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Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. Exploitation of these deposits for raw material is based on the economic viability of investing in the equipment, labor, and energy required to extract, refine and transport the materials found at the mine to manufacturers who can use the material. Ores recovered by mining include metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain most materials that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, and final reclamation or restoration of the land after the mine is closed. Mining operations usually create a negative environmental impact, both during the mining activity and after the mine has closed. Hence, most of the world's nations have passed regulations to decrease the impact; however, the outsized role of mining in generating business for often rural, remote or economically depressed communities means that governments sometimes fail to fully enforce regulation. Work safety has long been a concern as well, and where enforced modern practices have significantly improved safety in mines. Moreover, unregulated or poorly regulated mining, especially in developing economies, frequently contributes to local human rights violations and resource conflicts.
There are numerous occupational hazards associated with mining, including exposure to rockdust which can lead to diseases such as silicosis, asbestosis, and pneumoconiosis. Gases in the mine can lead to asphyxiation and could also be ignited. Mining equipment can generate considerable noise, putting workers at risk for hearing loss. Cave-ins, rock falls, and exposure to excess heat are also known hazards. The current NIOSH Recommended Exposure Limit (REL) of noise is 85 dBA with a 3 dBA exchange rate and the MSHA Permissible Exposure Limit (PEL) is 90 dBA with a 5 dBA exchange rate as an 8-hour time-weighted average. NIOSH has found that 25% of noise-exposed workers in Mining, Quarrying, and Oil and Gas Extraction have hearing impairment. The prevalence of hearing loss increased by 1% from 1991 to 2001 within these workers. Noise studies have been conducted in several mining environments. Stageloaders (84-102 dBA), shearers (85-99 dBA), auxiliary fans (84–120 dBA), continuous mining machines (78–109 dBA), and roof bolters (92–103 dBA) represent some of the noisiest equipment in underground coal mines. Dragline oilers, dozer operators, and welders using air arcing were occupations with the highest noise exposures among surface coal miners. Coal mines had the highest hearing loss injury likelihood. Proper ventilation, hearing protection, and spraying equipment with water are important safety practices in mines.
A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the use of these self-propelled vehicles is increasingly common for passenger trains, but rare for freight. Traditionally, locomotives pulled trains from the front. However, push-pull operation has become common, where the train may have a locomotive (or locomotives) at the front, at the rear, or at each end. Most recently railroads have begun adopting DPU or distributed power. The front may have one or two locomotives followed by a mid train locomotive that is controlled remotely from the lead unit. In 2002, the first 3.6 tonne, 17 kW hydrogen (fuel cell) -powered mining locomotive was demonstrated in Val-d'Or, Quebec. In 2007 the educational mini-hydrail in Kaohsiung, Taiwan went into service. The Railpower GG20B finally is another example of a fuel cell-electric locomotive. Steam-diesel hybrid locomotives can use steam generated from a boiler or diesel to power a piston engine. The Cristiani Compressed Steam System used a diesel engine to power a compressor to drive and recirculate steam produced by a boiler; effectively using steam as the power transmission medium, with the diesel engine being the prime mover.