EXPERIMENTAL DESIGN 



The Fuel Cribs 



This study was conducted under controlled 

 laboratory conditions using a standard fuel 

 crib, which meant we could control the vari- 

 ous environmental and fuel factors and their 

 influence on particulate production and 

 energy-release rate. The cribs were condi- 

 tioned to a known moisture content and 

 chemical treatment was accurately computed. 

 The flow and volume characteristics of the ef- 

 fluent gases were measured and the total con- 

 vection column accurately subsampled iso- 

 kinetically. This type of control is difficult to 

 achieve under field conditions. 



The cribs were constructed using about 20 

 pounds (9 kg.) of 3/4- by 3/4-inch (1.9-cm.) 

 ponderosa pine (Pinus ponderosa) sticks, 

 24-3/4 inches (62.9 cm.) long. These were 

 nailed together with 1-1/4-inch (3.2-cm.) wire 

 brads in a configuration that would insure 

 good combustion and allow insertion of five 

 24-inch (61-cm.) Douglas-fir (Pseudotsuga 

 menziesii) 4 by 4's (10.2 cm. by 10.2 cm.). 

 The average dry weight of a crib and 4 by 4's, 



excluding nails, was 44.0 lbs. (20.0 kg.) 

 (tables 1A and IB). Inasmuch as each crib had 

 a basal area of 4.25 ft. 2 (0.39m 2 and a load- 

 ing of 10.4 lb. ft." 2 (50.8 kg. m' 2 ), they were 

 equivalent to 227 tons acre" 1 (508,000 kg. 

 hectare -1 ). The approximate heat content of 

 each crib was 8,500 B.t.u. lb." 1 (4,722 cal. 

 g.-' ) or 3.74 by 10 5 B.t.u. (9.42 by 10 7 cal.). 



The 4 by 4's were conditioned in a sealed 

 cabinet maintained at 90° F. (32.2° C.) and a 

 relative humidity of 91 percent. The humidity 

 was held constant by the use of saturated 

 potassium nitrate solutions. Three sample 4 

 by 4's from different areas of the conditioning 

 cabinet were weighed daily and sampled for 

 actual moisture content. 



The cribs were conditioned in a room 

 maintained at 78° F. (25.6° C.) and approxi- 

 mately 30 percent relative humidity; the lat- 

 ter was maintained using a mechanical humid- 

 ifier. The cribs were weighed daily and mois- 

 ture contents were determined from sticks 

 identical to those used to build the cribs. 



Treatment 



A calibrated spray apparatus was used to 

 apply 10, 20, 30, or 40 percent solutions of 

 each chemical to the cribs and the 4 by 4's. 

 The preweighed fuel was placed on a dolly 

 and run back and forth under the sprayer un- 

 til completely coated with retardant. The 



highest treatment levels were achieved by al- 

 ternating several hours of drying with spray- 

 ing. The exact amount of chemical added was 

 calculated after each crib and 4 by 4 reached 

 a constant weight in their respective condi- 

 tioning area (table 1). 



3 



