The LWF Blog
Fire Safety Engineering for Design – Foam Fire Suppression Systems – Part 270
January 19, 2026 11:17 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 269, LWF looked at the composition and capabilities of film-forming fluoroprotein foams. In part 270, we discuss alcohol-resistant foam in more detail, as well as covering Class A foam.
Alcohol-resistant foams contain special polymeric additives, designed to remain in the foam until it comes into contact with water-soluble fuel. The fuel extracts water from the foam bubbles and, at this point, a tough polymeric membrane is formed on the surface of the fuel, which helps to preserve and protect the foam blanket over the membrane and fuel and more quickly extinguish the fire.
This process will not work on a standard hydrocarbon liquid, instead the foam will react as a conventional AFFF or FFFP, but with added stability and burnback resistance provide by the polymer additives. In this way, multi-purpose foams can be an effective firefighting agent to suppress fires involving both types of flammable liquid.
In the past, multi-purpose foams worked as a 3% mix for hydrocarbons and 6% for polar solvents, meaning while they could be used on both types of fire, the required concentrations differed. More recently, multi-purpose foams are available that provide 3% mix for both types of fuel.
A point of note for multi-purpose foam use is the viscosity of the concentrate. Multi-purpose foams have a tendency to be more viscous than other types of concentrate and may require different proportioner characteristics, especially in systems where concentrate pumps are to be used. This detail can have a significant impact on system design.
Class A Foams
A Class A foam works primarily as a wetting agent. It is designed to reduce the surface tension of the water, allowing greater penetration and effectiveness on fires fuelled by ordinary combustibles. Class A Foams may also be aspirated to allow their use as a surface fire barrier.
In part 271 of LWF’s series on fire engineering we will discuss fluorine-free foams and C6 foams. 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.