The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Alarm Systems – Part 12.

August 18, 2016 10:07 am

Our recent blog series for Architects and those working in building planning has been looking at how fire alarm systems are used within buildings to protect the occupants, the building or contents and to raise an alarm. In part 11 of this series, we looked at the use of zoning with addressable and analogue addressable systems and indicated that we would give you an overview of the use of manual call points and break glass units today.


A break glass call point or manual call point is a device that allows building occupants to raise an alarm in case of fire by breaking a frangible element within the call point, which in turn raises an alarm.


The situation of these points is important. They should be located on the exit route, normally at the storey or final exit, i.e. adjacent to the stair or the door leading to fresh air. The reason for this is that the person who discovers a fire situation should raise the alarm as close to the event as they can, but as they begin their own evacuation from the building.


Indeed, their placement should be such that no person needs to travel more than 45m from any position within the premises in order to reach and operate the call point. Their location on a given wall is normally around 1.2m (some deviation is permitted) above floor height, easily accessible and not obstructed in any way.


Each installation within a set of premises must work in the same way, to avoid confusion, unless the difference is one which has been considered essential.


When considering how call points work with zoning, each call point which is placed upon a staircase landing should be incorporated into the zone which serves the accommodation on that level.


A combination of manual and automatic devices can be used on the same system, however, it is suggested that the manual call points be on separate zones for speed and efficiency of identification.


There are multiple types of detector which can be used as a part of the fire alarm system in a building and these are grouped into three types – smoke, heat and flame detectors.


Smoke detectors include point ionisation, point optical, optical beam and aspirating systems. Types of heat detectors are point fixed heat, point rate of rise, line heat, combined and beam type heat detectors.  Flame detectors are made up of ultraviolet and infrared detectors.


The choice of detector type is dependent upon the environment within the premises where the fire alarm is to be used and the conditions under which fire might be deemed most likely to start.


In the next blog, we will look at each of the different types of detector. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.


Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.



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