Effect of the foam flow rate on extinguishing process for low-expansion foam AFFF, FP, and S based on CAF system

Abstract

Compressed air foam (CAF) system has been proposed as an excellent method for fighting liquid fuel fires, where the foam flow rate is the critical factor in determining the efficiency. However, the existing research of the effect of foam flow rate on CAF system limited to extinguishing time, while ignoring the detailed quantitative study on some characteristic parameters during the extinguishing process, particularly the flame height. Aiming at investigating the influence of foam flow rate on these parameters, a series of CAF extinguishing tests were carried out in the range of different foam flow rates from 10 to 80 L/h. Results indicate that with an increase in the gas–liquid ratio, the extinguishing time for AFFF, FP, and S initially decreases by 69.9 %, 47.1 %, and 59.0 %, respectively. This reduction continues until reaching a minimum at a gas–liquid ratio of 10:1. When foam is released onto the fuel surface at a low flow rate of 10 L/h, flame height increases rapidly by approximately 50 to 100 mm caused by air entrainment, whereas at a higher flow rate of 45 L/h, this parameter decreases quickly over time. Further, the extinguishing time decreases gradually with increasing foam flow rate, dropping from over 100 s to around 30 s in the range of 10 to 80 L/h. Based on experimental data of this study, the extinguishing time model on foam flow rate has been developed for typical foam of AFFF, FP and S. The findings of this study provide valuable insights for optimizing the effective utilization of the CAF system.