The objective of this project was to identify and experimentally test functional additives for per- and polyfluoroalkyl substance (PFAS)-free fire-fighting foams in order to improve the physical properties and fire-fighting capabilities of the foam. PFAS are a common ingredient in aqueous film-forming foams (AFFF) due to their oleophobic properties and stability at elevated temperatures, but are being banned due to both environmental and health concerns. The National Defense Authorization Act has ordered the phaseout of PFAS containing AFFF at U.S military facilities by 2024, however, none of the currently available PFAS-free formulations can meet the requirements laid out in the MIL-PRF-24385. To this end, the Johns Hopkins University Applied Physics Laboratory (JHU/APL) worked to determine readily-available additives that can act to enhance the firefighting capabilities of mature (i.e., commercially available) and emerging PFAS-free fire suppressants for military use.

Functional additives were selected based on an extensive literature review to assess their potential to improve physical properties critical to fire-fighting performance, including surface tension, foam expansion ratio, and viscosity. Key criteria were utilized to further down-select additives for testing, including prior use in fire-fighting formulations, cost, reduced toxicity, and environmental hazard. Physical property testing was conducted at various mixtures of additives and PFAS-free fire-fighting concentrates. Those with the most significant improvement on surface tension and viscosity were selected for fire-suppression testing. Small-scale fire suppression testing was conducted at JHU/APL to assess extinguish and burnback times in comparison with the PFAS-free foams with no additives. The foam-additive mixtures with the best performance were selected for larger-scale 28ft² fire suppression testing conducted in collaboration with Jensen Hughes.

For the two PFAS-free firefighting foams tested in this study, Greenfire Firefighting Foam (GFFF) and National Foam (NF) Avio F3 Green KHC, it was determined that four of the functional additives consistently altered and improved the foam solution physical properties most critical to fire suppression performance. These four additives were octanol, biochar, octanoic acid, and dodecanol. In particular, octanol was found to be the best performing additive, capable of both reducing surface tension of the foam solution and controlling viscosity. Results of the small-scale and larger-scale fire testing indicated an improvement in fire-fighting performance by both octanol and biochar in GFFF and NF, respectively, for both time to extinguish and burnback time, improving to nearly the requirements set out in the MIL-PRF-24385. Octanol added at 5% by weight ultimately improved time to extinguish in GFFF by 25 seconds and improved burnback time by 141 seconds, and biochar at 10% by weight improved NF time to extinguish by seven seconds and burnback time by 30 seconds. It was also observed that some additives, such as octanoic acid, completely destroyed the foam solution’s fire suppression ability, indicating that molecular scale interactions of additives in the foam solutions can have a dramatic effect on fire suppression capability. More work can be done to better characterize these interactions and produce better performing firefighting foams.

The work conducted in this study provides a basis for further development and assessment of additives to enhance the performance of commercially available PFAS-free foams with the ultimate objective of equaling the capabilities of legacy AFFF. Additional work to further characterize the successful additives tested, and related modified additives based on these results, is a critical next step in understanding the molecular basis for why these additives improve fire suppression and to optimize foam solution mixture ratios for military performance requirements. Building on this exploration, JHU/APL’s industry partners can help to conduct further testing and assess scalable production methods in order to transition to the use of novel additive mixtures that can supplant PFAS containing AFFF. This transition is essential due to the identified risks of PFAS, including persistence in the environment, bioaccumulation, and toxic human health effects.