The technical objective of this effort is to demonstrate and develop an understanding of the effects that foam quality has on the capabilities of new Fluorine Free Foams (FFFs) and relate these capabilities to the foam qualities produced by the various discharge devices used throughout the Department of Defense (DoD). This project was a two-year effort to assess the capabilities of per-and polyfluoroalkyl substances (PFAS)-free aqueous film-forming foams (AFFFs). AFFF alternatives including both traditional candidates such as fluorine-free and/or PFAS-free foams, and non-traditional options such as wetting agents and other water additives. Overall, the program provided an “apples to apples” comparison of the capabilities of the foams currently used by the DoD (AFFFs) and a range of commercially available PFAS-free alternatives. The objective was to quantify the capabilities of the “state-of-the-art” PFAS-free alternatives (PFAS-Free Foams (PFFs) and agents) in use today and provide information on the relationship between the actual fielded capabilities of the foam/agent and the current approval test requirements/results.
The systematic approach developed for this program included the following six tasks: (1) a literature search on potential PFAS-free AFFF alternatives; (2) a high-level environmental analysis to down-select agents for testing; (3) approval-scale fire performance testing using the tests described in Military Performance Specification (MIL-PRF)-24385F with and without modifications; (4) data analysis to rank the capabilities of the alternatives and to down-select agents for real-scale testing; (5) real-scale fire testing using two representative scenarios; and (6) the development of a database/final report that documents the findings and recommendations for the path forward.
From “Apples to Apples” comparison, the top five PFFs (PFF1-5) required about 1.5-2 times longer to extinguish the fires than the legacy Military Specification (MIL-SPEC) AFFF. However, all the fires were quickly controlled and ultimately extinguished with the performance difference measure in seconds or fractions of minutes. This program provides some of the required performance data needed to begin to answer the question “how good is good enough?” and in some respects, provides a fallback position if/when the use of AFFF is banned. If the capabilities of the top commercially available fluorine free products are deemed adequate, additional research and preparation will be required to identify the non-fire performance properties needed to deploy these in typical DoD applications. Issues such as agent capability and viscosity will need to be re-evaluated and potentially reconsidered going forward.
The primary performance limitation of these products is associated with the mechanisms of extinguishment and the need to produce aspirated foam to increase the extinguishment capabilities of these products. AFFF extinguishes a fire through the combination of two mechanisms: the formation of an oleophilic fluoro-surfactant film on the fuel surface; and a layer of aspirated foam. Both mechanisms combine to seal in the fuel vapors and to prevent the development of a flammable vapor mixture above the fuel surface. Fuel surface cooling may also be a contributor for higher flashpoint fuels. FFFs rely solely on the development of an aspirated foam blanket to contain the vapors and extinguish the fire. To date, the commercially available PFFs have no oleophilic properties and do not form a film on the fuel surface. The MIL-SPEC tests currently used to approve AFFF do not consider the foam quality that will be produced by the fielded system/hardware. In fact, the MIL-SPEC fire performance tests are conducted with an air aspirating nozzle that produces significantly better foam quality than any of the discharge devices used in actual DoD applications. This proposed program will begin to demonstrate the capabilities of these new PFFs from a mechanistic standpoint (i.e., foam quality) as well as the need to link the small-scale approval test conditions to actual fielded conditions. This link should serve as the first step in developing a new foam specification for land-based applications.