Main entry - A main haulage road. Where the coal has cleats, main entries are driven at right angles to the face cleats.
Main fan - A mechanical ventilator installed at the surface; operates by either exhausting or blowing to induce airflow through the mine roadways and workings.
Manhole - A safety hole constructed in the side of a gangway, tunnel, or slope in which miner can be safe from passing locomotives and car. Also called a refuge hole.
Man trip - A carrier of mine personnel, by rail or rubber tire, to and from the work area.
Manway - An entry used exclusively for personnel to travel form the shaft bottom or drift mouth to the working section; it is always on the intake air side in gassy mines. Also, a small passage at one side or both sides of a breast, used as a traveling way for the miner, and sometimes, as an airway, or chute, or both.
Measured coal resources – Coal for which estimates of the rank, quality, and quantity have been computed from sample analyses and measurements from closely spaced and geologically well-known sample sites, such as outcrops, trenches, mine workings, and drill holes. The points of observation and measurement are so closely spaced and the thickness and extent of coals are so well defined that the tonnage is judged to be accurate within 20 percent of true tonnage. Although the spacing of the points of observation necessary to demonstrate continuity of the coal differs from region to region according to the character of the coal beds, the points of observation are no greater than ½ mile apart. Measured coal is projected to extend as a ¼-mile wide belt from the outcrop or points of observation or measurement.
Meridian -– A surveying term that establishes a line of reference. The bearing is used to designate direction. The bearing of a line is the acute horizontal angle between the meridian and the line. Azimuths are angles measured clockwise from any meridian.
Methane – A potentially explosive gas formed naturally from the decay of vegetative matter, similar to that which formed coal. Methane, which is the principal component of natural gas, is frequently encountered in underground coal mining operations and is kept within safe limits through the use of extensive mine ventilation systems.
Methane monitor - An electronic instrument often mounted on a piece of mining equipment, that detects and measures the methane content of mine air.
Mine development - The term employed to designate the operations involved in preparing a mine for ore extraction. These operations include tunneling, sinking, cross-cutting, drifting, and raising.
Mine mouth electric plant – A coal burning electric-generating plant built near a coal mine.
Miner - One who is engaged in the business or occupation of extracting ore, coal, precious substances, or other natural materials from the earth's crust.
Mineral - An inorganic compound occurring naturally in the earth's crust, with a distinctive set of physical properties, and a definite chemical composition.
Mining Engineer - A person qualified by education, training, and experience in mining engineering. A trained engineer with knowledge of the science, economics, and arts of mineral location, extraction, concentration and sale, and the administrative and financial problems of practical importance in connection with the profitable conduct of mining.
Misfire - The complete or partial failure of a blasting charge to explode as planned.
MSHA - Mine Safety and Health Administration; the federal agency which regulates coal mine health and safety.
Mud cap - A charge of high explosive fired in contact with the surface of a rock after being covered with a quantity of wet mud, wet earth, or sand, without any borehole being used. Also termed adobe, dobie, and sandblast (illegal in coal mining).
Natural ventilation - Ventilation of a mine without the aid of fans or furnaces.
Nip - Device at the end of the trailing cable of a mining machine used for connecting the trailing cable to the trolley wire and ground.
Open end pillaring - A method of mining pillars in which no stump is left; the pockets driven are open on the gob side and the roof is supported by timber.
Outby; outbye - Nearer to the shaft, and hence farther from the working face. Toward the mine entrance. The opposite of inby.
Outcrop – Coal that appears at or near the surface.
Overburden – Layers of soil and rock covering a coal seam. Overburden is removed prior to surface mining and replaced after the coal is taken from the seam.
Overcast (undercast) - Enclosed airway which permits one air current to pass over (under) another without interruption.
Panel - A coal mining block that generally comprises one operating unit.
Panic bar - A switch, in the shape of a bar, used to cut off power at the machine in case of an emergency.
Parting - (1) A small joint in coal or rock; (2) a layer of rock in a coal seam; (3) a side track or turnout in a haulage road.
Peat – The partially decayed plant matter found in swamps and bogs, one of the earliest stages of coal formation.
Percentage extraction - The proportion of a coal seam which is removed from the mine. The remainder may represent coal in pillars or coal which is too thin or inferior to mine or lost in mining. Shallow coal mines working under townships, reservoirs, etc., may extract 50%, or less, of the entire seam, the remainder being left as pillars to protect the surface. Under favorable conditions, longwall mining may extract from 80 to 95% of the entire seam. With pillar methods of working, the extraction ranges from 50 to 90% depending on local conditions.
Percussion drill - A drill, usually air powered, that delivers its energy through a pounding or hammering action.
Permissible - That which is allowable or permitted. It is most widely applied to mine equipment and explosives of all kinds which are similar in all respects to samples that have passed certain tests of the MSHA and can be used with safety in accordance with specified conditions where hazards from explosive gas or coal dust exist.
Permit – As it pertains to mining, a document issued by a regulatory agency that gives approval for mining operations to take place.
Piggy-back - A bridge conveyor.
Pillar - An area of coal left to support the overlying strata in a mine; sometimes left permanently to support surface structures.
Pillar robbing - The systematic removal of the coal pillars between rooms or chambers to regulate the subsidence of the roof. Also termed "bridging back" the pillar, "drawing" the pillar, or "pulling" the pillar.
Pinch - A compression of the walls of a vein or the roof and floor of a coal seam so as to "squeeze" out the coal.
Pinch – A compression of the roof and floor of a coal seam so as to "squeeze" out the coal.
Pinning - Roof bolting.
Pitch - The inclination of a seam; the rise of a seam.
Plan - A map showing features such as mine workings or geological structures on a horizontal plane.
Pneumoconiosis - A chronic disease of the lung arising from breathing coal dust.
Portal - The structure surrounding the immediate entrance to a mine; the mouth of an adit or tunnel.
Portal bus - Track-mounted, self-propelled personnel carrier that holds 8 to 12 people.
Post - The vertical member of a timber set.
Preparation plant - A place where coal is cleaned, sized, and prepared for market.
Primary roof - The main roof above the immediate top. Its thickness may vary from a few to several thousand feet.
Primer (booster) - A package or cartridge of explosive which is designed specifically to transmit detonation to other explosives and which does not contain a detonator.
Prop - Coal mining term for any single post used as roof support. Props may be timber or steel; if steel--screwed, yieldable, or hydraulic.
Proximate analysis - A physical, or non-chemical, test of the constitution of coal. Not precise, but very useful for determining the commercial value. Using the same sample (1 gram) under controlled heating at fixed temperatures and time periods, moisture, volatile matter, fixed carbon and ash content are successfully determined. Sulfur and Btu content are also generally reported with a proximate analysis.
Pyrite - A hard, heavy, shiny, yellow mineral, FeS2 or iron disulfide, generally in cubic crystals. Also called iron pyrites, fool's gold, sulfur balls. Iron pyrite is the most common sulfide found in coal mines.
Raise - A secondary or tertiary inclined opening, vertical or near-vertical opening driven upward form a level to connect with the level above, or to explore the ground for a limited distance above one level.
Ramp - A secondary or tertiary inclined opening, driven to connect levels, usually driven in a downward direction, and used for haulage.
Ranks of coal – The classification of coal by degree of hardness, moisture and heat content. "Anthracite" is hard coal, almost pure carbon, used mainly for heating homes. "Bituminous" is soft coal. It is the most common coal found in the United States and is used to generate electricity and to make coke for the steel industry. "Subbituminous" is a coal with a heating value between bituminous and lignite. It has low fixed carbon and high percentages of volatile matter and moisture. "Lignite" is the softest coal and has the highest moisture content. It is used for generating electricity and for conversion into synthetic gas. In terms of Btu or "heating" content, anthracite has the highest value, followed by bituminous, subbituminous and lignite.
Reclamation – The restoration of land and environmental values to a surface mine site after the coal is extracted. Reclamation operations are usually underway as soon as the coal has been removed from a mine site. The process includes restoring the land to its approximate original appearance by restoring topsoil and planting native grasses and ground covers.
Recovery - The proportion or percentage of coal or ore mined from the original seam or deposit.
Red dog - A nonvolatile combustion product of the oxidation of coal or coal refuse. Most commonly applied to material resulting from in situ, uncontrolled burning of coal or coal refuse piles. It is similar to coal ash.
Regulator - Device (wall, door) used to control the volume of air in an air split.
Reserve – That portion of the identified coal resource that can be economically mined at the time of determination. The reserve is derived by applying a recovery factor to that component of the identified coal resource designated as the reserve base.
Resin bolting - A method of permanent roof support in which steel rods are grouted with resin.
Resources – Concentrations of coal in such forms that economic extraction is currently or may become feasible. Coal resources broken down by identified and undiscovered resources. Identified coal resources are classified as demonstrated and inferred. Demonstrated resources are further broken down as measured and indicated. Undiscovered resources are broken down as hypothetical and speculative.
Respirable dust - Dust particles 5 microns or less in size.
Respirable dust sample - A sample collected with an approved coal mine dust sampler unit attached to a miner, or so positioned as to measure the concentration of respirable dust to which the miner is exposed, and operated continuously over an entire work shift of such miner.
Retreat mining - A system of robbing pillars in which the robbing line, or line through the faces of the pillars being extracted, retreats from the boundary toward the shaft or mine mouth.
Return - The air or ventilation that has passed through all the working faces of a split.
Return idler - The idler or roller underneath the cover or cover plates on which the conveyor belt rides after the load which it was carrying has been dumped at the head section and starts the return trip toward the foot section.
Rib - The side of a pillar or the wall of an entry. The solid coal on the side of any underground passage. Same as rib pillar.
Rider - A thin seam of coal overlying a thicker one.
Ripper - A coal extraction machine that works by tearing the coal from the face.
Rob - To extract pillars of coal previously left for support.
Robbed out area - Describes that part of a mine from which the pillars have been removed.
Roll - (1) A high place in the bottom or a low place in the top of a mine passage, (2) a local thickening of roof or floor strata, causing thinning of a coal seam.
Roll protection - A framework, safety canopy, or similar protection for the operator when equipment overturns.
Roof - The stratum of rock or other material above a coal seam; the overhead surface of a coal working place. Same as "back" or "top."
Roof bolt - A long steel bolt driven into the roof of underground excavations to support the roof, preventing and limiting the extent of roof falls. The unit consists of the bolt (up to 4 feet long), steel plate, expansion shell, and pal nut. The use of roof bolts eliminates the need for timbering by fastening together, or "laminating," several weaker layers of roof strata to build a "beam."
Roof fall - A coal mine cave-in especially in permanent areas such as entries.
Roof jack - A screw- or pump-type hydraulic extension post made of steel and used as temporary roof support.
Roof sag - The sinking, bending, or curving of the roof, especially in the middle, from weight or pressure.
Roof stress - Unbalanced internal forces in the roof or sides, created when coal is extracted.
Roof support – Posts, jacks, roof bolts and beams used to support the rock overlying a coal seam in an underground mine. A good roof support plan is part of mine safety and coal extraction.
Roof trusses - A combination of steel rods anchored into the roof to create zones of compression and tension forces and provide better support for weak roof and roof over wide areas.
Room and pillar mining – A method of underground mining in which approximately half of the coal is left in place to support the roof of the active mining area. Large "pillars" are left while "rooms" of coal are extracted.
Room neck - The short passage from the entry into a room.
Round - Planned pattern of drill holes fired in sequence in tunneling, shaft sinking, or stopping. First the cut holes are fired, followed by relief, lifter, and rib holes.
Royalty - The payment of a certain stipulated sum on the mineral produced.
Rubbing surface - The total area (top, bottom, and sides) of an airway.
Run-of-mine - Raw material as it exists in the mine; average grade or quality.