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47. Simulation Research on Effects of Ambient Pressure on Plug-Holing Phenomenon in Tunnel Fires with a Shaft.

Author

Yao, Yongzheng, Wang, Yintong, Zhang, Yue, and Zhao, Jinlong

Subjects
*TUNNEL ventilation, *TEMPERATURE distribution, *NATURAL ventilation, *FLOW velocity, *PREDICTION models, *FIREFIGHTING, *SMOKE
Abstract

This paper studied the effects of ambient pressure on the plug-holing phenomenon in tunnel fires with a shaft by a Fire Dynamics Simulator. The influence of ambient pressures on the smoke movement, temperature distribution, critical Richard number (Ric) and critical shaft height for plug-holing were analyzed in detail. A new prediction formula of smoke flow velocity considering different pressures was modified. A prediction formula of smoke temperature distribution beneath the ceiling under different pressures was developed. As a result, a prediction model of Richard numbers to determine whether the plug-holing occurs was proposed by combining smoke flow velocity and smoke temperature distribution. The critical Richard numbers (Ric) and critical shaft height (hc) increases as the pressure decreases. Outcomes in this study can provide references for the design of a natural ventilation system in tunnel fires at a higher altitude. [ABSTRACT FROM AUTHOR]

Published
2023
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49. Fire Behaviors and smoke transportation law of tunnel fires under confined portal boundaries

Author

Yao, Yongzheng

Subjects
Transportteknik och logistik, model-scale tunnel, Under-ventilated, Infrastrukturteknik, Other Engineering and Technologies not elsewhere specified, Scaling effects, Equivalence ratio, Tunnel fire, Infrastructure Engineering, Mass loss rate, Confined portal boundaries, Gas temperature, Self-extinguishment, O2 volume fraction, CO volume fraction, Husbyggnad, Critical conditions, Övrig annan teknik, Combustion efficiency, Transport Systems and Logistics, Building Technologies
Abstract

An increasing number of tunnels have been built around the world. They play an important role to relieve traffic congestions and facilitate goods transportation. However, in the event of a fire in tunnels, the consequences can be serious due to its narrow-long structure. The previous studies about tunnel fire dynamics and mitigation measures are mostly based on good ventilation conditions in tunnels, such as longitudinal ventilation and natural ventilation with the premise that a tunnel has two open portals. However, the studies about the characteristics of tunnel fires under confined portal boundaries with complete or incomplete sealing at both portals are rare. Typical fire scenarios can appear in a subway train, a building corridor, an underground utility tunnel, a mining tunnel, a tunnel during construction and the application of sealing tunnel portals for fighting large tunnel fires and so on. The knowledge of tunnel fire dynamics for tunnels under good ventilation conditions is probably not applicable to the scenarios of tunnel fires under confined portal boundaries. Conducting the studies of tunnel fires under confined portal boundaries is of great significance for better understanding the characteristics of this type of tunnel fires and developing tunnel fire mitigation measures. Therefore, by combining model-scale tunnel experiments and theoretical analyses, this thesis studies the fire behaviors and smoke transportation law of tunnel fires under confined portal boundaries. The main research contents include: 1．Scaling effects of mass loss rate per unit area (MLRPUA) for well-ventilated pool fires are studied by summarizing large amounts of experimental data from the literature together with theoretical analyses. As a further extension of tunnel fire similarity theory, it provides the basis and reference for later model/medium-scale tunnel experiments. Results show that when a small-scale pool fire (DThis report contains a copy of the translated version of Yongzheng Yao’s PhDthesis. He has been educated at both University of Science and Technology of China and RISE Research Institutes of Sweden. On 26 Oct, 2019, he has successfully defended his thesis. His formal thesis in Chinese has been published by University of Science and Technology of China. The thesis consists of a significant amount of work that Yao conducted at RISE. To facilitate wider use of the results, he has translated it into this English version, which is published here as a RISE report.

Published
2019

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