The LWF Blog

Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 283

April 20, 2026 8:55 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 282, LWF discussed branch pipes and monitors (foam cannons). In part 283, we will talk about foam inlet (semi-fixed) systems.

A foam inlet system is referred to as semi-fixed because it has been partly installed into the building in question. It relies on the Fire Service bringing the relevant equipment to become functional and able to fight fires.

The initial installation will comprise the permanently installed items such as pipes, outlets and connections. The Fire Service using the system will bring foam concentrate and the pumps to enable the system to operate. Foam inlet systems are designed to fight fires involving flammable liquids, such as fuel, oil, petrol or chemicals.

The installed part of the system comprises an external inlet connection which is placed outside the building. The firefighters connect their hose at this point.

The dry pipework is installed inside the building and is referred to as ‘dry’ because it is empty, instead of charged with water or foam. The pipes are the route from the external inlet to the hazardous areas.

Foam discharge devices are installed inside the risk area and could be foam makers, branch pipes or discharge nozzles, designed to spread foam over the fire. The resulting foam blanket smothers the fire, cutting off oxygen supply as well as suppressing flammable vapours. This helps prevent re-ignition of the fire.

One of the advantages of such systems is that firefighters do not have to enter the dangerous environment of the fire. It might be a basement utilised as a fuel storage room and such spaces can be extremely hazardous, even to firefighters trained to deal with extreme situations. The deployment of foam through the system is much faster than firefighters running hoses into the building, allowing the fire to be suppressed before it is allowed to grow and spread too much.

A semi-fixed foam inlet system can be less costly to install, but relies on the prompt attendance of the Fire Service to be effective. A fully fixed system would cost more to install but can be fully automatic. Each risk should be assessed and the most appropriate tools/system for mitigation should be applied for effective fire protection in any environment.

In part 284 of LWF’s series on fire engineering we will talk about medium-expansion foam generators. 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.