Duct Detector Test

Q: During our inspection our surveyor was looking for 3/8″ holes, 3 feet upstream, before the smoke detectors in the ductwork. He requested testing procedures for the duct detectors from the tester who stated the test was performed by putting smoke onto the duct detector, which shut down the air-handler unit. The surveyor says the smoke must be inserted 3 feet prior to duct detector to test the actual tube for blockages. Can you tell me the actual regulation that states this requirement?

A: According to NFPA 72-2010, section 14.4.2.2, the method to conduct testing of fire alarm systems must comply with Table 14.4.2.2:

14(g) Smoke detectors

1) Smoke detectors/smoke alarms shall be tested in place to ensure smoke entry into the sensing chamber and an alarm response. Testing with smoke or listed aerosol, acceptable to the manufacturer of the aerosol or the manufacturer of the smoke detector/smoke alarm and identified in their published instructions, shall be permitted as acceptable test methods. Other methods listed in the manufacturer’s published instructions that ensure smoke entry from the protected area, through the vents, into the sensing chamber shall be permitted.

6) Duct detectors

In addition to the testing required in Table 14(g)(1), duct smoke detectors utilizing sampling tubes shall be tested by verifying the correct pressure differential (within the manufacturer’s published ranges) between the inlet and exhaust tubes using a method acceptable to the manufacturer to ensure that the device will properly sample the airstream. These tests shall be made in accordance with the manufacturer’s published instructions for the device installed.

Here is a summary on how to test duct detectors:

  1. The test must ensure smoke/aerosol enters the sensing chamber and an alarm responds.
  2. You must verify the correct air pressure differential between the inlet and exhaust tubes, in accordance with the manufacturer’s instructions.

So, while the vendor appears to be testing the detector, it does not appear he is testing the air pressure differential of the inlet and outlet tubes. I don’t see anything in NFPA 72-2010 that requires putting smoke/aerosol in the actual air tube for duct detectors. I do see where that is required for air sampling smoke detectors, but duct detectors are not the same as air sampling smoke detectors.