(a) All main fans shall be installed on the surface, in fireproof housings, the fan situated not less than 30 feet from its air shaft or air course and on one side of the line of such opening so that the fan will not be in direct line of the force of a blast or explosion. The air duct connecting the fan with the mine opening shall be fireproof and provided with self-closing explosion doors.

(b) In mines ventilated with multiple fans, each main fan shall be equipped with fireproof doors automatically closing in the event of a fan failure to prevent air reversal through the fan.

(c) Every main fan installed after August 12, 1949, ventilating a mine classed as gassy, must have an auxiliary drive mechanism that will operate the fan at not less than 80 percent of its regular volume. Dual fan installations, independently powered so that one is operative at 80 percent of regular volume during electrical failures, meet this requirement.

(d) All main fans are required to be provided with a pressure-recording gauge, or water gauge, and, unless attended constantly, an automatic device to give alarm when the fan slows down or stops. This device shall be placed so that its alarm will be seen or heard by a responsible person.

(e) Each main fan ventilating all or part of a mine shall be on a separate power circuit, independent of the underground circuit.

(f) Main fan installations shall be protected from wood fire, grass fire, and rubbish fire for at least 100 feet in all directions from the fan installations, where physical conditions permit.

(g) The main fan shall be inspected daily and a record kept of the inspection. This inspection may be made by any competent person so designated.

(h) In mines, when the main fan fails or stops, immediate action shall be taken to cut off power from the mine or the area of the mine ventilated by that main fan, and the men shall be withdrawn from the face regions. If ventilation is restored in a reasonable time, the face regions and other places where methane is likely to accumulate shall be reexamined by certified persons, and, if found to be free from explosive gas, power may be restored and work resumed. If the interruption continues for an indefinite or extended period, all underground employees shall be required to leave the mine or the part of the mine ventilated by the main fan that is out of operation. Mines ventilated by more than one main fan shall be considered as having only one fan in the application of this section unless all returns to the fans are entirely separated and escapeways to the surface are available from the areas ventilated by other fans without necessity for any person passing through any area not properly ventilated.

(i) Main fans ventilating mines shall be operated continuously, except when the mine is shut down with all power underground cut off and with all men out of the mine. When the fan is started again, the mine shall be examined for gas and other hazards by certified persons and declared safe before underground power may be restored and men other than the examiners permitted to enter the mine.