What Does Wildfire Containment Mean? Control Lines and More
When wildfires are reported, you'll often hear about wildfire containment or containment rate. News reports might say a fire is 30% or 75% contained, but what does that actually mean? Understanding containment helps you interpret fire updates and know where firefighters are in the suppression process.
Containment is a technical term fire agencies use to describe a wildfire's perimeter status. It doesn't mean the fire is extinguished, controlled, or has stopped spreading. Instead, containment means firefighters have established control lines around parts of the fire's edge that prevent it from spreading beyond those boundaries.
What Wildfire Containment Means
The term "containment" has a few different meanings when discussing wildfires. According to the Western Fire Chiefs Association (WFCA), containment or wildfire containment refers to the action of identifying or building control lines around a fire's perimeter. Containment percentage measures how much of the fire's perimeter is surrounded by a control line. A fire is only considered 100% contained when a control line completely encircles the fire and any spot fires, and can reasonably be expected to stop the fire's spread.
What Containment Does Not Mean
Hearing that a fire is contained is good news, but it doesn't mean the wildfire is over. The fire must still be controlled and extinguished. The NWCG glossary makes clear distinctions between containment and other fire status terms. Understanding these differences helps you stay informed during wildfire incidents.
Contained is not the same as controlled. Control is the next step after containment. It involves extinguishing the fire along the interior of the control line and putting out any hot spots that threaten the control line.
Contained is not the same as extinguished. An extinguished fire has stopped burning completely, and no more suppression actions are needed. You might hear phrases like "the fire is declared out" or "fire out," which both mean the fire is completely extinguished.
These distinctions matter for understanding fire risk. A 100% contained fire may still produce smoke, heat, and visible flames, even though it's no longer spreading. Knowing these terms helps you understand where firefighters are in the suppression process when you see updates in the news.
How Containment Is Measured and Reported
Containment is expressed as a percentage showing how much of the fire's perimeter is secured by control lines. According to the Western Fire Chiefs Association, this percentage represents how much of the fire's edge is protected by barriers that should stop the fire from spreading beyond those points.
Why Containment Is Not Based on Acreage
It might seem logical to measure containment based on how much land the fire has burned, but that's not how it works. Containment percentages aren't based on acres burned or how much area is on fire. Instead, containment focuses on the fire's perimeter, where the fire spreads. A fire might have burned 10,000 acres, but if firefighters have secured control lines around 50% of the perimeter, the fire is 50% contained, no matter how much is burning inside.
This perimeter-based approach makes sense because containment is about stopping the fire's active spread, not measuring its total impact. Securing the perimeter stops the fire from expanding, even if the interior continues to burn.
Why Containment Percentages May Stall, Increase, or Decrease
Containment percentages can behave in surprising ways, increasing, decreasing, or stalling for days on end. Here's what causes these changes:
Sudden increases: Containment percentage increases when control lines are completed. If a large control line is finished or a natural firebreak is connected to existing lines, the percentage can jump dramatically.
Decreases: Less commonly, containment percentages can decrease if the fire breaks through control lines and spreads beyond the secured perimeter. When this happens, the fire's perimeter expands, and previously secured sections may no longer be part of the fire's edge.
Stalling: Containment percentages may stay the same for days if firefighters are working in difficult terrain, facing dangerous conditions, or if the fire perimeter is still expanding in some areas. Building control lines takes time, and challenging conditions slow progress.
How Firefighters Achieve Containment
Firefighters achieve containment by establishing control lines around the fire perimeter. Here's how control lines work:
What Is a Control Line?
According to the NWCG glossary, a control line is any constructed or natural barrier used to control fire spread. Firefighters can create control lines directly next to the fire (direct attack) or further away (indirect attack), where they often connect to natural barriers.
Natural vs. Constructed Barriers
Control lines can be natural or constructed. Natural barriers are areas where a lack of flammable material stops fire spread. Common examples include wetlands, streams, floodplains, and rock outcroppings.
Constructed barriers are firelines firefighters create by digging, scraping, or clearing vegetation to remove fuel.
Firefighters often combine natural and constructed barriers. Using existing natural features reduces the amount of line that needs to be built, while constructed lines fill gaps where natural barriers aren't enough.
Burnouts and Backburns as Containment Tools
Burnouts and backburns are tactical operations used to secure control lines. These involve intentionally setting fires to consume fuel between the control line and the main fire, creating a wider barrier the main fire can't cross. When done correctly, burnouts strengthen control lines by removing fuel before the main fire reaches them.
Containment focuses on holding the perimeter edges, not extinguishing every flame inside the fire area. This approach lets firefighters stop fire spread efficiently, even when the interior continues to burn.
Why Understanding Wildfire Containment Matters
Wildfire containment measures how much of a fire's perimeter is secured by control lines. Understanding what containment means and what it doesn't helps you interpret fire updates and know where firefighters are in the suppression process.
A fire is only 100% contained when a control line completely encircles the fire and should stop its spread. However, containment doesn't mean the fire is controlled, extinguished, or has stopped burning.
Containment percentages aren't based on acres burned, but on how much of the fire's perimeter is secured. These percentages can change in surprising ways, increasing, decreasing, or stalling as conditions change and control lines are built or breached. Firefighters achieve containment by establishing control lines using natural barriers like wetlands and rock outcroppings, or constructed barriers created through digging and clearing, and using tactical operations like burnouts to strengthen these lines.
During active wildfires, staying informed through official sources and understanding containment terminology helps you interpret fire updates and understand suppression progress.