The objective of this topic area was to demonstrate and validate environmentally sustainable PFAS-free fire suppression agents against the current performance requirements outlined in the specification for fluorine-free foams (F3) MIL-PRF-32725. The following considerations were of interest:

• Demonstration and validation of F3 formulations. Due to the expense of large-scale testing, only PFAS-free fire suppression alternatives that demonstrate promise based on initial small-scale testing (28 ft² and 50 ft² tests of the current MILSPEC) are of interest for large scale demonstrations.
• Demonstration and validation of F3 formulations for dilution in seawater. Due to the expense of large-scale testing, only PFAS-free fire suppression alternatives that demonstrate promise based on initial small-scale testing (28 ft² and 50 ft² tests of the current MILSPEC) are of interest for large-scale demonstrations.
• Demonstration and validation of methods to improve the stability of F3 concentrate and diluted solution for use. Evidence has shown that some of these formulations may not be fully stable, and they can phase separate and change viscosity prior to use, which can affect firefighting performance. Projects that evaluate the stability of formulations as a function of conditions and/or demonstrate methods to increase the stability of F3 formulations are of interest.
• Testing and evaluation of the compatibility of multiple approved F3 formulations. Traditional PFAS-containing aqueous film-forming foam (AFFF) formulations from different manufacturers appear to be compatible, yet F3 formulations may not be compatible. Mixing with other PFAS-free firefighting formulations is not recommended by the manufacturer. The logistics issues associated with this would increase cost and time associated with AFFF management or require single source purchasing. Thus, MILSPEC testing on mixtures of PFAS-free AFFF is sought to determine whether certain mixtures could be used together or gain understanding of the degree of the compatibility problem. For compatible solutions, the duration of compatibility is also of interest. Note, that the FAA has conducted a series of tests in this regard (https://www.faa.gov/airports/airport_safety/aircraft_rescue_fire_fighting/f3_transition). Proposals should focus on remaining gaps.
• Pre-mixed solutions for firefighting foams are used in various applications within the DoD. PFAS-free foams that are pre-mixed that perform well according to MIL-PRF-32725 would be useful. The formulations should have a threshold of 6-month shelf-life stability with an objective of 12-month shelf-life stability.

The materials and processes to be demonstrated/validated should have already been developed to a minimum Technology Readiness Level (TRL) of 4, and the proposed project should bring them to TRL 7 or higher. Alternative formulations should have been production-level materials rather than laboratory-scale samples. Projects had to demonstrate producibility, defined as the ability to be produced in the near term to meet the current DoD airfield or shipboard use requirement.

Field testing in military relevant environments should have been included in the proposed project. Alternative formulations had to be compatible with generally used storage equipment (e.g., polyethylene) and piping (steel, copper-nickel, bronze alloys), while providing comparable corrosion rates acceptable according to the military specification MIL-PRF-32725. Formulations should have met requirements with fresh and/or salt water at multiple delivered concentrations. In addition, formulation stability had to be demonstrated.

Proposals should have included an assessment of the human health and environmental impacts of proposed ingredients, formulations, and byproducts if such testing has not already been completed. This should have expanded on commonly used aquatic toxicity, chemical oxygen demand, and biodegradability testing required in the MIL-PRF-32725. These proposals should have established a baseline lifecycle framework and identify the lifecycle inventory elements currently known, those to be investigated during the project, and those beyond the scope of the proposed work. Any completed testing on human health and environmental impacts of proposed ingredients, formulations, and byproducts should have been summarized in the proposal.

All projects had to involve at least one DoD organization as a funded co-performer that is considered a stakeholder for the intended application.

The benefits of this work are expected to be firefighting formulations with improved performance, increased sustainability, reduced cost, and/or reduced human- and eco-toxicity.

AFFF is a water-based foam used by the military since the 1970s for fire suppression in ships, shore fixed systems, aircraft hangars, and to extinguish liquid fuel fires. AFFF mixtures contain perfluorooctane sulfonate (PFOS) and related PFAS compounds. The 2020 National Defense Authorization Act required that the DoD publish a new military specification, MIL-PRF-32725, for F3 in 2023. As such, the military specification, MIL-PRF-24385F, has been replaced with MIL-PRF-32725. Efforts are now focused on transitioning from AFFF to F3 because the procurement and use of fluorinated AFFF is being phased out. Current qualified products work well, but improvements that reduce extinguishment time and burnback time would be beneficial. Industry has developed qualified F3 products, however, intercompatibility of these products has not been proven. Assessments of intercompatability and work that seeks to make formulations more compatible with each other would be beneficial.