Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content, and, since the 1880s, has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United Kingdom and South Africa, a coal mine and its structures are a colliery. In Australia, "colliery" generally refers to an underground coal mine. In the United States "colliery" has historically been used to describe a coal mine operation, but the word today is not commonly used.
- Methods of extraction
- Modern surface mining
- Strip mining
- Contour mining
- Mountaintop removal mining
- Underground mining
- Modern mining
- Dangers to miners
- Safer times in modern mining
- Environmental impacts
- Coal mining by country
- South Africa
- United Kingdom
- United States
Coal mining has had many developments over the recent years, from the early days of men tunneling, digging and manually extracting the coal on carts, to large open cut and long wall mines. Mining at this scale requires the use of draglines, trucks, conveyors, jacks and shearers
Small-scale mining of surface deposits dates back thousands of years. For example, in Roman Britain, the Romans were exploiting all major coalfields (save those of North and South Staffordshire) by the late 2nd century AD. While much of its use remained local, a lively trade developed along the North Sea coast supplying coal to Yorkshire and London.
The Industrial Revolution, which began in Britain in the 18th century, and later spread to continental Europe and North America, was based on the availability of coal to power steam engines. International trade expanded exponentially when coal-fed steam engines were built for the railways and steamships. The new mines that grew up in the 19th century depended on men and children to work long hours in often dangerous working conditions. There were many coalfields, but the oldest were in Newcastle and Durham, South Wales, the Central Belt of Scotland and the Midlands, such as those at Coalbrookdale.
Children would usually work as trappers; this is where they had to open and close trap doors to allow mine carts in. This made sure no harmful gases built up in the mine.
The oldest continuously worked deep-mine in the United Kingdom is Tower Colliery in South Wales valleys in the heart of the South Wales coalfield. This colliery was developed in 1805, and its miners bought it out at the end of the 20th century, to prevent it from being closed. Tower Colliery was finally closed on 25 January 2008, although production continued at the Aberpergwm drift mine owned by Walter Energy until suspended on 3 July 2015.
Coal was mined in America in the early 18th century, and commercial mining started around 1730 in Midlothian, Virginia.
Coal-cutting machines were invented in the 1880s. Before this invention, coal was mined from underground with a pick and shovel. By 1912, surface mining was conducted with steam shovels designed for coal mining.
Methods of extraction
The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and the geology and environmental factors. Coal mining processes are differentiated by whether they operate on the surface or underground. Many coals extracted from both surface and underground mines require washing in a coal preparation plant. Technical and economic feasibility are evaluated based on the following: regional geological conditions; overburden characteristics; coal seam continuity, thickness, structure, quality, and depth; strength of materials above and below the seam for roof and floor conditions; topography (especially altitude and slope); climate; land ownership as it affects the availability of land for mining and access; surface drainage patterns; ground water conditions; availability of labor and materials; coal purchaser requirements in terms of tonnage, quality, and destination; and capital investment requirements.
Surface mining and deep underground mining are the two basic methods of mining. The choice of mining method depends primarily on depth of burial, density of the overburden and thickness of the coal seam. Seams relatively close to the surface, at depths less than approximately 180 ft (50 m), are usually surface mined.
Coal that occurs at depths of 180 to 300 ft (50 to 100 m) are usually deep mined, but in some cases surface mining techniques can be used. For example, some western U.S. coal that occur at depths in excess of 200 ft (60 m) are mined by the open pit methods, due to thickness of the seam 60–90 feet (20–30 m). Coals occurring below 300 ft (100 m) are usually deep mined. However, there are open pit mining operations working on coal seams up to 1000–1500 feet (300–450 m) below ground level, for instance Tagebau Hambach in Germany.
Modern surface mining
When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast, open pit, mountaintop removal or strip) mining methods. Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Large open cast mines can cover an area of many square kilometers and use very large pieces of equipment. This equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks in which transport overburden and coal, bucket wheel excavators, and conveyors. In this mining method, explosives are first used in order to break through the surface, or overburden, of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded onto large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.
Most open cast mines in the United States extract bituminous coal. In Canada (BC), Australia and South Africa, open cast mining is used for both thermal and metallurgical coals. In New South Wales open casting for steam coal and anthracite is practised. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining.
Strip mining exposes coal by removing earth above each coal seam. This earth is referred to as overburden and is removed in long strips. The overburden from the first strip is deposited in an area outside the planned mining area and referred to as out-of-pit dumping. Overburden from subsequent strips are deposited in the void left from mining the coal and overburden from the previous strip. This is referred to as in-pit dumping.
It is often necessary to fragment the overburden by use of explosives. This is accomplished by drilling holes into the overburden, filling the holes with explosives, and detonating the explosive. The overburden is then removed, using large earth-moving equipment, such as draglines, shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the underlying coal seam will be exposed (a 'block' of coal). This block of coal may be drilled and blasted (if hard) or otherwise loaded onto trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it. This method is most suitable for areas with flat terrain.
Equipment to be used depends on geological conditions. For example, to remove overburden that is loose or unconsolidated, a bucket wheel excavator might be the most productive. The life of some area mines may be more than 50 years.
The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside. This method is most commonly used in areas with rolling to steep terrain. It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate these problems, a variety of methods were devised to use freshly cut overburden to refill mined-out areas. These haul-back or lateral movement methods generally consist of an initial cut with the spoil deposited downslope or at some other site and spoil from the second cut refilling the first. A ridge of undisturbed natural material 15 to 20 ft (5–6 m) wide is often intentionally left at the outer edge of the mined area. This barrier adds stability to the reclaimed slope by preventing spoil from slumping or sliding downhill
The limitations of contour strip mining are both economic and technical. When the operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not profitable to continue. Depending on the equipment available, it may not be technically feasible to exceed a certain height of highwall. At this point, it is possible to produce more coal with the augering method in which spiral drills bore tunnels into a highwall laterally from the bench to extract coal without removing the overburden.
Mountaintop removal mining
Mountaintop coal mining is a surface mining practice involving removal of mountaintops to expose coal seams, and disposing of associated mining overburden in adjacent "valley fills." Valley fills occur in steep terrain where there are limited disposal alternatives.
Mountaintop removal combines area and contour strip mining methods. In areas with rolling or steep terrain with a coal seam occurring near the top of a ridge or hill, the entire top is removed in a series of parallel cuts. Overburden is deposited in nearby valleys and hollows. This method usually leaves ridge and hill tops as flattened plateaus. The process is highly controversial for the drastic changes in topography, the practice of creating head-of-hollow-fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.
Spoil is placed at the head of a narrow, steep-sided valley or hollow. In preparation for filling this area, vegetation and soil are removed and a rock drain constructed down the middle of the area to be filled, where a natural drainage course previously existed. When the fill is completed, this underdrain will form a continuous water runoff system from the upper end of the valley to the lower end of the fill. Typical head-of-hollow fills are graded and terraced to create permanently stable slopes.
Most coal seams are too deep underground for opencast mining and require underground mining, a method that currently accounts for about 60 percent of world coal production. In deep mining, the room and pillar or bord and pillar method progresses along the seam, while pillars and timber are left standing to support the 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, termed second mining or retreat mining, is commonly started. Miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area 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 their 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's legs shorten and it is withdrawn to a safe area. The mine roof typically collapses once the mobile roof supports leave an area.
There are six principal methods of underground mining:
Coal is mined commercially in over 50 countries. Over 7,036 Mt/yr of hard coal is currently produced, a substantial increase over the past 25 years. In 2006, the world production of brown coal and lignite was slightly over 1,000 Mt, with Germany the world’s largest brown coal producer at 194.4 Mt, and China second at 100.6 Mt.
Coal production has grown fastest in Asia, while Europe has declined. The top coal mining nations are:
Most coal production is used in the country of origin, with around 16 percent of hard coal production being exported.
Global coal production is expected to reach 7,000 Mt/yr in 2030 (Update required, world coal production is already past 7,000 Mt/yr and by 2030 will probably be closer to 13,000 Mt/yr), with China accounting for most of this increase. Steam coal production is projected to reach around 5,200 Mt/yr; coking coal 620 Mt/yr; and brown coal 1,200 Mt/yr.
Coal reserves are available in almost every country worldwide, with recoverable reserves in around 70 countries. At current production levels, proven coal reserves are estimated to last 147 years. However, production levels are by no means level, and are in fact increasing and some estimates are that peak coal could arrive in many countries such as China and America by around 2030. Coal reserves are usually stated as either (1) "Resources" ("measured" + "indicated" + "inferred" = "resources", and then, a smaller number, often only 10-20% of "resources," (2) "Run of Mine" (ROM) reserves, and finally (3) "marketable reserves", which may be only 60% of ROM reserves. The standards for reserves are set by stock exchanges, in consultation with industry associations. For example, in ASEAN countries reserves standards follow the Australasian Joint Ore Reserves Committee Code (JORC) used by the Australian Securities Exchange.
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. Many jobs require four-year university degrees. Computer knowledge has also become greatly valued within the industry as most of the machines and safety monitors are computerized.
The use of sophisticated sensing equipment to monitor air quality is common and has replaced the use of small animals such as canaries, often referred to as "miner's canaries".
In the United States, the increase in technology has significantly decreased the mining workforce.The average number of employees at U.S. coal mines decreased 12.0% to 65,971 employees, the lowest on record since EIA began collecting data in 1978. As the number of coal workers has decreased, a study caused controversy as GreenTech Media pointed out that investment for the retraining all coal workers for solar jobs was modest - one year of coal CEO pay could retrain every US miner to work in the solar industry.
Dangers to miners
Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. In the US alone, more than 100,000 coal miners were killed in accidents in the twentieth century, 90 percent of the fatalities occurring in the first half of the century. More than 3,200 died in 1907 alone.
Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse, rock burst, outbursts, and gas explosions.
Firedamp explosions can trigger the much-more-dangerous coal dust explosions, which can engulf an entire pit. 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. Modern mining in the US results in approximately 30 deaths per year due to mine accidents.
However, in lesser developed countries and some developing 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 statistics claiming that 6,027 deaths occurred in 2004. To compare, 28 deaths were reported in the US in the same year. Coal production in China is twice that in the US, while the number of coal miners is around 50 times that of the US, making deaths in coal mines in China 4 times as common per worker (108 times as common per unit output) as in the US.
Mine disasters have still occurred in recent years in the US, Examples include the Sago Mine disaster of 2006, and the 2007 mine accident in Utah's Crandall Canyon Mine, where nine miners were killed and six entombed. In the decade 2005-2014, US coal mining fatalities averaged 28 per year. The most fatalities during the 2005-2014 decade were 48 in 2010, the year of the Upper Big Branch Mine disaster in West Virginia, which killed 29 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 4,000 new cases of black lung every year in the US (4 percent of workers annually) and 10,000 new cases every year in China (0.2 percent 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:
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, electrical equipment, and ventilation have reduced many of the risks of rock falls, explosions, and unhealthy air quality. Gases released during the mining process can be recovered to generate electricity and improve worker safety with gas engines. Another innovation in recent years is the use of closed circuit escape respirators, respirators that contain oxygen for situations where mine ventilation is compromised. Statistical analyses performed by the US 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, even in 2006, mining remained the second most dangerous occupation in America, when measured by fatality rate. However, these numbers include all mining, with oil and gas mining contributing the majority of fatalities; coal mining resulted in only 47 fatalities that year.
Coal mining can result in a number of adverse effects on the environment.
Surface mining of coal completely eliminates existing vegetation, destroys the genetic soil profile, displaces or destroys wildlife and habitat, degrades air quality, alters current land uses, and to some extent permanently changes the general topography of the area mined. This often results in a scarred landscape with no scenic value. Of greater concern, the movement, storage, and redistribution of soil during mining can disrupt the community of soil microorganisms and consequently nutrient cycling processes. Rehabilitation or reclamation mitigates some of these concerns and is required by US Federal Law, specifically the Surface Mining Control and Reclamation Act of 1977.
Mine dumps (tailings) could produce acid mine drainage which can seep into waterways and aquifers, with consequences on ecological and human health.
If underground mine tunnels collapse, they cause subsidence of the ground above. Subsidence can damage buildings, and disrupt the flow of streams and rivers by interfering with the natural drainage.
During actual mining operations, methane, a known greenhouse gas, may be released into the air.
Coal mining by country
Top 10 hard and brown coal producers in 2012 were (in million metric tons): China 3,621, United States 922, India 629, Australia 432, Indonesia 410, Russia 351, South Africa 261, Germany 196, Poland 144, and Kazakhstan 122.
Coal is mined in every state of Australia, but mainly in Queensland, New South Wales and Victoria. It is mostly used to generate electricity, and 75% of annual coal production is exported, mostly to eastern Asia.
In 2007, 428 million tonnes of coal was mined in Australia. In 2007, coal provided about 85% of Australia's electricity production. In fiscal year 2008/09, 487 million tonnes of coal was mined, and 261 million tonnes was exported. In fiscal year 2013/14, 430.9 million tonnes of coal was mined, and 375.1 million tonnes was exported. In 2013/14, coal provided about 69% of Australia's electricity production.
In 2013, Australia was the world's fifth-largest coal producer, after China, the United States, India, and Indonesia. However, in terms of proportion of production exported, Australia is the world's second largest coal exporter, as it exports roughly 73% of its coal production. Indonesia exports about 87% of its coal production.
Canada was ranked as the 15th coal producing country in the world in 2010, with a total production of 67.9 million tonnes. Canada's coal reserves, the 12th largest in the world, are located largely in the province of Alberta.
The first coal mines in North America were located in Joggins and Port Morien, Nova Scotia, mined by French settlers beginning in the late 1600s. The coal was used for the British garrison at Annapolis Royal, and in construction of the Fortress of Louisbourg.
Compared to other South American countries Chile has limited coal resources. Only Argentina is similarly poor. The three zones of coal mining in Chile are Zona Central Sur (36–38° S), Zona Sur (39–42° S) and Zona Austral (51–54° S) in southernmost Chile. Coal is Chile is mostly sub-bituminous with the exception of the bituminous coals of Arauco Basin in the southern part of Zona Centro Sur.
The People's Republic of China is by far the largest producer of coal in the world, producing over 2.8 billion tons of coal in 2007, or approximately 39.8 percent of all coal produced in the world during that year. For comparison, the second largest producer, the United States, produced more than 1.1 billion tons in 2007. An estimated 5 million people work in China's coal-mining industry. As many as 20,000 miners die in accidents each year. Most Chinese mines are deep underground and do not produce the surface disruption typical of strip mines. Although there is some evidence of reclamation of mined land for use as parks, China does not require extensive reclamation and is creating significant acreages of abandoned mined land, which is unsuitable for agriculture or other human uses, and inhospitable to indigenous wildlife. Chinese underground mines often experience severe surface subsidence (6–12 meters), negatively impacting farmland because it no longer drains well. China uses some subsidence areas for aquaculture ponds but has more than they need for that purpose. Reclamation of subsided ground is a significant problem in China. Because most Chinese coal is for domestic consumption, and is burned with little or no air pollution control equipment, it contributes greatly to visible smoke and severe air pollution in industrial areas using coal for fuel. China's total energy uses 67% from coal mines.
Some of the world's largest coal reserves are located in South America, and an opencast mine at Cerrejón in Colombia is one of the world's largest open pit mines. Output of the mine in 2004 was 24.9 million tons (compared to total global hard coal production of 4,600 million tons). Cerrejón contributed about half of Colombia's coal exports of 52 million tons that year, with Colombia ranked sixth among major coal exporting nations. The company planned to expand production to 32 million tons by 2008. The company has its own 150 km standard-gauge railroad, connecting the mine to its coal-loading terminal at Puerto Bolívar on the Caribbean coast. There are two 120-car unit trains, each carrying 12,000 tons of coal per trip. The round-trip time for each train, including loading and unloading, is about 12 hours. The coal facilities at the port are capable of loading 4,800 tons per hour onto vessels of up to 175,000 tons of dead weight. The mine, railroad and port operate 24 hours per day. Cerrejón directly employs 4,600 workers, with a further 3,800 employed by contractors. The reserves at Cerrejón are low-sulfur, low-ash, bituminous coal. The coal is mostly used for electric power generation, with some also used in steel manufacture. The surface mineable reserves for the current contract are 330 million tons. However, total proven reserves to a depth of 300 metres are 3,000 million tons.
Germany has a long history of coal mining, going back to the Middle Ages. Coal mining greatly increased during the industrial revolution and the following decades. The main mining areas were around Aachen, the Ruhr and Saar area, along with many smaller areas in other parts of Germany. These areas grew and were shaped by coal mining and coal processing, and this is still visible even after the end of the coal mining.
Coal mining reached its peak in the first half of the 20th century. After 1950, the coal producers started to struggle financially. In 1975, a subsidy was introduced (Kohlepfennig). In 2007, the Bundestag decided to end subsidies by 2018. As a consequence, RAG Aktiengesellschaft, the owner of the two remaining coal mines in Germany, announced it would close all mines by 2018, thus ending coal mining in Germany.
Coal mining in India has a long history of commercial exploitation covering nearly 220 years starting in 1774 with John Sumner and Suetonius Grant Heatly of the East India Company in the Raniganj Coalfield along the Western bank of Damodar River. However, for about a century the growth of Indian coal mining remained sluggish for want of demand but the introduction of steam locomotives in 1853 gave a fillip to it. Within a short span, production rose to an annual average of 1 million tonne (mt) and India could produce 6.12 mts. per year by 1900 and 18 mts per year by 1920. The production got a sudden boost from the First World War but went through a slump in the early thirties. The production reached a level of 29 mts. by 1942 and 30 mts. by 1946. With the advent of Independence, the country embarked upon the 5-year development plans. At the beginning of the 1st Plan, annual production went up to 33 mts. During the 1st Plan period itself, the need for increasing coal production efficiently by systematic and scientific development of the coal industry was being felt. Setting up of the National Coal Development Corporation (NCDC), a Government of India Undertaking in 1956 with the collieries owned by the railways as its nucleus was the first major step towards planned development of Indian Coal Industry. Along with the Singareni Collieries Company Ltd. (SCCL) which was already in operation since 1945 and which became a Government company under the control of Government of Andhra Pradesh in 1956, India thus had two Government coal companies in the fifties. SCCL is now a joint undertaking of Government of Telangana and Government of India sharing its equity in 51:49 ratio.
The Japanese archipelago counts four main islands, the richest coal deposits have been found on the northernmost and the southernmost island: Hokkaidō and Kyũshũ.
Japan has a long history of coal mining dating back into the Japanese Middle Ages. It has been told that the first coal has been discovered by a farmer couple in the region of Ōmuta, central Kyūshū in 1469. Nine years later, in 1478, local farmers discovered burning stones in the north of the Island, which meant the start of the exploitation of the Chikuhõ coalfield.
The discovery of the coalfields in the north are only since the Japanese industrialization. One of the first mines in Hokkaidō was the Hokutan Horonai coal mine. (see picture)
Russia was ranked as the 5th coal producing country in the world in 2010, with a total production of 316.9 million tonnes. Russia itself is the possessor of the world's second largest coal reserves. Russia also has equal rights to coal located in the Arctic archipelago of Svalbard, in accordance with the Svalbard Treaty.
Spain was ranked as the 30th coal producing country in the world in 2010. The coal miners of Spain were active in the Spanish Civil War on the Republican side. In October 1934, in Asturias, union miners and others suffered a fifteen-day siege in Oviedo and Gjion. There is a museum dedicated to coal mining in the region of Catalonia, called Cercs Mine Museum.
South Africa is one of the ten largest coal producing and the fourth largest coal exporting country in the world.
In Taiwan, coal is distributed mainly in the northern area. All of the commercial coal deposits occurred in three Miocene coal-bearing formations, which are the Upper, the Middle and the Lower Coal Measures. The Middle Coal Measures was the most important with its wide distribution, great number of coal beds and extensive potential reserves. Taiwan has coal reserves estimated to be 100-180 Mt. However, coal output had been small, amounting to 6,948 metric tonnes per month from 4 pits before it ceased production effectively in 2000. The abandoned coal mine in Pingxi District, New Taipei has now turned into the Taiwan Coal Mine Museum.
In 2012 coal production in Ukraine amounted to 85.946 million tonnes, up 4.8% from 2011. Coal consumption that same year grew by to 61.207 million tonnes, up 6.2% compared with 2011.
More than 90 percent of Ukraine’s coal production comes from the Donets Basin. The country's coal industry employs about 500,000 people. Ukrainian coal mines are among the most dangerous in the world, and accidents are common. Furthermore, the country is plagued with extremely dangerous illegal mines.
The United Kingdom was ranked as the 24th coal producing country in the world in 2010, with a total production of 18.2 million tonnes. Coal mining in the United Kingdom probably dates to Roman times; coal production increased significantly during the Industrial Revolution in the 19th century and peaked during World War I. As a result of its long history with coal Britain's economically recoverable coal reserves have decreased, and more than twice as much coal is now imported than produced.
The American share of world coal production remained steady at about 20 percent from 1980 to 2005, at about 1 billion short tons per year. The United States was ranked as the 2nd coal producing country in the world in 2010, and possesses the largest coal reserves in the world. In 2008 then-President George W. Bush stated that coal was the most reliable source of electricity. However, in 2011 President Barack Obama said that the US should rely more on "clean" sources of energy that emit lower or no carbon dioxide pollution. For a time, while domestic coal consumption for electric power was being displaced by natural gas, exports were increasing. US net coal exports increased ninefold from 2006 to 2012, peaked at 117 million short tons in 2012, then declined to 63 million tons in 2015. In 2015, 60% of net US exports went to Europe, 27% to Asia.US coal production increasingly comes from strip mines in the western United States, such as from the Powder River Basin in Wyoming and Montana.
Coal has come under continued price pressure from natural gas and renewable energy sources, which has resulted in a rapid decline of coal in the U.S. and several notable bankruptcies including Peabody Energy. On April 13, 2016 it reported, its revenue tumbled 17 percent as coal price fell and lost 2 billion dollars on the previous year. It then filed Chapter 11 bankruptcy on April 13, 2016. The Harvard Business Review discussed retraining coal workers for solar photovoltaic employment because of the rapid rise in U.S. solar jobs. A recent study indicated that this was technically possible and would account for only 5% of the industrial revenue from a single year to provide coal workers with job security in the energy industry as whole.