THE METHOD 



The development of a method to evaluate the effect of retardant chemicals on 

 flammability required considerable attention to the following: 



1. Type of fuel and fuel bed configuration; 



2. Method of chemical application; and 



3. Conditioning of fuel following chemical application and environmental conditions 

 during burning. 



Type of Fuel and Fuel Bed Configuration 



Previous research on the effects of fire retardants (Hardy, Rothermel , and Davis 

 1962; Rothermel and Hardy 1965) demonstrated the usefulness of ponderosa pine needle 

 fuel beds which were originally used because of their natural physical and chemical 

 characteristics; whether or not this type of fuel is representative of most forest fuel 

 was questioned. 



Ponderosa pine needles alone are not representative because they contain a rela- 

 tively high amount of ether extractives (approximately 10 percent) which apparently 

 volatilize at low temperatures and support combustion. Furthermore, woody fuels make 

 up a large portion of natural forest fuel and generally contain less extractives and 

 a larger percentage of cellulose. Aspen excelsior (0.021 inch by 0.021 inch by 3 

 inches), is a representative woody fuel and also exhibits a high degree of reproduci- 

 bility; thus, it has been used to successfully evaluate fire retardants (USDA Forest 

 Service 1970; USDA Forest Service 1969). This excelsior contains less than 1 percent 

 ether extractives but has nearly the same heat content as ponderosa pine needles. (A 

 comparison of chemical characteristics is given in table 1.) By using both of these 

 fuels the researcher was able to simulate the extremes of chemical fuel characteristics 

 normally found in forest areas. 



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