30 CFR § 57.22241 Advance face boreholes (I-C mines). (a) Boreholes shall be drilled at least 25 feet in advance of a face
whenever the work place is within-- (A) (1) 50 feet of a surveyed abandoned mine or abandoned workings which cannot
be inspected; or (A) (2) 200 feet of an unsurveyed abandoned mine or abandoned workings which
cannot be inspected. (b) Boreholes shall be drilled in such a manner to insure that the
advancing face will not accidently break into an abandoned mine or abandoned
working.
