Duct Detectors

Q: With regard to testing duct detectors in a hospital, I understand that on an annual basis the automatic shutdown of the AHU’s must be verified when duct detectors are activated. I am unclear if there is also an annual requirement to verify damper (pneumatic and/or electric type but excluding fused links) operation at the same time. Also, is there a requirement to test air differential on duct smoke detectors annually.

A: You don’t have to test the damper at the same time that you’re testing the duct detector or fan shut down and you do have to test duct detector air flow differential annually.

  • Per NFPA 72 (2010) testing frequency Table, emergency control functions that are interfaced with the fire alarm system must be tested annually.  The testing methods Table states an emergency control  function must be tested at the same frequency (not necessarily at the same time) as the initiating device that controls.  So technically, the damper doesn’t have to be tested at the same time as the duct detector; just tested annually by operating or simulating the alarm activation (test switch).  I clarify that in case there’s a reason you don’t want to close the damper or shut down the fan the day you’re scheduled for testing the duct detector.  As long as it’s tested within 365 days of its last test, you’re good to go.  Also, you have to observe the damper blades fully close.  It’s not enough to listen to the actuator operate, so you may want to pass that on to the testing team and ensure there’s a space on your testing form to confirm that the damper closure was visually confirmed.
  • Table covers duct detector testing methods.  It mandates not only testing smoke entry into the chamber and sensor sensitivity testing, but also air flow testing across the sensor.  The manufacturer should have an acceptable method in their installation manual, but the usual method is to use a manometer.  I don’t know of any manufacturer that wouldn’t use this method.  This is a new requirement with the implementation of NFPA 101 (2012) & NFPA 72 (2010) and your CMS enforcement agency will be looking for it on your testing paperwork, so if you’re using a 3rd party testing firm, ensure they’re employing this method as most won’t unless you hold their feet to the fire.

[NOTE: Gene Rowe from Affiliated Fire Systems contributed to this reply.]