Comparing Techniques for Estimating Flame Temperature of Prescribed Fires

A variety of techniques that estimate temperature and/or heat output during fires are available. We assessed the predictive ability of metal and tile pyrometers, calorimeters of different sizes, and fuel consumption to time-temperature metrics derived from thick and thin thermocouples at 140 points distributed over 9 management-scale burns in a longleaf pine forest in the southeastern US. While all of these devices underestimate maximum flame temperatures, we found several to be useful for characterizing other metrics of fire behavior. While the degree to which thermocouples underestimated maximum temperatures was based on thickness, metrics derived from thermocouple data that integrated time and temperature minimized this discrepancy between thin and thick thermocouples. Thermocouples also provided the most detailed spatial and temporal data of the devices tested. Pyrometers underestimated maximum temperatures relative to thermocouples, but due to their low cost, can be useful for examining spatial variation in temperature during fires. Use of calorimeters is disadvantageous given their lack of precision and high labor cost. Simple fire behavior observations taken during burns and indicators of fire severity observed post-burn were inexpensive to estimate and revealed useful differences among fires. Due to the wide variation among these techniques in cost, labor, accuracy, and level of detail of results, their suitability for a particular project will vary according to research objectives and available resources. Researchers should ensure that the fire behavior parameter measured has a logical relationship to the effect of interest, is measured at an appropriate level of detail, and is reported with attention to the limitations of the measuring devices used.