The LWF Blog

Fire Engineering Design and Risk Assessment – Sprinkler Installation Design – Part 31

February 2, 2018 11:03 am

In LWF’s Fire Engineering and Risk Assessment blog series for Architects and others in the building design business, we have been looking at how sprinkler design should be approached. In Part 30, we looked at how the situation and design of the building impacts upon both sprinkler design and water run-off. In Part 31, the importance of the placement, spacing and location of sprinklers is discussed.


Sprinkler spacing and location within a building is particularly important. It can make the difference between the same system performing sub-optimally, adequately or to its fullest effect. The speed of sprinkler response to a fire and the effectiveness of the reaction are both dependent upon the location of the sprinkler heads and can make a substantial difference to the outcome should a fire start.


While the basis of sprinkler placement design is simple, an understanding of fire dynamics is important. The person designing the system will use the maximum values provided as a guide, but these values should not be considered target values. It is likely that some areas will require an enhanced coverage and so the spacing will be reduced to provide increased performance. Conversely, other areas may be low risk and would be covered sufficiently with a slightly increased area between sprinklers.


Relevant engineering skills and experience are essential for the person responsible for the design of the sprinkler system within a building. It is probable that the installation is part of a fire engineered strategy for fire safety and so it is highly important that the sprinkler system is able to respond as quickly and effectively as in the design documents. While it may be that so far, we have been contemplating the spacing between sprinklers, the location of sprinklers relative to the ceiling or roof above must be considered.


Codes of practice, in this example NFPA, provide maximum values for sprinkler head spacing.


Normal (non-sidewall) sprinklers:


 Light Hazard – 21m2 per sprinkler

 Ordinary Hazard – 12m2 per sprinkler

 High Hazard – 9m2 per sprinkler.


The calculation method is typically based on four adjacent sprinkler heads.

There is a fairly common approach to sprinkler spacing in most countries, with the maximum allowable distances observed as:


 Light Hazard – 4.6m

 Ordinary Hazard – 4.0m

 High Hazard – 3.7m


In summary, noting that specific guidance must be followed for the bespoke scenario, based on the above figures, the maximum spacing for sprinklers in each hazard category is:


 Light Hazard – 4.6m x 4.6m (approx.)

 Ordinary Hazard – 4m x 3m

 High Hazard – 3.7m x 2.4m (approx.)


The NFPA code also gives input on sprinkler protection of small rooms. As the heat in a small space builds up more quickly and the sprinklers will activate faster, more spacing between sprinklers can be allowed. Special sprinklers are available and should they be suitable for the purpose, can be used as per the manufacturer’s guidance.


In Part 32 of this series, LWF will continue to look at the best location of sprinklers. 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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