30 CFR § 57.22208 Auxiliary fans (I-A, II-A, III, and V-A mines).
(a) Auxiliary fans, except fans used in shops and other areas which
have been so designed that methane cannot enter the airway, shall be approved
by MSHA under the applicable requirements of 30 CFR part 18, and be operated
so that recirculation is minimized. Auxiliary fans shall not be used to
ventilate work places during the interruption of normal mine
(b) Tests for methane shall be made at auxiliary fans before they are