The LWF Blog
Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 165
January 8, 2024 11:57 amLWF’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 164, LWF looked at the recommendations and guidance for fire alarm sounders as per BS 5839-1. In part 165, we continue on that subject.
When a voice fire alarm system is put into use, both the volume and the clarity of the message are important. The elevated level of volume required to ensure the message can be heard throughout the premises may distort the clarity and so care must be taken to ensure this is not the case. Additionally, the zoning of audible warnings when using voice alarm systems should be matched to the evacuation zones.
When implementing visual signal devices, commonly used when the building contains people with hearing difficulties, the signal should be red or white (unless this conflicts with other warning devices). The flash rates for the fire warning signals should be set to a suitable level to avoid triggering a seizure in people with photo-sensitive epilepsy. It should be noted that it wouldn’t be sufficient to say that nobody with photo-sensitive epilepsy will be in the building, because it’s not possible to know who will be in the building in the future and some people may have an undiagnosed condition.
Any audible warning device used on the same fire alarm system should have a similar sound and one that is distinct from any other warning sounder used for other purposes. It would not be appropriate to have different alarm sounders at different points in the building because the sound would be discordant and confusing. The frequency for alarm sounders should be within 500 – 1000 Hz for fire alarm sounders.
Modern alarm sounders come in a range of sound tones, both fluctuating and constant, and the choice made should reflect the environment into which it will sound. The sound power level will not change within a particular sounder, but trying different tones can help pinpoint the one which will be most distinctive against the background noise.
It should be noted that rather than having fewer louder sounders, which can cause noise levels in some areas to become too loud, it is better to have a greater number of quieter sounders to give a more consistently audible alarm tone.
In part 166 of LWF’s series on fire engineering, we will finish talking about the recommendations as per British Standards and begin discussing NFPA 72. 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.