What NFPA and FPRF advise on the move to fluorine-free foam

BriefingFoam transitionGlobal

Recent NFPA and FPRF advisories treat the move away from PFAS foams as an engineering exercise covering the whole system. Four areas are often overlooked: system integrity, concentrate procurement, hydraulics and storage.

Updated October 2026 with references. First published October 2024.

In recent months, NFPA and its research arm, the Fire Protection Research Foundation (FPRF), have published technical advisories on replacing PFAS-based firefighting foams with synthetic fluorine-free foam (SFFF).

PFAS (per- and polyfluoroalkyl substances) are the fluorinated compounds that give aqueous film-forming foam (AFFF) its performance, and they are being phased out. The advisories set out the steps needed for a compliant transition and point to areas the industry often overlooks.

The stakes lie in the gap between a foam that passes its fire test and a system that works. When a system is converted without being re-engineered, the common failures include incompatible hardware, foam pumps that do not work, proportioners that do not proportion correctly, and foam that is incompatible with the fuel it protects.

System integrity before any change of foam

NFPA has introduced a framework of 10 elements derived from fire and explosion hazard management processes. It aligns closely with the approach Archer takes: a full assessment of foam concentrate and system compatibility before any transition, covering the whole system and not the concentrate alone.

NFPA and most fire safety authorities call for a detailed review of system design. As one firefighter put it, SFFF is “not AFFF”. Marketing around new SFFF products is aggressive, and through disinformation or a lack of training they are often presented as drop-in replacements. They are not, and the failures listed above are what follow when a system is treated as if they were.

Procuring the foam concentrate

Selecting a concentrate involves more than meeting fire test specifications such as LASTFIRE, UL and EN standards. Material compatibility, shelf life and batch testing before acceptance all need to be assessed, because each bears directly on how the system performs.

The NFPA guidance also notes that, depending on the model or brand of concentrate, more than one application pass of foam onto the hazard may be required. Its overall position is that specific tests are recommended for each application type to confirm foam performance.

Hydraulic analysis for foam solution piping

NFPA 11, the standard for low-, medium- and high-expansion foam, specifies the Hazen-Williams formula for computing friction loss in foam solution piping.¹ The formula is empirical and was derived for water, so it may not represent the flow characteristics of fluorine-free foam solution, which is the fluid downstream of the proportioner.

A 2023 study by David Meyer and colleagues at Charles Darwin University measured the rheology of six foam solutions: five fluorine-free and one alcohol-resistant AFFF (AR-AFFF). For a DN 100 pipe at 5 °C and the usual design velocities of 1 to 3 m/s, the gap between the Hazen-Williams result and the models based on the measured properties was about 5% for the AR-AFFF solution and about 60% for one fluorine-free solution, with the others within 20%. The authors conclude that Hazen-Williams should not be used for fluorine-free solutions with high polysaccharide content. Their worked example shows what is at stake: with 1,000 kPa at the inlet and an actual pressure drop 20% above the Hazen-Williams figure, the nozzle sees 160 kPa instead of 300 kPa and the flow rate falls by 27%.²

This matters most for systems with centralised proportioning, where most of the piping carries foam solution. Pump sizing and system performance need to be checked on a revised basis.

Storage in hot, humid climates

A lesser-known point is that some commercially available SFFF blends are highly hygroscopic: they absorb moisture from the air. As they do, the concentrate becomes more gel-like, approaching a sludge, and that can affect both proportioning and firefighting performance.

Some SFFF blends absorb moisture, and in tropical climates most foam tanks sit outdoors.

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In the tropical climates of this region, humidity is high and most foam tanks are installed outdoors, so storage conditions have to be assessed and then maintained.

Taken together, the advisories ask owners to treat foam transition as a re-engineering of the system, with compatibility, hydraulics and storage assessed and tested for each application. The full update is in Archer’s October 2024 newsletter (PDF).