of coal dust or air from the mill. Each mill is completely enclosed in an insulated soundattenuating housing with panels that provide easy access to the mill. The mill is driven by a directcoupled motor through a speed reducer and final single helical gear set having the driven gear mounted on the mill .
Room and pillar mining involves cutting a system of rooms within the coal seem. Pillars are left in order to support the roof of the cut into coal seem. In a secondary mining method, called retreat mining, coal is systematically collected from the pillars, allowing the mine to close in behind them 2. This type of mining can be extremely dangerous.