The LWF Blog
Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 278
March 16, 2026 10:02 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 277, LWF began to look at foam system discharge devices and discussed foam chambers for fixed roof oil storage tanks. In part 278, we continue exploring foam system discharge devices, with Rimseal Foam pourers for oil tanks with open top floating roofs.
An open-top floating roof tank has an area of significant weakness. The seal (rim seal) of the tank is a high-risk for fires, because it is the place flammable vapours can escape the product surface. Additionally, the mechanical seals can undergo wear and tear which creates gaps in the seal. These issues and outside elements such as weather mean that the seal is the most likely ignition point from lightning, static or friction.
To protect against the additional risk, foam pourers are strategically placed around the top of the tank, foam is then discharged into the seal area. In most cases, a foam dam is fixed onto the tank roof to contain the foam in the seal area.
The foam pourers are evenly distributed around the tank shell to provide complete coverage of the circumference and can reach any point of ignition around the rim. The foam is distributed in a uniform manner, flowing gently onto the seal area without disruption to the floating roof. The provision of multiple pourers means the application of foam is even and controlled and shortens the foam travel distance to the point of ignition and therefore, also lessen the time to extinguishing. Multiple pourers means that if one pourer fails, protection will still be provided, although of course, this is not ideal and any issues with a pourer should be dealt with as a priority.
With a standard foam pourer system as described, it is only possible to apply foam over any secondary or water shield in the rim seal area (foam flows down). Catenary and coflexip systems are available which make it possible to inject foam into the space underneath (foam goes directly inside the seal space), but these are less commonly-seen and are more complex to maintain.
In part 279 of LWF’s series on fire engineering we will talk about subsurface foam units 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.