The LWF Blog

Facilities Management – Types of Fire Detection & Fire Alarm System – Part 16

September 21, 2016 11:21 am

In  our recent blog series for those who work in Facilities Management and those who are interested in the protection of buildings through fire safety, we have been looking at the different types of fire detection and fire alarm system which are currently in use. In the last blog, we talked about the differences between conventional (or non-addressable) and addressable fire alarm systems and how addressable systems can transmit alarm information from a single identifiable detector to the control and indicating equipment (CIE) whereas a conventional system can only report which circuit the alarm was triggered on. We also talked about analogue and multi-state systems and how they report to the CIE.


An analogue system contains the ability to further investigate the current signal level of each detector at the CIE and this function is of use to maintenance technicians when they need to ascertain which sensors require cleaning or other maintenance. This system also offers the flexibility so that more sensitive conditions can be set at certain times, for instance, when the building is empty. One reason for this is that when the building is occupied, there are more likely to be false alarms if the system detectors were set to a very sensitive level.


A consideration when a building is new or a fire alarm system must be replaced is that there are now ‘multi-sensor’ fire detection systems. This means that each detector can be capable of detecting more than one aspect of a fire, e.g. smoke and heat. As with an Analogue system, the signal is received and interpreted by software contained within the CIE.


While the main aim of a multi-sensor fire alarm system is to offer a wider range of fire detection methods, it could also be useful for identifying and filtering false alarms. If a multi-sensor is placed in an area with a lot of steam, for instance, the optical detector might trigger an alarm, but the smoke or heat element of that detector would not be triggered and so the CIE would be able to work out the source of the alert was not fire.


A multi-sensor alarm, therefore, can be a very useful fire alarm system to install in a building which is likely to or already has been subject to a large amount of false alarms. Indeed, BS5839:1 recommends the use of such systems where the building requires a system containing more than 1,000 fire detectors in order to limit false alarms.


In next week’s blog we will look at false alarms and how they are commonly caused. In our next blog, we will continue looking at conventional and analogue systems and how they work. 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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