In all factories, mercantile establishments, mills or workshops, proper and substantial handrails shall be provided on all stairways, and the treads thereon shall be so constructed as to furnish a firm and safe foothold. A proper light shall be kept burning by the owner or lessee in all main passageways, main hallways, at all main stairs, main stair landings and shafts, and in front of all passenger or freight elevators, upon the entrance floors, and upon other floors, on every workday of the year, from the time the building is open for use until it is closed, except at times when the influx of natural light shall make artificial light unnecessary. No floor space or any work room in any factory, mercantile establishment, mill or workshop, shall be so overloaded with machinery or other materials as thereby to cause serious risk to or endanger the life or limb of any employee, nor shall there be permitted in any such establishment a load in excess of the safe sustaining power of the floors and walls thereof. Machines shall not be placed so close together as to be a serious menace to those who have to pass between them. Passageways shall be of ample width, well lighted and free from obstruction.