Fire Zone Diagram of Flame-retardant Cables: Ignition and Upward Flame Spread

Electrical cable is a common fire risk and hazard, and once ignited, a cable fire can spread to other rooms and floors by following the direction and location of cables. This work investigated the ignition and upward flame spread over the 1-m long cable under a growing heat flux. Results showed that the flame-retardant cables could be easily ignited by a small flame after a weak irradiation (5 kW/m(2)) if preheated to 70 degrees C. As the external radiation increases, the cable surface temperature increases, and the upward flame spread rate increases significantly. Once the cable surface reaches 240 degrees C, piloted ignition can be achieved. With the combined effect of external heating (> 18 kW/m(2)) and smoldering, auto-ignition could be achieved once the cable sheath reaches 500 degrees C. Moreover, flame-retardant cable fire is intense with severe melting, dripping, swelling, and cracking. The falling cracks and dripping flow can form a pool fire to increase the fire hazard. Finally, a new fire-zone diagram with the surface temperature and critical mass flux was proposed to quantify the cable fire hazard. This work provides important information about fire behaviors of the flame-retardant cable under a real fire scene and may guide the design of fire-resistant cables.