Example of AFFF residue inside an AFFF foam tank after initial AFFF draining.
Per- and polyfluoroalkyl substances (PFAS) are being phased out and future firefighting activities need to involve minimal release of PFAS into the environment. Aqueous form filming foam (AFFF), used for extinguishing fuel and oil fires rapidly, contain PFAS compounds in concentrations of up to 60 grams per liter. Inside fire vehicles, PFAS residues form coatings and can be resistant to removal. Further, these residues do not dissolve readily in water. Multiple studies have shown that simple rinsing with water leaves large quantities of PFAS behind (Lang et al. 2022).
The steps of AFFF removal and cleanout are:
- Removal of AFFF concentrate
- Physical rinsing of foam tanks, pipes, and venturies
- Rinsing of the vehicle internal surfaces in touch with foam using water or another cleaning fluid
- Treatment or disposal of the rinsate on-site
- Waste disposal
After AFFF clean-out, the foam tank is filled with a fluid, left to equilibrate, and sampled. Water is circulated through the truck’s pipes, pumps, and hoses and sampled. You obtain samples from inside the foam tanks and from the water spraying components. These samples are analyzed for PFAS concentrations.
TRS Group (TRS) recently compared the effectiveness of triple-rinse (three rinses of the AFFF tank using potable water only) to rinsing with a PerfluorAd® solution. TRS cleaned a firefighting vehicle at a major international airport using established triple-rinse methodology. Then, TRS treated the same vehicle using a heated PerfluorAd® solution with flushing and agitation, rinsing the vehicle’s internal surfaces, similar to the action inside a dishwasher. TRS treated the resulting rinsate using PerfluorAd, which concentrates the PFAS by flocculation, and liquid-phase granular activated carbon (LGAC) filtration.
Figure 1 illustrates the results in terms of PFAS found in the post-rinsing testing.
The triple-rinse reduced the concentration of several PFAS compounds in the vehicle’s AFFF storage tank such as PFOA by 70-90 percent; however, there was no reduction in total PFAS concentrations. The dominant compound in the triple-rinsed water was 6:2 fluorotelomer sulfonic acid (6:2 FTS). In contrast, PerfluorAd® flushing resulted in a reduction of greater than 99 percent for all PFAS compounds (99.3% for 6:2 FTS and non-detect for PFOA and PFOS), indicating a more complete removal of PFAS from the internal surfaces of the vehicle.
These results are supported by Lang et al. (2022), who compared water rinsing to more aggressive rinsing of the surface of pipes from an AFFF system. They demonstrated that both heating and use of methanol and Fluoro Fighter (a proprietary liquid developed to dissolve AFFF residues) resulted in better PFAS reductions than the water rinse. The rinsate using these agents contained two to three times more PFAS than the water, and analysis of the pipe surfaces indicated that water rinsing left large quantities of fluorine-containing residues in the pipes. PerfluorAd showed similar results.
In addition to the PFAS contained in deposits on pipe surfaces, it is possible that AFFF residues as shown in Figure 2 remain after water rinsing. These residues are removed using hot fluids and agitation. PerfluorAd is heated to 60 degrees Celsius before circulation through the vehicles.
In conclusion, applying the PerfluorAd® process to fire vehicles leads to reductions of more than 99 percent in PFAS concentrations in water circulated through the vehicle. Triple-rinse resulted in some PFAS reductions of up to 90 percent, but with an insignificant change in total PFAS. PFAS-containing residues inside the vehicles cannot be removed effectively using water alone.
Johnsie R. Lang, Jeffery McDonough, T.C. Guillette, Peter Storch, John Anderson, David Liles, Robert Prigge, Jonathan A.L. Miles, Craig Divine (2022): Characterization of per- and polyfluoroalkyl substances on fire suppression system piping and optimization of removal methods. Chemosphere 308, 136254.