AFFF foam fire extinguishing by gas-permeated spreading and flame barrier with different foaming gases

Currently, there is a lack of delicate research on flame suppression by foam spreading on the fuel surface. In this study, we propose a new method of varying the foaming gases to control the foam spreading rate on oil surfaces. The kinetic process of foam extinguishing with various gas-liquid ratios is investigated. In addition, the synergistic effect of gas-permeated spreading and flame barrier on the extinguishing efficiency was examined. The results indicate a positive correlation between the extinguishing efficiency and the flame-free spreading rate of CO2 > He > Ar > N-2 > Air. The extinguishing efficiency decreases with increasing gas-liquid ratio, while the 6:1 ratio leads to a 59% increase in extinguishing time compared to 4:1, and a 90 % increase compared to 1:1. The consumption of foam by the flame enhances as the flame-free spreading rate decreases. The flame consumes over 80% flame-free spreading rates of Air and N-2 foams, leading to fast foam front consumptions by the flame and poor extinguishing performances. Gas permeation in the foam film exacerbates the bubble coalescence and foam drainage, enhancing the foam spreading performance while reducing the foam stability. The foam spreading induced by gas permeation plays a decisive role in spreading rates and extinguishing efficiency, whereas the effect of foam stability on extinguishing efficiency is less influential. Increasing the gas permeability and reducing the gas-liquid ratio enhance the overall foam mobility. Hence, the spreading rate and extinguishing efficiency increase with gas permeability. An empirical model expresses the relationship between extinguishing time and flame-free spreading rate, underscoring the decisive role of foam spreading in the fire extinguishing process.