The LWF Blog

Facilities Management – Voice Alarm Systems – Part 5

December 8, 2016 12:24 pm

In this blog series for those who work in Facilities Management, we have been looking at the use of voice fire alarm systems as a part of the fire protection provision in buildings. Last week, we gave an overview of the factors which should be considered in the design of such a system and today, we are going to look at the practical uses of a voice alarm system.


In the UK, it’s accepted practice that a voice fire alarm system can be used for other purposes too, although this is not usually acceptable in North America. While it is common for the system to be used for other purposes, such as bomb and security threats, for public address system purposes (moving of cars, summoning of staff etc.) and even for background music, it is important to note that the design should immediately shut out any non-essential fire related usage in a fire situation.


This means that, where this is considered acceptable practice, there are considerable economies to be made in cases where a public address system is required in addition to a voice fire alarm system. In addition, any such system, designed for use as a voice fire alarm system, is likely to be of a greater audio quality than a standard PA system, as well as being more reliable.


While ad-hoc PA messages and security risks which could not be pre-determined are usually made ‘live’ by personnel on site, it is the case that fire alarm messages must be pre-recorded. The message generators must be stored on solid state media rather than on media which has moving parts, as is the case with cassette tapes, compact discs or standard hard disks.


In many simple buildings, the pre-recorded messages are sufficient warning and instruction for the occupants of the building, but in more complex buildings and those where phased evacuations are in place, emergency microphones are a necessary addition to the system to ensure that an ongoing communication is possible during the evacuation process. An emergency microphone would have the highest priority possible and so would override all other inputs including the pre-recorded fire evacuation messages.


The sound level and intelligibility of the broadcast messages is also important. The sound pressure level of such messages must be at least as high as that required for conventional fire alarm signals. Of course, while a sounder must only achieve a certain sound level, it is extremely important that a voice message can be understood, even at a high volume. The quality of the sound system and speakers is one element of ensuring that the message can be clearly understood, but there are other factors which come to bear, such as the potential for reverberation within the building and other ambient noise.


In our next blog, we will look into the issue of sound quality of voice fire alarm messages in more detail. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.




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