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What does ‘containing a wildfire’ actually mean?

Establishing boundary around fire 1st step in controlling it

Alisal fire near Santa Barbara, California, in mid-October, 2021. (Photo: National Forest Service)

Large wildfires have been in the news a lot this year. When people hear about them, they often hear the phrase that the fire is X% contained.

A 95% contained fire sounds a lot less frightening than a 25% contained fire. For people debating whether to evacuate their homes near these fires, that number might make all the difference.

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But containment doesn’t necessarily mean a fire isn’t still raging. Rather than describing how much of the fire has been extinguished or beaten back, containment actually refers to the perimeter that firefighters create around a blaze to keep it from spreading. Containment has to be accomplished before a fire can be extinguished.

Containment lines are any physical barriers that stop the fire from passing a certain point. Those lines can be trenches, natural barriers like rivers or even already-burned patches of land. Most often, the containment line is a shallow, 10- to 12-feet-wide trench that firefighters dig into the dirt.

Northern California’s Dixie fire, the largest in the country at more than 963,000 acres, started in mid-July. Three months later, as of Monday morning, it was 95% contained. That means 95% of the fire — about 915,000 acres — is surrounded by containment lines. This is an immense span that’s almost twice the size of Jacksonville, Florida, the fifth-largest city in the country in terms of area.

Digging a line around an area that big can take a long time, especially if the fire is in a remote spot, in rugged terrain, or both. The line would have to be dug by hand. While that’s happening, the fire could spread toward areas that aren’t contained.

If a fire is 100% contained, that means firefighters were able to complete a perimeter around it and stop it from spreading. However, it could continue to burn for weeks or months.

This poses another problem — extreme weather conditions such as high winds and very low humidity can sometimes push fires across containment lines, undoing firefighters’ progress and putting more land at risk.

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Once a fire is contained, firefighters enter the “control” phase, the kind of thing people might typically associate with firefighting. According to wildfire officials, controlling a fire means ensuring that a fire can’t spread or cross the containment line. Besides putting up barriers, the control phase involves removing or burning any fuels that could help the fire spread, as well as cooling any hot spots — those particularly active parts of a fire that could suddenly jump.

Rain, snow and cooler weather have allowed crews to contain and control dozens of wildfires over the past few weeks. Midsummer, more than 100 large wildfires were scorching as many as 4 million acres across the country. According to the National Interagency Fire Center, as of Tuesday, only 18 large fires remained, burning 2.3 million acres.

Click here for more FreightWaves articles by Nick Austin.

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Nick Austin

Nick is a meteorologist with 20 years of forecasting and broadcasting experience. He was nominated for a Midsouth Emmy for his coverage during a 2008 western Tennessee tornado outbreak. He received his Bachelor of Science in Meteorology from Florida State University, as well as a Bachelor of Science in Management from the Georgia Tech. Nick is a member of the American Meteorological Society and National Weather Association. As a member of the weather team at WBBJ-TV in Jackson, Tennessee, Nick was nominated for a Mid-South Emmy for live coverage of a major tornado outbreak in February 2008. As part of the weather team at WRCB-TV in Chattanooga, Tennessee, Nick shared the Chattanooga Times-Free Press Best of the Best award for “Best Weather Team” eight consecutive years.