LAPSED TIME 2 4 6 8 10 



SLOW 



BURNING 



FUELS 



FAST 

 ■ BURNING 

 FUELS 



LAPSED TIME 2 4 6 



2 4 6 



Figure 1. — Fire front progress through two nonuniform hexagonal fuel arrays. 



The rate of fire spread also has a dependence on wind and slope. Rothermel 

 (1972) used only the maximum effect, i.e. wind and slope in the same direction. 

 Provision was not made for combining nonparallel wind and slope nor for the compu- 

 tation of rates of spread in the six spread directions required by the hexagonal 

 array. Albini,^ however, developed a method for combining wind and slope that 

 gave the resultant magnitude of rate of spread as a fuitCtion of an angle relative 

 to the directions of the wind and slope. With Albini's model, it was possible to 

 compute potential rates of spread in all six directions in the presence of wind 

 and slope. 



■^Albini, Frank A. Memorandum, subject. Combining wind and slope effects on 

 spread rate, to R. C. Rothermel, Northern Forest Fire Laboratory, Missoula, 

 Montana 59806, Jan. 19, 1976. 



5 



