All outside fire-escapes erected after October first, nineteen hundred and thirteen, on buildings theretofore erected and serving as required exits shall conform to the following requirements:
1. They shall be built of wrought iron or steel and shall be so designed, constructed and erected as to safely sustain on all platforms, balconies and stairways a live load of not less than ninety pounds per square foot with a factor of safety of four.
2. Whenever practicable a continuous run or straight run stairway shall be built.
3. All openings leading thereto shall have an unobstructed width of at least two feet and an unobstructed height of at least six feet. Such openings shall extend to the floor level or within six inches thereof, shall be not more than seven inches above the floor of the fire-escape balcony and shall be provided with fire doors, except in buildings five stories or under in height complying with the provisions of subdivisions five and six of section two hundred and seventy-four.
4. All windows opening upon the course of the fire-escape shall be fireproof windows.
5. On every floor above the first there shall be a balcony firmly fastened to the building and embracing one or more easily accessible and unobstructed openings. The balconies shall have a width of at least four feet throughout their length and shall have a landing not less than twenty-four inches square at the head of every stairway. There shall be a passageway between the stairway opening and the side of the building at least eighteen inches wide throughout except where the stairways reach and leave the balconies at the ends or where double run stairways are used. The stairway openings of the balconies shall be of a size sufficient to provide clear headway and shall be guarded on the long side by an iron railing not less than three feet in height. Each balcony shall be surrounded by an iron railing not less than three feet in height properly braced.
6. The balconies shall be connected by stairways not less than twenty-two inches wide placed at an incline of not more than forty-five degrees, with steps of not less than eight-inch tread and not over eight-inch rise and provided with a handrail not less than three feet above the treads. The treads of such stairways shall be so constructed as to sustain a live load of four hundred pounds per step with a factor of safety of four.
7. There shall be a similar stairway from the top floor balcony to the roof, except where the fire-escape is erected on the front of the building.
8. A similar stairway shall also be provided from the lowest balcony to a safe landing place beneath, which stairway shall remain down permanently or be arranged to swing up and down automatically by counter-balancing weights.
9. When not erected on the front of the building, safe and unobstructed egress shall be provided from the foot of the fire-escape by means of an open court or courts or a fireproof passageway having an unobstructed width of at least three feet throughout, leading to the street, or by means of an open area having communication with the street. Such fireproof passageway shall be adequately lighted at all times and the lights shall be so arranged as to insure their reliable operation when through accident or other cause the regular factory lighting is extinguished.