Employing fire to combat a wildfire is a tactic known as counter-fire. It involves intentionally igniting vegetation to remove combustible material in the path of a larger, advancing blaze. This maneuver is reserved for situations where direct attack with water or physical barriers is unsafe or infeasible. Implementing counter-fire requires meticulous planning, precise execution, and qualified personnel to manage the controlled burn within designated boundaries.
The Scientific Principle of Fuel Removal
All combustion relies on the presence of three elements: heat, oxygen, and fuel. To extinguish a massive wildfire, neither oxygen nor heat can be easily suppressed on a large scale. Therefore, the most effective strategy is to eliminate the fuel the fire needs to sustain itself.
This is the fundamental purpose of controlled counter-fire operations, which deliberately consume the vegetation ahead of the main fire front. By creating a wide zone of already-burned ground, firefighters establish an area where the advancing fire cannot find new material to burn.
When the two fires meet, the main wildfire runs out of fuel and burns itself out at the boundary of the blackened area. This process is referred to as “starving” the fire. The intentional fire is initiated from a secure line, allowing it to burn inward toward the wildfire, consuming intermediate grasses, brush, and trees.
Operational Methods: Backfiring and Firing Out
Two distinct operational techniques, backfiring and firing out, are employed to remove fuel. Backfiring involves igniting a fire designed to burn directly toward the main wildfire. The primary blaze’s immense heat creates a convection column and wind, which draws the smaller, controlled backfire toward it.
This technique is often set against the wind or downslope, causing the controlled fire to move slowly and completely consume fuel before the fires converge. The goal of a backfire is to widen the area of burned ground and deprive the main fire front of its fuel source.
Firing out, also known as a burnout operation, strengthens a pre-established containment line. Firefighters ignite vegetation immediately adjacent to a natural or constructed firebreak, such as a road or dozer line.
The fire is allowed to burn inward toward the main wildfire, typically moving with the wind or parallel to the fire’s flank to create a wider, defensible “blackline.” This operation eliminates unburned fuel pockets that could allow the main fire to jump the control line, securing the perimeter.
Critical Environmental and Containment Prerequisites
The decision to initiate a controlled burn follows a rigorous analysis of environmental factors that dictate fire behavior. Wind stability is a primary concern, as erratic or high wind speeds can easily push the controlled fire across containment lines. Managers require predictable wind direction and speed within a narrow range to maintain control.
Atmospheric moisture levels are a significant constraint; relative humidity often needs to fall within a target range (e.g., 10 to 20%) to ensure vegetation burns thoroughly. Fuel moisture content is also measured to predict fire spread. If the fuel is too wet, the fire will not carry; if it is too dry, it may become uncontrollable.
Before ignition, a robust and clearly defined control line must be in place to anchor the operation. This line can be a road, a river, a constructed dozer line, or a section of fire that has already been extinguished. The controlled fire is always started from the safe side of this barrier, preventing the intentionally set fire from escaping.
Tools and Personnel for Controlled Ignition
Specialized equipment is used to safely initiate the controlled burn from the containment line. The most common tool is the drip torch, a handheld device using a mixture of diesel and gasoline to drip flaming fuel onto the ground. This allows personnel to walk along the control line and light a continuous, low-intensity fire.
For igniting fuel in remote areas, firefighters use flare guns or specialized aerial ignition devices deployed from helicopters. These devices dispense small, chemically reactive plastic spheres that ignite upon impact. The use of any ignition tool requires highly trained personnel operating under a strict Incident Command System structure.
Every planned ignition must be overseen by a qualified burn boss who holds the legal authorization for the operation. This individual ensures all conditions outlined in the prepared burn plan are met before the operation begins. The team includes specialized firing crews, holding crews, and contingency resources ready to suppress the controlled burn if it threatens to breach the containment line.