Boulder County Sheriffs Office
5600 Flatiron Parkway Boulder Colorado 80301
Boulder County Office of Emergency Management
What is Containment?
We've been getting some questions about containment. Containment on a wildfire means that a fuel break has been completed around the fire’s perimeter and fire managers are confident that the fire will not spread past the line. The fuel break, or line, may include natural barriers or a manually or mechanically constructed line around the fire.
When building fireline, firefighters remove all vegetation down to “mineral soil,” meaning that there is no vegetation above or below the surface. Plant and grass roots can carry fire underground. Generally, a fireline is 10 to 12 feet wide, but it depends on fuel type. The guideline for the width of a fire line is 1.5 times the height of the burning fuels.
When determining where to place potential firelines, fire managers often use manmade or natural barriers, such as roads or rock outcroppings or bodies of water. On the CalWood and Lefthand Canyon Fires, firefighters have constructed hand lines and heavy equipment like bulldozers have been used to remove vegetation and improve roadbeds so that they could become stronger containment lines.
From the edge of the line, firefighters will “cold trail” on the interior of the line, which is checking to see whether there’s any heat that could compromise the line. When cold trailing, firefighters will remove their gloves and check areas with their bare hands to see if they feel heat. Cold trailing is an important part of mopping up a fire.
On the CalWood and Lefthand Canyon fires, firefighters are checking from one to two “chains” toward the interior, depending on fuel type. A chain is a method of measurement in wildland firefighting and one chain is 66 feet.
The black line you see on a fire map designates the containment line. On the CalWood Fire today, containment is 76%. The Lefthand Canyon Fire has been 100% contained since Thursday.