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The spectacular run of the Sundance Fire 

 on September 1, 1967, appears to have been a 

 result of the combination of dry fuels from a 

 sustained drought, low humidities for over 72 

 hours, increasing winds sustained for a period 

 of 9 hours, and a 4-mile active fire front exist- 

 ing on the morning of September 1. The fire 

 advanced 16 miles in 9 hours and created spot 

 fires 10 to 12 miles northeast of the place of 

 origin. Spotting activity increased during the 

 day, reaching a maximum intensity during the 

 period of highest winds in the late afternoon. 

 Whereas spot fires early in the day contrib- 

 uted to the fire spread, late in the day a multi- 

 tude of firebrands created fuel voids leading 

 to the breakdown of the main front and con- 

 tributing to the fire's termination. Other 

 factors influencing the decreasing rate of 

 spread were the increasing humidity after 

 2200, the decreasing wind after 2200, the 

 downslope direction of burning, and to some 

 degree the disruption of fuel continuity due 

 to prior logging activities in the area. 



The average rate of spread ranged from 1 

 to 6 m.p.h. with brief periods of spread rates 

 having higher or lower values. The fire inten- 

 sity built up to 22,500 B.t.u./sec.-ft. of fire 

 front and was releasing nearly 500 million 

 B.t.u./sec. A convection column rose to 

 35,000 ft. Extensive firebrand activity and 

 debris were transported from the fire. These 

 brands were either lifted as high as 18,000 feet 

 and transported by the wind or carried in 

 vortices produced by the wind blowing 

 around the convection column. Fire-induced 

 winds could have been greater than 95 m.p.h., 

 and caused the extensive tree blowdown. 



Fire buildup indices rated the conditions as 

 "extreme" and spread indices forecast agreed 

 reasonably with actual conditions. The aver- 

 aged spread index for September 1 was "very 



high" and when combined with a buildup 

 index of "extreme" produced a rating of "ex- 

 treme fire danger." The National Fire-Danger 

 Rating System Handbook describes it as: 



EXTREME. —Fires under extreme condi- 

 tions start quickly, spread furiously, and bum 

 intensely. All fires are potentially serious. 

 Development into high intensity burning will 

 usually be faster and occur from smaller fires 

 than in the very high danger class. Direct at- 

 tack is rarely possible, and may be dangerous, 

 except immediately after ignition. Fires that 

 develop headway in heavy slash or in conifer 

 stands may be unmanageable while the ex- 

 treme burning condition lasts. Under these 

 conditions the only effective and safe control 

 action is on the flanks until the weather 

 changes or the fuel supply lessens. 



This very aptly described the Sundance 

 Fire. The present rating system estimated the 

 conditions properly and provided warnings of 

 what could be expected. 



This analysis of the Sundance Fire did not 

 reveal any phenomena incompatible with 

 existing knowledge and principles. The exten- 

 sion of laboratory findings and theoretical 

 developments to a field situation resulted in 

 estimates of burning rates, fire intensities, 

 firebrand ranges, and induced windspeeds 

 which are realistic. Evidence of various phe- 

 nomena gathered during this study has height- 

 ened interest in additional research that will 

 provide fuller explanations of such items as 

 vortex generation, firebrand propagation, and 

 spot fire ignition characteristics. The research 

 people assigned to this study have gained valu- 

 able experience and we hope our interpreta- 

 tions will be useful and informative to other 

 research and fire control personnel. 



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