## 1 Introduction
The results showed that the optimal ventilation velocity was between 5 m/s and 7 m/s, and the optimal side length of the ventilation outlet was between 1 m and 1.25 m in practical engineering. By comparing the crude oil explosion experiment results with the Fluent simulation results, [PERSON] et al. [18] found that the two results are basically consistent. [PERSON] et al. [19] adopted Fluent to establish the coupling relationship between the first velocity peak, the first overpressure peak, and the filling length of the shock wave propagated by the gas explosion in the utility tunnel. [PERSON] et al. [20], [PERSON] et al. [21], and [PERSON] et al. [22] proved by numerical simulation or experiment that the presence of obstacles in the pipeline or utility tunnel increased the maximum pressure peak of shock wave overpressure. In recent years, risk assessment models for leakage, explosion, and other disaster coupling situations of utility tunnels have been studied by scholars. Generally, there are three main kinds of approaches for assessing the risks of natural gas accidents in utility tunnels: graphical methods, numerical simulations, and experiments. Graphical methods such as fault tree, event tree, Bow-tie diagram, and Bayesian network (BN) were applied to illustrate the causation topology and quantify the probability of different accidents in utility tunnels [23; 24]. [PERSON] et al. [25] proposed a Bayesian network (BN) and computational fluid dynamics (CFD)-based quantitative risk assessment of natural gas explosions in utility tunnels. The results indicated that the failure of the emergency shutdown system (ESD) is the most fatal of all safety barriers, and significant attention should be paid to prevent its failure. [PERSON] et al. [26] proposed an integrated model based on dynamic hazard scenario identification (DHSI), Bayesian network (BN) modeling, and risk analysis for the risk assessment of urban utility tunnels. The results indicated that the integrated quantitative risk assessment framework is an alternative and effective tool for safety assessment and land-use planning of urban utility tunnels. [PERSON] et al. [27] conducted a large-scale 3D combined geomechanical model test to investigate the mechanical characteristics of linings of asymmetrically closely spaced twin tunnels constructed in sandy ground. In summary, research on natural gas leaks, dispersion, and explosions in utility tunnels has mostly focused on the distribution of natural gas after leaks and the risk analysis of each hazard, with little consideration given to construction solutions that enhance monitor detection and optimise monitor placement while ensuring safety. In response to this problem, [PERSON] et al. [28] proposed an optimisation scheme for combustible gas detection systems involving the addition of gas baffles, but the technical parameters given have large work differences. The gas cabin is a restricted space, and the additional gas baffle is an added obstacle. The effect of the gas baffle on the propagation law of the explosion shock wave in the gas cabin is not clear, and it is not known whether the gas baffle can improve the monitoring efficiency of the monitor and whether it can take into account the role of explosion isolation. Therefore, it is necessary to verify its effectiveness through numerical simulations and further study the effect of gas baffles on the diffusion of gas leaks in the utility tunnel and the propagation law of explosion shock waves in order to better guide the optimal arrangement of the combustible gas monitoring system in the gas compartment of the utility tunnel.