How wildfire containment works: What it means to contain the L.A. fires

Deadly wildfires continue to ravage the Los Angeles area, as firefighters battle windy conditions to contain the out-of-control blazes.

But what does it mean to “contain” a wildfire?

Containment does not mean that a blaze has been completely extinguished. Rather, it refers to how much of a perimeter has been established around an active fire, preventing it from growing and engulfing more land.

Fire crews aim to suppress a wildfire by creating containment lines around it — either with roads and highways or natural barriers such as rivers or other waterways — that are meant to surround the flames and stop them from spreading.

Containment lines can also be constructed, by digging wide trenches around a fire’s flank or by eliminating vegetation and other “fuel” in the immediate area that could ignite.

Fire containment is usually given as a percentage that indicates the extent to which a fire has been hemmed in, according to the Western Fire Chiefs Association, a nonprofit group made up of leaders of fire organizations across western U.S. states and Pacific islands.

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The largest of the blazes in the Greater Los Angeles area is the Palisades Fire, which ignited almost a week ago in the Pacific Palisades and Malibu neighborhoods. The blaze has burned more than 23,000 acres and is only 14% contained as of Monday, according to the California Department of Forestry and Fire Protection. That means fire crews have established containment lines around 14% of the perimeter.

Meanwhile, the Eaton Fire, which has burned more than 14,000 acres in Altadena and Pasadena, is 33% contained. The Hurst Fire, which burned almost 800 acres in the Sylmar neighborhood, has been 95% contained, according to Cal Fire.

While containment is a good indicator of how firefighting efforts are progressing, situations can change as wildfires evolve or if environmental conditions improve or deteriorate.

In Southern California, for instance, Santa Ana winds are forecast to cause critical fire conditions over the next three days across parts of Los Angeles and Ventura counties. Dry and windy conditions often help existing fires grow and are favorable for new ignitions to spread rapidly.

Still, fully contained fires can continue to burn for some time. The key strategy, however, is to eliminate the threat of fires jumping the containment lines.