The location and extent of a fire is the most important size-up factor. A growing fire follows the path of least resistance. The fuel is first ignited and begins to draw in air from the surrounding space. It is then rapidly affected by the ceiling and walls of the fire compartment. The location of the burning fuel in relation to the fire compartment walls affects the temperature in the developing hot-gas layer above the fire. The hot gases begin to rise and spread out when they hit the ceiling. For example, the path of least resistance for fire travel in a two-story home, where the fire is on the first floor, is likely to be an open stairwell.

Tip: Company Officers must have a good understanding of fire and the way it behaves. Fire ground operations cannot begin until the location and extent of the fire is determined. With this knowledge, the company officer can better evaluate the conditions, head off the fire spread, and take steps to localize it.