Wildfire field guide
Head, Flank and Rear of a Wildfire: what do they mean?
Wildfire reports often describe different parts of the perimeter because they can behave very differently at the same moment. The head is usually the fastest-moving portion; the flanks and rear describe other sectors relative to that main spread direction.
Parts of a fire
The perimeter is not one uniform front.
NWCG divides the fire perimeter according to the predominant direction of spread, from the fastest-moving portion to the slowest-moving portion.
The head is generally the most rapidly advancing part of the perimeter and is often aligned with wind, upslope spread or both.
The left and right flanks are the portions of the perimeter roughly parallel to the main direction of spread.
The rear is opposite the head and often spreads into the wind or downslope under otherwise steady conditions.
Why it matters
Fire behavior changes around the perimeter.
One incident can simultaneously have rapid, high-intensity spread at the head and much slower behavior at the rear. That is why a single spread rate or flame-length value should not automatically be assigned to the entire perimeter.
- The head commonly has the highest forward rate of spread.
- Flanks can become more active if wind or slope alignment changes.
- The rear may have lower spread and intensity under current conditions.
- Observed behavior must be tied to the perimeter sector where it was measured.
Wind shift
A flank can become the new head.
These labels are not permanent geographic names. They describe the fire relative to its current dominant spread direction. If the wind changes, a previously quiet flank or rear can become aligned with the new direction of spread.
Connect the concepts
Direction and rate belong together.
Sources
NWCG terminology.
NWCG Firefighter Math — Head, Flank and Rear ↗
Published 21 September 2026.