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Chapter 2: Smoke control system hardware
down the fan if smoke is detected and the FSCS must
have a detector override for the fan.
A relief damper for a pressurized stairwell, operable from
the FSCS should be located at the top of the stairwell to
prevent over-pressurization in addition to venting any
smoke which may enter the stairwell. Damper relief is
set by the Building Smoke control System Designer,
normally at not less than 2,500 cfm (1,180 L/s) with a
differential pressure of 0.15 inches (37,035 Pa) of water.
The FSCS designer should anticipate a control point for
the relief damper.
Smoke shaft exhaust systems
Smoke, as covered in Chapter 1, has a tendency to
move upward in a building. Buildings may be designed
with a smoke shaft as a mechanical method of
exhausting smoke from a selected floor. A smoke shaft
serving a smoke zone will assist a smoke control system
by reducing smoke spread and static pressures on the
fire floor which have a tendency to push smoke into
adjacent zones or to other floors.
Smoke shaft systems consist of an exhaust fan mounted
on the top of a vertical shaft which runs up the entire
height of a structure. The shaft is constructed of fire
rated material and connects to each floor through an
FSCS and SCS operable combination fire/smoke
dampers. Dampers are normally kept closed with the
damper on the fire floor opening upon detection of fire
followed by the startup of the shaft fan. The fire/smoke
dampers, which connect each zone to the smoke shaft
are to be reopening, within the limits of NFPA 90A-3-4.5,
to allow for operation from the FSCS if their temperature
activating mechanism causes them to automatically
close and mechanical venting is needed. The smoke
fan's discharge must be a minimum of 3 feet (0.9144 m)
above the roof level or deck.
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Figure 22: Smoke shaft system
Elevator shaft pressurization systems
Elevator shaft pressurization systems are similar in
concept to stairwell pressurization systems, but of two
types. The first is the pressurization of the elevator
system in order that it may be used for occupant
evacuation. In the second type, the pressurization of the
elevator shaft prevents or limits smoke spread from the
fire floor into the shaft. Meeting ADA area of refuge and
egress requirements in tall buildings will often bring
elevator shaft pressurization into a building's life safety
system design.
The Building Smoke control System Designer must
evaluate the possible effect of positive elevator
pressurization upon a smoke zone's ability to maintain a
negative pressure.
Elevator car movement, as reviewed in Chapter 1, may
present additional challenges in maintaining shaft
pressurization.
Elevator smoke control will involve the turning on of one
or more pressurization fans and controlling the static
pressure within the elevator shaft. Design approaches
today inject air into the shaft near the main floor with air
VM-1 Smoke Management Application Guide
Exhaust
3 ft (0.91m)
fan
ZONE 8
ZONE 7
ZONE 6
ZONE 5
Smoke
shaft
ZONE 4
ZONE 2
ZONE 1
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