What is the term for the part of a fire's perimeter that runs parallel to its main direction of spread?

The term that describes the part of a fire's perimeter running parallel to its main direction of spread is known as the flank of a fire. In the context of wildland fire behavior, the flank can be thought of as the sides of the fire that extend outward from its head, allowing the fire to spread laterally while the main advance of the fire occurs at the head. Understanding the location and behavior of the flank is crucial for firefighting strategies as it helps predict where the fire might spread next and how crews can best manage containment efforts.

Other terms used for different parts of a fire include the head, which is the front or leading edge where the fire is actively spreading, and the rear, which is the portion of the fire that is generally the most stable and least active. The fingers of a fire refer to narrow extensions that project from the main body of the fire, often influenced by localized conditions such as terrain or wind. Knowing these distinctions helps in strategizing based on the fire's behavior and containment tactics.