Duct Detector Requirements

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theophilus88

Professional Architectural Engineer
Location
St. Louis, MO
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Professional Architectural Engineer
Not sure if this is more of a mechanical question or an electrical, but I am confused on if the following scenario would require a duct detector on the supply side? Currently I have a Dedicated Outdoor Air Unit that is serving 100% outside air to a space that does not require a fire alarm system. The unit supplies above 2000 CFM. Would I be required to provide a smoke detector on the supply side?
 
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IMC 606.2.1 only on a return that would recirculate within the building.
 
theophilus88 said:
Not sure if this is more of a mechanical question or an electrical, but I am confused on if the following scenario would require a duct detector on the supply side? Currently I have a Dedicated Outdoor Air Unit that is serving 100% outside air to a space that does not require a fire alarm system. The unit supplies above 2000 CFM. Would I be required to provide a smoke detector on the supply side?
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Per NFPA 90A-2015 (6.4.2.1(1)), yes.
 
I have reviewed NFPA 90A and maybe I am not comprehending as to being on the supply side from outside air unit. Not debating at all just help clarifying. I do not have the book reference tried pulling up on line.
Thanks
 
JGinIndy said:
I have reviewed NFPA 90A and maybe I am not comprehending as to being on the supply side from outside air unit. Not debating at all just help clarifying. I do not have the book reference tried pulling up on line.
Thanks
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No problem.
6.4.2*Location.
6.4.2.1 Smoke detectors listed for use in air distribution sys-
tems shall be located as follows:

(1) Downstream of the air filters and ahead of any branch
connections in air supply systems having a capacity
greater than 944 L/sec (2000 ft3/min)
(2) At each story prior to the connection to a common return
and prior to any recirculation or fresh air inlet connec-
tion in air return systems having a capacity greater than
7080 L/sec (15,000 ft3/min) and serving more than one
story

A.6.4.2 The summation of the capacities of individual supply-air fans should be made where such fans are connected to a
common supply air duct system (i.e., all fans connected to a
common air duct supply system should be considered as con-
stituting a single system with respect to the applicability of the
Chapter 6 provisions that are dependent on system capacity).

So, this means at the outlet of the AHU after the last filter stage (if any) and before the first branch takeoff. I've seen roof-mounted AHU's that basically dump their output into a space immediately after penetrating the roof. Usually there's a spot inside the AHU to mount a duct detector in that case.
 
Excellent! Thanks for the education. When I tried to pull up the link it wacked out, that and my wife had her Covid vac and was also wacking out “ God love her” thanks again
 
I did some digging since our conversation. IMC does not reference NFPA 90A which I knew but what I found Indiana has not adopted NFPA 90A which I find is odd at best.
gadfly56 thanks for the “heads up”
 
theophilus88 said:
If the codes contradict each other, which do we follow? The IMC or NFPA 90A?
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Here in Indiana which is pretty far behind (still under 2008 NEC) I would check into your local adoptions I have put a call into our engineering department.
 
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