The LWF Blog

Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 288

May 25, 2026 9:10 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 287, LWF talked about the components and materials of a foam fire suppression system. In part 288, we consider the testing that should take place before a foam fire suppression system is put online.

A foam fire suppression system is designed to extinguish and suppress flammable liquid fires. The testing of such systems prior to commissioning and on a regular basis during their lifespan is essential to ensure correct operation during a real emergency.

Prior to commissioning, the system pipework, pumps, foam proportioners, discharge devices, valves and foam concentrate supplies must be tested to ensure each part functions as intended and the system will work as a whole.

Ideally, the new system should be allowed to discharge foam during testing. A real discharge test will verify the foam is generated correctly, that it reaches the protected hazard as intended and that adequate foam coverage is achieved.

When testing cone roof tank foam chambers, it may be that for testing purposes the special chambers can be rotated or diverted away from the tank and into a temporary containment area instead of into the fuel product itself. This can help avoid polluting the product contained in the tank and the resulting issue of disposal.

During a discharge test, a sample of the foam should be taken for quality testing to confirm the foam produced matches the necessary performance standards.

The expansion ratio of the foam should also be checked, comparing the volume of the finished foam to the volume of foam solution used. Correctly proportioned and expanded foam ensures blanket thickness, foam stability, intended foam flow characteristics and vapour suppression. If the expansion of the foam is too low, the foam may be too watery. When expansion is too high, the foam may be too light and unfit for purpose.

The drainage time should also be considered. Foam stability should exhibit in the region of 25% drainage time. This is the time taken for 25% of the liquid within the foam to drain out. A longer drainage time means more stable foam, better heat resistance and longer-lasting vapour suppression. If a foam drains too quickly, the foam blanket cannot retain cohesiveness, allowing fuel vapours to reignite.

In part 289 of LWF’s series on fire engineering we will continue to discuss testing of foam fire suppression systems. 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 since 1986 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.