30 CFR § 75.332
Working sections and working places.
(a)(1) Each working section and each area where mechanized mining
equipment is being installed or removed, shall be ventilated by a separate
split of intake air directed by overcasts, undercasts or other permanent
(2) When two or more sets of mining equipment are simultaneously
engaged in cutting, mining, or loading coal or rock from working places
within the same working section, each set of mining equipment shall be on a
separate split of intake air.
(3) For purposes of this section, a set of mining equipment includes a
single loading machine, a single continuous mining machine, or a single
longwall or shortwall mining machine.
(b)(1) Air that has passed through any area that is not examined under
of this subpart, or through an area where
second mining has been done shall not be used to ventilate any working place.
Second mining is intentional retreat mining where pillars have been wholly or
partially removed, regardless of the amount of recovery obtained.
(2) Air that has passed by any opening of any unsealed area that is
not examined under §§75.360
of this subpart, shall not be used to ventilate any working place.