Measurements 



Records began when needles on the treated fuel bed first caught fire. 



Rate of spread. --A marker board lay alongside the untreated fuel bed. An observer with 

 a stopwatch recorded the length of time required for the fire front to travel each 6-inch in- 

 crement of fuel bed. He also noted any unusual or erratic behavior. 



Weight loss. --The loss of weight as the flame front advanced was measured by a system 

 of strain gages used as the sensing element; it transmitted the information onto a strip chart 

 recorder. The record was continued after the flames reached the end of the fuel bed until 

 no more appreciable loss was encountered. 



Radiation. - -A radiometer mounted 8 feet above the fuel bed measured and transmitted to 

 a strip chart recorder the radiant energy released between the 5- and 7 -foot marks of the 

 burning fuel bed . 



RESULTS 

 Drying Test 



Results of the drying test are shown in figures 8a, 8b, and 8c. These uncorrected data 

 clearly show that the retardants dry according to the environmental conditions as well as the 

 initial amount of retardant applied. Contrary to popular belief, all retardants dry at practically 

 the same rate. Retardants applied in heavier application amounts than the mean stayed high in 

 the grouping; conversely, those that were applied lighter than the mean stayed low. Any real 

 difference in drying rate would be shown by crossing lines and definite trends away from the 

 mean; to be significant, such divergences would have to exist in all nine conditions tested. No 

 such trends are apparent . 



The data shown in all three parts of figure 8, when plotted on semilog paper, produce 

 straight lines until the retardant is almost dry. The deviation at the dry end of the curve is 

 attributed to the depletion of surface water and the slower release of water from within the fuel 

 itself. An equation for the straight portion of the line is: 



M = M Q e~ rt (1) 



where: M = moisture at anytime (grams) 



M = initial amount of moisture (grams) 

 r = drying rate constant 

 t = time (minutes) 

 e = the base of natural logarithms 



Equation (1) is the integrated form of the classical differential equation: 7 



dM w /ON 



— = rM (2) 



Equation (2) shows that the change of M with time depends upon a constant r and the amount 

 M that is present at that time . 



7 The form of equations (1) and (2) is used to describe the discharge of a capacitor, the 

 growth of bacteria, or, as Sir Isaac Newton showed, the cooling of a cannonball. 



12 



