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

Abstract

Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. 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 μm), is more effective in reducing the extinguishment time than the high-pressure spray nozzle mist (d ~ 20 μm), which introduces sprayinduced 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. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S ACRONYM(S) 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR / MONITOR'S REPORT NUMBER(S)Office