An algorithm is developed that converts three time measurements to the direction and rate of spread of a fire across any triangle. Procedures are also developed for analyzing the uniformity of fire spread, given four time observations. Flexible sampling techniques allow the procedures to be adapted to a wide variety of fire-related phenomena on prescribed fires or wildfires. Using the procedure, we stratified rate of spread data for a prescribed fire into two significantly different groups. Forest Sci. 30:51-64.