Characterization of PFAS residuals: A case study on PFAS content in a firefighting foam delivery system of an aircraft rescue and firefighting vehicle

When fire suppression systems that held aqueous film forming foams (AFFF) are transitioned to per- and polyfluoroalkyl substance (PFAS)-free firefighting formulations, PFAS can dissolve from the wetted surfaces of the systems and release into the new firefighting formulations. The overall objective of this work was to characterize PFAS residual mass on the wetted surfaces of aircraft rescue and firefighting (ARFF) vehicle on-board fire suppression system components from the water, mixed fire water, and foam concentrate systems with various geometries, materials of construction, and locations within the fire suppression system. The ARFF vehicle components were dismantled from the system after a triple water rinse procedure which removed 19,600 mg total measured PFAS post-TOP assay from the foam concentrate system and 23 mg total measured PFAS post-TOP assay from the water system. Results for total mass of PFAS on each part indicate most of the residuals were present on parts which have large surfaces areas or the rubber or brass parts. For large surface area plastic parts (i.e., foam and water tanks), the overall mass on these parts was greater than other parts even as the PFAS residual concentrations were lower compared to other material types due to larger surface areas for accumulation. Parts constructed of rubber or brass appeared to have higher measured PFAS surface residual concentrations as compared to parts constructed of plastic or stainless steel.