Section 273. Fire-escapes erected after October first, nineteen hundred and thirteen, on buildings theretofore erected

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.