30 CFR § 75.331
Auxiliary fans and tubing.
(a) When auxiliary fans and tubing are used for face ventilation, each
auxiliary fan shall be--
(1) Permissible, if the fan is electrically operated;
(2) Maintained in proper operating condition;
(3) Deenergized or shut off when no one is present on the working
(4) Located and operated to avoid recirculation of air.
(b) If a deficiency exists in any auxiliary fan system, the deficiency
shall be corrected or the auxiliary fan shall be deenergized immediately.
(c) If the air passing through an auxiliary fan or tubing contains 1.0
percent or more methane, power to electrical equipment in the working place
and to the auxiliary fan shall be deenergized, and other mechanized
equipment in the working place shall be shut off until the methane
concentration is reduced to less than 1.0 percent.
(d) When an auxiliary fan is stopped--
(1) Line brattice or other face ventilation control devices shall be
used to maintain ventilation to affected faces; and
(2) Electrical equipment in the affected working places shall be
disconnected at the power source, and other mechanized equipment shall be
shut off until ventilation to the working place is restored.