INTRODUCTION 



Fire behavior in a woody fuel array such as found in the forest is a complex 

 physicochemical process that does not lend itself to a simple solution. The process 

 is further complicated by the spatial nonunif ormity of the fuels involved in the 

 combustion process. A fire responds to fuel nonunif ormity by changing its rate of 

 spread and intensity. As a result there is a distribution in the rate of spread 

 and intensity experienced by the fire as it spreads through the fuel array. 



For the purposes of this study nonuniform fire behavior is predicted by modeling 

 fire spread through a hexagonal network of fuel cells. Fire spread is assumed to be 

 a process of contagious growth between cells. Fuel properties are allowed to vary 

 from cell to cell in a prescribed manner but have uniform properties within the 

 cell. Consequently, the nonunif ormity of the actual fuel array is simulated through 

 cell to cell variations and has a resolution limited by the cell size. Because of 

 the nature of the modeling process it is necessary to devise a scheme for collect- 

 ing data describing nonuniformity and a scheme for filling the hexagonal cell array 

 in a manner that simulates the actual fuel nonuniformity. 



Historically, it was necessary that uniformity be addressed first. This ap- 

 proach laid the groundwork for present development. Rothermel (1972) chose a path 

 of research into fire behavior that allowed the result to be applied to the needs 

 of the fire manager. Rothermel 's variables were the fuels and the environment in 

 which they were found. That same view exists here. The fundamental approach of 

 the model described here is the assumption that small portions of a nonuniform fuel 

 bed can be considered uniform. Nonuniform fire behavior then can be examined by 

 following the progress of the fire as it changes speed while moving through differ- 

 ent but uniform subunits of the area. This model was developed as part of an inte- 

 grated effort for solving fire behavior problems at the Northern Forest Fire Labora- 

 tory. The model is not intended for direct simulation of actual fire situations 

 but rather is offered as a means to develop simplified methods for solving fire 

 behavior problems in the field. 



Some aspects of fuel nonuniformity such as occasional absences of fuel have a 

 direct effect on fire behavior. However, most often fuel nonuniformities are more 

 subtle and must be viewed through another interpretive system, a model of fire be- 

 havior. Consequently, we define fuel nonuniformity in terms of fire nonuniformity 

 through a model of fire behavior that responds to spatial variations of the fuel 

 array. 



1 



