Aqueous film forming foams (AFFF) are extremely effective in combating pool fires, but contain perfluoroalkyl surfactants that threaten the environment. These long, fluorinated-carbon chains persist in the environment, bio-accumulate to harmful concentrations, and are toxic. Strict environmental regulations have limited the length of the carbon chain in these surfactants to reduce their effect. To eliminate the harmful effects on the environment, commercial fluorine-free foams have been developed. But, they do not compare to AFFF extinction performance and fail to meet military standards.<br/>Many attribute the inferior firefighting performance of fluorine-free foams to the lack of aqueous film formation at foam-fuel interface. However, there is little direct evidence of film formation at high temperatures and its role in fire suppression. Our studies suggest that differences in fuel transport through the foam layer covering the pool surface exist between fluorine-free and fluorinated foams that relate directly to fire suppression. Foam degradation, for example, reduces the foam layer thickness and its ability to prevent the fuel from reaching the fire. It is known that heat from the fire causes foam degradation. Here, we show that foam degradation can also occur because of exposure to fuel and quantify the difference in degradation rate between MILSPEC qualified fluorinated foams and fluorine-free foams at elevated fuel temperatures.<br/>Foam was placed in separate glass vials containing three different liquid fuels of the same vapor pressure to ensure the same concentration of vapors in each test; a control in an empty vial was also performed. We discovered that the presence of fuel increased the foam degradation rate. For example, there was a 90% difference in degradation rate between AFFF over heptane and AFFF in a glass vial at room temperature. We also observed a dependence of fuel type on the degradation rate; both foams degraded over the different fuels at different rates. Foam degradation rate increased as the fuel temperature increased as well. In all cases, AFFF had a longer foam lifetime compared to the fluorine-free foam. This difference in degradation contributes to the observed differences in fire suppression between fluorinated and fluorine-free foams. Improving the degradation rate of fluorine-free foams can improve its firefighting performance, thus eliminating the need for perfluoroalkyl surfactants.

Evaluating differences in foam degradation between perfluoroalkyl and fluorine-free foams for the development of environmentally friendly firefighting alternatives

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.