g/fire_alarm • Posted by u/fire_code_fred • 23 hours ago

Addressable smoke detector throwing "dirty detector" trouble — when do you clean vs replace?

Have a building with Notifier NFS-320 panel and a mix of FSP-851 and FSP-851T detectors. Getting sporadic dirty detector troubles — about 6 detectors across 3 floors, mostly in the warehouse area with airborne dust.

The detectors are 7 years old. Per NFPA 72, cleaning is required. But at 7 years and with recurrent dirty trouble, at what point is replacement the right call vs. repeated cleanings?

What's your replacement threshold for dusty-environment detectors?

💬 4 replies

4 replies

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u/panel_programming_paul • 23 hours ago

7 years in a dusty warehouse is actually pretty good life. I'd replace any detector that fails sensitivity testing post-cleaning rather than cleaning it again. Document your post-cleaning sensitivity readings in your inspection report. If the AHJ or insurance ever asks, you want proof you tested, not just cleaned.

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u/fire_code_fred OP • 23 hours ago

Thanks for the responses. Pulled the sensitivity readings post-cleaning: 4 of the 6 detectors are within 1 analog point of alarm threshold. Replacing those 4, keeping the other 2 that have more headroom. This approach is exactly what the AHJ will want to see documented.

u/smoke_detector_steve • 23 hours ago

NFPA 72 Chapter 14 says test at acceptance and then at intervals not exceeding 12 months. It also says replace if sensitivity can't be restored. The practical test: after cleaning, put the detector back and pull an analog sensitivity reading from the panel. Notifier NFS-320 gives you current chamber value vs. alarm threshold. If the cleaned detector is still within 1-2 points of the alarm threshold with no smoke present, replace it — cleaning bought you a few months at most.

u/suppression_sue • 23 hours ago

Consider drift compensation alarm sensors for that warehouse area going forward — they're designed to auto-compensate for gradual contamination. More expensive upfront but fewer false dirty troubles over their life.