FIRE VECTOR 



(A) 



X X 



X X 



L 



(B) 



Scale-. 



cm. 



Figure 4. — Cross-sectional views of the location of thermocouples within the transverse 

 and longitudinal members of the unit cell. A is transverse and B is longitudinal. 

 Thermocouple positions are indicated by the crosses. 



The velocity of an advancing thermal wave in the longitudinal member, along with 

 the rate of spread of the fire, is tabulated below. The packing ratio was held constant 

 at 0.08. 



brze 

 (Cm. ) 



0.6 



Velocity 



Fire spread Thermal wave 

 _ ( Cm. /sec. ) 



0.33 



2 0.53* 



.6 



.33 



.53* 



1.3 



33 



1.40 



1.3 



35 



.95 



The discrepancy between the rate of spread of the fire and the rate of spread of 

 the thermal wave within the unit cell is a result of the quasi-steady character of the 

 fire. Viewed at close range, the fire appears to stop at each transverse member and 

 then quickly travel down the longitudinal member to the next transverse member where 

 it waits again. Viewed from a distance, the average rate of spread draws our attention 

 away from the unsteady motion of the fire on the microscale. The thermal wave is 

 probably more representative of the longitudinal fuel member than of the fuel array. 



2 *Values obtained from adjacent longitudinal members in the same fire. 



10 



