Chapter 1: Fire geometry and smoke movement in buildings
VM-1 Smoke Management Application Guide 9
horizontally with floor ceiling assemblies. A smoke zone,
as used in this guide, is simply the area where the fire is
located. The two basic principles for containing smoke
within a smoke zone are pressurization and airflow.
Pressurization
Pressurization develops positive and negative pressure
differences across zone boundaries in order to control
smoke movement and is the most desirable means of
controlling smoke movement. See Figure 7 below.
Figure 7: Pressurization
Pressurization creates pressure differences across
partitions that separate the smoke zone from other
zones or areas. This is typically accomplished by
creating higher pressure in the nonfire or smoke areas.
Airflow will occur through construction cracks at floor to
ceiling slabs, around unsealed conduit and pipe
openings, and around doors that act as the primary
barriers to smoke movement from a smoke zone.
Pressure differences must be sufficient to contain the
smoke in the smoke zone and simultaneously allow
doors leading to safety to be opened.
Airflow
Airflow by itself can control smoke levels and movement
if the air velocity is high enough to overcome the
tendency of smoke to migrate to other zones. This
approach is typically used to prevent the flow of smoke
down corridors or through open doorways, as shown in
Figure 8 below. The airflow approach to smoke control
requires large quantities of air and is therefore not
practical for most applications.
Figure 8: Airflow
Purging
Purging may be used as a supplement to airflow or
pressurization methods in smoke control systems. When
there is a concern over smoke movement through open
doors into a protected area, outside air can be
introduced into the space. Purging uses an exhaust inlet
near the ceiling and a supply inlet commonly in the lower
half of a wall. The supply and exhaust points are placed
far enough apart to prevent the supply air from blowing
directly into the exhaust without the benefit of entraining
smoke-filled air. Purging is commonly used in smoke-
proof stairwells that contain a vestibule between the
occupant space and the stairs.
High
pressure
side
Low
pressure
side
Door
Airflow
Airflow
Airflow
Smoke
Smoke
Relatively
low air
velocity
Smoke
back flow
Relatively
high air
velocity
Diluted
smoke
Smoke
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