The LWF Blog
Fire Engineering Design and Risk Assessment – Fire Suppression – Foam Systems – Part 1May 2, 2018 1:45 pm
In LWF’s Fire Engineering blogs for Architects and others involved in building design, we have been looking at fire suppression systems, most recently sprinkler systems for both industrial and residential purposes. In part 1 of this series, LWF discusses the design criteria for foam systems.
Most commonly, foam systems are used to protect areas where flammable liquids and surface fire hazards are a risk factor. The type of foam used varies according to several criteria – the type of system, water supply pressure and if the water source is shared between several hazard areas or not.
Reference documents which are relevant to foam systems include:
BS 5306-3:2017 – Fire extinguishing installations and equipment on premises. Commissioning and maintenance of portable fire extinguishers. Code of practice.
BS EN 1568-3:2008 – Fire extinguishing media. Foam concentrates. Specification for low expansion foam concentrates for surface application to water-immiscible liquids.
BS EN 13565-2:2009 – Fixed firefighting systems. Foam systems. Design, construction and maintenance
NFPA 11 – Standard for Low, Medium and High-Expansion Foam
NFPA 16 – Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems
The foam concentrate most appropriate for a particular fire risk is mixed with an appropriate ratio of water which produces a ‘foam solution’. The solution is charged with air to form a bubbly mixture designed to flow onto the surface of a flammable liquid.
The charged solution is then able to extinguish a fire by smothering the flames. The foam mixture prevents air mixing with the flammable vapour emitted by the flammable liquid.
The coating of foam mixture also suppresses the release of flammable vapours from the fuel surface and provides a barrier between the flames and heat and the fuel surface. It cools the fuel surface and therefore the sources of fire ignition.
Foams must be able to flow freely, form a tough and consistent blanket over the flammable liquid, resist heat and fuel pick-up and retain water within the mixture in order to be effective in a fire.
While foam solutions are ideally suited to flammable liquid and surface fires, they can also be used for class A (ordinary combustible) fires where appropriate. However, they are not generally suitable for use where there are live electrical hazards or three-dimensional running fuel fires.
In part 2 of this series looking at Foam Systems, LWF will look at the types of foam concentrate which may be used. 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.