Figure 14. — Effect of (NH^) 2 HPO^ and (NH^) 2S0i+ on the residue in excelsior fuel. 



Regression equations were determined for each relationship. The data for both 

 chemical treatments of the same fuel type were then pooled and an analysis of covariance 

 completed. A measure of how well each regression equation fits the sample data is shown 

 by the coefficient of determination, r 2 . The r 2 for each relationship and the r 2 and 

 the F (variance ratio) for the pooled data are given in table 3. 



The statistical data indicate that for all parameters measured and for both 

 ponderosa pine needle and aspen excelsior fuel, ammonium phosphate and ammonium 

 sulfate have significantly different effects. The rate of spread in pine needles as 

 a function of the amount of chemical, for both treatments, was the only dependent 

 variable that was not significantly different at the 99 percent level (see table 3) . 



The regression equations in table 3 (also appendix tables 4 through 8) show that 

 ammonium phosphate reduces the rate of fire spread and rate of weight loss (or equiva- 

 lent energy release rate) to a greater degree than ammonium sulfate in both the excel- 

 sior and pine needle fuel beds. Ammonium phosphate also caused a greater increase in 

 residue, thus decreasing the total energy released. 



Ammonium phosphate is more effective than ammonium sulfate in reducing all 

 parameters measured in the study; the largest difference occurs in the greater ability 

 of ammonium phosphate to decrease the rate of weight loss or energy release rate and 

 increase the amount of char or residue formed. Residue in pine needle fuel beds 

 treated with ammonium phosphate showed an 80 to 160 percent increase over residue 

 formed in untreated beds. Ammonium sulfate used under the same conditions did not 

 increase the amount of residue beyond 50 percent. Excelsior fuel beds treated with 

 ammonium phosphate showed an increase in residue of 200 to 500 percent, depending on 

 the treatment level; ammonium sulfate increased the residue only about 50 percent. 

 Figures 15 and 16 show the effects of ammonium sulfate and ammonium phosphate on the 

 residue of combustion occurring in ponderosa pine needle and aspen excelsior fuel beds. 



15 



