Exterior stairs may be used as exits in lieu of interior stairs provided they comply with all of the requirements for interior stairs, except enclosure, and except as modified below:
(a) Capacity. The capacity of exterior stairs shall be as listed in table 6-1.
(b) Height limitation. No exterior stair shall exceed seventy-five feet or six stories in height.
(c) Construction. Exterior stairs shall be constructed entirely of noncombustible materials, except that in buildings classified in occupancy groups other than G, F, or H, of construction group II, located outside the fire districts, exterior stairs may be built of combustible materials when the buildings are two stories or thirty feet in height or less and have an occupant load not exceeding forty persons per floor above the street below. Exterior stairs shall be roofed, and shall be protected along their outer sides as required for exterior corridors in subdivision (f) of section 27-369 of this article. Treads, landings, and platforms shall be solid and unperforated. Risers may be partially open to permit water and snow to drain.
(d) Opening protective. In buildings four stories or fifty feet in height or more, there shall be no openings in the building walls adjoining exterior stairs other than one-quarter hour self-closing swinging fire doors, and no openings nearer than ten feet to the stair (measured horizontally) that are not provided with three-quarter hour opening protectives.
(e) Location. No exterior stair shall be located nearer than ten feet to an interior lot line.
(f) Discharge. Exterior stairs shall extend continuously to grade.
(a) Capacity. The capacity of exterior stairs shall be as listed in table 6-1.
(b) Height limitation. No exterior stair shall exceed seventy-five feet or six stories in height.
(c) Construction. Exterior stairs shall be constructed entirely of noncombustible materials, except that in buildings classified in occupancy groups other than G, F, or H, of construction group II, located outside the fire districts, exterior stairs may be built of combustible materials when the buildings are two stories or thirty feet in height or less and have an occupant load not exceeding forty persons per floor above the street below. Exterior stairs shall be roofed, and shall be protected along their outer sides as required for exterior corridors in subdivision (f) of section 27-369 of this article. Treads, landings, and platforms shall be solid and unperforated. Risers may be partially open to permit water and snow to drain.
(d) Opening protective. In buildings four stories or fifty feet in height or more, there shall be no openings in the building walls adjoining exterior stairs other than one-quarter hour self-closing swinging fire doors, and no openings nearer than ten feet to the stair (measured horizontally) that are not provided with three-quarter hour opening protectives.
(e) Location. No exterior stair shall be located nearer than ten feet to an interior lot line.
(f) Discharge. Exterior stairs shall extend continuously to grade.
Fire towers may be used as exits in lieu of interior stairs provided they comply with all of the requirements for interior stairs, except as modified below.
(a) The enclosing walls of fire towers shall be of incombustible materials or assemblies having a fire-resistance rating of at least four hours. Such walls shall be without openings, except for doors serving as means of egress.
(b) At each story served by a fire tower, access to the stairways of such fire tower shall be provided through outside balconies or fireproof vestibules. Such balconies or vestibules shall be at least three feet eight inches in width and shall have unpierced floors of incombustible materials and shall be provided with substantial guard railings at least four feet high, without any openings greater than five inches in width.
(c) Such balconies or vestibules of fire towers shall be level with the floors of the structure and the platforms of the stairs connected by such balconies. Such balconies or vestibules shall be separated from the structure and the stairs by self-closing swinging doors with a one and one-half hour fire protection rating, capable of being opened from both sides without the use of a key or other unlocking device.
(d) Balconies or vestibules of fire towers shall open on a street or yard, or on a court open vertically to the sky for its full height, having a minimum net area of one hundred five square feet and a minimum dimension of seven feet. The opening from the vestibule to the street, yard or court shall have a minimum area of eighteen square feet and a minimum dimension of two feet six inches. It shall be unlawful to leave openings in the court walls surrounding an interior fire tower, other than the openings from the vestibules, within fifteen feet of the balcony, except that self-closing windows with a three-quarter hour fire protection rating may be used if such windows are at least ten feet from the balcony, provided that the area of the court is at least twelve feet by twenty-four feet.
(e) Fire towers shall terminate at grade level and shall exit directly to the street independently of corridors serving other stairways, except when the fire tower terminates in the ground floor corridor outside of the inner vestibule and within ten feet of the building line.
(f) Fire tower stairs shall comply in all other respects with the applicable requirements of section 27-375 of this code.
(a) The enclosing walls of fire towers shall be of incombustible materials or assemblies having a fire-resistance rating of at least four hours. Such walls shall be without openings, except for doors serving as means of egress.
(b) At each story served by a fire tower, access to the stairways of such fire tower shall be provided through outside balconies or fireproof vestibules. Such balconies or vestibules shall be at least three feet eight inches in width and shall have unpierced floors of incombustible materials and shall be provided with substantial guard railings at least four feet high, without any openings greater than five inches in width.
(c) Such balconies or vestibules of fire towers shall be level with the floors of the structure and the platforms of the stairs connected by such balconies. Such balconies or vestibules shall be separated from the structure and the stairs by self-closing swinging doors with a one and one-half hour fire protection rating, capable of being opened from both sides without the use of a key or other unlocking device.
(d) Balconies or vestibules of fire towers shall open on a street or yard, or on a court open vertically to the sky for its full height, having a minimum net area of one hundred five square feet and a minimum dimension of seven feet. The opening from the vestibule to the street, yard or court shall have a minimum area of eighteen square feet and a minimum dimension of two feet six inches. It shall be unlawful to leave openings in the court walls surrounding an interior fire tower, other than the openings from the vestibules, within fifteen feet of the balcony, except that self-closing windows with a three-quarter hour fire protection rating may be used if such windows are at least ten feet from the balcony, provided that the area of the court is at least twelve feet by twenty-four feet.
(e) Fire towers shall terminate at grade level and shall exit directly to the street independently of corridors serving other stairways, except when the fire tower terminates in the ground floor corridor outside of the inner vestibule and within ten feet of the building line.
(f) Fire tower stairs shall comply in all other respects with the applicable requirements of section 27-375 of this code.