Effect of slope on smoke movement and temperature profile in underground utility tunnel

Underground utility tunnels with various municipal pipelines inside provide convenience for cities and contribute to their sustainable development, but also bring potential fire risks. Previously, the relevant studies have predominately focused on horizontal section, while ignoring the influence of slope at the intersection of utility tunnels. In the present study, the smoke movement and temperature distribution were investigated in utility tunnel fires with five slopes and six heat release rates by numerical simulation. Four different sizes of pool fire experiments were also conducted in a full-scale utility tunnel. The results indicated that: (1) Smoke movement can be divided into five stages, including free rise, diffusion under inclined ceiling, diffusion under horizontal ceiling, flow back, and steady circulation. (2) Temperature upstream is larger than that downstream of the fire source, which is asymmetrically distributed and shows different characteristics with the change in slope. (3) Downstream ceiling temperature decreases gradually with increasing distance from the fire source. An empirical formula is proposed to predict the downstream maximum ceiling temperature rise considering the slope and dimensionless heat release rate. Good agreement was obtained between predicted and experimental values.