Division .1 All stairways shall be of steel frame construction, except where the Administration sanctions the use of other equivalent material, and shall be within enclosures formed of ‘A’ class divisions, with positive means of closure of all openings except that:F1

a stairway connecting only two decks need not be enclosed, provided the integrity of the deck is maintained by proper bulkheads or doors in one between-deck space. When a stairway is closed in one between-deck space, the stairway enclosure shall be protected in accordance with the tables for decks in Regulations 4 and 5;

stairways may be fitted in the open in a public space, provided they lie wholly within such public space.