Section 270. Construction of buildings erected after October first, nineteen hundred and thirteen

No  factory  shall  be  conducted in a building
  erected after October first, nineteen hundred and thirteen, unless  such
  building shall conform to the following requirements:
    1.  Fireproof  construction.  All  buildings more than four stories in
  height shall be fireproof.
    2. Roofs and walls. Roofs shall be covered either  with  incombustible
  material,  or tar and slag, or plastic cement or such other materials as
  the  board  may  approve,  supported   and   laid   according   to   its
  specifications. Cornices shall be constructed of incombustible material.
  All  exterior  walls within twenty-five feet of a non-fireproof building
  shall be built of brick, stone, concrete, cinder or  concrete  block  or
  tile,  terra  cotta  or other fireproof material acceptable to the state
  department of labor.
    3. Required exits. a. On each floor used as a factory there  shall  be
  not  less  than  two  exits remote from each other, except that a single
  exit may be accepted by the commissioner from a floor or other area,  of
  one  thousand  square  feet  or  less, so long as no person is regularly
  employed on such floor or other area. One such exit on each  floor  used
  as  a  factory  shall  be a grade exit, an interior or exterior enclosed
  fireproof stairway or ramp. The other shall be either such a grade exit,
  stairway, ramp, or a horizontal exit, except  that  unenclosed  exterior
  stairways  or  ramps  within  the property line, extending up or down to
  grade may be substituted for enclosed stairways from a floor immediately
  above or below the ground or first floor. Elevated runways  and  working
  platforms  on which there is no regular or permanent occupancy shall not
  be construed as floors.
    b. No point in any floor above or below  the  ground  or  first  floor
  shall  be  more  than  one hundred feet distant from the entrance to one
  such exit at that floor and in a  sprinklered  building  more  than  one
  hundred  and  fifty feet distant from such exit. No point in any ground,
  or first floor shall be more than two hundred feet distant from an  exit
  from  that floor and in a sprinklered building more than two hundred and
  fifty feet distant from such exit; provided that no point in any ground,
  or first floor of a building erected after July first, nineteen  hundred
  forty-eight,  in  which  a  factory is conducted, shall be more than one
  hundred fifty feet distant from  an  exit  from  that  floor  and  in  a
  sprinklered building more than two hundred feet distant from such exit.
    c. In every building over one hundred feet in height there shall be at
  least one exterior fireproof enclosed stairway which shall be accessible
  from any point in the building.
    4.  Stairways  and ramps. a. All required interior stairways and ramps
  shall be constructed of  incombustible  material.  Two  hour  fire  test
  enclosures  shall  be  provided in buildings over two stories in height,
  and in all subgrade stories. One hour  fire  test  enclosures  shall  be
  provided for all other stairs and ramps in buildings two stories or less
  in  height.  All stairways and ramps shall have an unobstructed width of
  at least forty-four inches throughout  their  length  except  that  hand
  rails  may  project  not  more  than three and one-half inches into such
  width.  There shall be not more than twelve feet six  inches  in  height
  between  successive  landings.  The  treads  shall  be not less than ten
  inches wide and the risers shall be closed and not more than  seven  and
  three-fourths inches. No stairway with "winders" shall be permitted as a
  required  exit.  The treads shall be constructed and maintained so as to
  prevent persons from slipping thereon. Ramps used in place  of  required
  exit  stairways  shall have a slope not exceeding one foot in eight feet
  and shall comply with the requirements for  stairways  as  to  material,

  width,   enclosure,   ventilation,  landings  and  shall  have  non-slip
  surfaces.
    b.  Every  such  required  interior  stairway  shall  be  enclosed and
  ventilated in a manner conforming to rules adopted by the board,  except
  that  unenclosed  stairways, no part of whose floor opening is more than
  twenty feet from an open side of the mezzanine and  which  lead  to  the
  floor  immediately  below,  may be accepted from an unenclosed mezzanine
  not  exceeding  twenty-five  hundred  feet  in  area,  unless  otherwise
  specified by the board in its rules.
    c.  Exterior  windows  within  twenty-five  feet  of  a  non-fireproof
  structure shall be fire windows. Skylights, unless provided  with  wired
  glass,  shall have thereunder a shield of wire mesh in substantial frame
  work.
    d. Whenever safe egress may  be  had  from  the  roof  of  a  building
  exceeding  two  stories in height to an adjacent structure all stairways
  serving as required exits shall extend to the  roof,  provided  that  in
  buildings  over  five  stories  in  height at least one of the stairways
  serving as required exits  shall  extend  to  the  roof.  All  stairways
  serving  as required exits shall lead (a) continuously to the street, or
  (b) to a fireproof  passageway  independent  of  other  exits  from  the
  building  opening  on a road or street, or (c) to an open area affording
  unobstructed passage to a  road  or  street,  except  that  unobstructed
  access  to  exits  on  the  floor  immediately below may be accepted for
  stairways from a mezzanine floor unless otherwise specified by the board
  in its rules. Provision shall be made for the adequate lighting  of  all
  stairways,  ramps  and  passageways by artificial light. Where more than
  two stairways are provided in a building, not more  than  two  may  lead
  through  a  common  fireproof  passage  to  a street. Required stairways
  terminating at a floor below roof shall be connected at floor  at  which
  such  stairs terminate through a fireproof passage to at least one other
  required stairway.
    5. Doors and doorways. All doors at required exits  or  that  lead  to
  required  exits  shall  open  outwardly.  The  width  of  the  fireproof
  passageways and exit doorways including stops, leading to the street  at
  the  grade  level shall be not less than the aggregate required width of
  all stairways and ramps leading to them. The aggregate capacity  of  all
  other  required  exit  doorways  shall  be  calculated  on  the basis of
  twenty-two inches for each fifty  persons  or  fraction  thereof  to  be
  served  by  such  doorways,  but  no  such  doorway  shall  be less than
  thirty-six inches in width.
    The provisions of this section shall not apply to  a  building,  in  a
  city  having  a population of more than one million, used exclusively by
  one employer and in which not more than one-tenth  of  all  the  persons
  employed therein are engaged in work for a factory and which, except for
  such factory work, would be classified as a mercantile establishment.