The LWF Blog

Fire Engineering Design and Risk Assessment – Sprinkler Installation Design – Part 34

February 22, 2018 12:30 pm

In this Fire Engineering and Risk Assessment blog series for Architects and others in the building design business, LWF has been looking at the design of sprinkler systems along with installation challenges. In Part 33, the different types of pipework system used to feed a sprinkler system were outlined and in part 34, we take a look at pipe arrays which are fully hydraulically calculated.


A fully hydraulically calculated pipe array is a pipe system is one where analysis takes place to ascertain the capabilities of the system to relay water and to take into account the availability of the water supply.


The calculations which are undertaken aim to pinpoint the least effective part of the installation, hydraulically speaking. In addition, they will highlight the most effective areas of the installation in terms of supply of water and look at how that may cause an overload of demand on the water supply. In cases where water is supplied from a storage tank, an area of the system which demands and receives the maximum amount of water could limit the duration of water available in time and could be detrimental to the performance of the system overall.


The assumed maximum area of operation (AMAO) must be considered in order to ascertain the strongest and weakest points of the sprinkler system. The weakest point of the individual sprinklers in the system will be as close to rectangular as possible. The strongest will be close to square. The AMAO is calculated by considering the area covered by each sprinkler within the system, giving the design area of operation.


The minimum rate of flow is calculated by multiplying the design density, which is 1.m.-2.min-1, by the area covered by each sprinkler. Each sprinkler must be assessed operating at maximum running pressure to ascertain the correct spray characteristic, which varies according to hazard and location. These can be broken down as follows:


Light hazard – all groups – 0.7 bar


Ordinary hazard – all groups – 0.35 bar


High hazard – intermediate rack systems – 2.0 bar


High hazard – other groups – 0.5 bar


ESFR, which varies depending upon the risk and type of sprinkler.

It should also be borne in mind that some calculations may be undertaken on sprinklers which are below obstructions, such as ducts. In the case of intermediate rack systems, the calculations must include both roof and rack systems operating at the same time, as they would be in a fire situation. This applies even when the roof and rack system are not in the same part of the area, as the racks may be moved in the future.


In part 35 of this series, LWF will continue to look at the calculations for fully hydraulically calculated pipe arrays. 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.


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.




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