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/m²) if preheated to 70°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°C, piloted ignition can be achieved. With the combined effect of external heating (> 18 kW/m²) and smoldering, auto-ignition could be achieved once the cable sheath reaches 500 °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.