The LWF Blog

Facilities Management – Fire Alarm Systems and False Alarms – Part 17

September 27, 2016 2:54 pm

In this blog series for those who work in Facilities Management, we have been looking at fire safety in buildings – in particular, types of fire alarm system and alarm detectors and their uses. In today’s blog we will continue talking about fire alarm systems in relation to the issues experienced in terms of false alarms.


False alarms can be more than a nuisance. Repeated false alarms in a building can lead its tenants or occupiers to dismiss further alarms because they feel the system is not effective. Of course, this is potentially very dangerous if effective evacuation is in question in a fire situation.


Additionally, a high proportion of calls to the Fire Service are as a result of false alarm signals given by a fire alarm system and every false alarm call means that those fire fighters are not available to deal with other fire situations.


While we can classify these alerts as ‘False Alarms’, the fire alarm system is simply reacting to a range of stimuli which trigger its sensors and the more of these that can be eradicated, the better. One of the ways to avoid false alarms is to have an updated fire alarm system. Many modern fire alarms are much better at isolating actual fire situations from the range of activities which may affect the detectors.


BS 5839:1 gives a list of common causes of fire alarms, as follows:


– Cooking fumes – including the making of toast

– Steam – from industrial processes, bathrooms etc.

– Cigarette smoke

– Dust which may have built up over time or been suddenly released as a part of a process

– Insects

– Aerosol Sprays – such as deodorants, hairspray, cleaning fluids

– High air velocities

– Smoke from an outside source – e.g. a bonfire outside

– Hot work – such as cutting and welding

– Any processes which include the use of smoke or flame, including smoke machines

– Incense or candles

– Electromagnetic interference

– High humidity

– Water ingress

– Substantial temperature changes

– Testing and maintenance of the alarm system itself, without adequate system preparation

– Pressure surges of the water mains which serves the automatic sprinkler systems


BS5839:1 also gives benchmarks of what is considered ‘acceptable’ levels of false alarms from a fire alarm system. Of course, there are situations where what might be considered acceptable by British Standards may not be acceptable to the building occupant, due to environment, activities etc. False alarms are, however, usually proportional in amount to the number of detectors in use as a part of the system. Those buildings which use heat detection rather than smoke are also less likely to suffer from excessive false alarms.


In next week’s blog we will look at how many false alarms you might expect to have, what you can do to mitigate the false alarms and some recommendations to limit them. 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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