Air Attack - Retardants, Rheology and Some New Options

Abstract

The rheological properties of forest and brush land fire retardant solutions significantly affect their performance during and following aerial discharge and subsequent distribution within the fuel ladder. The degree of dispersion, the integrity of the retardant cloud, the magnitude of wind-induced drift, the continuity of coverage and retention on and penetration of the fuel complex are among diose performance related characteristics impacted. The viscous character of the solution during periods of extreme and relaxed shear and its elasticity are known to be important rheological properties. While applicable specifications and the technical literature document the importance of these factors, only the extremes (water-like and highly viscous and elastic fluids) have been available to the fire manager. A series of new fluid concentrate type retardants are now being evaluated jointly by the United States Forest Service and private industry. Upon simple dilution to use level concentration, these low viscosity fluids increase in viscosity and elasticity to one of three predetermined levels, i.e., low, medium or high as defined by the Federal Specifications. Selection of the proper rheology can, thus, be made by the fire manager dependent on the type and characteristics of the delivery platform, safe drop height relative to die terrain, atmospheric conditions, fuel characteristics and the management objective.