One thing that most Fire Fighter I and II courses do not teach is the simple fact that fire behavior is not always predictable. We can predict—probably—where the fire is going to go and what it will do—probably—when it gets there, but these predictions are without certainty.

Part of fire behavior is determined by the structure in which it occurs. Is the structure combustible or noncombustible, fire-resistive or not, small compartment or large open space, rooms finished with low-flame spread or other type materials? Also, are the materials lightweight or does it have enough mass to provide some inherent fire resistance.

Part of fire behavior is determined by the fuel, whether it is cellulose- or petroleum-based, and the geometry of the fuel (the size and shape of its pieces or particles, their arrangement, and their location within the compartment).

Part of fire behavior is determined by the ventilation, i.e., whether the compartment is closed with limited air supply or has openings and an available supply of fresh air and an opening for the escape of the products of combustion. Forcible entry into the structure, wind speed and direction, or removal of upper floor windows for use as secondary exits changes the ventilation characteristics of the building and the fire. Which openings are used for which purpose depends on the temperature differential between the fire compartment and the incoming fresh air; wind direction and velocity; and the volume of, and the path followed by, the combustion products that are trying to escape.

We do not have absolute control over most of these.

Photo 1 shows an acquired structure (platform framed with joists and rafters of sawn lumber) used for live fire training in compliance with NFPA 1403, Standard on Live Fire Training Evolutions. After the individual room fire attacks had been completed and overhauled, fires were set on each floor to burn down the remaining structure. These fires were located in stacks of pallets and arranged so that the structure should have burned down symmetrically. Even though the wind (five miles per hour) was blowing from the B-C corner to the D-A corner, most of the products of combustion vented from the missing patio doors and windows on the C side and from the roof ventilation hole.