These fires are fed by the oxygen in the small but continuous flow of air through natural pipe networks, fractured strata, cracks, openings or abandoned mine shafts which permit the air to circulate into the subsurface. The reduced heat losses and high thermal inertia of the underground together with high fuel availability promote long-term smouldering combustion and allow for creeping but extensive propagation. These fires prove difficult to detect, and frustrate most efforts to extinguish them.
Underground fires are fueled by oxygen circulating through natural pathways like cracks in rock formations, abandoned mine shafts, or fractured strata. The underground's low heat loss and high thermal inertia, combined with abundant fuel sources, promote long-term smoldering combustion and enable slow but extensive spread. These fires are challenging to detect and difficult to extinguish.