Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants


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Lawrence Webster Forrest
Legion House
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Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583

Fire Engineering Design and Risk Assessment - Compartmentation & Life Safety - Part 5

Posted by LWF: 13/09/2018 13:10

In LWF’s Fire Engineering blog series for Architects and others working in the building design business, we have been discussing compartmentation. In part 4 of this series, the ways in which compartmentation supports life safety functions in a fire situation were summarised. In part 5, we look at the ways the issue of compartmentation and life safety is covered in the national building regulations, before looking at the spread of fire. 

Approved Document B, the guidance which supports Part B of the Building Regulations in England and Wales, recommends the use of fire-resisting compartmentation throughout multi-storey buildings to maintain the structure of the building in a fire situation and for the provision of protected escape routes.

The regulation also allows designs to incorporate large open-plan areas where necessary, provided that maximum escape distances are not exceeded. Such designs, while taking into account life safety requirements, would leave those open-plan areas more open to fire and smoke damage.

Similarly, NFPA 101 Life Safety Code ( offers a range of requirements relating to the protection of escape routes with fire-resisting construction.

Fire Spread

During a fire’s early stages, its rate of growth is determined by the immediate surroundings of the area of fire origin. A fire needs fuel and therefore the contents of a space and the nature of any exposed surfaces are important when determining the likely size of a fire or, indeed, how to limit growth of a fire. 
The exposed surfaces are controlled by restricting the combustibility and flame spread characteristics, along with heat release characteristics. 

The British Standard Fire Tests Parts 4, 6, 7 and 11 (BS 476)  contain the results of laboratory tests relating to flame spread and heat release characteristics, although the results have been subject to criticism relating to the use of empirical evidence rather than scientific. The testing of materials in laboratory conditions has often come under criticism as each country tests in a different way with varying classifications. This is an area in which specific advice should be sought, particularly when adopting new materials.

The way, speed and direction that a flame spreads over a given surface is a function of the nature of the surface and the transfer of heat from the flame to the surface ahead of the flame. Where flame travels vertically upwards, this is due to convection and, to a lesser extent, radiation from the flame. Flames spreading upwards can do so quickly due to the close contact between the flame and the surface. 

Horizontal flame will spread more slowly. Flames spread sideways due to convective heat transfer from the edge of the flame and, less so, by conduction through the solid surface material.

In part 6 of this series, LWF will continue to look at how fire spreads before moving on to consider Firefighting in the context of compartmentation and life safety. 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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