A simple theoretical model of the transition to flame attachment

Flame attachment occurs when a fire lays forward under the influence of wind, bathing fuels ahead of it in combustion gasses. The transition from unattached flame to attached is thus capable of producing a rapid increase in fire intensity and a surge in forward spread. Using simple fluid dynamics arguments, one can derive an equation for the conditions that trigger the transition to attachment, as a function of wind speed, rate of spread, and fuel loading (as well as other parameters.) In spite of its simplicity, this model allows exploration of the relationships among these variables. It retains several assumptions, specifically those related to spatial scales, so that their importance can also be examined. The derivation, some implications, and relationships to earlier fire behavior studies will be presented.