The LWF Blog
Fire Engineering Design and Risk Assessment – Fire Alarm Systems – Zoning – Part 10August 4, 2016 2:39 pm
As a part of this Fire Engineering Design and Risk Assessment blog series for architects and building planners, we’ve been looking recently at Fire Alarm Systems. In Part 9, we looked at systems suitable for residential buildings and today we move on to look at the particulars of Zoning as a part of active fire protection.
Zones are effectively a method of reducing the building into a series of smaller compartments, for example, a 3-storey building may be divided into 3 zones – ground, first and second which would become zones 1,2 and 3 respectively.
A fire in zone 1 would indicate a fire on the ground floor. Larger floors may also be sub-divided further. The division of a protected area into zones is useful in that it can assist the system controller in pinpointing the location of a fire within a building.
Consideration should be given to the areas to be covered by a zone under the various headings – accessibility of the area, size, fire management strategy and access from the main circulation routes leading to the control panel itself.
While zoning is still required, an Addressable system is able to give more accurate information about the location of a fire source than a simply zoned system. We will talk more about that in the next blog.
BS 5839 gives guidelines for determining the size of a zone, as follows:
– If the total floor area of the building is not greater than 300m2 (and that includes the sum of all floors of the building), then the building may be considered a single zone, even if it comprises multiple storeys.
– The total floor area of any zone must not exceed 2000m2
– The distance which must be searched within a zone to visually confirm the position of a fire should not exceed 60m. Remote indicator lamps placed outside doors may reduce the number of zones required.
– Where there are stairways or other structures which extend beyond the floor of origin, but are contained within one fire compartment, it should be treated as a separate fire zone.
– Where a zone covers more than one area of fire compartment, the zone boundaries should follow compartment boundaries.
– In cases where the building has several occupancies, a zone cannot encompass areas inside two occupancies, but should split at the point of boundary.
When planning the placement of zones, the following items should be taken into consideration too:
– A fire compartment is an area enclosed in fire resisting construction of at least 30 minutes fire resistance duration.
– Zone limits can be relaxed only for certain M-type systems
– Upon finding a fire, a person escaping it may use a break-glass point on the escape route that is not near to the original point at which the fire is located. Because this can lead to misleading information about where the fire is located, it might be advantageous to place manual call points on separate zones to those of the detectors.
– As stated in BS 5839:1, detectors should be wired in such a way that a fault in one detection zone does not interfere with the operation of detectors in another zone.
In next week’s blog, we will look at zoning with addressable and analogue addressable systems. 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.