MSHA-57.22241
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MSHA - Title 30 CFR
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.