The LWF Blog

Fire Engineering Design and Risk Assessment – Sprinkler Heads – Part 22

November 23, 2017 1:08 pm

In LWF’s Fire Engineering blogs for Architects and those who work in the building design business, we have been recently discussing sprinkler systems and in particular, sprinkler heads. In part 21, an overview of different types of sprinklers which are used to address particular fire safety concerns was given. In part 22, we will look at thermal sensitivity of sprinkler heads and how this affects their reaction time.


The time taken for a sprinkler head to react to a fire situation is dependent upon the heat-sensitive element reacting to a change in temperature, but there are other factors which will influence the result, such as the size and type of the fusible bulb or link, the materials used to make the sprinkler body and its size and shape and also, the way the sprinkler is fitted.


The reaction speed can be measured and compared during the approvals process and the results compared with alternatives. The reaction speed is measured using the Response Time Index (RTI), which is a grade of sprinkler thermal sensitivity.


Sprinklers will fall into one of three response classes, as follows:


Standard Response A – indicates an RTI value of 80 – 200


Special Response – for RTI values between 50 and 80


Quick Response – relates to RTI values of 50 or less


The fire engineering consultant may carry out various calculations in order to assess the sprinkler reaction time, although recessed, concealed and horizontal sidewall sprinklers are not classified and will be referred to as unrated. In order to carry out a successful RTI assessment and ensure the sprinklers are suitable as a part of a fire engineered solution, more information may be needed from the manufacturers of the sprinkler in order to ascertain the RTI of a sprinkler head.


A quick response sprinkler system is advantageous to a fire engineered system in more ways than are immediately obvious. The system will respond earlier than a standard system and so when a fire is in the earlier stages of development and the fire size is less. Because the fire size is not as large, it will not require as much water to extinguish it through the sprinkler system and so will place less demand on both the water supply and hydraulic demand on the system. Any smoke management system in use will be under less demand too.


The combination of these factors means that when a quick response sprinkler system is in use, the building will not sustain as much damage as it might have done were a standard response sprinkler used and less damage overall means reduced costs and impact.


In part 22, LWF will give an overview of the different types of sprinkler system installation. 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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