The LWF Blog

Facilities Management – Fire Alarm Systems and False Alarms – Part 19

October 12, 2016 11:34 am

In this blog series for those who work in Facilities Management and who have an interest in or responsibility for fire safety, we have been looking at how fire alarm systems work and most recently, how they sometimes don’t work, which results in false alarms. False alarms can be more than a nuisance factor and so it is important to gain an understanding of what causes them and what can be done to reduce persistent false alarms. In part 18 of this series, we began looking at how many false alarm instances constitute a problem, in comparison to the size of the fire alarm system by detector amount and will continue today.


Where the fire alarm system is based in a large building with many detectors, even the acceptable rate of one false alarm per 100 detectors can be unacceptable to the user. If the system has 5000 detectors, one false alarm per 100 would mean at least one false alarm per week, which can be very disruptive to the occupants. In cases such as this, it can be that a ‘staff alarm’ is issued which means that if a single detector triggers an alarm with the control system, a notification is sent to trigger alarm pagers held by nominated personnel or an alarm is sounded within a restricted area only. This enables the recipient to investigate the cause of the alarm, prior to a general alarm being sounded.


As a safety back stop, if a limited alarm has been issued and no response is received by the control system from the user to say that there is no fire, a general alarm is sounded within a predetermined amount of time and evacuation should proceed as normal. Operation of a manual call point by an individual within the building would override this ‘staff alarm’ and a general alarm would sound. Indeed, if two or more detectors are triggered on the system within the investigation period, the general alarm will sound too.


Many fire alarms are installed with the sole purpose of protecting the occupants of the building from fire, but some are designed to protect the property too and in these cases, it is most likely that the alarm system will be linked to the Fire and Rescue Service, to ensure they are summoned without delay to the scene of the fire. In protected buildings with systems which are not constantly staffed, this means that the signal should be sent automatically, rather than waiting for staff intervention to make the call.


For an automatic fire detection system to be recognised by the building’s insurers, automatic transmission of the fire alarm to an alarm receiving centre is often required.


In next week’s blog, we will continue looking at alarm signals and their transmission. 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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