Major revisions to Rothermel's fire spread equations include the propagating flux ratio, reaction velocity, and moisture damping coefficient. The reaction intensity is of the flames alone and specifically excludes energy derived from burning char whether or not it lies in the flaming zone. In this new formulation, moisture damping is completely divorced from fire extinction. Fire extinction is a probability function.
United States Department of Agriculture, Forest Service, "Reexamination of Rothermel's Fire Spread Equations in No-wind and No-slope Conditions" (1990). Wildfires. Paper 8.