltheseindividualriskvaluesgivesanoverallfireriskvalueinabuildingthatcanbeusedforcomparisonswiththoseofalternativefiresafetydesigns.Itshouldbenotedthattherearesemi-quantitativeassessments,whereonlyoneofthetwoparameters(probabilityorconsequence)isassessedquantitatively.Theotherparameterthatisnotassessedquantitativelyisassessedqualitatively(seeChapter4).Thistypeofassessmentisneitherqualitativenorquantitative.Inthischapter,wediscussedonlyquantification