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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 Behavior ChronologyThe fire started near Seneca Pond at approximately 1400 hours at 6600 feet elevation in a dense stand of fir and pine and quickly transitioned to an active crown fire. Initial fire spread was down Angora Creek to the northeast driven by a strong southwest wind. Spotting distances were estimated at about quarter mile downwind. At the same time, the fire made strong topographically driven crowning runs up to the top of Angora Ridge on the west flank. The fire spread a total of three miles during a four-hour period, reaching the top of Tahoe Mountain at about 1800 hours. Many spot fires developed on the northeast aspect above South Tahoe High School. 
Figure 4: Fire behavior above South Tahoe High School Sunday Night, June 24th-25th Nighttime cooling and a slackening of wind speed late Sunday evening caused a reduction in fire intensity and rate of spread. However, the fire continued backing down slope toward the high school during the early morning hours of Monday, June 25th. Suppression action contained this portion of the fire to a fire line immediately above the high school. The first known house ignition occurred in the North Upper Truckee Subdivision just west of the intersection of Lake Tahoe Boulevard and Angora Creek Drive in the SW corner of section 18 and was extinguished by firefighters. The house survived with only minor damage to the deck and garage. This house was easily accessible from Lake Tahoe Boulevard and was adjacent to several safety zones (wet grassy areas Full Angora Creek and large paved areas formed by road intersections) allowing effective suppression action. Heavy smoke limited early detection of structural ignitions to the north (Mule Deer Drive area). By the time firefighters discovered houses burning on Mule Deer Drive, several were burning with too much fire to extinguish. Interviews with firefighters indicate that the structure fires grew rapidly and began producing a great number of large firebrands. Most of these firebrands were transported by winds only a short distance but many landed on or immediately adjacent to downwind houses. Many of the downwind houses caught fire in successive cycles. Some houses were not saved by firefighters due to low visibility and inability to detect many of the house ignitions until they were too large to extinguish with handcrews and fire engines. 
Figure 5: First house to ignite (saved by suppression action) indicated by blue circle. Wind direction indicated by arrow. Full subdivision map is available in Appendix A. One house in the Angora Highland Subdivision (about one mile north of Mule Deer Drive) burned. It was located very close to the rim of a steep slope which caused it to receive greater amounts of convective heat and direct flame impingement. In addition, 
Figure 6: Single house which burned on Heather Circle in the Angora Highlands Subdivision. Note the location of house (red circle) on the edge of a steep slope exposed to an upslope crown fire run. this house had a large amount of firewood which ignited, producing a great amount of radiant and convective heat which made approach to the house difficult for firefighters. Most of the other houses in this subdivision were showered with firebrands and experienced spot fires on and adjacent to them. Many of these houses would have burned without aggressive firefighting by engines and hotshot crews. Some houses to the south on Zuni Street, Shoshone Street and Cayuga Circle burned later. The wind shifted to a more westerly direction in the late afternoon pushing the fire more directly toward these houses (see Appendix D). Fire spread into this residential area with relatively low flame lengths. Almost all of the trees immediately to the west of the residences (in the fuel treatment unit) have unburned crowns indicating low to moderate intensity surface fire behavior. Photographic and video evidence support this conclusion. 
Figure 7: Arrow indicates late afternoon wind direction. Note intact crowns of trees ("browned" by the surface fire heat but not burned). Surface fire spread through this Fuel Treatment Unit into the subdivision with low flame lengths (photo evidence and eyewitness estimates indicate flame lengths were less than 4 feet). 
Figure 8: Note the unburned tree crowns and very low flame lengths in adjacent vegetation and surface fuel. After spreading into the residential area the fire ignited combustible material adjacent to houses which then ignited the houses. Interviews with homeowners indicated that many of the houses had attached decks with combustible material stored under the deck. In some cases direct flame impingement from a low intensity surface fire ignited these combustibles, which then ignited the deck and ultimately the house. Visual examinations on the ground and aerial photos reveal that much of the vegetation between houses did not burn or burned with surface fire. 
Figure 9: Note the unburned vegetation immediately adjacent to the structure indicating the ignition was from a spot fire. Interviews with firefighters, other eyewitnesses, and video examination indicate that many houses ignited from burning embers produced by house fires upwind. A cycle of spotting from house to house in this area ended only when the fire ran into a buffer of trees with reduced house density to the northeast of Mt Shasta Circle. 
Figure 10: Arrows indicate fire spread. Upper slope fire spread (above the red line) occurred between 1430 and 1630. Lower fire spread (below the red line) occurred between 1700 and 1900 following a wind shift from southerly to westerly. Note the green trees between Mt Shasta Circle and Lake Tahoe Boulevard. Fire spread and intensity was reduced in this area primarily due to USFS and CTC urban lot hazard fuel treatments and reduced concentration of houses and safer access by firefighters. Contents
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