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Fig.5.Aschematicilustrationofthemock-upboat.Locationswheremeasure- mentsweremadeareindicatedbynumbersineachcompartment.Ninelocations forcompartmentsA，B andD and 10forcompartm巴ntCwereselected.Two measurementsweremadeineachlocation，at1cmbelowthetopboardand3cm abovethebotomboard.
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Fig.6.Aschematicilustrationofthesmal-s日 lecombustionchamber.The combustionchamberhasthrecompartments:(A)modelingtheportsidefueltank compartment， (B) equivalent to the starboard bat tery compartment， and (C) equivalenttotheworkdeckcompartment.Thedimensionsofeachcompartment are10 0m mwide，10 0m mhigh，and160m mlong.
tankhadtwoholesthatcouldleakgasolinevapor.Therewasacor- rosionholeabout2m mindiameterinthesideofthefueltank，and anairventhole2m mindiameterinthetopoftherefuelingcap.
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Fig.7.Ordinaryphotographsandschlierenimages:(a)therefuelingcap，(b)aschlierenimageofemisionofgasolinevaporfromtheairventholeintherefuelingcap，(c)the corosionholeinthefueltank，and(d)aschlierenimageofemissionofgasolinevaporfromthecorosionhole.
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Fig.8.TherepresentativedatafromA-8(thepositionnearestthefueltankholesin compartment(A)，B-2(thepositionnearestthebateryterminalincompartment (B)，C-5(thepositionnearestthepartitionholeincompartment(C)，andD-6(the positionnearestthepartitionholeincompartment(D).Aflamablemixtureof gasolinevaporandairwasmaintainedfromthe1.7thdaytothe175thdayfromthe dayafterplacementofthefiledandleakingfueltank.
Leakageofgasolinevaporfromthetwoholeswasobservedwith theschlierenmethod.Anordinaryphotographandaschlierenim- ageoftherefuelingcapareshowninFig.7aandb.Emissionofgas- oline vapor from the air vent hole was observed.A n ordinary photographandaschlierenimageofthecorrosionholeareshown inFig.7candd.Theschlierenimagesverifiedthatgasolinevapor leakedfromthetwoholesintheoriginalfueltank.
4.2.D(酢lsionandacumulationofgasolinevapor
Thesecondstepneedstoexplainhowtodifusethegasoline vaporfromafueltanktoeachcompartmentsoftheboat，andto determinethetimerequiredtoreachtheflammablelimitofgasoIine vaporinthebatterycompartment.Thedifusionofgasolinevapor wasinvestigatedwiththemock-up.Theoriginalfueltank，fiIedwith gasoline，wasplacedintheportsidecompartmentofthemock-up. Vaporconcentrationwasmeasuredeveryhour，andforsafety reasonsthemeasurementsweresuspendedwhenthemaximum
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