The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 136

June 12, 2023 10:39 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 135, LWF began to consider how it is best to manage false alarms. In part 136, we continue to discuss false fire alarms and what can be done to remedy repeated false alarm signals.

Fire engineering principles offer one simple solution to false fire alarms through configuration of the fire alarm system. It is known as alarm filtering with alarm verification. In an environment where false alarms have historically caused significant disruption, the system can be configured to require two separate fire detectors to trigger for a full alarm to be commenced. If one detector is activated, the signal is sent to the CIE and building management will receive a local warning so that the signal can be investigated.

The prior warning has advantages to the organisation and for fire safety purposes, if properly acted upon. The alarm can be investigated and if it proves to be false, saves the building from having to be improperly evacuated. If the alarm is genuine, it may offer the chance for first-aid fire action to be taken and gives prior warning of building evacuation.

The use of the two detector activation method is known as ‘coincidence detection’ or ‘double knock’.

Some environments where alarm filtering may be advantageous include hospitals, shopping centres, theatres and cinemas and stadiums. Coincidence detection usually allows a set period of time for investigation of the first alarm signal after which, if the alarm is not cancelled, the fire alarm’s control and indicating equipment would progress to a full alarm signal and the building’s occupancy would evacuate as normal. This is a failsafe in case the first alarm signal is not investigated in a timely fashion.

Another helpful example of alarm filtering is known as ‘cross-zoning’. This system uses multiple detection loops with redundant detectors and is most commonly implemented where there is an automatic discharge (such as deluge or clean agent) to suppress a fire. In this case the alarm filtering has the purpose of avoiding accidental discharge due to a false alarm and the associated financial costs of such a system becoming operational.

False alarms may also be triggered by temporary or ‘hot works’ being undertaken in a building, as well as due to inadequate maintenance of the fire alarm system. Steps should be taken by building management to avoid the negative impact of such circumstances.

In part 137 of LWF’s series on fire engineering, we will begin to look at the classification of alarm systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.

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