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Underground mining

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Sub-surface mining

Most coal seams are too deep underground for open cast mining and thus this type of mining is called underground mining. In deep mining, the room and pillar or board and pillar method progresses along the seam, while pillars and timber are left standing to support the coal mine roof. Once room and pillar mines have been developed to a stopping point(limited by geology, ventilation, or economics), a supplementary version of room and pillar mining referred to as second mining or retreat mining is commonly started. This is

when miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area that is involved in pillar extraction is called a pillar section. Modern pillar sections use remote controlled equipment, including large hydraulic mobile roof supports, which can prevent cave ins until the miners and other equipment have left a work area. The mobile roof supports are similar to a

large dining room table, but with hydraulic jacks for legs. After the large pillars of coal have been mined away, the mobile roof support legs shorten, and the mobile roof supports travel out to a safe area. The mine roof typically collapses once the mobile roof supports leave an area.

There are four major underground mining methods:

• Longwall mining – accounts for about 50% of underground production. The longwall shearer has a face of 1000 feet or more. It is a sophisticated machine with a rotating drum that moves mechanically back-and-forth across a wide coal seam. The loosened coal falls onto a pan line that takes the coal to the conveyor belt for removal from the work area. Longwall systems have their own hydraulic roof supports for overlying rock that advance with the machine as mining progresses. As the longwall mining equipment moves forward, overlying rock that is no longer supported by the coal

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• that has been removed is allowed to fall behind the operation in a controlled manner. The supports make possible high levels of production and safety. Sensors

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• detect how much coal remains in the seam while robotic controls enhance efficiency. Longwall systems allow a 60-to-100% coal recovery rate where the surrounding geology allows their use.

• Continuous mining– Utilize a machine with a large rotating steel drum equipped with tungsten carbide teeth that scrape coal from the seam. Operating in a “room and pillar” system – where the mine is divided into a series of 20-to-30 foot “rooms” or work areas cut into the coalbed – it can mine as much as five tons of coal a minute – more than a miner of the 1920s would produce in an entire day. Continuous miners account for about 45% of underground coal production, and also utilize conveyors to transport the removed coal from the seam. Remote controlled continuous miners are used to work in a variety of difficult seams and conditions and robotic versions controlled by computers are becoming increasingly common.

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• Blast mining – An older practice that uses explosives such as dynamite to break up the coal seam, after which the coal is gathered and loaded onto shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with “cutting” the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5% of total underground production in the U.S. today.

• Shortwall mining– A method that accounts for less than 1% of deep coal production, shortwall involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, depending on other things like the strata of the Earth and the transverse waves.

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 being allowed 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.

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.

Modern mining in the United States of America

Technological advancements have made coal mining today more productive than it has ever been. To keep up with technology and to extract coal as efficiently as possible modern mining personnel must be highly skilled and well trained in the use of complex, state-of-the-art instruments and equipment. Future coal miners have to be highly educated and many jobs require four-year college degrees. Computer knowledge has also become greatly valued within the industry as most of the machines and safety monitors are computerized.

The increase in technology has significantly decreased the mining workforce from 335,000 coal miners working at 7,200 mines fifty years ago to 104,824 miners working in fewer than 2,000 mines today. As some might see this as a sign that coal is a declining industry its advances has reported an 83% increase of production from 1970 to 2004. These statistics are provided by the National Mining Association.

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 some parts of the developed world.

However, in lesser developed countries and some developed countries, many miners continue to die annually, either through direct accidents in coal mines or through adverse health consequences from working under poor conditions. China, in particular, has the highest number of coal mining related deaths in the world, with official statistic 6,027 deaths in 2004. To compare, the USA reported 28 deaths in the same year.Coal production in China is twice that of the United States, while the number of coal miners is around 50 times that of the USA, making deaths in coal mines in China 4 times as common per worker (50 times as common per unit output) as in the USA.

When compared to industrial countries such as China, the U.S. fatality rate is low. However in 2006 fatal work injuries among U.S. miners doubled from the previous year, totaling 47. These figures can in part be attributed to the Sago Mine disaster. The recent mine accident in Utah's Crandall Canyon Mine, where nine miners were killed and six entombed, speaks to the increase in occupational risks faced by U.S. miners.

Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy. In some mining countries black lung is still common, with 4000 new cases of black lung every year in the USA (4% of workers annually) and 10 000 new cases every year in China (0.2% of workers). Rates may be higher than reported in some regions.

Build-ups of a hazardous gas are known as damps, possibly from the German word "Dampf" which means steam or vapor:

• Black damp: a mixture of carbon dioxide and nitrogen in a mine can cause suffocation
• After damp: similar to black damp, an after damp consists of carbon dioxide and nitrogen and forms after a mine explosion
• Fire damp: consists of mostly methane, a flammable gas
• Stink damp: so named for the rotten egg smell of the sulfur, a stink damp can explode
• White damp: mainly carbon monoxide, suffocates like black damp [also, Carbon monoxide is very toxic, even at low concentrations]

Safer times in modern mining

Improvements in mining methods (e.g. longwall mining), hazardous gas monitoring (such as safety-lamps or more modern electronic gas monitors), gas drainage, and ventilation have reduced many of the risks of rock falls, explosions, and unhealthy air quality. Statistical analyses performed by the U.S. Department of Labor’s Mine Safety and Health Administration (MSHA) show that between 1990 and 2004, the industry cut the rate of injuries by more than half and fatalities by two-thirds. However according to the Bureau of Labor Statistics, mining remains the second most dangerous occupation in America.

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