Smoke control of common escape routes by natural smoke ventilation

Smoke vents should comply with one of the following.
a. They should be located on an external wall with minimum free area of 1.5m2.
b. They should discharge into a vertical smoke shaft, closed at the base, that meets all of the following criteria.
i. The shaft should conform to the following conditions.
• Have a minimum cross-sectional area of 1.5m2 (minimum dimension 0.85m in any direction).
• Open at roof level, minimum 0.5m above any surrounding structures within 2m of it horizontally.
• Extend a minimum of 2.5m above the ceiling of the highest storey served by the shaft.
ii. The free area of all the following vents should be a minimum of 1m2 in the following places.
• From the corridor or lobby into the shaft.
• At the opening at the head of the shaft.
• At all internal locations within the shaft (e.g. safety grilles).
iii. The smoke shaft should be constructed from a class A1 material. All vents should either be a fire doorset (see Appendix C, Table C1, item 2.e for minimum fire resistance) or fitted with a smoke control damper achieving the same period of fire resistance and designed to operate as described below. The shaft should be vertical from base to head, with a maximum of 4m at a maximum inclined angle of 30 degrees.
iv. If smoke is detected in the common corridor or lobby, both of the following should occur.
• Simultaneous opening of vents on the storey where the fire is located, at the top of the smoke shaft and to the stair.
• Vents from the corridors or lobbies on all other storeys should remain closed, even if smoke is subsequently detected on storeys other than where the fire is located.