## 1 Introduction  
The gas cabin of the utility tunnel hosting the natural gas pipelines has raised concerns about potential gas explosions as the gas cabin is a confined space. The installation of gas baffles on top of the gas cabin is one way to improve the efficiency of monitoring gas leaks and to initiate preventive and control measures in time to avoid subsequent disasters. In the literature review, published scientific papers, master's heeses, patents, and national standards are cited. The Web of Science and CNKI literature database were used to search the literature. Most of the literature cited include open papers published in China and other countries in the last five years. The keywords of the literature are utility tunnel, leakage and diffusion, confined space, gas explosion, Fluent numerical simulation, etc. In recent years, with the continuous promotion of new urbanisation construction, the Chinese government has promoted the construction of underground urban utility tunnels on a large scale to solve the problem of \"urban diseases\" [1]. A utility tunnel is a pipeline system with electricity, communication, water supply, drainage, heat, natural gas, and other municipal pipelines in one integrated system. As the utility tunnel is a confined space, the utility tunnel, which houses the natural gas pipeline, raises concerns about the possibility of a gas explosion. According to GB 50838-2015 Technical Specification for Urban Utility Tunnel Engineering [2] and GB 50058-2014 Code for Design of Electrical Installation in Explosive Atmospheres [3], the natural gas compartment of a utility tunnel must be a separate compartment and equipped with an alarm monitoring system and the lighting system must also be arranged in accordance with the specifications. Although there are some safety barriers, such as gas sensors, a mechanical ventilation system (ventilation inlet and outlet are also pressure relief vents), extinguishers, and fire doors, the delay effect of barrier activation may also result in an explosion [4; 5]. At present, the natural gas monitoring system for utility tunnels that have been built in China usually uses distributed fixed-point detection and concentration detection to achieve the monitoring of natural gas. This method is more effective in situations where the gas spread has already occurred. However, it is difficult to detect this in time before it becomes widespread. Particularly in the case of small holes and weak leaks, untimely detection can be a major safety hazard. There are many analyses by academics of the leakage, dispersion, and explosion of natural gas inside utility tunnels. Most of the recent research on natural gas pipeline leakages and explosions in utility tunnels is focused on CFD simulation and risk analysis. Computational Fluid Dynamics (CFD) tools and experiments have been widely used and integrated to analyse natural gas dispersion [6; 7; 8], explosion overpressure [9; 10; 11], and corresponding optimisation strategies [12; 13; 14]. In addition, the CFD simulation software Fluent is more realized as a feasible tool for modelling gas leakage and explosions in a utility tunnel. [PERSON] et al. [15] used experiments to derive a time response equation for the 50% lower explosive limit of the diffusion concentration of a leak in a gas chamber and simulated it with Fluent to demonstrate the accuracy of the numerical analysis and to provide a reference for the arrangement of monitoring probes. [PERSON] et al. [16] used Fluent to simulate the relationship between the gas leakage diffusion and alarm time of a 20 mm leakage hole in the gas cabin under different ventilation speeds and gas pipeline pressure. The results showed that the relationship between alarm removal time and wind speed of the inlet is approximately linear. [PERSON] et al. [17] used Fluent to simulate the scenarios of gas leakage and diffusion under different ventilation velocities and ventilation outlet sizes, respectively.