Wind-Aided Firespread Across Arrays of Discrete Fuel Elements. II. Experiment

Laboratory-scale experiments on wind-aided firespread across an array of very-small-diameter (1.3-4.4-mm), discrete fuel elements were carried out in a specially designed wind tunnel. The rate of firespread, ty, is inferred from the output of streamwise-disiributed, near-bed-surface thermocouples. The fuel consists of an array of identical, regularly arranged, wooden, toothpick-like Tuel elements, positioned upright in shallow holes drilled in a ceramic substrate. Adoption of this well-defined fuel bed facilitates repetition. Extensive testing suggests that νy ∼ (U/m)1/2 over a wide range of the uniform ambient wind speed U and the fuel-mass distribution m (fuel, per unit planform area of the bed, consumed with firefront passage). The effects on the firespread rate of other parameters investigated and reported include the type of wood species; fuel-element length; fuel-element diameter; fuel-bed width, including streamwise-varyjng width; enhanced moisture content of the substratum and/or fuel; small-scale variability within macroscop-ically identical fuel beds; and mixed beds (beds with combustible elements of multiple thicknesses; beds with thermoplastics or inert material in addition !o wooden elements). The firespread rates reported here are compared with the results of previous investigators. In addition to the rate of firespread, we report the flame-burn-time, fburn, inferred from the output of a very-thin-wire thermocouple in the fuel bed. Finally, we present preliminary work examining the rate of wind-aided firespread across more clumped fuel distributions (arrangements with fewer, larger elements).