The goal of this Limited Scope research effort was to develop new foam evaluation tools that would enable a more comprehensive understanding of per- and polyfluoroalkyl substances (PFAS)-free fluorine-free foam (F3) performance under extreme conditions. With the appreciation that fuel vapor composition is dynamic, existing laboratory-based techniques used to evaluate foam performance do not provide for the systematic understanding of foam failure as a function of vapor composition. As vapor composition is dynamic, and most effected by extreme conditions, it is critical to develop the proper tools to assess foam performance. This work demonstrated how the vapor composition of a fuel of interest varies as a function of temperature, determining the role that fuel composition has on the associated vapor. With that understanding, the project team evaluated PFAS-free foam performance as a function of vapor composition, identifying the critical components of fuel vapor that compromise PFAS-free foam performance. By relating vapor composition to novel foam stability metrics, the goal was to realize a tool wherein standard fuel property surveillance will include the ability to determine the most suitable F3 formulation for firefighting. This work provides critical information in support of identifying the most suitable PFAS-free firefighting formulations for a given fuel and firefighting conditions.

The efforts of this project focused on defining vapor composition as a function of temperature and evaluating foam performance as a function of vapor composition. This work had three primary tasks: the determination of the composition of fuel vapor headspace as a function of temperature, the development of a fuel vapor testbed for the quantitative generation of fuel-based vapor streams, and the use of those streams in the generation of PFAS-free foams for laboratory-based evaluation. Briefly, using a combination of Solid Phase Micro Extraction, direct vapor sampling, and gas chromatography-mass spectrometry, the project team identified the primary components of fuel head space as a function of temperature. This informed the development of a vapor generation testbed that provides quantitative vapor streams of single components and/or mixtures of fuel related vapor. These vapors were used to generate foams that were evaluated using traditional laboratory techniques (e.g. Dynamic Foam Analysis). By generating the foams from the fuel vapor stream, it will reduce the time necessary to determine the suitability of a foam for fighting specific fuel fires.

Work focused on identifying the vapor composition of two fuels of interest to the Department of Defense, JP-5 and F-24 aviation fuels. The composition and relative abundance of the fuels were established in the liquid and vapor phase, with a particular focus on identifying the most abundant high volatility components that are likely to contribute to foam diabatization. For both JP-5 and F-24, the component of highest interest was identified as octane. A vapor generation testbed was established to control vapor concentration for the purposes of generating foams from vaporous sources. Foams generated from these sources were analyzed, and showed that certain foam performance metrics as measured by a Dynamic Foam Analyzer including foam drainage rates and bubble radius are influenced by vapor concentration and indicative of destabilization.

The co-development of a fuel vapor testbed and new approach to evaluating F3 formulations will reduce the time necessary to comprehensively understand the role of fuel vapor composition on foam performance. Those components most disruptive to the foam can be identified and screened across different firefighting foam products to determine which foams are less sensitive to specific components. Long term goals, beyond the scope of this work, include the ability to analyze fuel composition to establish the most suitable F3 formulation as a function of fire conditions.