All ventilating fans shall be kept in operation night and day unless operations are indefinitely suspended, except written permission is given by the mine inspector of the district to stop the same, and the said written permission shall state the particular hours the said fan may not be in operation, and the mine inspector shall have the power to withdraw or modify such permission as he may deem best, but in all cases the fan shall be started three (3) hours before the time for work to begin, and such written permission to stop the fan shall not apply to fans in use at mines wherein explosive gas is generated. When the fans may be stopped by the permission of the mine inspector, a notice printed in the various languages used by persons employed in the mine, stating at what hours the fan will be stopped and the time it will again be set in motion, shall be posted by the mine foreman in a conspicuous place at the entrance or entrances to the mine: Provided, that should it at any time become necessary to stop the fan on account of accident or needed repairs to any part of the machinery connected therewith, or by reason of any other unavoidable cause, it shall then be the duty of the mine foreman, or any other official in charge, after first having provided for the safety of the persons employed in the mine, to order said fan to be stopped so as to make the necessary repairs or to remove any other difficulty that may have been the cause of its stoppage, and all ventilating furnaces in mines shall be started three (3) hours before the appointed time to begin work and during working hours be properly attended by a person employed for that purpose; in mines generating fire damp in sufficient quantities to be detected by the ordinary safety lamps, all main breakthroughs between slopes and aircourses, airbridges or overcasts shall be built of masonry or other noncombustible material of ample strength, or be driven through the solid strata. In all mines the doors used for guiding and directing the ventilation of the mine shall be so hung and adjusted that they will close themselves, or be supplied with springs or pulleys so that they cannot be left standing open, and an attendant shall be employed at all doors, through which cars are hauled, for the purpose of opening and closing said doors when trips of cars are passing to and from the workings, unless approved selfacting doors are used which doors shall be determined by the mine inspector and mine foreman. A hole for shelter shall be provided at each door, so as to protect said attendant from being run over by the cars while attending to his duties; and persons employed for this purpose shall at all times remain at their post of duty during working hours: Provided, that the same person may attend two doors where the distance between them is not more than one hundred (100) feet. At all principal doors and every inclined plane or roadway in any mine where haulage is done by machinery, and where a door is used, an extra door shall be provided to be used in case of necessity.

R.L.1910, § 3973.