Burn Out Operation on Indirect Fireline With Plastic Sphere Dispenser
Incident: Colockum Tarps Wildfire
Burn Out Operation on Indirect Fireline with a Plastic Sphere Dispenser
Colockum Tarps Fire 2013.
Burn out operations
Indirect fire line
Along portions of west edge of Colockum Tarps Fire, firefighters are using indirect fireline tactics to contain the fire. This strategy is used when it is not safe to put firefighters directly adjacent to the fire for various reasons such as when safety zones are too far away or when rocky terrain is too steep. In this case, on the west side of the fire, the fire is burning below the routes to access it. Putting firefighters down in these steep drainages with fire below them is not safe.
Why burn out
When indirect fireline is built, firefighters need to reduce the fuel near the line to moderate the fire activity. If unburned fuel remains between the fireline and the fire, the fireline could be breached. If left to reach the fireline on its own, the fire may reach the line with too much intensity and the line may not be able to contain it. A burnout operation is done to remove the unburned fuel between the containment line and the fire edge to reduce this potential. Burning out allows better control over the intensity of the fire against the fireline. A risk analysis and planning process is conducted and approved by the incident commander prior to undertaking a burn out.
Burn out process
After the fireline is constructed, when the weather (wind speed & direction, relative humidity, temperature) and fuel moisture is appropriate, the burn out operation can begin. Initially a “black line” is burned out directly against the fireline on the fire side. This is done by firefighters using drip torches or handheld flares to light strips of fire parallel to the fireline with each strip progressively further away from the fireline. By adjusting the distances between these strips and the amount of time between lighting each strip, firefighters can control the intensity of the burn. The width of a black line varies depending on terrain, wind and fuel. Approximately three hundred feet is planned for the width of this black line. If the burning of the black line has truly consumed the fuel, the black line increases the fireline.
With the fireline and black line in place, the unburned fuel that remains between the blackline and the uncontrolled edge of the fire can be burned out in a controlled manner using aerial ignition. Colockum Tarps firefighters plan to using a Plastic Sphere Dispenser (PSD) operated from a helicopter to accomplish this. Again, the weather conditions need to be within a specific window along with the temperature and moisture level of the burnable fuel prior to beginning the operation. The helicopter flies in a pattern that allows the plastic spheres to be distributed closest to the fireline and black line first. The plastic spheres are dropped in strips that keep the fire intensity at the desired level. The strips are laid down in a pattern that eventually reaches the edge of the uncontrolled edge of the fire.
Plastic Sphere Dispenser
The Plastic Sphere Dispenser (PSD) machine was developed to provide a method of igniting ground fuels, in a short time, on large acreage without causing undue damage to the tree canopy. With aerial ignition, firefighters on the ground are not required to perform the ignition hence it is safer.
The spheres, which look like pingpong balls, are made of high impact polystyrene containing approximately 3.0 grams of potassium permanganate. The PSD injects ethylene-glycol (antifreeze) into the plastic sphere, initiating an exothermic reaction, and then expels the primed sphere from the aircraft.
The PSD can be regulated to control the number of spheres being dispensed, establishing ignition patterns on the ground. It provides a reliable ignition and a time delay of at least 20 seconds. The rate of the chemical reaction is dependent on the particle size and concentration of the chemicals involved.
For more information:
Interagency Aerial Ignition Guide published by the National Wildfire Coordinating Group