Pyrolytic Transformation of PFAS Precursors in AFFF when Applied for Fire Suppression

Grenier, Drew

Etd

Pyrolytic Transformation of PFAS Precursors in AFFF when Applied for Fire Suppression

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Aqueous Film Forming Foams (AFFF) containing per- and polyfluoroalkyl substances (PFAS) have historically been the standard for extinguishing Class B flammable liquid fires due to superior performance in comparison to Fluorine Free Foams. Beginning in the early 2000s, fluorotelomer-based foams and C6-based fluorosurfactant-containing foams have risen in popularity among AFFF manufacturers due to environmental and public health effects associated with perfluorinated compounds, such as PFOA and PFOS. Currently, our understanding of the fate of these PFAS precursors in AFFF during use in fire suppression is limited. This study investigated the thermal stability of three pure fluorotelomer PFAS precursors – 10:2, 8:2, and 6:2 fluorotelomer sulfonate (FTS) – along with an AFFF sample known to contain each of these three precursors. Bench scale studies were conducted at high temperatures and pressures using a high pressure reactor vessel, and a simulated hydrocarbon fire scenario with AFFF suppression was conducted using a radiant panel. Post heat treatment samples were analyzed via liquid chromatography tandem mass spectrometry (LC/MS/MS). Results show that significant thermolysis of all three pure fluorotelomer PFAS precursors was achieved at 400 ºC over a 30 minute duration, and at least one PFAS compound currently regulated in the state of Massachusetts was produced. These results further support the theorized thermal decomposition mechanisms of random- and end-chain scission when analyzing potential transformation pathways. Moreover, a general increase in precursor, short-chain perfluoroalkyl acids (PFAA), and long-chain PFAAs was observed across increasing heat treatment time intervals of the AFFF sample, while a general decrease in short-chain PFAAs, and long-chain PFAAs was observed across increasing AFFF volumes. Ultimately, these results indicate that PFAS precursors have the potential to transform into other types of polyfluoroalkyl substances as well as perfluoroalkyl substances under relatively moderate pyrolytic conditions that simulate AFFF use during fire events.

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