INTRODUCTION 



The Problem 



More than 80 million gallons of fire retardant have been used in the control of 

 forest and rangeland fires by fire control agencies throughout the United States in the 

 last 10 years. These fire retardants are specially formulated and usually contain: an 

 active retardant chemical; coloring agent; corrosion inhibitor; thickening agent; and 

 spoilage inhibitor, when necessary. 



The most commonly used active retardant chemicals are ammonium sulfate (NHi+^SOij 

 and ammonium phosphate (NH^) 2HPO4 . These chemicals, when applied to cellulosic fuels, 

 alter the combustion process to produce less flammable products while increasing the 

 amount of nonflammable products. The most efficient use of these chemicals can only be 

 made after thorough quantification of their effects on flammability . 



Flammability has been defined as the interaction of ignitibil ity, sustainability , 

 and combustibility (Anderson 1970). Ignitibility is the ease with which a fuel will 

 ignite. Under given conditions, the most ignitible fuel will ignite with the least 

 energy input. Sustainability is a measure of how well the fuel will continue to burn 

 with or without the heat source after ignition. Combustibility is a measure of the 

 rapidity with which energy is released from the fuel following ignition. 



Fire retardant chemicals are often applied to reduce the overall flammability of 

 fuels. In other instances these chemicals are used specifically to reduce the sustain- 

 ability or combustibility. It is often thought that ignitibility is decreased by treat- 

 ing fuel with retardant chemicals such as ammonium sulfate and ammonium phosphate; how- 

 ever, recent empirical data indicate the reverse--i . e . , less energy is necessary for 

 ignition of treated fuel. 1 This fact is substantiated by more sophisticated thermal 

 analysis data which indicate that treated cellulose undergoes pyrolysis and combustion 

 at lower temperatures and with less energy inputs than does untreated cellulose (George 

 and Susott 1971). (Pyrolysis is the thermal degradation of a material.) 



Unpublished experimental data on file at the Northern Forest Fire Laboratory, 

 USDA Forest Service, Missoula, Montana. 



1 



