1-16
The building shown in Figure 1-6, Stairtower A has no vent to the outside. Compensated systems
adjust the airflow to make up for pressure lost through open doors. A compensated system
(Figure 1-6, Stairtower B) can use dampers (or vents) to relieve excess pressure in the stairtower
to ensure that the pressure does not go over the maximum limit.
There are a number of ways compensated stairtower smoke control systems can control
pressurization. In a basic system with a roof-mounted fan blowing air into the stairtower, pressure
can be regulated by varying the speed of the fan, the pitch of the fan blade, the inlet vanes, or the
number of fans operating (assuming there is more than one).
More sophisticated systems use ducts to deliver air to several points in the stairtower. The
dampers can be controlled to maintain the appropriate pressure in their zone. Duct systems can
also use bypass dampers and ducts to control the amount of air flowing from the fan to the outlets.
The bypass dampers are opened when the stairtower is at the proper pressure, so that excess air
flows into the bypass duct, then back to the air inlet not into the duct system.
The figure below shows a stairtower pressurization system that uses multiple pressure injection
dampers mounted in an air pressure duct. In this example, the vents to the building have
barometric dampers. While a roof-mounted fan is shown in the figure, the fan can be located at
any level. A manually-operated damper may be located at the top of the stairtower to aid the fire
department in purging smoke from the building during a fire.
Figure 1-7. Stairtower Pressurization by Multiple Injections (Roof-Mounted Fan)
Continued on next page
Designing a Dedicated Smoke Control System, Continued
Controlling Pressure
in a Stairtower
Pressurization Fan
Air Pressure Duct
Dampers
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