West Virginia Code Chapter 22A. Miners' Health, Safety and Training § 22A-2-11. Boreholes

It shall further be the duty of the mine foreman to have boreholes kept not less than twenty feet in advance of the face, one each twenty feet on sides of the working places that are being driven toward and in dangerous proximity to an abandoned mine or part of a mine which may contain inflammable gases or which is filled with water. These holes shall be drilled whenever any working place in an underground mine approaches within fifty feet of abandoned workings in such mine, as shown by surveys made and certified by a competent engineer or surveyor, or within two hundred feet of any abandoned workings of such mine which cannot be inspected.