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Coal miners work in two kinds of coal mines: surface and underground. The mining method used is determined by the depth and location of the coal seam and the geological formations around it. In surface or strip mining, the overburden—the earth above the coal seam—has to be removed before the coal can be dug out. Then, after the mining has been completed, the overburden is replaced so the land can be reclaimed. For underground mining, entries and tunnels are constructed so that workers and equipment can reach the coal.
The machinery used in coal mining is extremely complex and expensive. There are power shovels that can move 3,500 tons of earth in an hour and continuous mining machines that can rip 12 tons of coal from an underground seam in a minute. Longwall shearers can extract the coal at an even faster rate. The job of coal miners is to operate these machines safely and efficiently. Their specific duties depend on the type of mine that employs them and the machinery they operate. The following paragraphs provide more information about major specialties in the field:
Drillers operate drilling machines to bore holes in the overburden at points selected by the blasters. They must be careful that the drill doesn't bind or stop while in operation. They may replace worn or broken drill parts using hand tools, change drill bits, and lubricate the equipment.
Stripping shovel operators and dragline operators control the shovels and draglines that scoop up and move the broken overburden, which is pushed within their reach by the bulldozers. With the overburden removed, the coal is exposed so that machines with smaller shovels can remove it from the seam and load it into trucks.
Underground mining uses three methods to extract the coal that lies deep beneath the surface. These methods are continuous, longwall, and conventional mining.
Continuous mining is the most widely used method of mining underground coal. It is a system that uses a hydraulically operated machine that mines and loads coal in one step. Cutting wheels attached to hydraulic lifts rip coal from the seam. Then mechanical arms gather the coal from the tunnel floor and dump it onto a conveyor, which moves the coal to a shuttle car or another conveyor belt to be carried out of the mine. Continuous-mining machine operators sit or lie in the cab of the machine or operate it remotely. Either way, they move the machine into the mining area and manipulate levers to position the cutting wheels against the coal. They and their helpers may adjust, repair, and lubricate the machine and change cutting teeth.
In longwall mining, coal is also cut and loaded in one operation. With steel canopies supporting the roof above the work area, the mining machinery moves along a wall while its plow blade or cutting wheel shears the coal from the seam and automatically loads it onto a conveyor belt for transportation out of the mine. Longwall-mining machine operators advance the cutting device either manually or by remote control. They monitor lights and gauges on the control panel and listen for unusual sounds that would signal or indicate a malfunction in the equipment. As the wall in front of the longwall mining machine is cut away, the operator and face personnel move the roof supports forward, allowing the roof behind the supports to cave in.
Conventional mining, unlike continuous or longwall mining, is done in separate steps: First the coal is blasted from the seam, then it is picked up and loaded. Of the three underground methods, conventional mining requires the largest number of workers. Cutter operators work a self-propelled machine equipped with a circular, toothed chain that travels around a blade six to 15 feet long. They drive the machine into the working area and saw a channel along the bottom and sides of the coal face, a procedure that makes the blasting more effective because it relieves some of the pressure caused by the explosion. Cutter operators may also adjust and repair the machine, replace dull teeth, and shovel debris from the channel. Using mobile machines, drilling-machine operators bore blast holes in the coal face after first determining the depth of the undercut and where to place the holes. Then blasters place explosive charges in the holes and detonate them to shatter the coal. After the blast, loading-machine operators drive electric loading machines to the area and manipulate the levers that control the mechanical arms to gather up the loose coal and load it onto shuttle cars or conveyors to be carried out of the mine.
Coal mining technicians play an important role in the mining process. By the time the mining actually starts, coal mining technicians have already helped the managers, engineers, and scientists to survey, test drill, and analyze the coal deposit for depth and quality. They have also mapped the surface and helped plan the drilling and blasting to break up the rock and soil that cover the coal. The technicians have also helped prepare permits that must be filed with federal and state governments before mining can begin. Information must be provided on how the land will be mined and reclaimed; its soil, water conditions, and vegetation; wildlife conservation; and how archaeological resources will be protected.
The coal mining technicians also help the mining engineers and superintendents select the machinery used in mining. Such a plan must include selecting machines of a correct size and capacity to match other machinery and planning the sequences for efficient use of machines. The plan also includes mapping roads out of the mine pit, planning machine and road maintenance and, above all, using safety methods for the entire operation.
Ventilation technicians operate dust counting, gas quantity, and air volume measuring instruments. They record or plot this data and plan or assist in planning the direction of air flow through mine workings. Ventilation technicians also help prescribe the fan installations required to accomplish the desired airflow.
Geological aides gather geological data as mining activities progress. They identify rocks and minerals; record and map structural changes; locate drill holes; and identify rocks, coal, and minerals in drill cores. They also map geological information from drill core data, gather samples, and map results on mine plans.
Chemical analysts analyze mine, mill, and coal samples by using volumetric or instrumental methods of analysis. They also write reports on the findings.
Mining work is hard, dirty, and often dangerous. Mine workers are often characterized by the concern they have for their fellow miners. There is no room for carelessness in this occupation. The safety of all workers depends on teamwork, with everyone alert and careful to avoid accidents.