ABSTRACT 



Ponderosa pine needle and aspen excelsior fuel beds, chosen 

 because they exhibit different chemical fuel characteristics, were 

 treated with various amounts of ammonium sulfate and ammonium 

 phosphate and burned in a wind tunnel under controlled environ- 

 mental conditions. The rate of fire spread, rate of weight loss 

 (equivalent energy release rate), and the residue were measured 

 to quantify the retardants' effects on flammability. 



An increase in the amount of either fire retardant chemical 

 caused a reduction in rate of fire spread and rate of weight loss 

 while increasing the amount of residue. However, at all treatment 

 levels, ammonium phosphate was more effective than ammonium 

 sulfate. These two chemicals exhibit their primary difference in 

 their effect on glowing combustion. The rate of weight loss and 

 especially the residue are parameters that quantify glowing 

 combustion. 



Ammonium phosphate is much more effective in decreasing 

 the rate of weight loss and increasing the residue than is ammoni- 

 um sulfate, which has little effect on the residue. The superior 

 effectiveness of ammonium phosphate is probably due to the differ- 

 ence in thermal behavior of the two fire retardants; total decom- 

 position of ammonium sulfate occurs prior to 450° C. , about 

 250° C. sooner than ammonium phosphate. Temperatures at the 

 surface of the fuel bed probably are within the range of these total 

 decomposition temperatures. Although ammonium sulfate is effec- 

 tive in retarding flaming combustion, the majority of the chemical 

 may decompose prior to the glowing phase and thus not be avail- 

 able to alter reactions taking place during glowing combustion. 



The study provides general relationships which can serve as 

 standards for comparing the effects of other basic chemicals or 

 forest fire retardant additives. 



