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Pacific Southwest Region 
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An Assessment of Fuel Treatment Effects on Fire Behavior, Suppression Effectiveness, and Structure Ignition on the Angora FireFire Effects of Urban Lot Fuel TreatmentsDescription and prescriptionsWithin the fire perimeter and intermixed within neighborhoods, there were over 100 USFS owned urban lots totaling about 200 acres, about 175 lots owned by California Tahoe Conversancy (CTC), and about 28 lots owned by El Dorado County. Fuel treatments occurred on most of the urban lots. El Dorado County has also completed one vegetation treatment for erosion control on USFS lands within the Angora SEZ. The USFS urban lots within the fire perimeter had been treated between 1995 and 1997 with a similar prescription to the USFS area treatments, but with the addition of hand thinning 30-50% of the brush in a mosaic pattern (Appendix B). The intent of the treatments was to reduce crown fire potential, improve defensible space to adjoining private lands, and to reduce stocking levels to resist insect infestation. Fire BehaviorFire behavior was evaluated on 70 of the USFS owned urban lots within the fire perimeter. Sixty-eight of these lots exhibited surface fire behavior. Eyewitness accounts indicate flame lengths were less than four feet. Of the lots with crown fire behavior, one was not treated; the other was on a steep slope. 
Figure 17: Note intact tree crowns indicating that the fire burned at low intensity at the surface in treated Fire behavior was also evaluated on 80 CTC lots. Of these sampled lots, 11 had not been treated. Fifty-two lots exhibited surface fire behavior, 10 exhibited partial torching of the overstory, 14 burned with crown fire behavior, and four lots did not burn. In most cases the urban lots that burned with crowning or torching were immediately downwind from structures that burned intensely. Within the subdivisions, burning houses created the greatest fire intensities and produced the greatest amount of large embers. Most urban lot treatments provided fuelbreaks, slowing fire spread. According to interviews with firefighters and on-site inspections, fire intensity was significantly reduced when fire entered urban lots. Had these lots not been treated, they would have provided additional sources of firebrands, and sources of radiant heat to adjacent houses. Suppression effectiveness, structure ignition, and public safety/egressMany firefighters reported that the treated urban lots significantly increased suppression effectiveness because of the 
Figure 18: Note the intact, unburned vegetation surrounding this structure. It is evident from unburned vegetation and surface litter surrounding the house that it was ignited by a wind-borne ember (spot fire), not by surface fire spread, or radiant heat. relatively low intensity surface fire that enabled direct attack of spot fires, preventing adjacent houses from burning. In instances where a lot was adjacent to a house, firefighters were able to take "close-in" suppression action if an ember landed on the house or caused an adjacent spot fire. Firefighters reported that many structures were saved because of this. They also reported that suppression effectiveness was enhanced by reduced smoke production from the urban lot treatments enabling them to see spot fires when they were small and rapidly suppress them. Public safety and egress was enhanced by the urban lot treatments for similar reasons as the area treatments. Smoke production was reduced, increasing visibility, and because of reduced fire intensity, firefighters could more effectively protect houses adjacent to urban lots. There are a variety of reasons that houses burned. Some burned because firebrands landed on receptive locations such as on decks, shake roofs, or woodpiles. Some burned because a continuous fuelbed, such as pine needles, lay adjacent to a burnable part of the house. 
Figure 19: Note the small spot fire produced by embers from the burning house. There are also many reasons houses did not burn. Distance from firebrand sources reduced the number of embers landing on a house. Suppression resources saved many houses from either catching fire, or put them out before they became fully involved. Some houses did not burn because they had less burnable material exposed to firebrands or surface fire. Clearly, fewer houses would have burned had they had more effective defensible space, better access for firefighters, and contained less flammable material. Contents
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