Duct Smoke Detector Magnet Test at Annual Inspection
During the annual inspection of a six-story office building, the technician tests 26 duct smoke detectors by holding a magnet against the test switch on each detector head. All 26 annunciate at the fire alarm control unit within 8 seconds, and the technician records them as passed. You observe that the units serve air-handling units rated at 12,000 cfm and that the detectors are mounted on the return-air duct with sampling tubes that extend across the duct. The building owner is present and asks whether the system can be certified. The technician tells you the magnet is the manufacturer's listed test method and that introducing smoke would take too long for 26 devices. One detector, at AHU-4, has a sampling tube that appears loose at the entry point. The panel is an addressable system with no troubles.
1. Does the magnet test satisfy the inspection and testing requirements for duct smoke detectors? Explain your reasoning.
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The magnet test is not a complete acceptance or annual test for a duct smoke detector. The magnet operates the detector's internal test switch, which simulates an alarm condition and verifies the detector-to-panel signal. It does not verify that the sampling tubes are properly positioned, that air flows through the tubes, or that smoke will enter the sensing chamber. The standard requires duct detectors to be tested in accordance with the manufacturer's published instructions, and those instructions generally call for introducing smoke or aerosol into the duct upstream of the detector or using a listed test method that confirms sampling. Because the purpose is to prove the detector will respond to smoke in the duct, the 26 magnet tests are incomplete. Retest each device with an approved smoke or aerosol method and record the response.
2. What should you do about the loose sampling tube at AHU-4, and how does it affect the inspection result?
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The loose tube is a deficiency. A duct detector depends on both sampling tubes being sealed and oriented so that air moves across the chamber. A loose tube can allow air to bypass the detector or can change the sampling profile, so the detector may fail to respond to smoke even though the magnet test passes. The tube must be reseated, repaired, or replaced per the manufacturer's instructions, and the detector must then be retested with smoke or aerosol. The inspection cannot be certified as passed until the defect is corrected and the retest is successful. Document the location, the defect, the corrective action, and the retest result.
3. What documentation should be recorded for the retest?
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Record the device address and location, the test method, the test agent, the response time to panel annunciation, the pass or fail result, the loose-tube defect and repair, and the date and initials of the tester. Also note that the original magnet tests were not accepted and that all 26 devices were retested. Attach the manufacturer's test instructions if a nonstandard method was used. If any device remains impaired, document the impairment and the notification to the owner and AHJ.