(a) Construction.

1. (1) Walls shall be reinforced concrete, or brickwork with vertical as well as horizontal joints filled with mortar; or, in a fire-resistive building, a framework of heat-protected steel or reinforced concrete with panels of reinforced concrete or brickwork. Reinforcement for concrete shall consist of steel rods at least one-half inch in diameter spaced six inches on center and running at right angles in both directions. Rods shall be securely wired at intersections not over twelve inches apart in both directions and be installed centrally in the wall or panel.
2. (2) Where a structural steel frame is used the steel shall be protected with at least four inches of concrete, brickwork or its equivalent, tied with steel ties or wire mesh equivalent to No. 8 A.S.W. gage wire on eight-inch pitch. Brick protection if used shall be filled solidly to the steel with concrete.
3. (3) The walls of a structure-supported vault shall follow the panels of the building wherever possible and shall extend from floor to ceiling of the building in each story where a vault is located. If vaults are located on more than one floor of a building, they should preferably be placed one above the other in the several stories.
4. (4) No combustible material shall be used for trim or partitions.

(c) Openings in walls.

1. (1) Interior walls of vaults, that is, those walls which are entirely within the building, shall be unpierced except for protected openings which are required for essential facilities specifically mentioned in this standard. Door openings shall be protected with vault doors.

2. (2) Exterior walls of vaults, that is, those which are exterior walls of the building, shall be unpierced except by exhaust vents essential for proper ventilation. Such openings shall be protected with approved dampers or with approved fire doors suitable for openings in exterior walls.

   1. (d) There shall be no openings from vaults into elevator, stairway, conveyor or other shafts.