Not more than forty-five persons shall be permitted to work in the same air current and mines where ten or more persons are employed shall be provided with a fan or other artificial means to
produce the ventilation, but no furnace shall be used where mines generate gases in dangerous guantities, and all stoppings between main intake and return airways hereafter built or replaced shall be substantially built of suitable masonry, or concrete which shall be approved by the inspector of the district. R.L.1910, § 3972.