Field studies of spread of fire in beds of Douglas-fir and lodgepole pine slash showed faster spread where fuel loading was heaviest. Air velocity influenced rate of spread more than loading; the relation between these two factors was an exponential function. Fire intensities were correlated by relating flame length to the B.t.u./min./unit length of fireline front. Additional results reflect analyses of fuel bed characteristics, buoyant diffusion flame characteristics, and convection column velocities.