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T.Konishielal./FireSajきtyJournal43(208)363-375 Oigitalvid巴ocamera
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Fig.2.Positionsofsixdigitalvid巴ocamerasandinfraredcameras.Thevideocameraswereinstaledonplatformsat2m highabovetheground
temperaturedrop，temperaturerecoverytime，andrecovery temperaturebyaerialfirefightingwereanalyzedfromthe housetemperaturechangesmeasuredbythetwoinfrared cameras.
3.Resultsanddiscusions
3.1. Determination01coverageareaandlevel
Twenty chalenges of aerial firefighting against the burning mock-up houses were car ried out in the first experiment，andfivechalengesinthesecondexperiment. Fig.3(a)and(b)aretwoofthephotosfromthefirstand thesecondexperiments，respectively.
Threhelicoptersunderthefiredepartmentauthorities ofOitaandNagasakiprefecturesandFukuokaCitywere usedinthefirstexperiment.Thehelicopterusedforthe1st， 3rd，5th，7thand9thchalengeswasfromOitaprefecture， theoneusedforthe11th，13th，15th，17thand19thwas from Nagasaki prefecture，the one used for the other chalengeswasfromFukuokamunicipalgovernment.
The coverage areas of droping water of the first experiment，which are shown by encirc1ed areas in Fig.4(a)，wereanalyzedbythevideoimagestakenbythe sixvideocameras.Thelocationsofthevideocamerasare shown in Fig.2. The coverage level was ca1culated by dividingthemassofdropingwaterbythecoveragearea. T h e i n f o r m a t i o n a b o u t fl. i g h t h e i g h t ， a i r s p e e d ， c o v e r a g e areaandcoveragelevelareshowninFig.4(a).Thehit probabilitiestoalthehouseswere58%at0knots，31% at 5knots(9.3km/h)and35%betwen16and24knots(29.6 and 44.4km/h). The results of aerial firefighting by the large helicopter under Japan Ministry of Defense are showninFig.4(b).Thehitprobabilitiestoalthehouses were19%at0knots(hovering)，13%betwen15and25 knots(27.7and46.3km/h).Fig.5indicatesthatwiththe increase of the airsped，coverage area increases and
coverageleveldeceases.Thecorelationsbetwenairsped andcoverageareaandcoveragelevelareexpresedinthe folowingequations:
Sl=46.6+15.8V， (1)
Dl=7.60-0.348V， (2)
S2=15l.1+28.8V， (3)
D2=3.6-l.23V， (4)
whereSisthecoveragearea(m2)，D isthecoveragelevel (I/m2)，V is the airsped (knots)，and where subscripts mean: 1 is the first experiment; and 2 is the second experiment.SubstitutingEq.(1)into(2)andsubstituting Eq.(3)into(4)producethefolowingrelations:
Dl=8.63-0.0219Sl， (5) D2=40.0-0.0426S2・ (6)
Fig.5alsoshowsthecoveragelevelchangesofBambi324- galonandGrifith10-galonbucketswiththeairsped change[1].Thisdatashowssimilartendenciesasthedata we obtained with the 5301 bucket in the second expenment.
Wemustbearinmindthatforsupresingurbanfires，a largercoveragelevelisrequiredthanforwildfires，because dropwaterdoesnoteasilypenetrateintobuildings，while insupresingwildfires，whichspreadeasily，largercover- ageareaisrequired.
Fig. 6 shows the relation betwe en coverage area and coverage level expresed by Eqs. (5) and (6) with the airsped as parameters. In making a supresion plan against an urban fire by using helicopters，required coverage area and coverage level can be 0btained by determininghelibucketvolumeandairspedofhelicopters. Forexample，incaseofaburningareaof20mぺifthe60- 1helibucketisused，thecoveragelevel4.31/m2 wilbe
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