Developing SFFF foams: Beyond the limits of standard testing
Iain Hoey
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Jan-Erik Jönsson, Chief Chemist at Dafo Fomtec, discusses the complexities of developing SFFF foams and the importance of real-world testing
The development of new, high-performance SFFF foam concentrates has challenged many long-standing assumptions in the industry.
In the past, fuels were categorised into different groups, and application densities were determined accordingly.
Simply passing a fire test and securing approval was often considered sufficient for most applications, regardless of how closely the test conditions mirrored real-world scenarios.
During the transition to SFFF products, the need for foam testing is growing.
For better results, testing should be performed with the traditional test standards as well as in the actual conditions where the SFFF products will be used.
At Fomtec, we developed testing methods to help us predict and assess what kind of foam to use and what application density is necessary.
This progress has been made possible thanks to our extensive fire testing program that we started several years ago.
During these tests, we have encountered issues that were not considered in the past but are now important to address for SFFF products.
In this article, we discuss some of the key challenges we have identified that require special consideration.
The challenges of fuel compatibility for SFFF foams
Thanks to simpler formulations and fluoro-surfactants, the versatility of foam types like AFFF and AFFF-AR made them less sensitive to different fuels and application equipment.
However, with the transition to SFFF foams, it’s a different scenario.
Developing formulations that can pass fire tests with common polar solvents, like acetone and IPA, has been a struggle.
Without fluoro-polymers, the gel formation in SFFF alone is insufficient to achieve high performance.
A particularly difficult issue arose when testing foam stability on other polar solvents that inhibit gel formation, such as MEK, 1-butanol, 2-butanol, and short-chain acetates.
Initially, we assumed these would be easier to manage than IPA and acetone, especially since MEK had been straightforward in AFFF-AR fire testing.
Surprisingly, the foam disintegrated rapidly when applied to MEK at room temperature, and even faster on warm MEK.
Adding more foam temporarily extended its stability, but not for long.
Analysing the data on polar solvents revealed that a significant number of chemicals resist the necessary gel formation.
The challenge was determining how many of these acted as “foam killers” versus those that were benign.
Given the vast number of solvents—many of which are toxic and impractical for extensive fire testing—we needed a predictive method for foam stability.
This led to a comprehensive test program, where over sixty different solvents, selected based on their chemical nature and water solubility, were evaluated in the lab for foam stability.
Some of these solvents were also tested in full-scale fire scenarios to ensure consistency between lab results and real-world performance.
Moreover, for hydrocarbon fuels, the test fuel is frequently heptane.
This fuel has quite a high flash point and low vapour pressure.
In real-life applications, volatile fuels with higher vapour pressures and much lower flash points, like gasoline (with a flash point below -40°C), are common.
Conversely, longer-chained hydrocarbons like diesel or Jet A1, while having higher flash points (well over 30°C), burn extremely hot in fully developed fires.
As we move forward with SFFF products, it is necessary to understand how they respond to different situations.
This is the reason why we do tests to give our clients recommendations based on test results and not opinions.
Foam stability and degradation in polar solvents
The challenges we faced with partially water-soluble polar solvents led to the initiation of a project aimed at developing a straightforward yet representative test method.
This method could be distributed to clients for testing at their own facilities, allowing their findings to be evaluated and compared against our extensive database.
Over the years, this dataset has expanded significantly, encompassing numerous lab tests across a wide variety of solvents, with the corresponding fire test data points continuously being added.
By analysing all the collected data, we have developed a predictive model that can detect foam destroying properties of a huge number of solvents.
This model, approved with statistical methods, turned out highly reliable.
It leverages existing literature on the chemical and physical properties of both the solvent and the foam solution to predict potential foam instability.
With this model, we can anticipate foam stability issues without additional lab tests.
We can then use these predictions to recommend appropriate application equipment and densities.
Full-scale testing
Full-scale fire testing following standard methods provides valuable cost-effective data.
These tests are typically performed on small ~4.5 m² (50 ft²) fires; these are not a good representation of most real-life fire scenarios.
The size of the fire influences its performance.
Small-scale fire tests, such as those described in EN 1568-3, do not always correlate with full-scale fire performance, as smaller fires are easier to control, even with lower test densities.
Recognising this, we felt compelled to conduct large-scale fire tests, up to 300 m², using various fuels, equipment, and application densities to gather more accurate data.
These tests included fuels like gasoline, diesel, Jet A1, ethanol, and ethyl acetate, with foam applied through fixed monitors, handheld nozzles, and different sprinkler heads.
Height-based testing
Another critical issue often overlooked in standard tests is the height at which foaming devices are installed, particularly in tall buildings.
For example, a hangar for big airliners is often higher than 40 meters with foam sprinklers attached to the ceiling.
Standard tests performed at around 4 meters do not truly reflect a scenario like this one.
To respond to this challenge, we conduct fire tests at heights of up to 15 meters (45 ft) and plan to go higher up to 35 meters with appropriate fuels and sprinkler heads.
Sprinkler heads present another challenge.
Some test standards allow a single sprinkler head with a specific K-factor to pass, thereby approving all sprinklers with the same K-factor.
However, this approach does not account for the nuances of different sprinkler designs.
Our tests have shown that even minor design changes, such as to the deflector, can significantly impact fire performance.
Height is also a factor in high-expansion foam applications, where foam generators are typically installed high in a building.
Standard tests often require the foam to build up to about one meter in height, using a fan-driven generator that produces foam with an expansion ratio far exceeding what is typically achieved with passive generators.
Many foams can pass these tests, but when tested with standard generators, they fail to build beyond one meter before collapsing.
Fortunately, some standards address this issue by requiring the foam to build height and extinguish fires within a compartment.
We have conducted tests demonstrating that HiEx foams can build over 40 meters without collapsing, giving us the confidence to recommend them for even the tallest hangars.
Hidden gum
There is a strong focus on developing SFFF formulations with high fire ratings as replacements for AFFF.
One method to achieve higher ratings is by incorporating polysaccharides or similar gums into the foam formulation.
These substances improve the foam’s quality by extending its drainage time, keeping the foam blanket moist and effective during fire tests.
However, a less obvious approach involves loading the foam concentrate with a significant amount of gum, which indeed boosts fire ratings.
The downside is that a high gum content increases viscosity, which is generally undesirable.
Fortunately, by carefully selecting and balancing the ingredients in the formulation, it’s possible to maintain a viscosity well below 3,000 mPas.
This works because the limited water content prevents the polysaccharide polymer from fully hydrating and expanding to its full viscosity potential.
Instead, the polysaccharide remains in a semi-dispersed, metastable state.
Ideally, this state remains stable for extended periods, but it can rapidly destabilise under certain conditions.
For instance, at higher temperatures, the solubility of the liquid changes, causing the polysaccharide to stretch out in an environment with insufficient water, leading to phase separation or stratification in the foam concentrate.
Once this two-phase liquid forms, it’s typically irreversible.
Even if the concentrate appears stable at higher temperatures, another issue may arise.
When small amounts of water are added, instead of decreasing, the viscosity can dramatically increase.
This happens because the additional water allows the polysaccharide polymer to further expand, raising the viscosity.
It may require over 20% water addition before any viscosity reduction occurs.
This phenomenon, which we refer to as “Hidden Gum,” can lead to significant problems.
If the concentrate encounters water in storage tanks or piping systems, it can form a gel plug, obstructing the system’s proper operation.
Rhe dangers of making assumptions
We’ve realized that when switching to SFFFs (Synthetic Fluorine-Free Foams), we need data that reflects real-world situations, not just what was once common knowledge.
SFFFs aren’t as versatile as AFFF and AFFF-AR, so it’s risky to make recommendations based on opinions rather than facts.
For example, in the past, getting approval for one fuel in a group often meant that other fuels in that group were also approved.
This worked for AFFF and AFFF-AR, but it doesn’t apply to SFFFs.
Take acetone, for instance—a type of ketone.
While it’s possible to get approval for acetone, this doesn’t mean that a similar chemical like methyl ethyl ketone (MEK) will automatically be approved under the same conditions.
Our tests show that putting out a MEK fire needs much more foam, depending on how it’s applied.
Another example involves sprinkler systems.
It used to be assumed that if one sprinkler with a certain K-factor was approved, others with the same K-factor would work just as well.
But for SFFFs to be effective in sprinkler systems, the sprinkler head needs to produce the right kind of foam to pass the test.
We’ve confirmed this through many tests over the past eight years.
We’ll keep running tests beyond the usual standards to gather more accurate data, so we can give our clients advice based on facts, not just opinions.
About the Author
Jan-Erik Jönsson has been the Chief Chemist at Dafo Fomtec since 2009.
He holds a Ph.D.
in Polymer Technology from the University of Lund, where his research focused on emulsion polymerisation.
This expertise served him well during his tenure at Hoechst Perstorp AB (now Celanese Emulsions), where he led the R&D department, specialising in the development of water-based binders for paints, paper coatings, and environmentally friendly adhesives, such as solvent-free paints.
Jan-Erik’s journey into foam technology began in the summer of 2009 after meeting John-Olav Ottesen, the founder of Dafo Fomtec AB.
Captivated by the potential of foam, he was appointed Chief Chemist later that year.
Since then, he has led the development of Fomtec’s products, with a strong emphasis on fluorine-free solutions from the very beginning.
