retardant. The greatest amount lay near the fuel bed surface; progressively lesser amounts 

 penetrated the fuel toward the bottom . Virtually no retardant reached the bottom of the fuel bed 

 when the 1 gal./100 sq.ft. rate was applied. Application procedures described in an earlier 

 test 5 required use of only one -third of the retardant after each 1-inch layer of needles was 

 placed in the fuel bed, creating a sort of three-layered sandwich of fuel and retardant. This 

 system was not practicable for the present test series because the rigid drying schedules did 

 not allow for the time involved in the layered application method. The one -application method 

 used in the present tests was closer to what is encountered under field conditions, and fires 

 smoldered along the bottom of the fuel bed much as they do under field conditions. 



Operation of Retardant Application Equipment 



After weighing, the fuel beds were placed in the spray chamber, where the applicator tank 

 had been set at the correct pressure and height above the fuel bed. The operator opened the 

 ball valve and began spraying retardant beyond the end of the fuel bed. The retardant flow was 

 timed as the carriage crossed above the end of the fuel bed. The carriage continued to move 

 back and forth above the fuel until the time required for applying the desired amount had 

 elapsed. To prevent buildup when the carriage movement stopped or was reversed, the opera- 

 tor sprayed beyond the end of the fuel bed before changing directions. When the amount 

 estimated to be proper had been applied, we reweighed the fuel bed to determine the exact 

 amount of application. If when reweighed the fuel bed was more than 5 percent too light, 

 the carriage operator applied an additional light layer; if it was more than 5 percent too heavy, 

 we discarded the fuel bed and started over. (See fig. 14, p. 27, for sample record sheet.) We 

 weighed fuel beds in the drying rate pans to the nearest gram on a solution balance, and fuel 

 beds on the large burning trays were weighed on a platform scale that enabled the weight to be 

 determined to the nearest 0.01 pound. Immediately after final weighing, the operator hoisted 

 the pan or tray into position in the environmentally preconditioned wind tunnel for the drying or 

 burning test (figs. 3,4, and 5). 



5 Hardy et al . , op . cit . , p . 1 . 



Figure 3. --Applying 

 retardant --note 

 spray pattern. 



