A study of the critical velocity and the confinement velocity of fire accident in a longitudinally ventilated underground train with different door opening scenarios

Su, Zhihe; Li, Yanfeng; Feng, Shan; Zhong, Hua; Li, Junmei; Liu, Wenbo; Chen, Chao; Li, Jiaxin

doi:10.1016/j.tust.2022.104776

Cited by 7 publications

(7 citation statements)

References 30 publications

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“…At the same time, our previous study 20 on smoke back-layering length and critical velocity in a metro train and horizontal tunnel was validated through comparisons of ventilation velocity and critical velocity with simulation models and small-scale experiments. In this study, a comparison between the simulation data and experimental results was conducted to further validate the reliability of the numerical model.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…To better facilitate evacuation, all the train side doors are set to open. 20 The fire source was placed in the middle of the train to represent the typical situation of a metro tunnel fire. Each experimental scenario was repeated three times, and the uncertainty can be calculated by averaging the results of the repeated tests using X i = Xl¯ ± 2 σ , where Xl¯ is the mean value, and σ is the standard deviation.…”

Section: Model Experimentsmentioning

confidence: 99%

“…At present, the use of flame retardant materials in subway trains is now common practice and has been proven effective in limiting the train fire size. 20,36 Therefore, the T-Square fire was adopted for the fire growth, and the heat release rate (HRR) of the fire was set to 5 MW. According to equation (13a), this represents an HRR of 5.74 kW in the model experiment, also signifying the maximum fire heat release rate in metro tunnel fires.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…18,19 A previous study has shown that the back-layering length in a train is longer than that in a tunnel-blocking area. 20 Therefore, it is important to study the smoke spread inside the train. Second, the coupling effect of the side doors can produce a shorter smoke back-layering length than that of an ordinary tunnel.…”

Section: Introductionmentioning

confidence: 99%

“…Second, the coupling effect of the side doors can produce a shorter smoke back-layering length than that of an ordinary tunnel. 20 Third, smoke would overflow the train and continue to spread upstream in a metro tunnel with a small tunnel slope under natural ventilation. 21 The back-flowed smoke gas front might be stopped inside the train carriage in some extreme cases of large tunnel slopes, such as the transition section of the subway line from the aboveground platform to the underground station.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the fire hazard of underground space fire scenarios in urban metro tunnels under natural ventilation: Analysis of the impact of tunnel slope on smoke back-layering length

Su,

Li,

Zhong

et al. 2023

Building Services Engineering Research and Technology

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The smoke back-layering length is a crucial parameter for evacuating people in both road and subway tunnel fires. This study investigates the fire hazard induced by carriage fire in inclined metro tunnels under natural ventilation. The parameter ‘transition slope’ is defined to measure the smoke flow from the carriage head in the upstream direction to the tunnel or not due to the stack effect of the tunnel slope. The aim of this paper is to analyse the effects of changes in cross-section, downstream length, tunnel slope, and carriage side-door coupling on smoke behaviour characteristics by experiment and simulation methods. A piecewise function expression between dimensionless smoke back-layering length, downstream length, and tunnel slope for carriage fires in an inclined tunnel under natural ventilation is proposed by theoretical analysis. At the same time, a 1:15 scale model experiment was conducted to initially analyse the characteristics of smoke movement. Following this, full-scale numerical simulations were employed to complement the model experiment and quantify the principles governing smoke movement. The experimental results show that the tunnel slope has a significant effect on the smoke back-layering length. In contrast, the influence of the heat release rate was found to be relatively minor. In addition, simulation results show that the tunnel slope has no significant effect on the smoke back-layering length when the fire location is approximately 20 m from the train head, and the tunnel slope is in the range of 2.29° ∼ 3.43° (4% ∼ 6%). For small tunnel slopes, smoke spreads in the tunnel, and the smoke back-layering length produced by the virtual fire source shows a different law from the previous study model. Finally, the correlation coefficient of the piecewise function in theoretical analysis is fitted by combining the experimental and numerical simulation results. Practical application This study provides valuable insights into the practical implications of controlling and mitigating the impact of fires in inclined metro tunnels. By understanding the critical role of tunnel slope and providing a quantitative tool for smoke spread law assessment, this study contributes to the enhancement of safety measures and the protection of lives in tunnel environments during fire incidents.

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Section: Numerical Simulationmentioning

confidence: 99%