question. It is indicated in figure 3 at the end of the curve and in the region of 

 increasing slope (second knee except at g = 0.65) following the inflection of the 

 initial sigmoid curve. For (3 = 0.032 to B = 0.065, 39 to 79 percent of the fuel still 

 remains at 50 seconds- -wel 1 after the initial sigmoid load history. Consequently, the 

 depth, 15.2 cm, was sufficient for 6 = 0.032 to B = 0.065. For B = 0.004 to B = 0.016, 

 as little as 4 percent of the fuel remains at 30 seconds; however, each curve is sigmoid 

 and shows at least 17 percent more fuel consumed beyond the second knee, indicating that 

 the initial sigmoid curve v\Fas not foreshortened by lack of fuel depth. 



In the spreading fire, the major rate of fuel consumption is near the front of the 

 combustion zone--consistent with its early occurrence in the fuel basket--and is of 

 prime importance to the propagation of the fire (Frandsen and Rothermel 1972) . 



Converting an idealized load history to load-loss history provides us with an easy 

 reference for comparing the dynamics of burning fuel baskets of constant B having 

 different depths (initial loads) . Because the fuel below the pyrolysis zone has no 

 effect upon the present load-loss history, we can see that the load-loss curve for an 

 extreme depth will have all the characteristics of load-loss curves of lesser depth 

 (fig. 5), except that the period of constant load-loss rate becomes longer. The slope 

 of the curves in figure 5 to the right of the second knee is dependent on char buildup. 

 Char formation depends on the mineral content of the fuel and increases with oxygen 

 depletion that in turn increases with time as the pyrolysis zone travels down into the 

 basket. The char buildup for excelsior is negligible up to and including the maximum 

 load-loss rate because the maximum rate occurs early in the load history and the mineral 

 content is low (0.03 percent). Whatever the effect, it is the same for both the slice 

 and the basket. 



7 



