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SCS Series Manual —
P/N 15712:L 7/18/16
Concepts of Smoke Control
Smoke Control System Types
Single Injection
A single-injection system supplies air for pressurization at one location in the stairtower, usually at the top as shown in Figure 2.15a. One of
the main concerns with single-injection systems is that the pressurization of the stairtower could fail when a few doors near the supply fan
are open. The supply air being injected into the stairtower for the purpose of pressurization could be lost through these openings, thus pre-
venting the pressure differences necessary to limit the movement of smoke. For this reason it is recommended that single injection systems
be used in buildings that are eight stories or less.
Single-injection systems can also have supply air injected from the bottom of the stairtower, but the same failure can occur when the exterior
door is opened. The supply air can flow directly out the open doorway preventing pressurization of the stairtower. It is recommended that
supply air inlets be located at least one floor above or one floor below exterior doors.
Multiple Injection
Multiple-injection systems provide several supply inlets distributed over the height of the stairtower, as shown in Figure 2.15b and Figure
2.15c, thereby overcoming the limitations of single-injection systems. Multiple-injection systems can be built with supply air injection points
at each floor. Although this would overcome the problem associated with single-injection systems, it may be unnecessary. An acceptable dis-
tance for spacing of inlets is three floors. However, spacing of more than three floors can be used as long as the designer determines that the
loss of pressurization air through a few open doors does not lead to loss of stairtower pressurization.
Compartmentalization
Compartmentalization, used as an alternative to multiple injection, involves
dividing the stairtower into a number of sections, as shown in Figure 2.16.
The stairtower is divided in sections of one to eight floors each, where each
compartment is separated from the other by walls and doors that are nor-
mally closed. Each compartment would also have at least one supply air
injection point. Compartmentalization is used for stairtowers that would
normally be too tall for proper pressurization. However, stairtowers which
use compartmentalization require a larger floor area to accommodate the
walls and doors that separate the compartments. Another drawback for
compartmentalization occurs when the doors between the sections are open.
This would result in insufficient pressures to limit the movement of smoke.
For this reason, compartmentalization is not recommended for densely pop-
ulated buildings where total evacuation is planned for the stairwell.
Vestibules
A vestibule is a small room leading into another room, or in this case a stair-
well. For the purpose of smoke control, there would be a door leading into
the vestibule and a door leading from the vestibule to the stairtower. Since
the possibility of both doors being open is smaller than if only one door
were present, the possibility of smoke entering the stairtower and the possi-
bility of pressurization air escaping into the building would be reduced.
However, an evacuation analysis should be performed to determine the like-
lihood of both doors being open simultaneously. The vestibule can either be
pressurized or not pressurized.
Figure 2.15 Single and Multiple Injection Stairtower Pressurization Systems
Figure 2.16 Compartmentalization of a Pressurized
Stairtower
Stairwell is Divided
into Compartments