A study on fire safety provisions of public transport interchanges in well-developed cities

Pao Yue-kong Library Electronic Theses Database

A study on fire safety provisions of public transport interchanges in well-developed cities

 

Author: Qu, Lu
Title: A study on fire safety provisions of public transport interchanges in well-developed cities
Degree: Ph.D.
Year: 2012
Subject: Local transit -- Fires and fire prevention.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiii, 150, [123] leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2615877
URI: http://theses.lib.polyu.edu.hk/handle/200/6979
Abstract: With the requirements for better and more efficient transport systems in well-developed cities, public transport interchanges (PTIs) are built. As several catastrophic fires occurred in the transport system of dense urban areas in the past years in many places over the world, life safety and smooth operation of PTIs have to be ensured. PTIs with both building characteristics and occupant loading are different from other buildings. Fire safety problems have to be addressed differently and will be discussed in this thesis. The thesis starts with a review on the fire safety aspects of PTIs. Fire hazards in possible areas, long evacuation routes and high transient passenger loading were identified. Performance-based design fire engineering approach was commonly applied to provide fire safety of PTIs. Relevant standards, codes and other investigations were reviewed. Hardware provisions of fire safety such as the construction characteristics and fire service installations were investigated. Fire safety management is proposed to be enhanced as software provision. Detailed investigations on the fire risks in PTIs, evacuation of passengers, and smoke movement characteristics in long corridors were carried out to develop the fire safety strategies. Performance of ventilation and smoke control system is very important to prove fire safety. Smoke exhaust system is evaluated in an example public transport interchange including a subway station and a bus terminal under different fire scenarios. Train fire, luggage fire on platform and retail shop fire with different ventilation operations were simulated numerically to identify if there is a tenable environment for the evacuation of passengers. Computational fluid dynamics (CFD) model - Fire Dynamics Simulator (FDS) Version 5 was used to predict smoke spread and the available safe egress time during the fire. It is demonstrated that mechanical exhaust system is useful in delaying the spread of smoke.
Platform screen door (PSD) systems are starting to be popular in underground railway stations. There is a concern that PSDs would affect passenger movement during emergency particularly during rush hours. Effect of PSDs on emergency evacuation under crowded conditions was studied based on the surveyed passenger flow characteristics. As the passenger loading is important for the evacuation simulations, a field survey on the transient passenger loading of selected PTI in Hong Kong was carried out. It was observed that the transient passenger loading can be very high in rush hours. Evacuation times under different passenger loadings from a train vehicle were estimated by empirical equations. Simulations on train evacuation under normal and fire conditions were then carried out using the computer software FDS with evacuation. Several scenarios with different opening conditions of PSDs were considered. There are many long corridors built underground in many PTIs. Design of smoke control systems in such areas requires a good understanding of the smoke mass flux at different parts of the building. A density jump might occur when the smoke released by the fire flows along the ceiling. FDS was used to simulate the characteristics of the density jump along a long corridor. Characteristics of density jump to horizontal smoke movement underneath the ceiling induced by a fire were studied. Numerical experiments on density jump controlled by different types of smoke barriers in a long corridor were reported. From the predicted fire environment in a long corridor, the effect of smoke control system on density jump was identified. Fire safety problems on hazards due to density jump were then pointed out. Characteristics of density jumps with different Froude number in a long corridor were also studied numerically. Timeline approach was commonly applied in performance-based design for many big construction projects. Timeline analysis was carried out on construction projects with difficulties to comply with the prescriptive fire safety codes such as the public transport interchanges. An underground transport station was selected as an example to illustrate the common practice in performance-based design. Both the Available Safe Egress Time (ASET) and the Required Safe Egress Time (RSET) were estimated and then compared. Different fire scenarios with different fire sizes were identified. Fire simulations were carried out to predict ASET. Evacuation simulations were carried out to predict RSET. However, the conclusion will be entirely different with larger fire size and higher occupant loading. The challenges on applying the timeline analysis in performance-based design in crowded areas were pointed out.

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