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EAGLE HARDWARE & GARDEN
TIGARD, OREGON
" DUCT SMOKE DETECTOR APPEAL
The purpose of this report is to address the requirements for smoke detectors in the supply ducts of Air
Handling Units (AHUs) having a.capacity of 2000 cfm or more. Please accept this as Eagle Hardware &
Garden's formal request for variance of these requirements, which are contained in Section 608 of the Uniform
Mechanical Code (UMC). This Alternative Materials And Methods request is based on the latitude given in
Section 104.2.8 of the Building Code. _
As stated in Section 608 of the UMC, duct smoke detectors are required to initiate shutdown of AHUs having a
capacity of 2000 cfm or more in the, event of a fire. The purpose of this Alternative Materials And Methods
request is not to completely eliminate the automatic shutdown capabilities of the system, but rather to have a
more reliable means of initiating it. Accordingly, the alternative being proposed is to initiate shutdown of the
AHUs by a signal from the sprinkler system flow switches. The justification for this request is summarized as
follows.
• The intent of Section 608 of the Mechanical Code is two -fold. First and foremost, shutdown of the AHU is - -.�
intended to prevent the spread of smoke from the room of fire origin to other uninvolved and otherwise
separated areas (e.g. exit corridors, stairwells, or lobbies), where egress from the building could be adversely
affected. Smoke spread to uninvolved areas is certainly a concern for compartmentalized structures such as
office buildings, malls, or hospitals. However, in the case of a Eagle Hardware & Garden store the concern
is not as significant because the entire store is essentially one large open space and AHU return inlets draw
from the same general area in which the supply outlets are located. It is doubtful that arm single AHU will
have a significant impact, good or bad, on the natural spread of smoke within this large open area, regardless
of the operational status of the AHU.
• The requirement for automatic shutdown is also intended to prevent the spread of smoke should the AHU
itself catch fire (i.e. a filter or blower motor). Because of the large volume of the store (in excess of 2.5
million cubic feet), the relatively small amount of smoke produced by a filter or motor fire is not considered
a significant hazard and would most likely be dissipated without any adverse effects on the building's
occupants.
• ' It has been the experience of not only Eagle Hardware & Garden, but also several other similar high -rack
retail home improvement stores, that smoke detectors installed in this application eventually become an
alarm nuisance and a maintenance problem, even though they are listed for the application. The false alarm
problems are not only a burden on the fire department, but they also tend to desensitize the store employees
• to the importance of a fire alarm and can potentially result in delayed evacuation of the building.
2820 CAM1NO dEl Rio Sour1- • SUITE 200 • SAN DiEgo. CA 92108 • TEL (619) 296 -5666 • Fax (619) 296 -5656 .
Eagle Hardware & Garden, Tigard, OR
Duct Smoke Detector Appeal
Page 2 of 4
While the technology does exist to address the false alarin problems caused by detectors getting dirty, even
the alarm system manufacturers have admitted that the technology has not been sufficiently perfected for
this application. The problem is that with duct detector applications in this type of occupancy, the detector
tends to get dirty too quickly, thereby making it think that it has an alarm condition. In most cases this will
occur before the detector can generate a maintenance signal, and the detector will go into alarm.
• To fully evaluate the acceptability of a proposed method, the intent of the code requirement or a
performance objective must be identified. One such example exists in the Building Officials and Code
Administrators (BOCA) Mechanical Code. While we recognize that the Uniform Codes are the locally
enforced codes, the BOCA codes contain commentary that provides background and insight as to the intent
of these provisions within the codes. The requirements for automatic shutdown of HVAC equipment are
very similar between the BOCA and Uniform Codes, and this citation is provided as evidence of the code
writers' purpose in requiring automatic shutdown of the mechanical equipment. The intent of the cited code
requirements for shutdown of the air handling units, as they relate to this project, can best be summarized by
the following excerpt from the BOCA Mechanical Code Commentary:
The mechanical code contains requirements that provide protection against the spread of smoke
throughout a building by means of an air distribution system. Generally the spread of smoke via
the air distribution system occurs when the ventilation return air system conducts smoke from a
fire in a room or space back to the air - handling equipment where the smoke is spread into the
supply distribution system. The smoke may be diluted by mixing it with return air from other
parts of the building and by the introduction of outdoor air; however, the smoke will be routed
through the supply air distribution system to other parts of the building which may not be
involved with the fire. The provisions also intend to provide protection against the spread of
smoke from fires which begin in the air - handling equipment itself.
The intent of these provisions is to prevent ducted air distribution systems from distributing
smoke from the area of origin to other areas or spaces in the building. An air distribution
system can distribute smoke throughout a building much faster than the smoke would have
traveled by natural means and, of course, ducts can carry smoke across boundaries that would
have otherwise stopped the natural migration of smoke. For these reasons, duct system smoke
detectors are employed to shut down a ducted air distribution system before it can threaten the
building occupants by spreading smoke.
This section applies to ducted air distribution systems and, therefore, should not be applied to
installations of air handlers and HVAC equipment which do not involve ductwork and extensive
plenums. For example, rooftop HVAC units, suspended unit heaters, suspended horizontal
furnaces and blower /coil combination units are commonly installed without the distribution
ductwork In these examples, the extent of what might be considered as ductwork is typically
limited to short supply and return box plenums (drops) extending from the roof unit, or simple
supply and return plenum extensions of the suspended equipment cabinets that are used only to
accommodate return grilles, filter racks, flow splitters and similar direction discharge fittings
and devices. Because there is no distribution ductwork extending to areas and spaces beyond
Eagle Hardware & Garden, Tigard, OR
Duct Smoke Detector Appeal
Page 3 of 4
the immediate location of the HVAC equipment, it is not possible for the. HVAC equipment to
contribute significantly to the spread of smoke in the building; therefore, a duct - mounted smoke
detector would be of little value.
It is more important to keep in mind the. intended application of the code section, which is to
address the potential hazard caused by ducted air distribution systems' that link together rooms
and spaces within a building, thereby providing the means to distribute smoke to such rooms and
spaces. Air - handling systems of any type that cannot transport smoke beyond the area of fire
origin are exempt from the provisions of the code section.
This code section addresses the location of required smoke detection devices, the installation of
the devices, and the operations which must take place after smoke has been detected within the
air distribution system. The provisions of the code section apply to ducted air distribution
systems that are capable of spreading smoke from one area 'of fire origin to any other area of the
building.
• The intent of the code to require the installation of smoke detectors within ducted air distribution systems is
further demonstrated by the installation restrictions applicable to duct - mounted smoke' detection devices as
provided by NFPA 72, Figure A- 5- 10.6.2(b) (1996 - Edition). This provision of the code provides that the
installation of the duct - mounted smoke detectors should be 6 to 10 equivalent duct diameters downstream of
any bend, obstruction or the return air inlet. This can only be accomplished when extensive ductwork is
present. The air handling units serving the warehouse store area consist of roof top units connected to a short
drop box penetration of the roof for air return and supply which would not constitute a ducted air
distribution system. As a result, the system would not contribute to the spread of smoke from the area of
fire origin to any other area of the building; therefore, the proposed arrangement clearly meets the intent of
the cited code sections. Furthermore, the short drop box arrangement will not allow for the installation of
the duct detectors at the suggested location.
• Appendix section A -4 -4.3 in NFPA. 90A addresses this issue by allowing the AHUs to be shutdown by
activation of a sprinkler system flow switch.
There is no question that smoke detection devices placed in air distribution system ducting designed for
operation in buildings that have compartmented separation provide valuable smoke control. The installation of
such devices •have proven their value over and over and is heartily supported throughout the 'Fire Service
Community; however, it makes no sense whatsoever to install such devices in air handling units which serve
large open spaces. Eagle Hardware & Garden acknowledges the fact that at some point during a fire, it will
probably be beneficial to have the AHUs shutdown. Their position is that it does not necessarily have to happen
at the first `hint of smoke', especially since that `hint of smoke' may be nothing more than dirt, and a false
alarm will result. The question then is what is the most reliable method of initiating shutdown of the AHUs.
Since the primary means of detecting fires in this building will be the automatic sprinkler system (i:e. the only . .
smoke detectors being required are in the AHU supply ducts), it seems logical that the sprinkler system should
also control shutdown of the AHUs. This assumption can be further justified by the fact that the supply and
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- Eagle Hardware,& Garden, Tigard, OR
Duct Smoke Detector Appeal
Page4of4
return air openings for these units are positioned 3 to 4 feet below the underside of the roof deck, which means
the smoke layer will be 3 to 4 feet deep before smoke can actually be drawn into the unit. It is difficult to
imagine a fire that could develop this depth of smoke layer without tripping a sprinkler.
We would respectfully request that you review the justifications presented for granting this request. We feel the
requirements of the code are met by providing an alternative method of initiating AHU shutdown that is
recognized byNFPA 90A. If after reviewing this information you have any questions or comments, please do
not hesitate to contact us. We look forward to your response on this issue at your earliest convenience.
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