Methodologies for quantitatively comparing the effectiveness of chemical retardants for direct and indirect wildfire suppression using a combustion wind tunnel

Retardant chemicals are often used during wildfire fighting operations where they are primarily dropped from an aircraft onto unburned fuels in a fire's path. While there are established laboratory methods used to determine retarding effectiveness capacity relative to a standard, there are no specific methods for comparing the effectiveness of different retardant formulations in different operational applications. This paper develops four methodologies to assess and compare retardant effectiveness in a variety of tactical uses including retarding durability and effectiveness at different application depths. The resultant assessment methodologies use the consistent controlled environment of a combustion wind tunnel in which conditions reasonably represent field conditions and have low variability enabling fair comparisons between treatments. Evaluations of the assessment methodologies for two commercially available retardants and water are presented and demonstrate low variability in evaluation conditions and consistent, reliable results. These methodologies provide valuable and cost-effective insights into chemical performance and will help wildfire suppression agencies to make informed procurement decisions.