What are the requirements when installing smoke detectors in air duct systems (as per NFPA 72)?
NFPA 72 gives us the guidelines as to how to provide/install smoke detectors in ducts. First of all, and above all else, the detector must be listed for being used in air duct system (NFPA 72 18.104.22.168.1). When installing duct-type smoke detectors, they can be installed as described below:
(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
Pictured below is a smoke detector installed as per (3) above; where there detector is installed outside the duct and a rigidly mounted sampling tube protrudes into the duct.
This installation/scenario could be worded in the following manner when presented as a question in the NICET Certification Fire Alarm System exam:
True or False. NFPA 72 allows a smoke detector not listed for air duct system, as long as the detector is installated outside the duct system and complies with the manufacturers specifications.
Answer to this question is obviously Flase; as NFPA 72 only allows smoke detectors to be installed for duct detection to be listed for such.
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