Coal Seam Fire - Extinguishing Coal Fires

Extinguishing Coal Fires

In order to thrive, a fire requires fuel, oxygen, and heat. As underground fires are very difficult to reach directly, firefighting involves finding an appropriate methodology which addresses the interaction of fuel and oxygen for the specific fire in question. A fire can be isolated from its fuel source, for example through firebreaks or fireproof barriers. Many fires, particularly those on steep slopes, can be completely excavated. In the case of near-surface coal seam fires, the influx of oxygen in the air can be interrupted by covering the area or installing gas-tight barriers. Another possibility is to hinder the outflow of combustion gases so that the fire is quenched by its own exhaust fumes. Energy can be removed by cooling, usually by injecting large amounts of water. However, if any remaining dry coal absorbs water, the resulting heat of absorption can lead to re-ignition of a once-quenched fire as the area dries. Accordingly, more energy must be removed than the fire generates. In practice these methods are combined, and each case depends on the resources available. This is especially true for water, for example in arid regions, and for covering material, such as loess or clay, to prevent contact with the atmosphere.

Extinguishing underground coal fires, which sometimes exceed temperatures of 540°C (1,000°F), is both highly dangerous and very expensive.

Near-surface coal seam fires are routinely extinguished in China following a standard method basically consisting of the following phases:

• Smoothing the surface above the fire with heavy equipment to make it fit for traffic.
• Drilling holes in the fire zone about 20 m apart down to the source of the fire, following a regular grid.
• Injecting water or mud in the boreholes long term, usually 1 to 2 years.
• Covering the entire area with an impermeable layer about 1 m thick, e.g., of loess.
• Planting vegetation to the extent the climate allows.

Efforts are underway to refine this method, for example with additives to the quenching water or with alternative extinguishing agents.

Underground coal seam fires are customarily quenched by inertization through mine rescue personnel. Toward this end the affected area is isolated by dam constructions in the galleries. Then an inert gas, usually nitrogen, is introduced for a period of time, usually making use of available pipelines.

In 2004, the Chinese government claimed success in extinguishing a mine fire at a colliery near Urumqi in China's Xinjiang province that had been burning since 1874. However, a March 2008 Time magazine article quotes researcher Steven Q. Andrews as saying, "I decided to go to see how it was extinguished, and flames were visible and the entire thing was still burning.... They said it was put out, and who is to say otherwise?"

A jet engine unit, known as Gorniczy Agregat Gasniczy (GAG), was developed in Poland and successfully utilised for fighting coal fires and displacing firedamp in mines.