The LWF Blog

Fire Safety Engineering for Design – Fire Dynamics – Part 80

May 16, 2022 10:47 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 79, LWF looked at fire growth and compartment fire behaviour. In part 80, we continue to discuss the development of compartment fires.

Flashover is caused by a combination of circumstances, but a primary driver is radiation from the smoke layer. Any factors which involve a loss of heat from the smoke layer will help to reduce the potential risk of flashover. The volume and size of the compartment can be a contributory factor, if the compartment is high or wide, the smoke is less likely to reach the high temperatures necessary for flashover to occur.

Of course, the contents of the compartment which act as fuel to the fire are another very important factor and so the size and shape of the compartment is not the only consideration. A very large volume compartment, which is high or wide (or both) may still achieve flashover if it is stocked with a lot of items to act as fuel.

The four stages of development in a compartment fire are:

  • Initiation – the first stage where the fire grows slowly as flame spreads over the item ignited
  • Growth – the fire begins to grow at a faster rate and will spread to other items in the area of fire ignition
  • Fully developed steady-state or post-flashover: a state when all the combustible elements in the compartment are burning and flames appear to fill the entire space. The average temperature is at its highest
  • Decay – the average temperature of the fire has fallen and will continue to do so

Post-flashover, fire development in a compartment is limited by certain factors, namely the rate of air in-flow, availability of combustible material or by firefighting response.

Ventilation controlled fires are those which are unable to continue to burn because of lack of oxygen in the compartment post-flashover. If there are limited openings into the compartment, insufficient oxygen will be available to the fire. It may be that flames will project from the compartment openings, with combustion of heated fuel gases taking place outside, in the place where sufficient air is available.

In part 81 of LWF’s series on fire engineering, we will continue talking about fire development before discussing the calculation of fire parameters. 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 the LWF office on 0800 410 1130.

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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