Investigating correlations between physical properties and fire suppression performance of fluorinated and fluorine-free foams using a novel firefighting foam database

Abstract

Aqueous film-forming foams (AFFF) contain fluorinated surfactants, a class of perfluoroalkyl substances (PFAS) which have been shown to cause damage to the environment and human health. This has necessitated their replacement on military sites by the year 2024. But to date, no fluorine-free replacement firefighting formulation has showed comparable performance to AFFF. Fire extinction performance is measured in tandem with formulation physical properties, but whether various physical properties and fire suppression are correlated is poorly understood. Herein, we present the curation of a large amount of physical property and fire suppression data collected in-house. Chemometric regression was used to ascertain correlations between the critical micelle concentration (CMC) of both individual surfactant solutions and multi-component formulations and their corresponding (1) solution surface tension, (2) interfacial tension with heptane, and (3) fuel-induced foam degradation using heptane and (4) gasoline. After evaluating several algorithms, promising correlations are found between CMC and foam degradation on heptane and gasoline using locally weighted regression (LWR), as indicated by a large R2 of cross-validation (R2CV) from ∼0.6–0.9. Solutions with CMCs from ∼0.01–0.1 wt percent (%) exhibit the longest degradation times, whereas solutions with CMCs outside of this range had considerably faster degradation. This correlation is new but explains only 90% or less of the variation in the data partly because foam degradation is induced by fuel, which the CMC does not consider. However, this work will serve as a basis for future machine learning endeavors to predict fire suppression performance based on chemical structure.