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The prediction smoke back-layering length and critical velocity in the event of a fire in a utility tunnel are studied. In this paper, the method of numerical simulation is used to study the combustion characteristics of the cable tray in a utility tunnel. The prediction of smoke back-layering length is related to factors such as heat release rate, longitudinal ventilation velocity, and fire source location. The smoke back-layering length is determined by the temperature record. The temperature measurement is made by thermocouple tree in the utility tunnel. Results show that the dimensionless critical velocity has a certain influence on the dimensionless heat release rate in utility tunnel. The numerical simulation results show that there is an exponential relationship between the dimensionless smoke back-layering length with two fire locations (locations A and C) in the utility tunnel. This paper proposes a method for predicting the smoke back-layering length based on the correlation of numerical simulation data. In two fire locations (locations A and C), the numerical simulation data of the smoke back-layering length has a good correlation with the results of the Li model. The main contribution of this paper is to prevent the smoke propagation in utility tunnels and provide technical guidance. Therefore, this paper has certain guiding significance for the smoke propagation below the ceiling of the electric compartment in utility tunnel. [ABSTRACT FROM AUTHOR]

Utility tunnels are widely builtin many cities. When an unexpected fire occurs in the electrical compartment of utility tunnel, the smoke temperature below the utility tunnel ceiling is one of the most important factors for thermal detection and alarm. In this paper, the smoke temperature distribution under the longitudinal ventilation in a utility tunnel fire accident is studied by combining experiment and numerical simulation. The main purpose of this paper is to study the smoke temperature distribution below the ceiling under the effect of longitudinal ventilation in a utility tunnel, and provide guidance for the installation of detector in case of fire. In addition, three important factors such as ventilation velocity, heat release rate and vertical position of fire source are considered respectively. The thermocouple trees are used to measure the temperature along the longitudinal direction of utility tunnel. Results show that the maximum temperature of the utility tunnel is directly above the fire source without longitudinal ventilation. What’s more, with the ventilation velocity increases, the maximum temperature below the ceiling gradually moves to the downstream of the fire source in utility tunnel. Finally, a new correlation formula is proposed to predict the temperature distribution of smoke in utility tunnels on the basis of theoretical analysis. The longitudinal temperature distribution obtained by numerical simulation is in good agreement with the experimental tests. Therefore, the research in this paper is helpful to prevent utility tunnel fire and reduce people's property loss. [ABSTRACT FROM AUTHOR]

This paper studies the fire spread in horizontal long and narrow space with urban tunnels as the background. The length of the near-fire source area is a key factor to study tunnel fire with hybrid field-network simulation method. The length is influenced by the temperature difference in the cross section and the rate of temperature difference in long and narrow space with different tunnel widths and heat release rates. The theoretical analysis and numerical simulation methods are used to consider the influence of long and narrow space's width, heat release rate, effective ceiling height and the distance from fire source on the smoke propagation. The results show that the length of the near-fire source area are basically affected by the cross-sectional area of the long and narrow space and the heat release rate. For the type t2 ultra-fast fire model, when the heat release rate is 15MW and the length of the near-fire source area is 115m, the smoke flow can be fully developed. Finally, this paper proposes a prediction model for estimating the length of the near-fire source area. [ABSTRACT FROM AUTHOR]