n. The open wind speed above which an active crown fire is possible for the specified fire environment.
Crowning index is defined in general terms so that it can be used in a variety of applications and geographic areas. Open wind speed can be either 20-ft or 10-m, depending on the prevailing standard measurement height above ground. The specified fire environment can vary from project to project. Of the fire behavior calculation tools available, only the fire behavior model NEXUS directly computes crowning index. In the BehavePlus fire modeling system, crowning index represents the open wind speed at which the active ratio is 1.