Each monthly test takes around 4 seconds to complete. It is something that people do on a monthly basis, often without even a second thought as to why they are pressing the test button. Most people do not realise that the monthly test of the sounder has an interesting history and that by completing the test on a monthly basis it actually proves several things – and a few things that it does not!
The testing of fire alarms on a monthly basis was not given to us in some safety led committee’s ideal world. The testing interval has been reverse engineered from various failure records, including some of the industrial fires from the post war period where the cause of the fire had been due to faulty fire alarm systems that had been failing for weeks prior to the inspection. The biggest category of fault being silent failures of components between inspections. The testing of sounders on a monthly basis is the shortest practical period to detect silent failures of components before they cause a problem.
This will test the sounder and confirm the two components can communicate with each other. This will confirm the wiring is intact, the battery for the sounder is holding and the panel is working correctly.
What it doesn’t do is test the smoke detector for detection of smoke. There is a useful background explanation of official fire safety risk assessment guidance.
Most detectors, whether optical or ionisation, are prone to something known as sensitivity drift. This means that particles of dust, grease and even airborne grime can find their way into the sensing chamber and alter the detector’s sensitivity over time. This means that even though a detector may have passed its monthly test it may not be as sensitive to the presence of smoke as it was when first installed. In fact it may not even trigger at all in the presence of smoke, until such time as its sensitivity has reduced even further. Sensitivity drift is the reason why detectors are serviced every 6 years, or in some cases every 10 years, as part of a fire alarm system maintenance contract. This is in addition to the testing that is carried out on a monthly basis. In order to check the sensitivity of a detector a professional would use a test aerosol, which is a specially designed mixture that is released into the air as a fine mist. This mist is then drawn into the sensing chamber of the detector where it is detected.
The monthly test was always meant as a quick health check, not the whole picture. For more on this, take a look at https://firealarmsystems.co.uk/.