SUMMARY AND DISCUSSION 



The study objective was to compare the fire-retarding effec- 

 tiveness of diammonium phosphate and several samples of 

 monoammonium phosphate. Diammonium phosphate has been 

 the standard for several years; therefore, the other chemicals 

 were compared to its effectiveness. M-MAP and S-N4AP 

 proved to be as effective as DAP for retarding flaming and 

 glowing combustion when compared on an equal P2O5 equiv- 

 alent basis under statistical analysis. The other three 

 samples — D-MAP, A-MAP, and T-MAP — (even though fewer 

 burning tests were performed) appear to be equally as effective. 

 The differences in flammability reduction are because of experi- 

 mental error and are not statistically significant. They are prob- 

 ably caused by inconsistencies and variations in fuel bed con- 

 struction, fuel physical configuration, fuel moisture content, 

 environmental conditions, and so forth. 



These tests and others (George and Susott 1971) indicate that 

 the most important chemical characteristic is the available 

 phosphorus (P). As the chemical is heated, the phosphate (PO4) 

 compounds are converted to phosphoric acid (H3PO4) that 

 alters pyrolysis of the fuel. Both diammonium and monoam- 

 monium phosphates are converted easily to H3P04because the 

 ammonia cations (NHj) are driven off at low temperature: 



166° C 



(NH4)2 HPO4 -* NH4 H2PO4 + NH3 t 



^ 190° C 



-* H3PO4 + NHjT -H2O + P2O5 

 A 



Phosphate anions (PO4), when combined with sodium (Na), 

 calcium (Ca), potassium (K), and others, cannot be converted 

 to H3PO4 readily, and therefore do not make the PO4 available 

 in the most effective form as fire retardant. 



Whether or not one or two ammonias are associated with the 

 P does not appear to make a difference. The method for asso- 

 ciating the ammonia with the phosphate (PO4) also does not 

 appear to affect the fire-retardant ability. Whether ammonia is 

 extracted from coal smoke that is being "scrubbed" with 

 phosphoric acid (D-MAP) or whether the acid is being am- 

 moniated by bubbling ammonia gas into it (S- and T-MAP) 

 seems to make no difference in the availability of P and the 

 resulting fire-retarding effectiveness. A-MAP, produced from a 

 less pure acid, is as effective as the other MAP forms when 

 most of the impurities have been removed after ammoniation. 

 The fire-retarding effectiveness of each MAP (and also DAP), 

 when in a pure form, can be equated on the P or P2O5 content. 

 Any formulations containing impurities may change the level of 

 effectiveness. 



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17 



