Study on the Smoke Characteristics of a Cable Fire in an L-Shaped Utility Tunnel under Different Ventilation Conditions

Cable fires frequently occur in utility tunnels, causing incalculable economic losses. In order to reveal the smoke characteristics of an L-shaped utility tunnel cable fire under different ventilation conditions, the temperature distribution, CO concentration, and smoke spread caused by an L-shaped utility tunnel cable fire were numerically simulated. The results show that the air outlet is set on the side of the utility tunnel that is prone to ignition, and the air inlet is set on the side of the utility tunnel far away from the fire source, which is conducive to slowing down the fire temperature and reducing the diffusion rate of CO. The temperature first increases and then decreases along the longitudinal direction of the utility tunnel, taking on a single-hump shape as a whole. However, in Scenarios 4 and 7, the temperature change takes on a double-hump shape. In Scenario 3, the temperature of the utility tunnel decreases with the rise of ventilation speed, and the section that satisfies the safety standard temperature is the longest. With increase in the longitudinal length of the utility tunnel, the CO concentrations in Scenarios 1, 4, and 5 first rise and then drop, while those in Scenarios 2, 3, and 6 decrease gradually. At a ventilation speed of 1.75 m/s in Scenario 3, the CO concentration is controlled the best, and the smoke spread speed takes on a V-shaped variation pattern. Based on three factors, it is concluded that the optimal ventilation mode is a ventilation speed of 1.75 m/s in Scenario 3 (Inlet C and Outlets A and B). By studying different ventilation methods, the most suitable ventilation system for the L-shaped utility tunnel is selected to improve the fire prevention and control capabilities and reduce the loss of personnel and property caused by fire.