ASHRAE Journal - July 2014 - 44

Column EnginEEr's notEbook

Smoke Partitions (Section 710) are used to enclose
storage rooms, trash rooms, boiler and furnace
rooms, and similar rooms that have a higher-thanaverage chance of fire. These are not as significant
as smoke barriers. Smoke partitions are intended to
contain the smoke and heat resulting from a fire just
long enough to activate sprinklers or smoke detectors quickly. A Class I or II smoke damper is required
at each air transfer opening in a smoke partition.
Nothing is required in ducted penetrations of smoke
partitions, and this is where I most often see overspecification. Ducted penetrations of smoke partitions do not require smoke dampers.
The final type of smoke boundaries we encounter
are corridor walls in a hospital, which are required
to form "barriers to limit the transfer of smoke" but
are not smoke barriers. If corridor walls were smoke
barriers, then every single patient room that opens to
the corridor would have to have listed/labeled doors
and automatic door closers, which is not the case. The
difference between a "barrier to limit the transfer of
smoke" and a smoke barrier is subtle in syntax, but
important to an HVAC designer. Corridor walls in a
hospital are actually considered smoke partitions,
not smoke barriers (IBC ¶407.3). This is another area
where some designers use smoke dampers unnecessarily. No dampers are required in ducted penetrations of smoke partitions, including those in hospital
corridor walls.

Other Rules
1. Do not put any dampers in Type 1 grease exhaust
and clothes dryer exhaust systems (IBC ¶717.5.3). If your
hood or dryer exhaust duct crosses a rated wall or floor,
then instead of a damper you must encase the duct itself
in a rated enclosure such as a fire-rated gypsum board
shaft or a listed/labeled fire-wrap insulation material.
Use sub-ducts in lieu of dampers at vertical shafts.
2. If a fire or smoke damper placement will interfere
with the operation of an engineered smoke exhaust
system (such as for an atrium), approved alternate protection shall be used (IBC ¶717.2.1). What I have usually
done in this case is to specify a remotely resettable fire/
smoke damper addressable by the fire department at a
fire command center.
3. Fire dampers are available in 1.5 hour and threehour ratings. Those are generally the only two choices.
44

ASHRAE JouRnAl

ashrae.org

J u ly 2 0 1 4

Use a 1.5 hour fire damper in one-hour or two-hour
walls. Use a three-hour fire damper in three-hour or
four-hour walls.
4. Fire dampers are available as "static" or "dynamic."
Static fire dampers are only tested to close without air
moving in the duct. Dynamic fire dampers are tested to
close with or without air moving in the duct. I recommend you always specify dynamic fire dampers since the
cost difference is trivial.
5. Fire damper Frames: Frame A means the blades,
in the open position, partially block the free area
of the duct. Frame B means the blades, in the open
position, are completely outside the free area of the
duct. Frame C is for round ducts. These frame types
apply only to curtain-type fire dampers, not to multiblade type dampers like most combination fire/smoke
dampers.
6. Fire dampers and smoke dampers must be accessible for service. If reaching inside the duct is necessary
(for example, to re-open a closed fire damper) then you
must provide a duct access door and a ceiling access
panel or an accessible ceiling type.
7. For buildings where engineered smoke control is
required by code, such as high-rise buildings and atria,
smoke damper open/closed status indication is required
for all dampers that affect the proper operation of the
smoke control system. Typically, status is indicated by
switches that are physically connected to the damper
blade, or auxiliary end-switches from direct-coupled
actuators.

Summary
It is important to learn the differences between a
fire wall, fire barrier, and fire partition and between
a smoke barrier and smoke partition, so that you can
properly apply (or not apply) fire and smoke dampers. Unwillingness by some mechanical engineers and
designers to explore the architectural portions of the
International Building Code, and not learn of these distinctions, has led some to over-specify fire and smoke
dampers in HVAC systems.

References
1. ICC. 2012. International Building Code. Chicago: International
Code Council, Inc.
2. NFPA. 2012. Standard 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems. Quincy, MA: National Fire Protection
Association.

ASHRAE Journal - July 2014

Table of Contents for the Digital Edition of ASHRAE Journal - July 2014