Since the 1970s, the Department of Defense (DoD) and the civil aviation community have used aqueous film forming foam (AFFF) as a firefighting agent for the suppression of liquid fuel (Class B) fires, particularly in Aircraft Rescue and Firefighting (ARFF). Legacy C8 and C6 AFFF, however, contain per- and poly-fluoroalkyl substances (PFAS)—primarily perfluorooctanoic acid, perfluorooctane sulfonate, perfluorohexane sulfonate, and perfluorohexanoic acid — fluorinated surfactant compounds that have been shown to persist in the environment and are of concern for the environment and human health. The 2020 National Defense Authorization Act (NDAA) prohibits the use of currently approved PFAS-containing AFFF beginning October 1, 2024.

The Battelle/Air Force Civil Engineer Center (AFCEC)-Tyndall Air Force Base Team has tested more than 10 PFAS-free foam (PFF) products using a conventional aspirated nozzle as well as an enhanced foam delivery system called compressed air foam, and has shown that no current PFF meets military specification (Mil-Spec) MIL-PRF-24385F, particularly the 30 seconds fire extinguishment time requirement. The objectives of this project are to (1) identify and prepare functional, point-of-use (POU) additives that can be added to, or co-delivered with, existing PFFs; (2) evaluate fire performance with and without the POU additives, relative to extinguishment and burnback times against the Mil-Spec; and (3) show feasibility of new and previously deployed nozzles for co-delivery of POU additives and PFFs.

The project team will identify and test POU additives and co-delivery nozzles to improve fire suppression performance of PFFs. The approach covers the following tasks: (1) identify and select up to eight POU additives; these are mostly commercial off-the-shelf (COTS) products but unexplored as additives for firefighting; (2) acquire/prepare new additives; (3) test additives in an existing, 45-in² fire test set-up; (4) test novel nozzles for co-delivery of PFF and additives in a 314-ft² fire set-up; and (5) conduct a preliminary sustainability analysis for the down-selected additives. In FY20, Battelle-funded an internal research and development project to address PFF formulations and identified two promising liquid-based additives, which underwent preliminary fire testing in collaboration with AFCEC under a Cooperative Research and Development Agreement. Additionally, in a parallel AFCEC/Battelle SERDP SEED project, additional promising siloxane-based additives were identified for improving fire performance. The project team has identified several potential POU additives based on a literature search and based on prior work conducted by AFCEC. Collectively, these additives utilize the three mechanisms of fighting fires (i.e., remove heat, remove oxygen, or disrupt the fire), only the first two of which are relied upon in the available PFFs.

The POU additives opens up a new avenue of PFAS-elimination opportunities for Class B firefighting, as well as other types of fires, and benefits the DoD by identifying a solution that achieves compliance with the NDAA requirement by the October 1, 2024 deadline. None of the COTS or developmental PFFs are able to meet the Mil-Spec performance standards, although some are close to achieving that goal. The availability of additives that can be used by firefighters to meet the Mil-Spec fire performance specifications has the benefit of utilizing COTS or near-commercial PFFs without the need for time-consuming and expensive reformulation work by multiple vendors. The use of previously explored, as well as new, simple-design nozzles for co-delivery of additives will allow transition to existing ARFF trucks to help improve the fire performance of PFFs. Most importantly, the deployment of such POU additives does not require a deep knowledge of the PFF chemistries, which vary a great deal, and that vendors are reluctant to share due to potential intellectual property issues, nor is it impacted by lack of storage stability of PFF when combined with liquid/solid additives.