concept

Fireline intensity

The energy released each second by one metre of advancing fire front, in kW/m. George Byram published it in 1959 as I = H·w·r, where H is the fuel's heat of combustion, w the fuel mass consumed per unit area, and r the rate of spread. It is the most operationally useful single number in wildfire suppression: above roughly 2000 kW/m, direct attack by crews and hoses on the ground fails outright. It also ties to the flame length anyone can see, through L = 0.0775·I^0.46, so a witness estimating flame height is already estimating intensity.