Tried and Tested: Smoke detector sensitivity testing

By Thomas P. Hammerberg | Mar 15, 2022
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There is a functional test for smoke detectors that essentially allows an installer to pretest the circuits and ensure the smoke detectors will report to the fire alarm control unit when they go into alarm or trouble. There is also a smoke entry test to ensure the smoke detector will go into alarm when it should.

Both are important at various stages of the life of the system. However, sensitivity testing is the most important test because it ensures the smoke detector will operate within its listed sensitivity range. Many things can affect the sensitivity, and fire alarm testing is needed to address these. Correcting the problems can also have an added benefit—reducing unwanted alarms. Remember, smoke detectors are installed to provide early warning to allow occupants more time to escape from a fire. Here are some items that need to be addressed.

First, smoke detection systems need to be designed and installed properly. Some things that will affect the smoke detector operation include air velocity, stratification, dust and dirt, bugs, humidity or steam from showers, smoke color, temperature, cooking fumes and more. Starting around A. of Annex A in NFPA 72, there is a lot of good information about what affects the different types of smoke detectors.

Systems designed and installed properly will provide better life safety protection and far fewer unwanted alarms. You should be aware of the environment the detectors will be installed in. If you have doubts about the location, it should be brought to the attention of the designer, and in some cases, the authority having jurisdiction (AHJ). Don’t just install them because they are shown in a particular location on the drawings. Make sure smoke detectors are not installed in drafty areas or near air diffusers.

Addressable fire alarm systems that monitor sensitivity and give a trouble signal when the detector is near the extent of its sensitivity range are the best because testing personnel do not need to manually test sensitivity. The control unit does that automatically. However, there are still many nonaddressable fire alarm systems installed, and any smoke detectors installed must have the sensitivity tested manually.

Unfortunately, in my experience, sensitivity testing is not enforced well enough. Owners don’t want the tests because of the increased cost. Many AHJs do not uniformly enforce the NFPA 72 requirements for sensitivity testing. If they did, there would be fewer unwanted alarms. Testing personnel should explain the benefits to owners when providing a test plan.

You will find the smoke detector sensitivity testing requirements in NFPA 72, and in Table, item 17(8). Sensitivity testing is not required when smoke detectors are first installed, but must occur within one year, then every two years after that. If, after the second test, the results show the sensitivity has remained within range, NFPA 72 allows testing every 5 years, provided that you keep track of unwanted alarms and perform tests if there is an increase from previous years.

Clean smoke detectors in accordance with the manufacturer’s published documentation where needed. Too much dust, dirt or insects can alter the sensitivity testing, and at some point, the smoke detectors may no longer work.

Manual testing

If you must manually perform sensitivity tests, there are a number of options. Smoke detector manufacturers will usually have their own sensitivity test equipment. There are a couple of sensitivity testers on the market that are listed to test any smoke detector. One is called a Gemini Smoke Detector Analyzer, which is an old system and uses an emulsified oil for operation, and another is called Trutest. There may be others. NFPA 72 requires that smoke entry testing be performed in place, but not necessarily sensitivity testing. Sometimes making a test cart to use for sensitivity testing is useful, provided that you do a smoke entry test when reinstalling it.

From a liability protection point of view, it is important to perform these tests and document the results. If your client has a fire, insurance companies will send an investigator and look at fire alarm test reports. If there is no record of smoke entry testing or sensitivity testing, the testing company could be held partially liable for the loss. Remember that the owner is the one responsible for the system. If you make recommendations to them for testing, be sure to document it.

The bottom line is that smoke detectors provide early warning and will only do so if they are operating properly. As life safety professionals, it is our responsibility to ensure the systems we install, test and maintain operate correctly.

About The Author

HAMMERBERG, SET, CFPS, is an independent fire alarm presenter and consultant in The Villages, Fla. He can be reached at [email protected]

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