Comparative studies on foam stability, oil-film interaction and fire extinguishing performance for fluorine-free and fluorinated foams

Oil droplets destabilize the fluorine-free foam by spreading over the film, while they slightly influence the film stability for fluorinated foam. By adjusting the expansion ratio, the fire extinguishing performance of the fluorine-free foam can be significantly improved. [Display omitted] The application of fluorocarbon surfactants in fire-fighting foam has been restricted due to their serious environmental hazards. Thus, it is necessary to develop the fluorine-free foam for fire-fighting and understand their characteristics from different perspectives compared with the fluorinated foam. The present study investigated foam stability, oil-film interaction, and fire extinguishing performance for fluorine-free and fluorinated foams. The results show that the adverse effect of oil on the stability of fluorinated foams is much less than that of fluorine-free foams. Besides, the trends in foam stability are not predicted by the entering, spreading, and bridging coefficients based on the measurement of surface and interfacial tensions. The differences in stability of fluorine-free and fluorinated foams are found to be consistent with the observation of oil-film interaction. Oil droplets destabilize the fluorine-free film by spreading over the film, whereas they tend to be rapidly expelled out of the fluorinated film in the form of oil lenses slightly affecting the film stability. Since the film is unstable in contact with oil, the fluorine-free foam cannot suppress the pool fire effectively at the expansion ratio of 6.8–7.2. By adjusting the foam expansion ratio, the fire extinction performance of the fluorine-free foam can be comparable to that of the fluorinated foam, and the burnback performance is significantly enhanced.