Containment is one of the most commonly misunderstood numbers associated with a wildfire. A fire's containment percentage tells you how much of its perimeter has a barrier that is expected to prevent the fire from spreading beyond it.
It does not tell you how much of the fire has been extinguished or how actively the fire is burning.
What does the containment percentage mean?
Containment is measured around the perimeter of a fire. A portion of the perimeter is considered contained when firefighters are confident that barriers are in place that are expected to stop the fire from spreading across that section.
Those barriers can include:
- Fire lines constructed by crews
- Roads
- Previously burned areas
- Large bodies of water
- Other natural or constructed barriers
For example, if a fire is 25% contained, approximately one-quarter of its perimeter has barriers that incident officials are confident will hold. The fire may still be able to spread beyond the remaining portions of the perimeter.
Does a higher containment percentage mean the fire is less active?
Not necessarily.
Containment describes the security of the fire's perimeter, not the intensity or activity of the fire itself.
A fire can still be actively burning within its perimeter even at a high containment percentage. Likewise, a fire with low or 0% containment isn't necessarily burning intensely across its entire area.
Containment should therefore not be used by itself to determine how active or dangerous a fire currently is.
Who determines a fire's containment?
Containment percentages are determined by the officials managing the incident, such as the Incident Commander or Incident Command Team.
Watch Duty does not calculate or estimate containment percentages. We report containment information provided through official incident sources, including Incident Command and official systems such as WildCAD and the National Interagency Fire Center (NIFC).
If officials haven't provided an updated containment figure, Watch Duty doesn't estimate one based on how the fire looks or how active it appears to be. When a containment figure is unknown, it will appear as “-” instead of 0%.