Initial Attack Assessment (IAA)

Initial Attack Assessment

In addition to the fire behavior outputs, an Initial Attack Assessment Index (IAA) output is calculated for each fire spread prediction. Initial Attack are the actions taken by the first resources to arrive at a wildfire incident. Initial actions may be size up, patrolling, monitoring, holding action, or aggressive Initial Attack (NWCG, 2014).

The IAA model provides an estimation of the difficulty of fire control in the first 1-2 hours after the ignition time. It is a qualitative index ranging from 1 (low difficulty) to 5 (extreme). Although IAA gives a quick approximation of the suppression difficulty of each single fire, note that the index is not valid for longer fire durations than 2 hours (i.e., when the fire is not contained in the initial attack). This index is not recommended to estimate suppression difficulty in an Extended Attack Assessment (EAA).

The IAA index is compound of two sub-indices as follows:

Initial Attack Assessment Index = f(Fire behavior Index, Terrain Difficulty Index)

A description of the sub-indices is provided.

1h-Fire Behavior Index (FBI)

The 1h-FBI calculates the fire characteristics if burning without suppression during the first hour since ignition. It is calculated based on the Rate of Spread of the fire in chains per hour (80 ch/hr = 1 mi/hr), and Flame Length in ft. These values have a direct relation to suppression activities, as the commonly use Hauling Chart summarizes.

FireSim uses the following matrix to calculate FBI ranging from 1 to 5 based on the aforementioned variables and ranges.

The different values of FBI vary from 1 (Low) to 5 (Extreme) as shown in the next table.