Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
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Fire Engineering Design and Risk Assessment - Types of Foam System - Part 5

Posted by LWF: 30/05/2018 12:03

In LWF’s Fire Engineering blog series for architects and others in the building design business, we have been looking at Fire Suppression systems. In part 4, the different methods of foam proportioning were outlined and in part 5, we will discuss types of foam system.

Low expansion foam is a solution which is aspirated in ratios between 1:1 and 20:1. The ratio indicates the volume of foam required in comparison to the foam solution produced, once aspirated. So, a solution with a ratio of 10:1 indicates that 1m3 of 'raw' foam would produce 10m3 of finished foam solution.

It is used for the protection of flammable liquid storage tanks in cone and floating roof situations, bays for the loading and off-loading of tankers, areas for aircraft landing and servicing, spaces where oil-fuelled machinery is operated and process areas. They can also be used to protect bunds and dikes, which are a brick-built form of secondary containment around storage areas of flammable liquids.

The foam and water mixture is aspirated by a compressed air foam system before it is discharged via the nozzles.

Medium expansion foams are those solutions which are aspirated in ratios between 20:1 and 200:1, although it is most common to utilise a mixture of around 50:1. While a medium expansion foam system can be used to protect dike and bunds, as above, they can also be used for manual firefighting for flammable liquid spills of a minor nature. 

It has proved effective at limiting the effects of flammable or toxic vapours rising from spills which helps to protect any persons in the surrounding area from the fumes and to prevent ignition of the flammable vapours.

High expansion foam is aspirated between 200:1 and 1000:1. It is commonly used for outdoor spills of liquefied natural gas at a ratio of 500:1. 

High expansion foam can be used to protect warehouses, tunnel and aircraft hangars, as well as cable voids where water damage could be an issue or water may not be available.

While high expansion foam is extremely effective, it must fill the hazard area to above the height of the highest hazard. This can cause problems with people in the area breathing, hearing or having an accurate sense of direction. Firefighters can also experience problems in finding the source of the fire. 

In part 6 of this series, LWF will look at Foam System Discharge Devices and give a brief overview of how they work. 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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