Sec. 929. [=Hoisting and lowering of persons.=] The owner, lessee or agent of a mine, at which the only means of ingress and egress for the persons employed therein is by a vertical shaft or shafts, of fifty feet or more in depth, shall designate one or more persons whose duty shall be to attend to the lowering and hoisting of persons into and out of such mine, and give and receive the proper signals, governing the movement of the cage while engaged in handling men. Not more than ten persons shall be lowered or hoisted at any one time. The lowering of persons shall begin in time for persons to reach their working places by hour appointed for mine to commence work and continue until starting time. Hoisting of persons shall commence at time for mine to cease work, and continue until all have had time to be hoisted. Persons may be hoisted at such other times as will not interfere with the hoisting of coal, or other products. No person shall be lowered into or hoisted out of a mine, with powder, explosives, tools or material on any cage, in the same shaft, and no person shall be lowered or hoisted in a vertical shaft in a mine car. When the vertical shaft is less than fifty feet in depth, and a stairway approved by the district inspector of mines is not provided, the owner, lessee or agent shall be required to lower or hoist persons, as above prescribed, but when such stairway is provided, the hoisting of persons shall not be required. Sec. 930. [=Owner, lessee or agent shall provide second opening.=] The owner, lessee or agent of a mine shall not employ or permit any person to work therein except as hereinafter provided, unless to every seam worked in such mine there are at least two openings, separated by natural strata of not less than one hundred feet in breadth at any point, by which distinct means of ingress and egress are always available to the persons therein employed. Such openings need not belong to the same mine so long as the persons employed therein have safe, ready and available means of ingress and egress, by not less than two openings, provided, however, that no air shaft with a ventilating furnace at the bottom be designated or used as a means of ingress or egress. The provisions of this section shall not apply to opening a new mine while being worked for the purpose of making the second opening and the communication therewith, and the making of the landing or bottom and extending of the main entries one hundred feet while such communication is being made; to a mine in which the second opening has become unavailable from any cause while said second opening is being restored or another is being made; nor to a mine in which the second opening has become unavailable by reason of the final robbing of the pillars previous to abandonment, so long as not more than twenty persons in either case are employed therein at one time.