Fireproof windows which meet the requirements of § 376 of the Building Code (as it existed before December 6, 1968), constructed of metal frames and sash equipped with non-corrodible hardware and fittings consisting of counterbalancing arms with rollers on both upper and lower sash operating in vertical grooves and permitting the free adjustment of the sash by a light pull on the lower sash handles may be installed for use, without an automatically closing device arranged to operate under the action of heat, in all exterior openings of factory buildings except those located as described in subdivisions (a), (b), (c) and (d) of this section, provided the window is fitted with an automatic sash-fast which holds the sash locked in the closed position:
   (a)   Openings within thirty (30) feet in a direct line of another building not in the same vertical plane;
   (b)   Openings on a court or space less than thirty (30) feet wide;
   (c)   Openings within fifty (50) feet in a vertical direction above the roof of a building within thirty (30) feet thereof;
   (d)   Openings along the course of fire-escape or other means of egress.
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