Northern Rockies Incident Management Team 3

Heat lingers in heavy fuels in the higher elevation areas of the Derby Fire. The term “heavy fuel” refers to dead trees (also called snags) that are larger than 3 inches in diameter. Large stumps, standing snags and fallen logs are all included in this category.

The larger size of these dead trees makes them slow to ignite, but once smoldering, they’ll hold heat for extended amounts of time. It can take multiple weeks for them to adjust to changes to moisture levels in the atmosphere – earning them the label of “1,000 hour fuels.”

On Wednesday, August 27, 2025, firefighters worked to construct handline on the southeast side of the Derby Fire. When crews encounter burning snags as they construct control lines they use a variety of tools to extinguish the flames. S.Rawding/Derby Fire.