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As a kind of critical infrastructure of energy transportation, so-called 'utility tunnels' have been developed around the world. Hosting a natural gas pipeline inside the natural gas compartment of a utility tunnel facilitates its maintenance but also brings potential explosion concerns due to the confined space. Although some work focuses on the risk analysis of the natural gas pipeline inside utility tunnels, a resilience assessment is needed for dynamically modeling leakage with interacting safety barriers. In this paper, a resilience assessment model of the natural gas compartment of utility tunnels is elaborated based on numerical simulation considering interacting barrier modeling, including sensors, a ventilation system, and the possibility of emergency shutdown. Based on the calculated (natural gas compartment) resilience for casualty and economic loss, ventilation strategies and sensor layouts can be recommended and optimization is possible. Meanwhile, the delay effect of safety barriers is investigated in this work, and the unequal interval layouts of sensors are explored and proven to be effective without any further cost. The proposed resilience assessment model can be important to further improve the safety management of utility tunnels and other confined spaces where hazardous gases are transported. • Dynamic resilience assessment of natural gas compartment considering various safety barriers • Interactions and the delay effect of safety barriers are modelled and identified • optimizing emergency strategy and supporting the resilience management of utility tunnel [ABSTRACT FROM AUTHOR]

• Energy transfer and conversion could be a novel pattern for risk assessment. • Coupling risk assessment framework for utility tunnels is proposed. • Risk assessment of typical coupling accidents in utility tunnels is conducted. • The relation between coupling effect, synergistic effect, and cascading effect is distinguished. As a kind of highly integrated urban critical infrastructure, the urban underground utility tunnel hosts various pipelines to facilitate the city life. But the integration of hazardous pipelines like natural gas pipelines and electric cables inside a confined infrastructure also brings emerging risks due to coupling effect, which have not been systematically analysed by the existing method. So, there is an essential need for a coupling risk assessment (CRA) model to tackle coupling effects and corresponding coupling accidents in utility tunnels quantitatively. A clear definition and classification of coupling effect, synergistic effect, and cascading effect are proposed in this work. By introducing the energy transfer and out-of-control theory, it is feasible to identify interacted hazards systematically and coupling accidents in utility tunnels. Natural gas explosion, cable fire, and rain-triggered ponding are identified as typical coupling accidents to perform CRA. The results indicate that the risks of the 3 coupling accidents are considerable, and fatality is possible in the case of gas explosion and ponding. It can be concluded that the current firefighting systems and drainage systems are not sufficient for risk mitigation of utility tunnels with coupling effect. [ABSTRACT FROM AUTHOR]

With rapid urbanization in China, many underground utility tunnels have been established these years. This huge underground construction facilitates city life, but may introduce societal risks due to the installation of high‐risk pipelines. Natural gas pipelines have the potential to cause catastrophic accident if a gas leakage and a subsequent explosion occurs. The potential hazards in the gas compartments of a utility tunnel are quite different from those in conventional directly buried gas pipelines. This study developed a dynamic quantitative risk analysis method for natural gas pipelines in a utility tunnel. First, potential accident scenarios of natural gas pipelines situated in a utility tunnel were identified and implemented in a Bow‐tie diagram based on case studies of typical gas pipeline accidents and expert experience. Then, a Bayesian network was established from the Bow‐tie diagram using a mapping algorithm. Based on a comprehensive analysis of the results of probability updating and sensitivity analysis, critical influencing factors were identified. The proposed framework provides a predictive analysis of the gas pipeline accident evolution process from causes to consequences and examines key challenges in gas pipeline risk management in utility tunnels. © 2019 American Institute of Chemical Engineers Process Saf Prog: e12051 2019 [ABSTRACT FROM AUTHOR]

• A consequence rapid prediction model (CRPM) in gas leakage and scenarios is developed. • A risk-based optimization approach for emergency response systems in utility tunnels is proposed. • The effectiveness of the proposed approach is validated using an engineering case study. Focusing on the effective configuration of emergency response systems in utility tunnels, this study proposes an innovative approach to optimize existing emergency response systems based on a consequence rapid prediction model and genetic algorithm. In the proposed approach, the interactions between different emergency response components are considered to perform a rapid gas dispersion prediction. Furthermore, the predicted gas concentration distribution is employed to estimate the quantitative explosion risks by combining the equivalent cloud method and the Baker-Strehlow model. Finally, the cumulative and cascading risk index are proposed and combined for systematic optimization by using a genetic algorithm. A case study is performed to demonstrate the feasibility of the proposed approach. The results indicate that the optimized emergency response systems effectively reduce both the cumulative and cascading risk level. This study provides technical support for emergency response system design and helps to improve the safety-risk-control capabilities of utility tunnels. [ABSTRACT FROM AUTHOR]

The energy-absorbing material of metal foam have enormous potential in mitigating the consequences of natural gas explosion disaster in urban utility tunnels. When double-layer metal foam with different pore structures of first larger pores and then smaller pores (LP-SP model), the suppression efficiency of explosion overpressure can reach more than 60% and is 2–3 times that of first smaller pores and then larger pores (SP-LP model), and the error between that and that of the same thickness all with smaller pore structure is only 0.86%. Similarly, the metal foams with the LP-SP model can block the explosion flame propagation chain entirely, while reversing the combination order weakens the suppression effect on the explosion flame. Two suppression mechanisms of double-layer metal foam, including the Sudden Shrinkage Effect (SSE) of the LP-SP model and the Amplification Effect (AE) of the SP-LP model. The metal foam barrier device based on SSE is designed for utility tunnels, which can take effect within 0.1 s under electromagnetic force and gravity. This study can provide scientific theoretical support for designing gas explosion suppression measures in utility tunnels. • Double-layer metal foam have enormous potential in suppressing the gas explosion. • Metal foam with different pore structures effects explosion suppression mechanisms. • Metal foam barrier device is designed to suppress explosion in utility tunnels. [ABSTRACT FROM AUTHOR]

• BI-IEnKF coupling model for gas leakage estimation in utility tunnels is developed. • Source term estimation and gas concentration revision are performed simultaneously. • The implementation of mobile sensors benefits both model prediction accuracy and investment costs. As an effective way to facilitate the increasing demand for reliable infrastructure, energy supply and sustainable urban development, underground utility tunnels have been developed rapidly in recent years. Due to the widespread distribution of utility tunnels, the safe operation of natural gas pipelines accommodated in utility tunnels has caused great concern considering fire, explosion, and other coupling consequences induced by the gas pipeline leakage. However, the limited information on leakage source terms in accidental leakage scenarios could preclude timely consequence assessment and effective emergency response. In this study, a BI-IEnKF coupling source term estimation (STE) model is developed, with the combination of gas dispersion model, Bayesian inference (BI) and iterative ensemble Kalman filter (IEnKF) method, to achieve the effective source term estimation (including leakage location and leakage rate) and gas concentration distribution prediction. The newly developed model is first evaluated by the twin experiment with good reliability and accuracy. Furthermore, three contributing factors affecting the performance of the developed BI-IEnKF coupling STE model were investigated to assist parameter selection for practical use. Additionally, the novel application of mobile sensors serving as an alternative for fixed sensors is explored, and an application framework is sequentially given to guide the deployment of the developed coupling model in utility tunnels. The results show that the developed model has great performance in accuracy, efficiency and robustness, as well as the potential to be applied in actual utility tunnel scenarios. This study can provide technical supports for safety control and emergency response in the case of natural gas pipeline leakage accidents in utility tunnels. Also, it could be helpful to reasonable references for gas lekage monitoring system design. [ABSTRACT FROM AUTHOR]

The prevention and control of natural gas explosion accidents in utility tunnels have drawn great concern due to the unexpected severe consequence. In this study, put forward an explosion suppression measure apply to utility tunnels. An experimental platform for simulating the process of the natural gas explosion in utility tunnels is set up to study the flame propagation law and pressure dynamics distribution under the suppression effect of porous media. Seven experimental configurations of different pore density PPI (pores per inch) and thickness of the porous media are evaluated to investigate the influencing factors of explosion suppression efficiency. The results indicate that lining the sidewalls with porous media does have a certain explosion suppression effect. However, the quenching efficiency of media with small PPI is not significant, or even result in quenching failure, which may be related to flame acceleration due to the interaction between affiliated facilities and flame front. The PPI of porous media is kept constant, and the explosion suppression efficiency is pretty enhanced as the thickness of media increases. Besides, when selecting the suitable porous media as the explosion suppression materials, the acceleration effect of surface roughness on flame propagation cannot be ignored. ∙ An experimental apparatus for modeling the process of natural gas explosion in utility tunnels was established. ∙ An explosion suppression method applied to utility tunnels was put forward, and verified the feasibility. ∙ The influencing factors of explosion suppression efficiency of porous media were studied. [ABSTRACT FROM AUTHOR]