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Automatic smoke detector fire alarm head on the ceiling. The smoke detector is triggered by a small amount of aerosol smoke, the red indicator lights up

Why Do Some Commercial Smoke Detectors Re-Alarm After Testing?

Posted in: Testing Product Support Training
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It can be a common occurrence during a maintenance visit that a smoke detector goes into re-alarm after testing. Here we'll delve into the intriguing world of smoke detectors and explore why some of these essential safety devices re-alarm after testing. 

These nuisance re-alarms can lead to increased test times per site, affecting efficiency and productivity.

Understanding Nuisance Re-Alarms

Nuisance re-alarms occur when a detector, equipped with a smoke sensor, triggers an alarm after a successful functional smoke test. This can incur extra time spent per detector by the fire alarm engineer, potentially costing up to half an hour or even more!  But why does this happen? Let’s break it down:

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  1. Type of detector: Conventional detectors often do not have any auto reset feature and require a manual reset to be carried out by the fire alarm engineers. This involves going to the Fire panel (which could be some distance from the detector under test) to press reset. If detector continues to activate, more visits to the panel are required further wasting time. Analogue Addressable detectors often have some level of automatic reset, which lessens the issue.
  2. Ambient Temperature: When temperatures drop below 15°C, test smoke evaporates more slowly. Consequently, it lingers within and around the detector chamber, increasing the likelihood of re-alarms.
  3. Detector design: Some detectors feature insect-resistant gauzes to keep out bugs that could hold the test smoke in the chamber for longer and cause false activations. leading to re-activation.
  4. Stagnant Air Areas: Domes, cupboards, and other spaces with slow or no air movement can trap smoke, causing prolonged reactivation.
  5. Integrating time: Or the time to alarm. As detectors become more sophisticated to combat unwanted false alarms, the average time to alarm has increased. This means for an untrained fire alarm engineer using smoke from an aerosol canister (where the smoke release is controlled by the engineer), could easily over apply. There are several issues this could cause, most noticeable is in the increase in time for the test smoke to clear from in or around the detector chamber, especially when testing conventional detectors.

In most cases the causes of nuisance re-alarms can be attributed to two or more of the above points.

Understanding the causes of nuisance re-alarms helps test engineers troubleshoot effectively and minimize disruptions during testing. So, next time you encounter a re-alarm, consider these factors, and take the necessary steps to ensure accurate and efficient smoke detector testing.

Reduce or Eliminate the Problems

For an aerosol canister user, the issue can be controlled but not eliminated by correct and careful application of test smoke. It is also important to take into consideration cooler ambient temperatures. Training is essential to make sure that the causes are understood and how to limit the impact.

It is easy to eliminate the problem and associated with lost time by switching to using an electronic tester, such as Testifire, XTR2 or Solo 365.

The new electronic testers include a ‘Clear’ feature that blows clear air through the detector, removing any lingering test smoke. 

Usually, 5 or 10 seconds is all that is required, which means you can move on swiftly to the next detector to test. This can end up as a big time saving over a maintenance visit.

If you want to learn more or are currently use aerosol canister based Solo test solutions, check out our CPD webinars that are free to book on our website.

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