Duct detector location around dampers

[EHanson]

I’ve read that duct detectors need to be located within 5’ from damper, but it does not state on which side of the damper regarding air flow.
Does it matter?
I would assume it would need to be in the direction of airflow before it hits the damper but some of these locations are almost impossible.
I’ve got duct detectors on both supply and return side of the duct.
Is it ok to put the duct detector on the other side of the damper that the air flow goes through the damper before it hits the duct detector?

 

[ron]

It depends on what the damper is doing, if it is a specific application or part of smoke control or general fan shutdown, but from NFPA 72 (2013 version which I have handy), there is no specific distance. See below.
For a smoke detector controlling a door closure, it would require a specific distance.

17.7.5.3.4 If duct detectors are used to initiate the operation of smoke dampers within ducts, the requirements of 17.7.5.5 shall apply.
17.7.5.5 Location and Installation of Detectors in Air Duct
Systems.
17.7.5.5.1 Detectors shall be listed for the purpose for which they are being used.
17.7.5.5.2* Air duct detectors shall be installed in such a way as to obtain a representative sample of the airstream. This installation shall be permitted to be achieved by any of the following methods: (1) Rigid mounting within the duct (2) Rigid mounting to the wall of the duct with the sensing element protruding into the duct (3) Installation outside the duct with rigidly mounted sampling tubes protruding into the duct(4) Installation through the duct with projected light beam
17.7.5.5.3 Detectors shall be mounted in accordance with the manufacturer’s published instructions and shall be accessible for cleaning by providing access doors or control units in accordance with NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems.
17.7.5.5.4 The location of all detectors in air duct systems shall be permanently and clearly identified and recorded.
17.7.5.5.5 Detectors mounted outside of a duct that employs sampling tubes for transporting smoke from inside the duct to the detector shall be designed and installed to allow verification of airflow from the duct to the detector.
17.7.5.5.6 Detectors shall be listed for operation over the complete range of air velocities, temperature, and humidity expected at the detector when the air-handling system is operating.
17.7.5.5.7 All penetrations of a return air duct in the vicinity of detectors installed on or in an air duct shall be sealed to prevent entrance of outside air and possible dilution or redirection of smoke within the duct.

 

[gadfly56]

Duct detector locations are specified in the mechanical code with respect to fire/smoke dampers. If the ducts in question are not used as part of a smoke control system, you can bypass the requirement by simply shutting down the the air handler and closing all the dampers on activation of either the supply or return air duct detectors.