During a run (1 day's operation) we applied a specified amount of each of the six retard- 

 ants (1, 2, or 3 gal. /1 00 sq.ft.) to each of three 3- by 18- by 24 -inch pans. The entire group 

 of 18 pans was then subjected to one of the three environmental conditions (I, II, or III) 

 described in tables 2 and 3. 



The operator reweighed each pan to the nearest gram on a direct- reading balance after he 

 brought it into the wind tunnel and before placing it in its assigned cell. Weighing continued at 

 15-minute intervals until the loss in moisture showed a difference of 2 grams or less between 

 any three readings . After each weighing the pans were rotated in sequential order from cell to 

 cell to reduce any effect of possible unequal airflow through the wind tunnel's cross section 

 (fig. 6). 



Burning Test 

 Burning Plan 



The burning plan held the total number of test fires to a minimum by restricting the 

 number of considerations . The considerations to be covered were two retardant types , three 

 environmental conditions, three drying times, three application amounts, and three replications 

 of each test. Complete coverage of all these would have required 162 fires, plus reruns in the 

 event of instrument failure. Such complete coverage was beyond the scope of our time, budget, 

 and fuel supply; however, the number of tests finally chosen covered the most pertinent data 

 and answered our questions satisfactorily. 



The total number of fires actually burned was held to 73 by reducing the number of drying 

 conditions from three to two and by adjusting the application amounts as dictated by the test 

 conditions. The short-term retardants were tested when they were 33- and 67-percent dry; 

 the long-term retardants, when they were 67- and 95-percent dry. Since previous testing 6 had 

 shown that short-term retardants were ineffective after severe drying, there seemed to be no 

 need to test short-term retardants when they were 95-percent dry. The same report clearly 

 showed long-term retardants to be superior to short-term retardants under any given condition, 

 and thus eliminated need for extensive comparative testing now. 



6 Hardyetal., op. cit., p. 1. 



Figure 6. - -Drying test equipment 

 in wind tunnel. Rack in back- 

 ground has screen and baffles 

 on upwind side to establish 

 uniform airflow over the pans . 



