After having identified the coalfield and its position and shape, the mine building site is started. If the coal is found a at depth not exceeding 30 m, it is extracted in open pit mines, where the field is made accessible after the elimination of the top layers of rocks and soil by means of explosive charges. If the coal is deeper than 30m, the field is accessed by digging underground mines including at least two galleries to let miners and machines reach the coal.