Improving Fire Hazard Assessment at the Urban-Wildland Interface ...

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North Central, and Sierra. It had no effecton the 0% defensible space compliance ratefor Heavenly.IrrigationOver half the parcels citywide had irrigationon less than half of the vegetation found onthe parcel. The vegetation in the Keys,which was dominated by turf grass andplanted exotics, was well irrigated, whileover 75% of the parcels in Heavenly, whichwere dominated by native conifer stands,showed little evidence of irrigation. Lessthan one third of the parcels in the NorthCentral neighborhood were irrigated. From41% - 55% of the parcels in the otherneighborhoods were irrigated.SlopeMost of the parcels that were sampledexisted on little or no slope, with theexception of parcels in Heavenly, where themean was 15% and the range was from 0%to 53%.Wall materialThe preferred building material for homes inSouth Lake Tahoe was wood. 96% of thehomes in the sample had exterior walls thatwere shakes, logs, or wood siding. Thirteenpercent of the homes in the Keys werepredominantly brick, stucco, or stone, butfrom 95 – 100% of the homes in theremaining neighborhoods had woodexteriors.Roof materialCitywide, 31% of the sampled homes had asignificant increase in susceptibility toignition because of wood roofs.Neighborhoods where more than half thehomes had wood roofs were North Central(54%) and Heavenly (56%). The fewestnumber were found in the neighborhood ofthe Y (18%).Window panesCitywide, 29% of the sampled homes hadincreased fire hazard due to the presence ofsingle-paned glass in over half the windowsof the home. The highest percentage ofhomes that had predominantly single-panedwindows was in the neighborhood of the Y(41%), while the lowest was in Heavenly(22%).Hazardous decksHazardous decks were found on 67% of thehomes citywide. Deck construction andplacement was particularly problematic inHeavenly, where slopes were greatest. Inthat neighborhood, eight of the nine parcelssampled had hazardous decks. In Bijou only48% of the homes had hazardous decks,while 60 – 73% of the homes in theremaining neighborhoods had hazardousdecks.DiscussionThe results of this study clearly indicate thatstandard city-scale fire hazard rating inSouth Lake Tahoe will not providemanagers and planners with sufficientlydetailed information to implement aneffective fire hazard mitigation program.While the city’s infrastructure is good,individual homeowners in the communityrarely choose for fire safety in terms ofconstruction materials, propertymaintenance, and landscaping or defensiblespace. The problem of non-compliance isworsened by the fact that many of the city’slots are so small they are influenced by thefire hazard of neighboring lots.Furthermore, results indicate that firehazard rating should be improved toaccount for the fire hazard created byneighboring vegetation and houses in areasdominated by small lots. Also, eachcomponent of a fire hazard rating systemshould produce results than can be used asdecision support for fire management,including identifying priority areas fortreatment, identifying problematic areas in8
terms of non-compliance, and identifyingreasons for non-compliance. Each of the sixneighborhoods in South Lake Tahoe has aunique profile in terms of the suite of factorsthat contribute most significantly toneighborhood-scale fire hazard. Theneighborhood profiles can be used to directand focus management and homeownereducation efforts. The obvious differencebetween the Keys and Heavenly, forexample, provides managers with a clearset of management objectives, but there arealso important, less obvious differencesbetween the other neighborhoods.For example, results indicated that the Yhad an average fire hazard for the city, butcompared to the rest of the city thisneighborhood was characterized by a lowpercentage of wood roofs, better irrigation,average compliance with PRC 4291, and anaverage hazard created by decks.However, the fire hazard rating was thesame as the citywide average becausethese positive factors were offset by its 85%non-compliance rate for defensible space.This figure increased to 91% when adjustedfor small lot size. Compared to Sierra, the Yhad a lower compliance rate but rated betterin terms of construction materials anddecks. Compared to North Central, the Yexhibited comparable compliance rates andwas slightly better in terms of deck hazards,but the Y rated far worse in terms of thepercentage of wood roofs and single-panedwindows. These data can guidemanagement decisions, including both fuelsreduction programs and outreach andeducation that focus on the particular needsin each neighborhood.In addition to the education efforts thatfocus on defensible space andmaintenance, there is clearly a need toeducate residents about other practicesrelated to fire hazard. Education is neededin Heavenly and elsewhere about thebenefits of irrigation in terms of fuelmoisture content and the relationshipbetween drought stress, bug kill, and firehazard. Most homes already have doublepanedwindows for better insulation againstwinter weather, but many residents do notrealize that double-paned windows alsodecrease the risk of structural ignition.Hazardous decks are a chronic problem inHeavenly, where most decks hang oversteep slopes covered with continuoussurface fuels. In this community, which ischaracterized by small lots and manyseasonal residents, education on theimportance of neighborhood-scalecooperation is critical.In sum, standard fire hazard analysis inSouth Lake Tahoe and similar communitiesis likely to underestimate individual firehazard. First, the city’s fire-safeinfrastructure is included in the parcel-scaleanalysis, which offsets the increasedindividual fire hazard associated with a lackof defensible space and maintenancearound the home. Compliance with PRC4291 is perhaps the most important factor instructure survivability, but the influence ofthe city’s good infrastructure on its overallfire hazard rating obscures the fact thatthree-quarters of the parcels citywide arenon-compliant with defensible space codesand two-thirds are non-compliant withmaintenance codes. Second, the hazard onsmall lots will be further underestimatedbecause of the influence of the fire hazardof neighboring parcels.A more appropriate approach to fire hazardassessment in South Lake Tahoe is toassess parcels for compliance, lot size, andthe individual choices homeowners make interms of construction materials andirrigation. Analysis of compliance rates andhomeowner choices will provide a moreaccurate estimate of individual fire hazard.The analysis can also serve as decisionsupport for focusing outreach and educationefforts and for prioritizing areas that aremost in need of homeowner compliance andcooperation.9
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Page 7: Table 2. Fire hazard rating, non-co
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