Coal mining
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Coal mining is the extraction of coal from the Earth for use as fuel.
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Methods of extraction
The most economical of methods of coal extraction from coal seams depends on the depth and quality of the seams, and also the geology and environmental factors of the area being mined.
If the coal seams are near the surface, the coal is extracted by strip mining. Strip mining exposes the coal by the advancement of an open pit or strip. As the coal is exposed and extracted, the overburden from the still covered coal fills the former pit, and the strip progresses. Most open cast mines in the USA extract bituminous coal. In South Wales open casting for steam coal and anthracite is practised.
Most coal seams are too deep underground for open cast mining. In deep mining, the room and pillar method progresses along the Mammoth coal vein seam, while pillars and timber are left standing to support the coal mine roof. A most dangerous method of operation in deep mining and is known as robbing the pillars. This is where miners attempt to remove and/or retreat between the timbers in order to get coal out of the main coal seam, allowing the roof to cave in. This method of mining is used principally in the United States and has contributed to many fatalities in the early history of coal mining.
Longwall mining is conducted along the seam with the use of self-advancing hydraulic roof supports known as "chocks" or "shields". These supports are placed in a line (up to 400 metres long), known as a "longwall" and as coal is removed from in front of the longwall, the supports are advanced. As the longwall advances, the cavity created behind the longwall known as the "goaf" caves in. Longwall mining is the principle method of underground mining in Australia.
Highwall mining is a form of coal mining in which a continuous miner is controlled remotely from outside the mine, and is guided along the seam straight back drilling holes in excess of 500 feet. A highwall is the unexcavated face of exposed overburden and coal in a surface mine. As the coal is sheared off the face of the seam, it falls below to a conveyor belt that transports the coal to the surface. A large amount of capital is required to purchase a highwall mining unit, but the labor costs are low because an operation does not require a full crew.
Highwall auger mining is generally applied in an open cast mine, once open cut mining becomes uneconomic.
History
- Main article: History of coal mining
The oldest continuously worked deep-mine in the UK and possibly the world is Tower Colliery at the northern end of the south Wales valleys. This colliery was started in 1805 and at the end of the 20th century it was bought out by its miners rather than allow it to be closed.
The World Championships in coal-carrying take place every Easter Monday, at Ossett in West Yorkshire, UK The race starts from the site of the old Savile & Shaw Cross colliery.
The first commercial coal mines in the United States were started in 1748 in Midlothian, Virginia, near Richmond, Virginia. [1]
In the 1880s, Coal-cutting machines became available (prior to that, coal was mined underground by hand.)
By 1912, surface mining was underway with steam shovels specifically designed for coal mining.
The industry has been subject to sometimes violent labor relations in the U.S. (for example, see Ludlow massacre). Union organizers were sometimes killed by management and vice-versa. See Molly Maguires. Today, coal mining is highly unionized, and the unions are sometimes militant. Mining communities are often close-knit with a strong sense of community spirit and religious faith.
Dangers to miners
Historically, coal mining has been a very dangerous activity. Open cut hazards are principally slope failure, underground mining roof collapse and gas explosions. Most of these risks can be greatly reduced in modern mines, and multiple fatality incidents are now rare in the developed world. Improvements in mining methods (i.e. longwall mining), gas drainage, safety-lamps, and ventilation have reduced many of these risks.
However, in lesser developed countries, thousands continue to die annually in coal mines. China in particular has the highest number of coal mining related deaths in the world, with official estimates of around 6,000 fatalities in 2004. Unofficial estimates place the figure much higher, at around 20,000 deaths. China also leads the world in the production and consumption of coal.
Chronic lung diseases, such as pneumoconiosis are common in miners, leading to reduced life expectancy. Black damp, a mixture of carbon dioxide and nitrogen in a mine can cause suffocation. There have been many deaths related to the safety conditions that exist in mines around the world.
Environmental impacts
Coal mining frequently causes significant adverse environmental impacts. Strip mining typically destroys most environmental value in the land through which it passes. All forms of mining are likely to generate areas where coal is stacked and where the coal has significant sulphur content, such coal heaps generate highly acidic metal rich drainage when exposed to normal rainfall. These liquors can cause severe environmental damage to receiving water-courses. In addition, the waste heaps are subject to slipping, as in the Aberfan disaster which killed 144 people in 1966.