Burnout time 



• Charcoal sphere - 17.0 mm 

 X Cvhnder - 19.3 min. 

 □ " Plate — 14.5 min. 



• Pine cone - 9.0 min. 



Figure 1 6. — Range of various types of firebrand 

 material. 



the brand to the proper height. The results of 

 these calculations are shown in figure 16. 



Any of the charcoal brands could have 

 traveled the 10 to 12 miles in a glowing state, 

 whereas the pine cone could have transported 

 fire up to 7 miles. With a convection column 

 developing to over 31,000 feet, it appears 

 reasonable that vertical velocities of 45 m.p.h. 

 would have existed and material could have 

 been carried to altitudes over 18,000 feet in 

 the convection column. Winds of 44 m.p.h. or 

 greater did exist and could have carried the 

 brand once it tumbled out of the column. 



This method of firebrand transport appears 

 quite reasonable but other possibilities do 

 exist. Currently under investigation is the pos- 

 sibility that moving vortices are generated by 

 the fire and prevailing wind. The swirling air 

 or vortices would move on downstream carry- 

 ing firebrands and debris with them. The in- 

 tensity and range of these vortices would 

 depend on the amount of heat "pumped" 

 into them by the fire and strength of the 

 wind. Particles carried aloft would tend to 



either stabilize within the vortex or centrifuge 

 out. Particles with low drag configurations 

 (fig. 15) would tend to stabilize, and as the 

 vortex street dissipated far downstream of the 

 convection column, the suspended debris 

 would "touch down" (1). 



Several behavior characteristics noted by 

 the people interviewed support this possibil- 

 ity. It has been stated earlier that the pickup 

 man for the Roman Nose lookout encoun- 

 tered very intense winds and what he de- 

 scribed as "dust devils" in Falls Creek ahead 

 of the fire. The occurrence of these dust 

 devils was periodic. The same man encoun- 

 tered similar winds later in the Snow Creek 

 area. The lookout on Black Mountain ob- 

 served a spot fire which fanned out in all 

 directions in a circular manner. The tree-fall 

 pattern in Falls Creek suggests the trees fell 

 toward the centerline of the fire path from 

 each side. These pieces of evidence have en- 

 couraged the investigation of the potential ef- 

 fectiveness of this phenomena (1). 



FIRE ACTIVITIES IN PACK RIVER 



The Pack River area has received the 

 greatest attention by the news media because 

 of its accessibility, the obvious destructive 

 forces associated with the fire, and the dra- 

 matic burning of the Pack River bridge. This 

 area was surveyed by the research team in an 

 attempt to localize the forces the fire exerted; 

 however, these forces appear to have been so 

 dynamic and fluctuating that the evidence re- 

 maining is not coherent. 



Shortly before the fire entered this area we 

 know men near the river felt very little wind 

 but could hear it overhead. Yet trees that had 

 toppled into the river had green unscorched 

 boughs underwater and burned limbs above 

 water. This indicated that strong winds were 

 present in the valley bottom very shortly be- 

 fore the fire arrived, or before the fire ignited 

 the crown material. Some downed trees 

 showed no signs of burning on the underside, 

 although the upper side was charred. 



Winds of different magnitudes and direc- 

 tions may be inferred from the pattern of 

 blowdown and breakage. The tops of many 

 trees were snapped out either by a sudden 

 sharp rush of air or from whipping back and 



20 



