The LWF Blog

Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 277

March 9, 2026 10:14 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 276, LWF continued the exploration of types of foam system available by talking about medium and high-expansion foam systems. In part 277, we begin to look at foam system discharge devices, starting with foam chambers for fixed roof oil storage tanks.

 

Foam chambers for fixed roof oil storage tanks

Fixed foam pourers are commonly seen in use as the fire protection method for cone roof storage tanks containing flammable or combustible liquids. They are designed to deliver the foam mixture in a controlled manner. The aspirated foam produced is designed to suppress flammable vapours rising from the fuel, extinguish fire on the surface of the fuel and help to prevent re-ignition.

There are three main components to a typical foam pourer:

Foam Generator – mixes the foam concentrate with water and air to create aspirated foam at the intended expansion ratio

Vapour seal box – prevents hydrocarbon vapours from escaping through the foam line during normal tank operation. It is designed to protect the foam system components from damaging exposure to flammable vapours and reduce the potential for ignition within the piping system. The seal will open automatically when the foam is discharged.

Discharge device/Pourer – directs the finished foam into the tank. It’s designed so the aspirated foam flows down the internal surface of the tank wall and is not deposited directly onto the liquid fire. This method minimises agitation of the fuel surface and avoids splashing.

Foam pourers are designed for installation immediately below the weak seam joining the roof to the tank shell. The weak seam is designed to fail in the event of an explosion inside the tank, which would allow the roof of the tank to lift. This failsafe would relieve pressure without blowing the shell sides and the contents being spread. As the pourers are positioned just below the seam, structural protection is maintained.

Once activated, the aspirated foam flows into the tank and spreads across the liquid surface forming a blanket to suppress vapours, cool the fuel surface and isolate the fuel from oxygen.

 

In part 278 of LWF’s series on fire engineering we will continue looking at foam system discharge devices with Rimseal foam pourers for oil tanks with open top floating roofs. 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.