Room and Pillar      The coal seam is accessed by a main slope or shaft. The coal is then mined along a series of roadways that intersect at right angles, leaving pillars of coal at the intersection to support the roof. The rooms created vary in width from 12 to 21 feet and are the main source of coal output. Doors are used to direct air throughout the working area to keep the mine ventilated and free of dangerous gas build up. The pillars of coal can later be extracted in retreat mining, letting the roof collapse into the open space that is created. There are a number of variables that determine the width and depth of the pillars. The deeper the coal seam form the surface, the larger the pillars need to be in order to give sufficient strength to support the increased pressure of the overhead layers of rock. Soft or easily broken coal requires larger pillars than harder coal, and if the roof material is soft or weak, large pillars are required to distribute the weight of the coal. If the coal seam has a steep angle, large pillars are also needed.      Naturally, is is better to be safe than sorry and make the pillars larger and therefore stronger than thought necessary. Small pillars may needlessly risk the lives of the miners, as well as the risk and expense of losing the mine and equipment.      One important aspect of laying out a mine is the possibility of recovering or drawing the valuable coal left in these pillars. This is usually done when one area of the mine has been worked out or when the life of the colliery is coming to an end. There are many methods of drawing pillars, but it is sufficient for our purposes to remember that this is an important part of the mining operation.

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