N
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.
O
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�C Coal that appears at or near the surface.
Overburden�C 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.
P
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�C 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�C 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 rem
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