Estimating the Two-Dimensional Thermal Environment Generated by Strong Fire Plumes in an Urban Utility Tunnel

Abstract Although utility tunnels act as an innovative technique for the sustainable development of city’s utilities and limited underground space today, the fire issues in this type of tunnel should be carefully treated as they are different from traffic tunnel fire scenarios. In order to propose an easy-to-use two-dimensional (2D) temperature estimation methodology that is helpful to the designers, operators and firefighters, the temperature distributions and ceiling jet thickness (the vertical distance from the ceiling to where the temperature within the fire-induced smoke flow drops to half of its maximum at a certain location) were investigated with full-scale fire tests in a utility tunnel. The vertical temperature distributions were represented as a normalized single convex-concave profile. Self-similarity was confirmed and three types of similarity profiles were found. In order to correlate the inner boundary layer region and outer region of these ceiling jet flow profiles, a series of mathematical functions combining a power function and Gortler’s error function were employed. Furthermore, the ceiling jet thickness was found to vary as a power function with the longitudinal distance, rather than being a constant as previous research suggested. The vertical distribution model, the ceiling jet thickness model and the longitudinal temperature decay model were combined into a framework to empirically estimate the 2D thermal environment generated by strong fire plumes in utility tunnel’s fire protection engineering practice.