Specification 21 Smoke exhaust systems
2019: Spec E2.2b: 1
This Specification describes the requirements for mechanical smoke exhaust systems.
Smoke exhaust capacity
2019: Spec E2.2b: 2
- within a smoke reservoir formed in accordance with S21C4 and not less than 2 m above the highest floor level; and
- above the top of any openings interconnecting different smoke reservoirs.
|Classification||Fire load (MW) for unsprinklered buildings||Fire load (MW) for sprinklered buildings|
|Class 2, 3 or 5||5||1.5|
|Class 7 or 8||15||5|
|Class 9 — generally||5||1.5|
|Class 9b buildings covered by Part I1 (see Note) or exhibition halls||10||5|
Smoke exhaust fans
2019: Spec E2.2b: 3
Each smoke exhaust fan, complete with its drive, flexible connections, control gear and wiring must—
- be constructed and installed so that it is capable of continuous operation (exhausting the required volumetric flow rate at the installed system resistance) at a temperature of 200°C for a period of not less than 1 hour; and
- in a building not fitted with a sprinkler system, be capable of continuous operation at a temperature of 300°C for a period of not less than 30 minutes; and
- be rated to handle the required volumetric flow rate at ambient temperature to be capable of exhausting cool smoke during the early stages of a fire and to allow routine testing; and
- have any high temperature overload devices installed, automatically overridden during the smoke exhaust operation.
2019: Spec E2.2b: 4
- a non-combustible bulkhead or smoke baffle/curtain must be provided around the underside of each opening into a building void to minimise the spread of smoke to other storeys; and
- the depth of the bulkhead or smoke baffle must be not less than the depth of the smoke reservoir provided under (3) plus an additional 400 mm.
Smoke exhaust fan and vent location
2019: Spec E2.2b: 5
Smoke exhaust fans and vents must be located—
- such that each smoke reservoir is served by one or more fans with the maximum exhaust rate at any one point limited to avoid extracting air from below the smoke layer; and
- to prevent the formation of stagnant regions resulting in excessive cooling and downward mixing of smoke; and
- at natural collection points for the hot smoky gases within each smoke reservoir having due regard to the ceiling geometry and its effect on the migratory path of the smoke; and
- away from the intersection of walkways or malls; and
- to ensure that any voids containing escalators and/or stairs commonly used by the public are not used as a smoke exhaust path; and
- to discharge directly to outdoor with a velocity of not less than 5 m/s, at a suitable point not less than 6 m from any air intake point or exit.
2019: Spec E2.2b: 6
- any disturbance of the smoke layer due to turbulence created by the incoming air; and
- the risk of smoke migration to areas remote from the fire due to the effect of make-up air on the air balance of the total system.
Smoke exhaust system control
2019: Spec E2.2b: 7
2019: Spec E2.2b: 8
A smoke detection system must be installed in accordance with Specification 20 to activate the smoke exhaust system.