Holes drilled in from gates either side of the seam parallel to the face are of diameter 65 mm opt cased in plastics to 8 m from the hole mouth and serve to drain off the gas (methane) liberated when charges strung out in relatively narrower shotholes run in at right angles from the face are fired so as to break up the coal. These shot holes should reach right into the forward abutment pressure zone.
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