§ 57.22220 — Air Passing Unsealed Areas (i-a, Ii-a, Iii, And V-a Mines)

Air that has passed by or through unsealed abandoned or unsealed inactive areas and contains 0.25 percent or more methane shall—

(a) Be coursed directly to a return airway;

(b) Be tested daily for methane by a competent person; and

(c) Not be used to ventilate work places.