When it’s reported that a wildfire is a certain percentage contained, how is that calculated?

Question

While reading news of the wildfires in Maui, I see that they’re estimating fires are something like 50% or 80% contained. How do they go about calculating that percentage for such a wide area and with the expectation that the fire will continue to grow?

Source: https://www.cnn.com/2023/08/12/us/maui-wildfires-hurricane-dora-saturday/index.html

In: 7

Answer 1

Containment % typically refers to how much of a fire is encircled by a fire guard or a natural fire break (ie. river, rock face, etc.) As a fire burns down and depletes the fuel in an area, that area also becomes a natural fire break, making it very difficult for a fire to double back on itself. Consequently, you’ll almost never see “100% containment” except for fires that have nearly burned out.