The acceleration phase of a forest fire, from ignition to the equilibrium rate of spread, is perhaps the most important phase of fire behavior because often it represents the only time period in which suppression efforts could be effective. A series of experimental fires in a wind tunnel were conducted to evaluate this acceleration phase. Two types of fuel and a total of three fuel loadings and four wind speeds were tested. The results were analyzed as distance/time data, and a predictive equation produced of the form: Distance = B x Time. The derivative of this equation relating rate of spread at a specific elapsed time since ignition compares favorably with theoretical acceleration model curve forms. The elapsed time required to achieve an equilibrium rate of spread was constant for each fuel type over the range of conditions tested.© Society of American Foresters, Bethesda, MD. Abstract reproduced by permission.