The LWF Blog

Facilities Management – Fire Detection and Fire Alarm Systems – Alarm Devices, Part 11.

August 18, 2016 10:25 am

In our blog series for those who work in Facilities Management, we have been looking at Fire Alarm Systems and methods of fire detection. Today, we will begin on the subject of Alarm Devices with the aim of giving an overview of how they work and some details which need to be considered when choosing the right type of alarm system for your premises.


One of the most essential components of a fire alarm system are the alarm signals. This is the sound that the system emits when a fire is detected. It can be in the form of a bell or an electronic sounder and there is no reason beyond taste as to which should be chosen. The only restriction on sounders is that your choice should be consistent throughout the building, as it would be confusing to have two different sounds.


The sound level of the devices is also an important consideration. The device should emit sound of not less than 65 dB(A), or if you take into account background noise, not less than 5 dB(A) above that, whichever is greater. There are some areas of a building which do not require a level of 65 dB(A), such as stairways and smaller rooms which measure less than 60m2 and these are reduced to a minimum of 60 dB(A). In addition, when you are considering a large open plan area, the very edges of that area which are most remote from the sounders can receive a sound level of only 60 dB(A), provided that the vast majority of the whole area receives the alarm sound at 65 dB(A), without that contravening relevant codes.


In the case of those buildings which may contain sleeping occupants, a sound level of 75 dB(A) should be emitted at the head of the bed to rouse any persons sleeping when the alarm is sounded. In the case of hospitals, the alarm is not sounded with a view to waking sleeping patients, but to alert staff to the presence of fire. For this reason, it is not necessary for the sound level of 75 dB(A) to be achieved in those circumstances. The Department of Health indicates that the achieved sound level within hospitals should be between 40 and 55 dB(A) in patient areas, although precise levels may be dependent on different considerations.


While the levels themselves are not complex to understand, they can be tricky to achieve in all areas. For instance, more than one door between an area and a sounder can mean that the correct level of 65 dB(A) is most unlikely to be obtainable in that area without further sounders being fitted. As previously mentioned, the level of 75 dB(A) should be achieved at the head of a bed where an occupant sleeps, but unless there is a sounder in the room itself, this sound level would be unlikely. For this reason, a sounder is usually included in each room of a hotel, for instance, sometimes as a part of the smoke or heat detector which is also installed in the bedroom.


In our next blog, we will continue discussing alarm devices and provide some information on the legislation covering this area of fire safety. 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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