§ 266. Exterior enclosed fireproof stairway. "Exterior enclosed
fireproof stairway" means a stairway conforming to the following
requirements:

1. It shall be completely enclosed from top to bottom by walls of
fireproof material not less than eight inches thick extending from the
sidewalk, court or yard level to the roof, and above the roof so as to
form a bulkhead.

2. It shall in all other respects except as herein provided conform to
the requirements of section two hundred and seventy in regard to the
construction of stairways and their enclosures, except that stairways
and landings in an exterior fireproof enclosed stairway not exceeding
one hundred feet in height may be constructed of other than
incombustible material to be approved by the board.

3. There shall be no opening in any wall separating it from the
building.

4. Access shall be provided to the stairway from every floor of the
building by means of an outside balcony or vestibule of steel, iron or
masonry. Every such balcony or vestibule shall have an unobstructed
width of at least forty-four inches and shall be provided with a
fireproof floor and a railing of incombustible material not less than
three feet high. Access to such balconies from the building and to the
stairway from the balconies shall be by means of firedoors. The level of
the balcony floor shall be not more than seven inches below the level of
the door sill of the building. The doors shall swing outward onto the
balcony and inward from the balcony to the stairway, and shall be
provided with locks or latches with visible fastenings requiring no key
to open them in leaving the building. The balconies shall be open on at
least one side, upon an open space not less than one hundred square feet
in area.

5. The landings shall be of such width that the doors in opening into
the stairway shall not reduce the free passageway of the landings to a
width less than the width of the stairs.

6. Such stairway shall be provided with a proper lighting system
furnishing adequate light and shall be so arranged as to ensure its
reliable operation, when through accident or other cause the regular
factory lighting is extinguished.