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The Chemistry of Aqueous Film-Forming Foam vs. Firefighting Alternatives

The biggest chemical difference between AFFF and FFF firefighting suppressants is whether the foams were manufactured with fluorine. When carbon mixes with fluorine in firefighting foam, the bond generates a PFAS (per- and polyfluoroalkyl) substance. These PFAS or “forever chemicals,” as they are known, produce the film component of aqueous film-forming foam (AFFF) that makes it an effective suppressant, but they also cause devastating health effects and diseases due to bioaccumulation and contamination.

What Is Fluorinated Foam?

A fluorinated foam is a synthetic suppressant designed to combat Class B fires, including jet fuel, diesel, and other flammable liquid fires. AFFF is a general term used for many of these Class B fire-extinguishing formulas. Though AFFFs are known by various brand names, all were developed by manufacturers who used a hazardous mix of chemical components—carbon plus fluorine—that generated PFAS. The lack of warning about the effects of exposure to fluorinated foams jeopardized the health of firefighters and the public for decades. 

What Is Fluorine-Free Foam?

Fluorine-free foams are firefighting suppressants, referred to as F3 or FFF, that do not contain any PFAS in the composition. Early firefighting suppressants were technically fluorine-free, made from protein sources rather than synthetics, but those were widely replaced by AFFF. Today’s synthetic FFFs are currently the preferred alternatives to AFFF when combatting difficult Class B fires. Though testing of F3 suggests it does not provide as effective a barrier for preventing reignition as fluorinated foams, it is acceptable compared to classic protein foams, which require very precise applications. 

The Difference Between AFFF and FFF

The presence, or lack, of PFAS is the main differentiator between the chemical makeup of AFFF and FFF. PFAS are generated when chains of carbon and fluorine atoms bond. This carbon-fluorine interaction produces an aqueous film that spreads to smother flames, prevents evaporation and reignition, and deprives the fuel surface of oxygen. FFF lacks this fluorine-carbon bond, reducing its suppression and knockdown capabilities. Beyond chemistry, additional differences between AFFF and FFF include:

  • Viscosity: AFFF is a low-viscosity (water-like) substance and FFF  has a high viscosity, each requiring different proportioning systems.
  • Application Methods: Higher application rates may be needed for FFF to be effective against certain fuel types.
  • Burnback Resistance: The foam “blanket” of FFF breaks down faster than AFFF, providing less resistance to direct flame.
  • Environmental Persistence: AFFF resists degradation; many FFF are believed to be biodegradable.

The Troubling Composition of AFFF

AFFF has been categorized into two types, legacy and modern. Despite their names, production of both formulas began in the 1970s. The difference between these two foams is the number of long-chain or short-chain PFAS present. Both contain a mixture of forever chemicals as a result of the fluorinated makeup. The legacy formula contains a higher concentration of long-chain PFAS, and its discontinuation due to this hazardous composition earned it the ‘legacy’ moniker. The makeup of modern foam, which is still in use today, has a lower concentration of long-chain PFAS and is presumed to be a safer alternative. 

Whether because of miscalculations or a lack of research, when legacy AFFF was retired, the modern formula became the dominant extinguisher for Class B fires—despite its similarity to the discontinued solution. There is insufficient evidence to suggest that any exposure to short- or long-chain PFAS is harmless. The discontinuation of the legacy formula came too late and the same may be said about the modern formula. Since both were manufactured for a long shelf life, stockpiles remain at military bases and firehouses. Anyone living or working nearby is still susceptible to exposure from accidental releases, pump failures, and holding tank leaks.

Not enough is known about the fluorine-free firefighting foams to deem all of them safe alternatives to AFFF, but the lack of PFAS offers promise. Unlocking methods to break the bond that holds carbon and fluorine together is the key to managing AFFF compounds in the environments where they persist. Switching to F3 may help future generations of firefighters avoid the damaging health effects of AFFF as long as manufacturers do not repeat their past failures.