(a) No sidewalk door or doors for any purpose shall exceed four (4) feet in one (1) dimension and six (6) feet in the other dimension, nor shall the dimension at right angles to the curb be more than one-third (1/3) of the sidewalk width.
(b) No sidewalk door or doors shall be installed in any sidewalk six (6) feet or less in width, measured at right angles to the curb.
(c) No sidewalk elevator or sidewalk door or doors shall be installed in any sidewalk in front of any building where unloading space for off-street unloading and loading is available or required by this Building Code, except that in cases of undue hardship such installations may be permitted by the Board of Building Standards and Building Appeals.
(d) All sidewalk doors shall be constructed of noncombustible material; shall be capable of supporting the sidewalk loads prescribed by this Building Code; and shall have surfaces which will prevent persons from slipping on them. No glass lights shall be installed within such doors and any perforations or gratings within them shall conform to the requirements hereinbefore specified for gratings in sidewalk vault roofs.
(e) All sidewalk doors shall be installed so that one (1) side is two (2) feet from the outer face of the curb and parallel to the curb, and so that all portions of the frame and the door or doors are flush with the sidewalk surface.
(f) Not more than one (1) sidewalk door or pair of doors shall be installed for each eighty (80) feet of frontage of a building.
(g) All sidewalk doors shall be kept closed and sidewalks unobstructed except when sidewalk doors are in actual use for the transfer of objects through such doors. When closed, sidewalk doors shall be securely fastened from the underside. When open, sidewalk openings shall be properly protected and safeguarded.