It is virtually impossible to determine precisely the amount of fuel consumed in the active combustion zone of a forest fire under field conditions. The amount of fuel consumed by secondary combustion and residual burning after passage of the main fire front (Fig. 1) will increase w and consequently result in an overestimation of fire intensity. Glowing combustion and persistent smoldering are more commonly associated with heavy woody surface fuel concentrations and (or) deep organic layers and low fuel moisture conditions (Kiil 1971). Reductions in the total w measured may be necessary if
significant quantities of fuel are consumed subsequent to passage of the flaming front. In the absence of pre- and
post-fire measurements, and on-site observations during the fire, appropriate reductions will have to be based on
experience and judgment.