DISCUSSION 



When attempting to characterize the effects of retardant chemicals on f lammability, 

 the measurement of three parameters provides a more complete picture than does the use 

 of a single parameter. For example, the study has shown that chemicals can have 

 similar effects on the rate of fire spread while having greatly different effects on the 

 energy release rate and residue. Since retardant chemicals are used primarily to 

 reduce both the combustion rate and the ability of the fire to propagate itself, it is 

 necessary that these parameters be quantified to completely evaluate a retardant' s 

 effects on f lammability . 



For purposes of discussion, the effects a chemical has on f lammability can be 

 grouped under two primary considerations: 



1. The effect the chemical has on flaming combustion, and 



2. The effect the chemical has on glowing combustion. 



Previous studies (George and Susott 1971) have indicated that the different effects 

 ammonium phosphate and sulfate have on pyrolysis and combustion of cellulose are due to 

 availability of the inorganic fraction involved in the reaction or to a different 

 mechanism by which these chemicals alter pyrolysis and combustion. The results of this 

 study indicate that although there are significant differences in the effects ammonium 

 sulfate and phosphate have on flaming combustion, the differences in their effects on 

 glowing combustion are much greater. It is theorized that the difference in the effects 

 these chemicals have on glowing combustion is due to a difference in the availability 

 of the inorganic fraction or retardant chemical. Figure 17 shows thermal decomposition 

 curves for ammonium sulfate and ammonium phosphate. 2 The curves show that ammonium 

 sulfate has completely decomposed by about 425° C. while ammonium phosphate decomposi- 

 tion is not complete until about 675° C. This suggests that by the time the fire has 

 spread through an ammonium sulfate treated bed, and prior to the majority of the glowing 

 combustion process, the ammonium sulfate may have decomposed. If this were true, the 



Figure 17 is taken from the paper by George and Susott (1971). 



IS 



