The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 147

August 29, 2023 10:45 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 146, LWF looked at addressable systems (including analogue addressable) and detection zoning. In part 147, we consider the formal recommendations for zoning of fire alarm systems as per BS 5839-1.

When looking at the formal recommendations for zoning of fire alarm systems, NFPA 72 does not contain any formal suggestions for zoning, except for wireless systems, where each detector position has to be individually identifiable.

BS 5839-1 contains recommendations which are quite specific:

• A building with total floor area (of all storeys) of up to 300 m² may be considered as a single zone, even if it is multiple storeys in height. In buildings with greater than 300 m² floor area, each zone should not extend over more than one storey.
• The total floor area of a zone should not exceed 2000 m² (where non-addressable detection is used).
• The search distance, (which is the distance travelled by a person searching inside a zone to ascertain the position of a fire), should not exceed 60 m, unless addressable detection is used. The use of remote indicator lamps outside doors may reduce the number of zones required.
• When stairwells or similar structures between floors are in one fire compartment, this area should be treated as a separate fire zone.

Points which should be considered when planning zones:

• The zoning arrangements put into place should support the overall fire strategy. E.g. in a large building using phased evacuation, the zones should reflect those areas.
• Detection zone limits may be relaxed only for certain category M systems.
• If an individual discovers a fire in person, they may activate a manual call point on their route away from the fire. It can be an advantage to put manual call points in separate zones to those of the detectors to avoid misleading or confusing information regarding the position of the fire within the building.
• The wiring of detectors should be such that a fault within one detection zone does not prevent the detectors in another zone operating.

In part 148 of LWF’s series on fire engineering, we will look at the recommendations for buildings outside British Standards. 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 since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.