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74 主 Konishieta.ljS日ifetyScience53ρ013)73-81
compartmenttotheworkdeck，and(iv)toexplaintheabsenceof anexplosioninthestarboardcompartment，wheretheinitialigni- tionmayhapen.
2.Outlineofacidentaleisureboatexplosion
AsshowninFig.1，theleisureboatthatexplodedhadanoveral lengthof560cm，amaximumwidthof178cm，andaheightof 72cm(bow)，50cm(center)and54cm(stern).Mostoftheboat wasmadefromfiber-reinforcedplastics，butthefueltankwas madeofiron.Theownerpurchasedtheboatin1991.In1993， theownerreplacedarustyfueltankwithonethatwassubse- quentlyusedfor1years，untilthedayoftheexplosioninMarch 201.Atthattime，theownerintentionalyboredholesinthebulk- headsofthecompartmentsinordertoremoveacumulatedsea- waterfromthebottomoftheworkdeckcompartments.Inso doing， he unintentional ly provided pas sages for gasoline vapor fromtheportsidefueltankcompartmenttothestarboardbatery compartmentviatheworkdeckcompartments.Therefore，asgas- olinevaporwascontinuouslyemitedfromthefueltank，alarge amountofgasolinevaporisthoughttohaveacumulatedinthe workdeckcompartmentsandthestarboardbaterycompartment.
Aboatoperator(nottheboatowner)refueledat8:30a.m.on thedayoftheacident.Heput4Lofgasolineinthefueltankin theportsidecompartment.Acordingtohistestimony，hedidnot spilgasolineoutsidethefueltankduringthisoperation.Then， heandhisfamilyboardedandmooredforawhile.At1:13a.m.， inordertomovetheboatagain，hesatonthelidofthestarboard storagecompartmentandpresedthestarterbutonoftheout- boardmotor2or3times.Theexplosionocuredimediately， completelydestroyingtheworkdeckandinflictingseriousinjuries onhisfamily，whoweresitingontheworkdeck.Mysteriously，the explosiondestroyedtheworkdeckexceptforthelidofthestar- boardcompartment，onwhichtheoperatorwassiting.Wewere requestedtoelucidatethemechanismofthisexplosion.
3.Experimentalaparatusandprocedures 3.1.Mock-upboat
Photographsofthemock-upboatareshowninFig.2a-e.The mock-upboatwasconstructedfrom12m mthickplywod.The size of the mock-up boat was 224 c m long， 159 c m wide and 50cmhigh.仁ompartmentsAandBwerepreparedforafueltank andabatery，respectively.CompartmentsCandDrepresentthe workdeckcompartments，whichweredestroyedbytheexplosion. AsshowninFig.2b，compartmentsAandBwereconectedbyan openingthathadalreadybeenmadebyaboatcompanybeforethe acident.CompartmentsAandCwereconectedbyholes，which were made by the boat owner (Fig. 2c)， and similarly， a hole conectedcompa此mentsBand，仁 andcompartmentsCandD，as showninFig.2dande.
Fig.1.A photographoftheleisureboatthatexplodedhadanoverallengthof 560cm，amaximumwidthof178cm，andaheightof72cm(bow)，50cm(日nter) and54cm(stern).
Theconcentrationofgasolinevaporintheboatwasmeasured by a portable hydrocarbon gas detector (RUくEN KEIKI RI-415)， showninFig.2.fAstheRI-415gasdetectorwasspecificalyad- justedfori-butane，itcouldnotmeasuretheconcentrationofgas- oline vapor directly. Therefore， the reading of the RI-415 gas detector(fori-butane)wascalibratedtoindicatetheconcentration ofgasolinevaporwiththeReidmethod，specifiedinJISK2258， which is equivalent to ISO 3007 and ASTM 4953 (Takahashi eta，.l203).Fig.3showstheevaporationcurvesforgasolinevapor measuredbytheRI-415gasdetectorandtheReidmethod.The conversioncurvefortheRI-415gasdetector(fori-butane)togas- olinevaporwasdeterminedbyFig.3.Forourconvenience，two conversioncurvesareshowninFig.4，oneplotedonavolumetric percentage(vol.克)scaleandtheotheronapercentageofleanflam- mablelimit(LFL%)scale.
Fig.5showsaschematicilustrationofthemock-upboat.Loca- tionswheremeasurementsweremadeareindicatedbynumbers ineachcompartment.NinelocationsforcompartmentsA，Band D and10forcompartmentCwereselected.Twomeasurements weremadeineachIocation，at1cmbelowthetopboardand 3cmabovethebottomboard.Measurementwasbegunassoon asgasolinewassupliedtothefueltank.
Theleakageofgasolinevaporfromthefueltankwasvisualized withtheschlierenmethod(Setles，201;SmitsandLim，20)， whichdetectsvariationsintherefractiveindexofatransparent mediumthatareduetolocaldiferencesofdensityorcomposition. Inthisinvestigation，astheexperimentalaparatusissimpleanda large field of view is ne eded. the schlieren method has many advantagesoverothermethods(Itoeta，.l19)thatmightbeused tovisualizethegasolinevapor.
3.2.Smal-scalecombustionchamber
Fig.6isaschematicilustrationofthesmal-scalecombustion chamber.Thecombustionchamberhasthrecompartments:A， modelingtheportsidefueltankcompartment;B，equivalentto thestarboardbaterycompartment;and，仁 equivalenttothework deck compartment. The dimensions of each compartment are 100m mwide，100m mhigh，and160m mlong.Thecompartments wereconstructedfromanaluminumplatewithathicknesof 10mm. Ignition and flame behavior were observed through a 1 0 m m t h i c k g l a s s p l a t e i n t h e f r o n t o f e a c h c o m p a r t m e n t. I n o r d e r topreventgIasbreakagefromanexplosion，anopening(25cm2) was made in each compartment at the top of the combustion chamber.Theseopeningswerecoveredwithpapershetsanda plasticmembrane.Thesimilaritybetweenthemock-upboatand thesmalcombustionchamberwasdemonstratedfortwoofthe routesofgasolinevaportransportshowninFigs.5and6.Pasage 1directlyconectedcompartmentsA andBandpasageIcon- nectedcompartmentsAandBviacompartment仁 The5m mcIear- ance in the upper part of the compartments conected compartmentsA andBwithanarrowpasageatthetop.The 10m mCI回 ranceinthelowerpartofthecompartmentsconected compartmentsAandBviacompartmentC.Afuelcontainer10m m wide，30m mdeepand150m mlongwasmadefromPyrexglasas describedinourpreviousreport(Konishi，2000，202;Itoetaし 19).Anignitiondevicewasconstructedfromabatery，adistrib- utor，andanautomobilesparkplug.
4.Resultsanddiscusion
Wewilfocusouratentiononthedetailsoftheboatexplosion mechanism.Theconfigurationoftheboatisquitecommonin industrialinstalations，whereveselsareinterconectedbypipes， andalsoinconectedsegmentsoftankers，aircraftandbuildings.
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