In every tenement erected after April eighteenth, nineteen hundred twelve, all stairs shall extend from the entrance story to the roof, except as otherwise provided in section two hundred thirty-three, and the stairs and public halls shall each be at least three feet in clear width. Every apartment in such a tenement shall be directly accessible at each story to such stairs and public halls, and every story of such apartment shall be so accessible to such a stair and public hall or to a tower fire-escape or stairway, as provided in this section and sections two hundred thirty-five to two hundred thirty-nine inclusive.
In every tenement erected after April twelfth, nineteen hundred one, except as provided in paragraph b of subdivision two of section two hundred thirty-eight, all stairs and public halls shall be completely separated from all other stairs and from every elevator by brick walls or partitions of terra cotta blocks at least four inches thick, or hollow cement blocks at least four inches thick which have successfully withstood a three-hour standard fire test and been approved by the department and have fireproof doors and assemblies with the doors self-closing at all openings. From any portion of a public hall in such a tenement there may be a recess which shall not be deemed a public hall if the walls, floor and ceilings enclosing it are fire-retarded and such recess is at all times adequately lighted by electric lights of at least fifteen watts or equivalent illumination. Such a recess shall not be more than twenty feet long and shall not be used as a means of egress from more than three apartments.