Where ventilation is provided by means of an automatic opening vent(s) (AOV) from the protected corridor / lobby to natural smoke shaft, the system should conform to all of the following:

(a) The minimum ventilation area from the protected corridor / lobby into the shaft, and at the opening at the head of the shaft, and at all internal locations within the shaft (e.g. safety grilles) should be at least 1 m2, in accordance with Para 6.1.5; and

(b) The top of the protected corridor / lobby vent should be located as close to the ceiling of the protected corridor / lobby as is practicable, and should be at least as high as the top of the door connecting the protected corridor / lobby to the stairwell or lobby; and

(c) The ventilation openings from the protected corridor / lobby to the vent shaft should achieve the same fire performance as the shaft, but not exceeding 60 minutes; and

(d) The smoke shaft should have a minimum cross-sectional area of 1.5 m2 (minimum dimension 0.85 m in any direction); and

(e) The natural smoke shaft should be closed at the base; and

(f) The shaft should extend a minimum length of 2.5 m above the ceiling of the highest storey which is served by the shaft; and

(g) The opening at roof level should be at least 0.5 m above any surrounding structures within a horizontal distance of 2.0 m; and

(h) The smoke shaft should be constructed in accordance with Para 3.5.16; and

(i) No services other than those relating to the smoke shaft should be contained within the smoke shaft; and

(j) The shaft should be vertical from base to head but may have not more than 4m at an inclined angle not more than 30o from the vertical plane; and

(k) Inlet air should be provided through an automatic opening vent having a clear openable area of not less than 1 m2, in accordance with Para 6.1.4, located at the top of the stairway enclosure; and

(l) The design of the system should be such that, on activation of the fire detection and alarm system, the ventilator on the fire floor, the ventilator at the top of the smoke shaft and the 1 m2 ventilator at the head of the stairway should all open simultaneously.

Where there are multiple shafts due to multiple corridors, the system should be designed to activate the relevant shaft only. The ventilators from the common protected corridors / lobbies on all other floors, and unaffected corridors on the fire floor should remain closed.

6.6.2.2 Automatic Vents Opening to Natural Smoke Shafts