Mechanism of Suppression and Extinguishment of Communication Cable Fire by Ultra Fine Water Mist in Cross-Flow

Abstract

Abstract : Water mist fire suppression experiments were performed in cross-flow on bare (without outer jacket) communication cables to simulate a worst-case scenario. As fine water droplets are injected at low inlet velocities, an initial envelope flame that engulfed the circumference of the cable recedes and forms a wake flame stabilized behind the cable. At high mist concentration and/or high air velocity, the flame is extinguished by flame shrinking rather than by flame blow-off, as is the case in flat plate boundary layer flames. Ultra fine mist (UFM), with droplet diameter (d ~3 micrometers), is more effective in reducing the extinguishment time than the high-pressure spray nozzle (d ~20 micrometers), which introduces spray-induced turbulence. Extinguishment proceeds rapidly after a threshold concentration is exceeded, and the threshold concentration decreases with air velocity. Finally, the copper cylindrical mesh, which is part of the cable, significantly enhances the effectiveness of UFM in flame extinguishment.