Abstract: With the expansion of Ultra-High Voltage (UHV) transmission projects into remote, high-altitude regions such as the Western Sichuan Plateau, Aqueous Film-Forming Foam (AFFF) extinguishing agents used in compressed air foam systems are being increasingly deployed under challenging high-altitude conditions. This study investigates how water quality variations at different altitudes affect the physicochemical performance of AFFF. Firefighting water samples were collected from locations at elevations ranging from 500 m to 4 000 m across the Western Sichuan Plateau and analyzed for water quality parameters. The influence of water quality on key AFFF foam performance characteristics, including drainage, coarsening, and liquid film properties, was systematically evaluated. Results demonstrate that firefighting water at 4 000 m elevation exhibits the lowest conductivity, while water at 2 500 m elevation shows the highest turbidity. Turbidity significantly affects foam stability, with high-turbidity water samples accelerating foam drainage and coarsening processes, disrupting liquid film structure and compromising film stability. Additionally, high-conductivity water samples reduce drainage time. Divalent ions (such as Ca²⁺ and Mg²⁺) present in water samples can shield intermolecular charges, reducing water polarity and potentially hindering gas molecule diffusion, thereby decreasing coarsening rates, as observed in the 4 000 m elevation water sample. These findings provide theoretical support for the efficient utilization of AFFF extinguishing agents in high-altitude applications.

Key words: aqueous film-forming foam extinguishing agent, Western Sichuan Plateau, plateau water quality, drainage, ionic concentration, ultra-high voltage project