A root fire, also known as a ground fire, is a specialized type of wildfire that burns beneath the surface of the earth. This combustion occurs in the organic layer of the soil, often called duff, and extends into the network of tree roots, peat, and other decomposed materials. Unlike a surface fire, a root fire progresses slowly as a flameless, smoldering reaction. They are notoriously difficult to extinguish because the fuel is insulated by the surrounding soil, allowing the fire to persist for days, weeks, or even months.
Recognizing a Root Fire
The primary challenge in addressing a root fire is that it provides minimal visual warning, as surface flames are often absent. The most common sign is wispy smoke or vapor rising from the ground, which can be easily mistaken for residual smoke after a surface fire has passed. This smoke often contains high levels of toxic gases like carbon monoxide, a dangerous byproduct of flameless combustion.
Another strong indicator is excessive heat felt through the soil, detected by carefully holding a hand low over the suspected area. The fire itself can reach temperatures between 400°F and 600°F underground, severely altering soil composition and structure. In extreme cases, the fire can burn out large root systems beneath the ground, creating hidden voids, or ash pits, that look deceptively solid on the surface.
These voids pose a severe physical danger, as stepping onto a seemingly stable patch of ground could cause collapse into a deep, burning sinkhole. The phenomenon of “zombie fires” is also associated with ground fires, where a smoldering fire can survive harsh winter conditions and re-emerge as a full-fledged surface fire in the spring.
Safety First Before Fighting
Before attempting any suppression, assessing the immediate environment for personal safety is paramount. Ground stability must be the first consideration, as walking on suspected areas is extremely hazardous due to the possibility of collapse into hot cavities. Always probe the ground ahead with a long tool, such as a shovel or stick, to check for soft spots or underlying voids before taking a step.
Contacting the local fire department or emergency authority is a requirement, even if the fire appears small. Root fires are complex incidents requiring specialized knowledge and resources, and professional personnel should always be notified to manage the scene and provide assistance. Never attempt to fight a fire that is rapidly spreading or beyond the scope of a small, contained smolder.
Securing a reliable and abundant water source is necessary before approaching the area, as these fires require huge volumes of water for complete saturation. Appropriate personal protective equipment (PPE) should be used to protect against heat, smoke, and physical hazards. Sturdy, high-topped leather boots, heavy-duty leather gloves, long sleeves, and fire-resistant materials are highly recommended.
A respirator or breathing apparatus is advisable if the smoke is heavy, given the risk of carbon monoxide and other toxic fumes released by smoldering organic material. Maintaining a clear escape route and ensuring communication with others is also a foundational safety measure.
Extinguishing Techniques for Deep Fires
Extinguishing a deep-seated fire requires a direct and aggressive approach focused on separating the fuel from the heat and oxygen. The primary technique involves physically exposing the smoldering material to break the insulating layer of soil and duff. This is accomplished by excavating the hot spot, using tools like shovels, pulaskis, or hoes to dig down and expose the burning roots and organic matter.
Firefighting crews often employ a technique called trenching, digging a perimeter around the fire’s edge to stop its spread through underground root networks. The trench must extend down to the mineral soil layer, where no organic fuel remains, effectively starving the fire of new material. The excavated, smoldering material must be immediately pulled out and spread thinly onto the non-burning ground.
Once the material is exposed, the next step is thorough saturation. Water applied to the surface alone will simply run off or turn to steam without penetrating the dense, compacted fuel. Water must be poured directly onto the smoldering material in large volumes until the entire area is completely soaked, cooling the material below its ignition temperature.
To enhance penetration, especially in fuels like peat or thick duff, a wetting agent or foam may be mixed with the water. These additives reduce the surface tension of the water, allowing it to soak into tightly packed organic matter more effectively than plain water. This ensures deep-seated embers are reached and cooled.
The physical action of mixing and stirring the water into the exposed, burning fuel is essential. Use the shovel or other tool to churn the wet material, ensuring that every piece of smoldering matter is completely drenched and cool to the touch. This process also helps eliminate residual air pockets, which contain oxygen necessary for the smoldering reaction to continue. This is repeated until no steam or smoke rises from the churned material.
Verifying the Fire is Truly Out
The final step is to confirm that the fire is fully extinguished and cannot reignite. The most reliable method is to check for residual heat, which can be done by carefully using the back of the hand near the ground surface or by using an infrared thermometer. The entire affected area must feel cool to the touch, not merely warm.
Residual heat deep within the soil can persist even after surface cooling, so the search for hot spots must be thorough, checking several inches below the surface. Any smoke or steam rising from the ground after a prolonged period of dousing indicates that combustion is still occurring, requiring a return to the saturation and mixing process. The fire is not considered truly out until the material remains cool and no smoke is visible for a long time.
The “mop up” phase involves ensuring the excavated and saturated material remains spread out and cool. This cooled debris should be separated from any remaining unburned fuel to prevent any smoldering material from transferring heat and reigniting the fire. Continuous monitoring of the site is necessary for several hours and ideally for the following days, as ground fires have a tendency for re-ignition if any ember survives.