AIR ATTACK - RETARDANTS, RHEOLOGY AND SOME NEW OPTIONS

The rheological properties of forest and brush land fire retardant sol utions significantly affect their performance during and following aer ial discharge and subsequent distribution within the fuel ladder. The degree of dispersion, the integrity of the retardant cloud, the magnit ude of wind-induced drift, the continuity of coverage and retention on and penetration of the fuel complex are among diose performance relat ed characteristics impacted. The viscous character of the solution dur ing periods of extreme and relaxed shear and its elasticity are known to be important rheological properties. While applicable specification s and the technical literature document the importance of these factor s, only the extremes (water-like and highly viscous and elastic fluids ) have been available to the fire manager. A series of new fluid conce ntrate type retardants are now being evaluated jointly by the United S tates 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, mediu m or high as defined by the Federal Specifications. Selection of the p roper rheology can, thus, be made by the fire manager dependent on the type and characteristics of the delivery platform, safe drop height r elative to die terrain, atmospheric conditions, fuel characteristics a nd the management objective.