Foamed backfilling for combatting mine fires

Although mine fires and attempts to extinguish them have existed for as long as coal mining, there has so far been no reliable practical method developed for extinguishing mine fires burning for a long time under deep cover. A new ‘foamed backfilling’ method combines nitrogen-enhanced foam with non-combustible solids to create a fluid, slurry-like mixture, which is injected into the mine workings remotely through boreholes to extinguish a mine fire. When injected in the area of the fire, the foamed backfill material will smother the active fire, provide moisture, block ventilation and absorb heat. Nitrogen gas released as the bubbles decay and the foam dissipates creates an inert oxygen-deficient atmosphere to inhibit combustion. Finally, the non-combustible solid particles suspended in the foam will backfill the mine workings, rubble zones, burnt-out areas and fractures to block ventilation permanently after the foam dissipates. Thus, injection of foam-transported backfill material addresses all three legs of the fire triangle; heat is removed, oxygen is excluded and the fuel is isolated, which increases the odds of success. Economic benefits include the ability to use low-cost non-combustible materials derived from on-site sources or waste from other industries, low water consumption and wider borehole spacing.