The LWF Blog

Fire Engineering Design and Risk Assessment – Fire Suppression & Sprinklers – Part 8

August 17, 2017 4:03 pm

In this Fire Engineering Design and Risk Assessment blog series for Architects and others in the building design business, LWF has been looking at the various advantages of sprinklers as part of a building’s fire protection arsenal.


In Part 7, we looked at the concessions that may be made in cases where sprinklers are present. In Part 8, we discuss how an understanding of the ways sprinklers can be used as per the prescriptive guidance can give an insight into how sprinkler system installation might be used as part of a fire engineered solution.


While prescriptive guidance can be used to ascertain and reasonably predict the size of a fire, using variables such as fire load and rate of release, the use of sprinkler systems may be exploited as part of a fire engineering solution.


It is accepted that a fire will cease to grow in physical size and intensity either at the point of sprinkler activation or shortly after and so the size the fire grows to initially is dependent upon how long it takes the sprinkler to activate. While the time taken for a specific circumstance can be calculated accurately, sprinkler activation is subject to a range of variables, such as:


 The growth rate of the fire

 The temperature of the area surrounding

 The temperature rating of the sprinkler

 The RTI (response time index) of the sprinkler

 The sprinkler arrangement’s conduction factor

 The radial distance of the sprinkler from the fire

 The vertical distance of the sprinkler from the fire

 The distance between the sprinkler and the ceiling


The speed of sprinkler activation can also be affected by the type of fire risk, the type of fuel and the predicted heat release rate. The fire size is most affected by the fuel load and so this needs to be fully understood before a sprinkler system is chosen or installed. One example is that a sprinkler system that is built to control a fire of up to 8.5MW total heat output will be unlikely to be able to contain a fire of 16MW.


It is important, therefore, that the expected fire size or design size fire is ascertained to ensure the sprinkler system water release rates are appropriate. The design codes give prescriptive information on this subject or when a sprinkler is to be used as part of a fire engineered solution, the size and type of fuel load and the rate of heat release will be considered, along with the building’s construction materials, by an experienced fire engineer.


In part 9 of this series, we will continue to talk about sprinkler usage. 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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