The LWF Blog

Fire Engineering Design and Risk Assessment – Compartmentation & Fire Severity – Part 11

October 25, 2018 12:57 pm

In LWF’s fire engineering blog series for Architects and others in the building design business, we have been looking at the uses of compartmentation in buildings. In part 10, the concept of the use of equivalent fire-resistance rather than prescriptive guidance was discussed. In part 11, we continue from that point we continue looking at equivalence as a means of determining the fire-resistance standard required for a building.


While using an equivalent fire resistance concept may sound like a completely different way of working to the prescriptive guidance, it is still based on traditionally recognised fire-resistance tests with the addition of calculating the potential fire severity in a building.


The analysis must be undertaken along with a sensitivity study as extreme conditions may not produce the most severe fire conditions in a building; the most severe conditions may develop from a fire in a compartment of a limited area and ventilation conditions rather than a fire in a larger or more open-plan area.


A determination was made regarding equivalent fire-resistance for a high-rise office building in the Building Regulations. It stated that:


 The fire load should be based on the 80% fractile and not the 50% fracile as used in the Eurocode and its associated National Application Document.


 The importance of the conversion factor (k) in the analysis and the need to consider how the linings may change as a result of fitting-out of the building or other changes to the building during its lifetime.


The flexibility of using equivalent fire resistance means that it offers an advantage to architects and others in the building design team in that it can be used to reflect the individual requirements of each building. It can also prove more cost-effective as it provides the fire-resistance that is needed, rather than being unnecessarily onerous where it is not necessary.


Although the advantages are considerable, there are also disadvantages which should be taken into account. Unless the design team is careful, the use of equivalent fire-resistance can mean future use of the building is restricted, as the fire-resistance requirements will have been assessed against a very particular set of circumstances. The resulting complexity of use can limit the uses to which the building or parts thereof can be put should the occupancy change. The design of the building may become more critical in a way it would not with a more standard conservative approach.


In part 12 of this series, LWF will look at how BS 9999 addresses equivalent fire resistance, before this blog series moves on to discuss firefighting. 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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