TEST RESULTS AND DISCUSSION 



ROLE OF FUEL DESCRIPTORS 



During the development of the equation to describe fire spread in terms of radiant 

 heat transfer, a group of fuel descriptors was established. This group, Og^X/pfQig, can 

 be determined prior to a test fire; by correlating it to the rate of spread, a best 

 estimate of the heat flux can be obtained. Figure 2 shows the results of 3 or more 

 test fires averaged at each condition. Taking an increment along the linear portion 

 of the curve, the maximum heat flux into the fuel is found to be 40 X 10^ B.t.u./ft.^ - 

 hr.(3.0 cal./cm.2 - sec). Low fuel moisture contents resulted in the high rates of 

 spread and as moisture content increased a point was reached where a departure from a 

 linear relation occurred. Following the departure to zero rate of spread, the inter- 

 cept represents the point where moisture content prevents fire spread. By determining 

 and referring to figure 1, the moisture contents for no spread were found: 



t .u. 



Ponderosa pine: a X/p^Q. = 1.13 X 10 , Q. = 412 



^ a f^ig ^ig lb . 



MC = 24.2 percent 



Western white pine: a X/p^Q. = 1 . 13 X 10" ^ , Q. = 412 ^'^ 



^ a f^ig ^ig lb . 



MC = 24.2 percent 



Lodgepole pine: a X/p^Q. = 0.81 X lO"^, Q. = 359 



^ ^ ^ a f^ig ^ig lb. 



Figure 2. — A near linear relation is exhibited between the experimental rate of spread and 

 the fuel descriptor's set. Note the rolloff at the low end. 



