The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Alarm Control Equipment – Part 22

October 25, 2016 1:47 pm

In our recent blogs for Architects and building planners, we have been looking at Fire Alarm Control Equipment and how its use in a new building is guided by the type and usage of the building as well as current fire safety regulations. In today’s blog we will be discussing audible warning devices and sounders as per the requirements laid out in BS 5839: Part 1.


All audible warning devices in the same fire alarm system must have a similar sound and pitch. The frequency aimed for should be between 500-1000Hz and the building occupants should not be able to confuse it with any other sounders which may be in use within the premises. If, for instance, the fire alarm sounders were substantially different in adjacent areas of a building, this can promote confusion amongst those people who must evacuate to a place of safety.


Traditionally, actual fire alarm bells were sounded, but now electronic sounders have a wider variety of available tones and it is possible to choose between a constant sound and one that fluctuates. It is possible, through tweaking the tones, to produce a sound which is instantly recognisable and distinct.


While it is most economical to have the minimum permissible amount of sounders at the maximum sound level, it might be more practical to have a more consistent level of sound throughout the premises by the installation of more sounders, with those emitting the alarm at a lower level of volume. This means that those areas which are directly beneath a sounder would not be quite so deafening in terms of volume.


When considering the amount of sounders necessary for a new build and their placement, various factors should be taken into account. One sounder per compartment is required, as once the sound has to be passed through walls and doors, it substantially reduces the sound level. The level of sound should be unmistakable and should be louder than any background or persistent work area noise, but it should not be so loud as to potentially damage the hearing of building occupants. This means that the sound level in each area of the building should be tested for adequacy.


Each fire alarm system should have the amount of sounders necessary for the size and amount of compartments within the building, but even in a smaller premises, there should be at least two sounders.


Where the fire alarm system is P-type (a property protecting system), the alarm signal is sent to a central point so that the Fire Service can be alerted to attend, but these systems should also have an external sounder, which must be coloured red and marked ‘FIRE ALARM’.


In our next blog, we will be looking at the requirements for fire alarm sounders as per NFPA 72, before moving on to look at how fire alarm panels can be used to do more than simply monitor fire alarm signals. 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 for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.


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