Why are there explosions in coal mines

For more information about methane ». CMM emissions represent a wasted potential source of energy when not captured and a safety hazard. The recovery and use of CMM emissions have benefits for local and global environments. See ways to mitigate CMM. Other minor sources of methane from coal mines include surface mines and post-mining activities, as coal continues to emit methane as it is stored in piles and transported.

More information on sources of CMM. When coal mines are no longer operated to produce coal, they are known as closed or "abandoned" mines. Even though active mining no longer occurs, these abandoned mines can still produce significant methane emissions from diffuse vents, fissures, or boreholes.

This methane can be deliberately extracted and used to generate power or for other end uses. There are several thousand abandoned coal mines in the United States. Of these, EPA has identified some abandoned mines that are considered "gassy" and has developed profiles of successful projects at abandoned mines and mines that might be good candidates for project development.

Project developers review available data on the coal mine such as drainage efficiency, gas quality and quantity, potential markets, and other considerations about potential projects. Likewise, fine particles of coal dust in the right concentration that contact a source of heat can also be explosive. Hybrid explosions consisting of a combination of methane and coal dust can also occur. Methane is formed as a byproduct of the coal formation.

The methane that is adsorbed in the coal is released as the coal is mined or it migrates from surrounding sources above or below the coal seam through fractures created by the coal extraction process.

Large fans circulate air in mines to provide ventilation to the working areas. Mines with excessive methane can remove the gas prior to mining by drilling drainage holes. A common cause of methane face ignitions is the spark or hot streak created when cutting roof or floor rock with the mining machine.

Applying directed water sprays behind the cutting bit to cool and limit the size of the hot streak can prevent these frictional ignitions.

Coal mines generally have active mining zones and areas that were previously mined. These mined-out areas can be abandoned areas that are no longer ventilated and are separated from the active mining areas by explosion-resistant structures called seals. Large fans are used to blow air out or draw air into mines, but Luo stated that mine ventilation is still a complicated science. Mine explosions can also be triggered when fine particles of coal dust come into contact with a source of heat.

While methane is easier to ignite, the explosion pressure and heat value of methane is not as high as coal dust. In most cases, dust explosions are first caused by methane explosions, said Luo. But, the shock wave caused by methane explosions can blow up coal dust within the mine, and the heat generated by the methane reaction can ignite the dust, which greatly intensifies the energy of the explosion.

So, in a worst case scenario, a methane explosion has the potential to ignite a more catastrophic coal dust explosion. Coal mines in the United States have taken safety measures to avoid dust explosions, including spreading limestone powder over the coal dust. Download PDF. Abstract IF a cloud of dry dust is suddenly raised by a current of air and projected against an insulated conductor, the latter becomes charged with electricity to such a potential that sparks several centimetres in length may be obtained.

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