Wildfire field guide
What does “mop-up” mean in wildfire suppression?
Why crews can spend days extinguishing hidden heat, removing burning material and securing the edge after the main flaming front has passed.
Definition
Mop-up makes the fire edge safer after burning.
Interagency wildfire terminology defines mop-up as work such as extinguishing or removing burning material near control lines, dealing with hazardous snags and logs, and reducing residual heat or smoke so the fire is less likely to escape or rekindle near the line.
Typical work
What crews actually do during mop-up.
Water, hand tools and pumps can be used to extinguish smoldering wood, duff, stumps and other residual heat.
Crews focus especially on hot material near fireline because a small rekindle there can threaten containment.
Operations can include felling dangerous snags or trenching logs so burning material cannot roll across a control line.
Crews repeatedly check contained sections for smoke, heat, spot fires or other signs that require additional work.
Containment
Why mop-up continues at 80%, 90% or even 100% containment.
Containment is primarily a statement about the perimeter. Mop-up addresses residual burning and threats to that perimeter. The two concepts overlap operationally but are not the same thing.
- A contained edge can still have hot material nearby.
- Interior logs, roots or duff can continue to smolder.
- Crews may continue patrol after containment rises substantially.
- Incident resources can be reduced gradually as risk falls rather than disappearing the moment a percentage threshold is reached.
Detection
Hidden heat is part of the problem.
Residual heat may not always present as visible flame. Firefighters can look for smoke, ash, heat signatures and other signs, while incident teams may also use infrared or aerial systems to locate heat in difficult terrain.
That is why a fire can look visually quiet from a distance while crews are still conducting substantial work inside the perimeter.
Sources