Flame Length 



The relationship between flame length and certain fuel properties was examined 

 using a stepwise multiple regression analysis. The fuel properties that varied sub- 

 stantially from plot to plot served as the independent variables. The following equa- 

 tion resulted using data from all plots: 



Y = 4.28(Xi) + 0.00151(X2) - 2.92 



where : 



Y = flame length, ft. 



Xj = total loading, Ib./ft.^ 



X2 = average particle surface area-to-volume ratio weighted by fuel surface 

 area in each size class, ft."-^ 



= 0.60 



Standard error of estimate (0.05 confidence level) = 1.52 



The packing ratio was nonsignificant as an independent variable. Flame length was 

 expected to correlate with packing ratio because (1) flame length relates closely to 

 rate of energy release (Rothermel and Anderson 1966; Thomas 1963), and (2) packing 

 ratio is quite sensitive to rate of energy release for the smaller size fuels in the 

 spread model. If data covering a greater range of packing ratios had been acquired, it 

 probably would have been significant in the regression analysis. However, loading of 

 fine fuel (certainly particles less than 2 to 3 cm. in diameter) appears to be by far 

 the most important physical property relating to flame length. 



°W. H. Frandsen. The effective heating of fuel particles ahead of a spreading fire. 

 USDA Forest Serv., Intermountain Forest and Range Exp. Station, Ogden, Utah. (Manuscript 

 in preparation.) 



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