Role of salts in fire extinguishing performance of aqueous film-forming foam (AFFF)

Abstract

The active ingredients for aqueous film-forming foam (AFFF) are supplied as a concentrate, and the water used to dilute AFFF concentrates generally come from water sources around the fire site including seawater and river water. However, the effects of salt in water on fire-extinguishing performance of AFFF remain unclear. In this paper, we investigated the relationship between the interfacial properties, foam stability, and fire-extinguishing performance of three homemade AFFFs (nonionic AFFFAPG, amphoteric AFFFCAB and anionic AFFFSDS) and four commercial AFFFs. The seawater, firefighting water from different regions of China and deionized water were used to dilute AFFF concentrates. The results showed that AFFFAPG and AFFFCAB had a better performance than AFFFSDS in resisting the negative effects of salts on interfacial properties and foaming ability. In the fire-extinguishing tests, we found that dilution of AFFF with water samples containing high concentrations of Ca2+ and Mg2+ would weaken the fire-extinguishing performance. The traditional indicators characterizing the properties of foam (surface tension, liquid drainage rate, and spreading coefficient) could not explain the trend of fire extinguishing performance. The stability of AFFF in the presence of oil could be used to explain the difference in fire-extinguishing time of AFFF.