1-11
Since air pressure is what keeps smoke from spreading, the primary design factors are the amount
of pressure needed to confine the smoke, and the size of the system used to create this pressure.
For the smoke control system to create a barrier of air pressure between the smoke zone and
surrounding zones, the amount of pressure required varies with the height of the ceiling and
whether or not the building has a sprinkler system. The table below gives examples of the
minimum pressure differential needed to keep smoke out of rooms surrounding the fire site as
defined in NFPA 92A.
Table 1-1. Examples of Fire Zone Minimum Pressure Differential
* in. = Inches, Water Gauge
Pressure buildup in an area depends on the amount of leakage. Leakage occurs through joints,
cracks, openings for pipes and wires, gaps between doors and their door jams, and so forth.
The better the zone is sealed off from neighboring zones, the easier it is to maintain the required
pressure. Since larger openings, like normally-open doorways, require large amounts of air to
maintain pressurization, you should avoid this type of situation.
You must separate smoke zones from one another by “smoke barriers,” which prevent smoke from
passing through them. Smoke barriers can be a wall, a floor, or a ceiling. Any openings in the
smoke barrier must be closed with a smoke-proof fitting. For example, any duct work going
through a smoke barrier must have “smoke dampers” installed. A smoke damper is a damper that
prevents smoke from passing through it when fully closed. During a smoke emergency all of the
fittings should seal themselves, so that smoke cannot penetrate the barrier.
Since the smoke control zones should be the same as the fire control zones, you usually separate
your zones with a “fire-rated partition.” A fire-rated partition is a wall that is built of fire resistant
materials and that reaches from floor to ceiling. Different floors should be separated by a “fire-
rated ceiling,” a ceiling made of fire-resistant materials. Both fire-rated partitions and fire-rated
ceilings are rated for the amount of time they can withstand a fire. Any openings in a fire-rated
partition or ceiling must be capable of being sealed with a fire-rated closure, such as a fire-rated
door or fire damper.
The fans and duct work used in the smoke control system must be capable of providing the
amount of pressure you calculated earlier. In a non-dedicated system, this may mean that you
need to install fans that have a higher capacity than the HVAC system normally requires. The
ducts must be capable of taking the pressurization (or the depressurization, for the fire zone's
return duct) that the smoke control system demands. Both the fans and the ducts should meet local
requirements such as those stated in NFPA 90A, Standard for the Installation of Air Conditioning
and Ventilating Systems.
Continued on next page
Designing a Smoke Control System, Continued
Determining the
Smoke Containment
Pressure
Sprinkler System Ceiling Height
Minimum Pressure
Differential (in.)*
Yes Any 0.05 in.
No 9 ft. 0.10 in.
No 15 ft. 0.14 in.
No 21 ft. 0.18 in.
Separating Smoke
Zones Properly
Selecting the Proper
Fans and Duct Work
To Next Page
Loading...
Need help?
General
