Brent Gaspard, Product and Marketing Manager at Williams Fire & Hazard Control, explains flammable liquid firefighting without film-forming foams in simple terms.
Amongst industrial firefighting community, much has been studied, written and debated about Class B firefighting foams, the retirement of PFAS oriented Aqueous Film-Forming Foams (AFFF) foam formulations and our transition to synthetic fluorine free foams (SFFF/NFFF).
In the realm of flammable liquids firefighting, effective Class B foams are a responder’s greatest weapon. We go to extreme lengths – and expense – to store, proportion and effectively deliver foam to the fuel surface in hopes of suppressing flammable vapors and ultimately gaining control of an incident.
My emphasis is simple: to alert first responders to the false sense of security we have adopted through the unique and exemplary performance of film-forming AFFF foams. I would also like to emphasize the responder’s role as “active firefighters” on scene. A key takeaway here is an operational imperative to “actively” defend and maintain the foam blanket in flammable liquids response. Breaks in the blanket can cause responders to lose ground in the fight and may threaten their safety, especially when working in spill scenarios.
In simple terms, SFFF response operations require continued vigilance in foam application and blanket maintenance.
Evolution of firefighting foams has essentially seen two primary eras: “mechanical” and “chemically enhanced mechanical” foam formulations. We know the application of a finished foam solution in Class B firefighting efforts is meant to suppress vapor yield of a flammable liquid to intermediate the flammable range at the fuel surface. Throughout history foam applications have been founded in the form of a mechanical foam blanket applied across and atop the fuel surface. However, for approximately the last 60 years, AFFF foam formulations gave us fluorinated surfactants – chemical enhancements – that produced an aqueous oleophobic film that effectively sealed the fuel surface.
For foams, the magic was in the name. AFFF foam formulations used fluorine-based surfactants that produced an oil-resistant (oleophobic) film with a surface tension that was substantially less than the surface tension in most hydrocarbon fuels. The delta between the lower aqueous film surface tension and higher hydrocarbon fuel surface tension was large enough to produce an impermeable film that spread spontaneously across the surface of the fuel.
While the water within the blanket cooled surfaces, chemistry within the foam blanket continued to replenish the film over time – inhibiting vapor yield.
Even without a foam blanket, Williams has seen incidents where the residual film continued suppressing vapors. So effective was this film in suppressing vapors that emissions monitoring indicated no VOCs long after the blanket was depleted by wind or time.
This performance leads to my cautionary message that firefighters understand today’s non-fluorinated foams and that foam blanket integrity is so vital with SFFF foams.
In the absence of the film-forming magic of AFFF, mechanical foam blankets rely strictly on a matrix of physical and mechanical factors that effectively suppress vapor evolution and inhibit air exposure at the fuel surface.
Traditional foam ‘quality’ has been defined by expansion ratio and drain time, but these are poor predictors of real-world mechanical foam performance. In practice, effective SFFF blankets are better judged by their ability to maintain an intact, resilient vapor barrier over the fuel surface.
Several factors determine how effectively a foam blanket performs during extinguishment and long-term vapor suppression. Expansion ratio influences how quickly an effective blanket can be established and how much depth is achieved at a given application rate, while also affecting its ability to remain in place under wind and heat.
Foam mobility, or “wetness”, governs how readily the blanket flows across fuel and around obstacles. Highly mobile foams spread quickly to aid initial control but may drain rapidly and expose fuel under heat, whereas stiffer foams provide greater burn-back resistance but may struggle to flow into and reseal coverage gaps.
Resistance to fuel pickup is equally important. Foams that absorb fuel too readily lose structural integrity, allowing flames to work back through the blanket and reducing their ability to suppress vapors, particularly over hot or volatile fuels.
Bubble size and distribution also play a significant role. Fine, uniform bubbles create a tighter, more resilient blanket that better resists flame penetration, while larger or uneven bubbles drain faster and create pathways for vapor release.
Finally, blanket depth and continuity are critical. A thick, continuous blanket provides effective cooling, maintains separation between the fuel and atmosphere and limits vapor escape, whereas thin or broken coverage around walls, obstructions or drains creates weak points that increase the risk of vapor release and re-ignition.
In any non-fluorinated mechanical foam application, if the physical barrier of the foam is lost or scarred, the blanket will not readily re heal itself without intervention. While this impacts long-range applications, it is most concerning for active operations and entry of firefighters into spill fires or pooling fuel zones.
The conclusion is straightforward: while fluorine free foams can be effective, they are not behavioral equivalents to legacy film forming AFFF and tactics must adjust accordingly.
Effective use of fluorine-free foams in industrial Class B firefighting, particularly on fuels in depth, requires a reset in expectations. Do not sacrifice performance for mix rate or percentage of concentrate.
Today’s SFFF foams are hard-pressed to replicate the exemplary performance of their AFFF predecessors at 1%. Yet a 1% operational mindset throughout industry persists in high expectations and sometimes misguided performance interpretations.
Without advanced film-forming fluorosurfactants, SFFF foam formulations continue to explore effective hydrocarbon chemical balancing – performance ranges are broad.
Higher application rates, foam concentrations or both may be necessary for certain foam products especially for light, high-vapor-pressure fuels.
As performance challenges persist in demanding industrial flammable liquid scenarios, some test protocols are being weakened to imply performance rather than prove it.
Validation of foam concentrates under realistic conditions; fuel-specific, scale-appropriate and using actual field hardware and tactics should be practiced. Class B response teams must adopt an explicit operational focus on foam blanket structure, blanket integrity and continuous vapor monitoring.
The loss of the film-forming quality of legacy AFFF is not simply a regulatory footnote. It is a fundamental change in the tools industrial firefighters bring to the most dangerous incidents they face. The foams have changed. To maintain an equivalent level of safety and effectiveness, tactics must change as well.
Stay active. Stay vigilant.
