The objective of this project was to increase the understanding of specific physical and chemical processes that underlie fire-fighting foams, and how specific components of a foam formulation can deliver the properties required for good fire performance whilst minimizing environmental burdens. Model fluorine-free foam formulations were developed and optimized for fire performance in the MIL-PRF 24385F 28ft2 test. A life cycle assessment compared the environmental impact of aqueous film-forming foam (AFFF) and fluorine-free foams in order to identify routes of improving environmental performance.
The generation and deployment of fluorine-free fire-fighting foam was broken down into individual processes. For each, the desirable physical properties were hypothesized and tested with laboratory physical measurements and small-scale fire tests. All foam components were limited to readily biodegradable surfactants, solvents, polymers and other additives. Life cycle analysis of fire-fighting foams used the method described in ISO 14040 and 14044.
Model foam formulations of increasing complexity were evaluated using surface chemistry techniques to understand their behavior in aqueous solution, and at air/water and fuel/water interfaces in fresh and salt water. These physical measurements were correlated with key foam properties such as foam stability to fuel, spreading and with fire performance requirements of extinguishment and burnback times. The roles of primary and secondary surfactants, solvents and water-soluble polymers were tested.
Statistical optimization of one formulation gave an extinguishment time of 36” in fresh water in the 28ft2 MIL-PRF 24385F fire test on heptane and burnback of 477”. An alternative formulation gave 75” extinguishment and 286” burnback on gasoline in salt water.
Data on the manufacture of AFFF and fluorine-free foams have been collected and the ReCiPe method used to compare environmental mid and endpoints. AFFF foams typically had greater impact on resource depletion, environmental quality and human health. A model AFFF foam containing C6 fluorosurfactant exposed to fire did not show evidence of new fluorocarbon species. Water draining from the foam is initially severely depleted in fluorocarbon content, with implications for clean-up of spent foam.
The project has given a better understanding of the role of specific foam components in delivering the properties required of a fire-fighting foam, and show that foams based on hydrocarbon surfactants can extinguish within 30-60”, and give burnback times longer than 360”. The life cycle analysis shows that the manufacture of fluorocarbons imposes higher environmental cost than hydrocarbon surfactants.