INTRODUCTION 



Frandsen and Rotherrnel (1972) have presented a method of measuring the energy- 

 release rate of a spreading fire through the load-loss rate of a section of the fuel 

 bed. This paper describes an alternative fuel bed that uses less fuel, that takes less 

 time to construct, and that is less complex to measure than the fuel bed used previ- 

 ously. Fuel arrays to be examined are contained within a circular basket. The top is 

 ignited uniformly over the surface and the basket's fuel load loss is continuously 

 recorded as the fire moves vertically downward. 



Rothermel (1972) has shown that the fundamental dynamics of fire spreading through 

 a porous fuel array can be expressed through r, the reaction velocity, the ratio of the 

 efficiency of mass degradation during pyrolysis to the elapsed time of pyrolysis exper- 

 ienced during fire spread. Its product with w , the net original ovendry load of a fuel 

 bed, is equivalent to w, the maximum load-loss rate of a portion of the fuel bed as the 

 fire spreads through the fuel: 



w = w r 



n 



The method of obtaining w experimentally has been covered by Frandsen and Rothermel 

 (1972) in their investigation of the reaction intensity of the combustion zone of a 

 spreading fire. (The rate w is properly a loss; however, the negative sense is inter- 

 nally compensated.) The reaction intensity, Ij^, is another important dynamic parameter 

 of the fire. It is the total energy-release rate evolved from the combustion zone, and 

 is related to w through h, the low heat of combustion: 



1„ = hw = hw r 

 R n 



The load-loss rate, w, is an important basic parameter that relates to the dynamics of 

 a spreading fire. The maximum load-loss rate of a burning fuel array can be obtained 

 by monitoring the load of a basket of fuel as the fire moves with a horizontal plane 

 downward through the basket (fig. 1). The purpose of this paper is to show that, for 

 excelsior, the fuel basket experiences a maximum load-loss rate similar to that expe- 

 rienced by a horizontal fuel bed slice Ax, (fig. 2) at the same packing ratio, the 

 ratio of the bulk density to the particle density. Although the bed fire travels 

 horizontally, the observer at Ax views a downward moving front that is similar to the 

 front illustrated in figure 1; namely, as Ax tends to zero, the boundaries of the pyrol- 

 ysis zone can be easily approximated as horizontal planes. Because only the fuel slice 

 is weighed, the rate of change of the load within the slice is hypothesized to be 

 identical to the rate of change of the load in the burning basket. 



1 



