Maintenance and Testing of Duct Detectors

Duct Smoke detectors are designed to be as maintenance-free as possible. However, dust, dirt, and other foreign matter can accumulate inside the housing of a duct detector and change its sensitivity.  They can become more sensitive, which may cause unwanted alarms, or less sensitive, which may reduce the level of protection.  Both are undesirable. Therefore, the smoke detector head inside of a duct smoke detector should be tested periodically and maintained at regular intervals. Make sure to follow the manufacturer’s specific recommended practices for maintenance and testing. Also refer to Chapter 10 of NFPA 72, 2007.

Typical maintenance practices

Under normal conditions duct detectors require routine maintenance annually, but harsher environments may require an increased maintenance schedule.  Notify the proper authorities that the smoke detector system is undergoing maintenance; therefore, the system will be temporarily out of service.

***Warning***

Place the system on test with the Central Station Monitoring Company and disable the zone or system undergoing maintenance to prevent unwanted alarms and possible dispatch of the fire department.

Most duct smoke detectors have smoke detector sensors that can be accessed for cleaning. Use a vacuum cleaner Eureka 71B Hand-Held Vacuum and remove dust from the detector by placing the nozzle as close as possible to the openings in the outside housing. A nozzle with a brush attachment will assist in dust removal. Some smoke detectors can be removed for more thorough cleaning; refer to manufacturer’s recommended procedure for details. Also check the sampling tube holes and filters to make sure they are not clogged.

Test each duct detector’s sensitivity.

If a duct detector’s sensitivity is within specifications, nothing further needs to be done to the smoke detector. If the duct detector’s sensitivity is outside specifications, replace the smoke detector or follow the manufacturer’s recommended procedure.  Restore the zone or system at the completion of testing.  Notify the proper authorities that testing has been completed and the system is back in service.  Also be sure to place the system back online with the Central Station Monitoring Company.

Other maintenance checks:


• Holes or cracks in duct work near vicinity of duct detector.
• Air leaks where duct detector housing or sampling tubes are attached to duct.
• Dust accumulations in or on sampling tubes, sampling tube filters, and    smoke detector head.
• Wiring terminal screw tightness.

Typical Testing Procedures

All duct detectors should be:

(a) Tested or inspected at least annually to ensure that they sample the air stream.

(b) Tested at least annually causing them to initiate an alarm at their installed location to ensure that they are opperating effectively to produce the intended response.

(c) Checked within one year after installation and every alternate year thereafter to assure that they are within their listed and marked sensitivity range.

It is not recommended that duct fires be used to test duct smoke detectors. This procedure does not provide a consistent, measurable method of determining if the detectors are performing properly. The test procedures and test equipment recommended by the duct detector manufacturer are the best way to test these detectors.  These could include canned smoke GE Security SM200-12PKG Smoke-in-a-Can. Canned Smoke for Functional Testing. Item Requires Ground Shipment, 12-Pack, magnets and remote test stations.

Most duct detectors are equipped with a built-in test mechanism, electronic metering equipment, or aerosol test apparatus.  Refer to manufacturer’s specifications for details.  Notify the proper authorities that the smoke detector system is being tested. All persons who would automatically receive
a real fire alarm signal should be notified to prevent an unnecessary response.

Follow the manufacturer’s recommended test methods.

If a duct detector functions properly and its sensitivity is within specifications, nothing further need be done to the smoke detector.

Restore the zone or system at the completion of the testing.  Notify all the persons contacted at the beginning of the test that testing has been completed and the system is again operational.  Place system back online with the Central Station.