Byram Derivation of the Energy Criterion for Forest and Wildland Fires

Abstract

G.M. Byram's energy criterion for forest and wildland fires consists of two equations: one for computing the rate of flow of kinetic energy in the atmosphere due to the wind field (P_w), and one for estimating the rate of conversion of thermal energy to kinetic energy in the convection column (P_f). The derivation of the equations has remained unpublished since their introduction in 1959. Byram considered the dimensionless ratio of P_f to P_w an indicator of the vertical structure of convection over a fire and referred to the ratio as the convection number, N_c. In view of past and current interest in the behavior of large fires, Byram's derivation of the equations for P_w and P_c is presented along with a sketch and some additional wording for purposes of clarification. The assumptions and possible limitations in Byram's analysis are discussed.