Synergisms between siloxane-polyoxyethylene and alkyl polyglycoside surfactants in foam stability and pool fire extinction

Abstract

Fluorocarbon surfactants in firefighting foams must be replaced with environmentally friendly surfactants without loss of fire suppression performance. Aqueous foams generated from commercial siloxane-polyoxyethylene and alkyl polyglycoside surfactants were characterized individually and as mixtures in a formulation by measuring the solution and foam properties, foam degradation and fuel transport rates through a foam layer on a hot heptane pool, and foam’s ability to suppress a heptane pool fire rapidly using minimum amount of foam. The results showed significantly smaller fire extinction times for the surfactant mixtures than for either of the individual components exhibiting a synergistic fire extinction rather than following the law of averages; 5 times enhancement in extinction performance. The measured foam degradation rate with the foam exposed to a hot heptane pool also showed a similar synergism. The reduced foam degradation rate resulted in a reduced fuel vapor transport for longer times and a more rapid fire extinction for the siloxane-glycoside mixture. By increasing the hydrophilicity with increased size of the polyglycoside head, the synergistic effect was enhanced. Both benchtop (19 cm diameter) and large scale (6 ft diameter) heptane pool fire extinction with the siloxane-glycoside surfactant mixture showed that the extinction time was 1.5 times (60% effectiveness of AFFF) that of an equivalent AFFF formulation containing a fluorosurfactant in place of the siloxane surfactant at a fixed foam application rate (22 L m−2 min−1). An understanding of the molecular interactions at the interface causing the synergistic effects may lead to improved siloxane-glycoside systems and other novel surfactant systems with performance matching that of fluorocarbon surfactants.