What is the 'heel' in the context of fire terminology?

In fire terminology, the 'heel' refers to the slowest moving part of a fire. This section typically represents an area where the fire's intensity and spread are less aggressive compared to other parts of the fire. Understanding the characteristics of the heel is important for firefighting strategy because it can present opportunities for fire containment efforts. The heel can often act as a safe area for firefighters to position themselves or to establish control lines.

While the other options describe various aspects of fire behavior, they do not capture the essence of what the heel signifies. For instance, the most dangerous part of the fire is generally known as the 'head,' and the actively burning edge is typically referred to as the 'flank' or 'head' depending on the context. Smoke density can vary throughout the fire and does not specifically identify a particular area in relation to the fire's progress. Thus, recognizing the heel as the slowest part assists in strategic planning for safe and effective firefighting.