Figure 14. — Blowdown in Falls Creek area. 



has provided a means of estimating indraft 

 winds. His equation also provided the means 

 of determining whether our values for flame 

 depth and energy release were reasonable or 

 not. The equation is 



(88X10-3) (^^) 



1/3 



where 



= windspeed, m.p.h. 



dErp 



= total energy release rate, B.t.u./sec. 



A = combustion area, sq. miles. 



Values for four areas where blowdown was 

 evident in aerial photographs (fig. 14) were 

 tested with this equation: 



Up Soldier Creek 

 Down Upper 



McCormick Creek 

 Over Apache Ridge 

 Across Falls Creek 



Vw = 80 m.p.h. 



= 95 m.p.h. 

 = 96 m.p.h. 

 = 80 m.p.h. 



It has been generally estimated that winds in 

 excess of 80 m.p.h. are needed to cause blow- 

 down. Owen Cramer of the U. S. D. A. Forest 

 Service, Pacific Northwest Station, after view- 

 ing slides of the damage, informally estimated 

 the winds to be near 120 m.p.h. The agree- 

 ment of our values with other estimates, con- 

 sidering the extrapolations we used, encour- 

 ages continued efforts to develop theories and 

 mathematical descriptions of field-observed 

 phenomena. 



FIREBRAND ACTIVITY 



Firebrands and spotting were evident 

 throughout the fire run and are believed to 

 have played an important role in the fire's 

 behavior. From the pattern of rate of spread 

 and the record of reported fires, it was ap- 

 parent that firebrand material had been car- 

 ried 10 to 12 miles in advance of the main fire 

 front. Much debris was found northeast of the 

 fire area (fig. 15) in the form of moss and 

 lichen strands or wreaths, larch and hemlock 

 cones, needles, cedar fronds, branches the size 

 of a pencil, and pieces of bark up to 4V2 

 inches long and IV2 inches wide. The fallout 



18 



