The samples were basically the same except for minor differ- 

 ences in composition and manufacturing process. The chemicals 

 and their apparent differences are: 



M-MAP - Fisher Scientific, ACS grade, granular form. 



Contains less than 0.03 percent impurities. 



S-MAP - Technical grade, granular form. Produced from 

 » technical grade phosphoric acid (white acid 



process) that has been neutralized with anhy- 

 drous ammonia. 



D-MAP - Technical grade, crystalline form. Technical 



grade phosphoric acid neutralized by ammonia- 

 rich gases that are given off by burning coal to 

 make coke. 



T-MAP - Technical grade, crystalline form. Produced 

 from technical grade phosphoric acid that has 

 been neutralized with anhydrous ammonia. 

 (T-MAP and S-MAP are manufactured by simi- 

 lar processes, but by different companies.) 



A-MAP - Technical grade, crystalline form. Manufactured 

 from wet-process phosphoric acid and then re- 

 purified to produce a technical grade product 

 with less than 0. 1 percent of impurities. 



The phosphate quantities were calculated as P2O5 equivalents 

 to aid effectiveness comparisons because all MAP or DAP for- 

 mulations should be equally effective if the phosphate (PiOs) in 

 each (the principal fire-retarding element) is present and avail- 

 able in equal concentrations. 



The study was an indirect way to determine if the manufac- 

 turing process, manufacturer, or quality of fire retaidant chem- 

 ical causes any reduced availability of the phosphorus at the 

 precise time or temperature during p>Tolysis when the retardant 

 would have the needed effect (George and Susott 1971). Com- 

 parison of like quantities of different chemicals that are equally 

 effective fire retardants will indicate how much added chemical 

 is necessar>' to increase the total available phosphorus in a par- 

 ticular chemical formula. All effectiveness data are compared 

 to DAP because it has been used as a standard of comparison 

 since 1970 (George and Blakely 1972). 



STUDY METHODS 

 Fuel Beds 



Combustion-retarding effectiveness data were gathered by 

 burning m.at-type fuel beds treated with different retardant 

 chemicals. Two fuels were used for the study — ponderosa pine 

 needles and aspen excelsior. The pine needles, gathered locally, 

 were cleaned of debris, grass, and sticks, and stored to dry. 

 The excelsior was ordered in compact bales that were pulled 

 apart and allowed to come to equilibrium moisture content 

 under inside conditions. The two fuels were used to determine 

 the fire-retarding effectiveness of chemicals on fuels with a high 

 cellulose (42 percent) and a low crude fat (1 percent) content 

 (excelsior), and fuels with a low cellulose (18 percent) and a 

 high crude fat (10 percent) content (needles). These fuels were 

 not necessarily used to duplicate natural wildfire conditions, 



but because they (1) are relatively easy to obtain, (2) respond to 

 temperature and humidity changes, (3) are similar in chemical 

 content to many fuels encountered on wildland fires, and (4) 

 provide predictably reproducible fu"es under controUed environ- 

 mental and fuel moisture conditions. 



Standard techniques were used (George and Blakely 1972) for 

 constructing and treating the 8-ft- (2.44-m-) long, 

 3-inch-(7.62-cm-) deep, 18-inch- (45.72-cm-) wide fuel beds. 

 Each pine needle bed contained 6 lb (2.72 kg) of fuel, and each 

 excelsior bed contained 4 lb (1.81 kg) of fuel. The fuel moisture 

 content (measured by xylene distillation) was between 4 and 5.5 

 percent for excelsior, and 6 and 7.5 percent for needles after 

 preconditioning and before chemical treatment application. 



Adjustments for Differences in Untreated Fuel 

 Burning Rates 



The burning characteristics of different batches of untreated 

 fuels have varied somewhat in previous laboratory studies. Pine 

 needles gathered in the fall have combustion rates that differ 

 from those gathered in the spring, and fall needles may vary^ 

 slightly from year to year. The same is true of batches of com- 

 mercially prepared excelsior that may vary somewhat in un- 

 treated flame spread rates and total weight-loss rate. Because of 

 the variations in untreated fuels used in this study, adjustments 

 were necessarv' to make burning data comparable. One method 

 was to calculate the percentage that untreated fuel combustion 

 rates for individual fires are reduced by each treatment. By this 

 means, the differences in untreated burning rates (flame spread 

 and fuel bed weight loss) are taken into account and numerical 

 comparisons can be made. A rating indicates that a retardant 

 has no effect on combustion, and a 100 rating indicates that a 

 chemical totally stops flaming and glowing combustion. The 

 percentage rating is calculated using the flame-spread rate and 

 weight-loss rate for untreated and treated fuels (pine needles 

 and aspen excelsior). For comparisons to be valid, treatment 

 levels for different fires or chemicals must be approximately 

 equal. Spread- and weight-loss rates for treated fuels are 

 calculated as percentages of spread- and weight-loss rates for 

 untreated fuels (percent reduction). Equal numbers of fires for 

 each treatment level (or weighted averages) must be used if 

 statistically meaningful percent reduction factors are to be 

 averaged for two or more treatment levels. 



Another method was to adjust each treated fuel burning rate 

 by a percentage corresponding to the differences in average un- 

 treated burning rates for different batches of fuel. Recently 

 used untreated fuels have burning rates varying from 5 to 17 

 percent higher than rates for untreated fuels used in the past 

 when the DAP and M-MAP bums were conducted; therefore, 

 in this study S-MAP burning rates have been adjusted down- 

 ward. This adjustment also permits the use of the actual spread 

 and weight-loss rates for computations and graphing, rather 

 than conversion to percent reduction of untreated rates. Table 

 1 shows the untreated averages and the differences between 

 needles and excelsior used in 1970 and 1980. 



2 



