The LWF Blog
Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 281
April 6, 2026 9:01 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 280, LWF discussed foam water sprinklers. In part 281, we will talk about water sprinklers and sprayers.
Conventional sprinkler and water spray systems are fire protection systems that usually discharge water. They are capable, however, of delivering certain types of firefighting foam, such as fluororsurfactant-based foams, which are effective even when they are not heavily aspirated.
They key foams that a sprinkler system may be able to use are:
AFFF – Aqueous film-forming foam
AR-AFFF – Alcohol-resistant AFFF
FFFP – Film-forming fluororoprotein foam
The lack of aspiration (aeration) provided by a standard conventional water sprinkler system means that the foam output will not be a highly-aspirated foam, such as you would see from most foam fire suppression systems. Conventional sprinklers do not aspirate much air as they are designed to spray liquid. Only foams that do not rely on air-mixing to work are suitable for use with a water sprinkler system.
The main reason that some foams will still be effective when used unaspirated is that they are capable of forming a thin aqueous film on the surface of the fuel. The film spreads quickly across the flammable liquid, cutting off oxygen, suppressing flammable vapours and helping to extinguish the fire.
AFFF works well with non-aspirating sprinkler systems and as it forms a fast-spreading film over hydrocarbons such as petrol or diesel. It is most commonly used in aircraft hangars and fuel storage areas.
AR-AFFF is designed to protect against alcohols and acetone fire hazards. It forms a protective polymer layer.
FFFP combines protein foam, which has good stability, with fluorochemical film-forming ability. It’s less than ideal without aspiration, but can still work with some sprinkler systems, especially if foam nozzles are installed.
The fact that some foams may be used with a sprinkler system designed for water allows some systems to be retrofitted to provide foam fire suppression without having to replace the entire system. The simpler sprinkler system design often means faster deployment in a fire situation and offers a level of protection in large hazard areas. However, the limitations should also be taken into account in that there will not be the level of foam expansion typically seen in a foam fire suppression system, it does limit the choice of foam type and there may be environmental concerns with some fluorinated foams.
Fluorosurfactant foams (including AFFF, AR-AFFF and many FFFP products) are being phased down or restricted in the UK and EU due to PFAS environmental concerns. Alternatives are available but the majority of fluorine-free foams require aspiration to be effective. Specialist advice should be sought in relation to specific foams.
In part 282 of LWF’s series on fire engineering we will talk about foam branch pipes and monitors (foam cannons). 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.