In this study, fires on which the retardants were judged to be effective continued to burn 

 deep within the fuel bed where there was Little or no retardant. These fires could have been 

 stopped easily by a heavier application of retardant or by deeper penetration, or by a break in 

 fuel continuity such as is found in wildland fuels. 



The amount of retardant to be applied was determined by using first the median amount at 

 each new condition, and then adjusting the next amount of application according to the success 

 or failure of the first amount. The amounts applied thus varied from 1 to 3 gallons per 100 sq. 

 ft. If the retardant was judged to be effective, even with the minimum application, the environ- 

 mental conditions were increased to a higher Spread Index for the next series of tests. If 

 judged ineffective, the quantity of retardant applied was increased. 



Positioning of Tray 



Immediately after the 3- by 18- by 96-inch burning tray had been treated, the operator 

 lifted it into the large wind tunnel and placed it on the strain gage weighing system attached to 

 the fixed support frame (fig. 7). An untreated 3- by 18- by 36-inch fuel bed (igniter tray) placed 

 upwind from the longer, treated bed afforded the fire a chance to approach a steady rate of ad- 

 vance before it came in contact with the retardant -treated fuel- -a situation comparable to what 

 might occur in nature. End and side ground plane aprons designed to produce uniform airflow 

 over the needle surface were placed on all sides of the treated and igniter trays . The final 

 preparation included placing the alcohol ignition trough at the upwind end of the igniter tray. 



Drying 



The fuel bed was ready to be burned as soon as the designated amount of retardant - 

 associated moisture had evaporated. The evaporation was monitored on the same weighing 

 system used to measure rate of fuel consumption during the fire. 



Ignition 



Just before test time, an observer poured 15 cc . of alcohol into the ignition trough. A 

 remotely controlled electric spark ignited the alcohol, which in turn set afire the igniter tray 

 of untreated needles. The fire in the untreated fuel bed established a strong flame front, which 

 burned into the retardant-treated fuel bed. 



Figure 7 .- -Instrumented 

 support frame in wind 

 tunnel. Note the side 

 and front ground 

 planes in place. 



