The LWF Blog

Fire Engineering Design and Risk Assessment – Compartmentation & Fire Severity – Part 10

October 18, 2018 10:12 am

In LWF’s Fire Engineering blog series for Architects and others in the building design industry, we have been looking at the use of compartmentation to avoid the spread of fire. In part 9, the use of compartments with sprinkler systems was discussed and in part 10, we look at the potential severity of fires in enclosed spaces.


The severity of a fire in an enclosed space is dependent upon factors such as heat leaving the compartment through openings in the enclosing walls and floors, fire load and ventilation. Test fires and calculations have been carried out which measure fire load against such factors and predict the percentage of heat dissipated through windows, openings, as fuel and by radiation.


The results showed that a small proportion of fire heat was lost through the enclosing walls and floors of a room or compartment and that the majority was lost through windows and other openings in the enclosure. The predictions also allowed for the creation of temperature-time curves for differing ventilation conditions and fire loads which can be used to assess the standard necessary for enclosing walls and floors. However, it can be challenging to relate existing information on wall and floor constructions under standard test conditions to real life examples.


Equivalent fire resistance differs from that approach as it relates to the empirical relationship between the likely fire severity in a space and the exposure conditions in a standard fire resistance test. It is often a more practical way of determining the necessary fire resistance of the elements of compartmentation.


CIB Report W14 ‘A conceptual approach towards a probability based design guide on structural fire safety’ Fire Safety 6  1-79 (1983) (PDF) was the first to codify the concept, with BS EN 1991-1-2: 2002: Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire (London: British Standards Institution) (2002) producing a similar method a short time after.


Equivalent fire resistance is increasingly used to provide a means of identifying the fire-resistance standard necessary for buildings rather than prescriptive recommendations from guides such as Approved Document B ( in the UK. This is applicable to compartments and structural fire protection.


In part 11 of this series, LWF will continue looking at the equivalent fire-resistance concept and its use in determining fire-resistance levels in buildings. 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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