The LWF Blog
Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 276
March 2, 2026 9:39 amLWF’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 275, LWF began to discuss the types of foam system available, starting with low-expansion systems. In part 276, we continue to discuss the types of foam system available by taking a look at medium and high-expansion foam systems.
Medium-expansion foam systems
A medium-expansion foam system has an expansion ratio of between 1:20 and 1:200, although a typical operational ratio is around 1:50. They are able to provide rapid coverage with thick foam and are suitable for flammable liquid spills and material vapour suppression. They are commonly used for dyke/bund protection and for manual firefighting on minor spills where a thick and stable foam blanket is necessary.
Although medium-expansion foam is sometimes used to suppress flammable and/or toxic vapours from spills, it isn’t 100% effective at vapour suppression. As this type of suppression is designed to protect any persons in the area and to prevent ignition of the vapours, caution is always recommended in ensuring the correct foam and system is used for the hazards presented.
High-expansion foam systems
A high-expansion foam presents a ratio of between 1:200 and 1:1000. Such high foam expansion is designed to fill an area quickly, suffocating a fire and providing rapid cooling. They are most suitable for high risk and total flooding applications. High-expansion foam systems may be used for limited vapour suppression and fire control of outdoor spills of LNG at expansions up to 1:500.
The types of spaces protected by high-expansion foam systems might include warehouses, tunnels, aircraft hangars or even cable voids – places where water damage or water availability could be an issue. Due to the low water content foam, potential damage to protected and sensitive equipment from water is significantly reduced.
High-expansion foam is designed to fill the hazard area to above the height of the highest hazard. This means that any people in the area would have issues breathing, hearing instructions or navigating the area. It can also obscure the seat of the fire when firefighters attend.
In part 277 of LWF’s series on fire engineering we will discuss foam system discharge devices, such as foam chambers for fixed roof oil storage tanks. 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.