EVALUATION OF THE FIRE CHARACTERISTICS AND ITS EFFECTS ON HUMAN EVACUATION OF SINGAPORE �S MASS RAPID TRANSIT SYSTEM

Abstract

Fire safety is of paramount importance in every structure and its magnitude in populated underground structures such as the Mass Rapid Transit (MRT) is immeasurable. The MRT system is the backbone of Singapore’s public transport with an average daily ridership of 2.124 million. As Singapore’s population continues to increase, the ridership of the MRT will hit 4.5 million by 2020. However, the recent train disruptions have shown the limitations of the train operator’s response and preparedness during an emergency. This is an imperative concern as a fire breakout in the MRT system can result in dire consequences as seen in the Deagu (in South Korea) subway fire incident. As such, the purpose of this study is to study the fire smoke movement in Singapore’s MRT system and its effect on the evacuation behaviour of commuters. To understand the characteristics of fire smoke and its influence on commuters, a laboratory experiment which uses a Cone Calorimeter was conducted to obtain the thermal properties of six common polymeric materials (polystyrene, polypropylene, high-density polyethylene, polymethyl methacrylate, polycarbonate and polyethylene terephthalate) that could be found in Singapore’s MRT system. From the experiment, it was observed that amongst all the polymeric materials, polypropylene had the highest heat release rates of 1550kW/m2 with carbon monoxide and carbon dioxide yields of 0.075g/g and 4.5g/g respectively. It was found from literature reviews that a higher heat release rate and carbon monoxide concentration not only results in heat and respiratory inflammatory related injuries leading to death, but also impairs the judgement of an evacuee during an evacuation. Therefore, to provide a worst case scenario, these data served as an input for a case study in Singapore’s underground MRT system. Through the use of Pyrosim, a computational fluid dynamics software, this paper studies the distribution of temperature, CO concentration and smoke movement during a fire in an underground MRT station. There were two scenarios included in the case which were studied at 1, 2, 3, 4, 5, 6 and 20 minutes after a fire ignition. The first scenario was a fire at the front carriage of the train whereas the second scenario was a fire at the center carriage of the train. In both the scenarios, the platform screen doors near the fire reached its threshold limits of all three parameters within 1-2 minutes. In addition, it was found that the platform level would reach the carbon monoxide concentration and visibility threshold limit in 500 seconds. Conversely, all the exits in the station and the concourse level did not reach their threshold limits and were accessible throughout the simulation. Hence, the crucial issue from the findings obtained from Pyrosim was whether commuters were able to evacuate from the station’s platform within 500 seconds. To evaluate the ability of commuters to evacuate from the platform and their evacuation behaviour, this paper coupled the findings from the Pathfinder evacuation software with the findings obtained from Pyrosim. Based on the comparison between a non-smoke and smoke environment, it was found that the total time for a complete evacuation in a smoke environment can increase by up to 84.5 seconds. This increase was caused by inaccessible exit points resulting in commuters having to change their evacuation paths thus taking more time. The total evacuation time of 275.5 seconds in a non-smoke environment was able to meet the NFPA 130 requirements. In an evacuation in a smoke environment, the total evacuation time was 354.28 seconds and 360 seconds in Scenario 1 and 2, an increase of 28.60% and 30.67% when compared to a non-smoke environment. Nevertheless, the increase in total evacuation time was still within the 4 and 6 minutes time required by the NFPA. In addition, it was observed that the fatality rates were 4.59% and 12.34% in Scenarios 1 and 2 respectively. However, it is vital to understand that the findings in this study are only specific to the two scenarios defined in this paper. More often than not, there are other factors that result in a different finding which may not fulfill the NFPA 130 requirements. Such factors include an electrical fault leading to a blackout during an evacuation or the effect of other toxic gases on evacuees in which Pyrosim and Pathfinder are unable to simulate. Nonetheless, the findings and results justify the need to study the fire smoke movement and its effect on the evacuation behaviour of commuters. The findings from this study provide a comprehensive understanding for fire safety managers in formulating their fire safety evacuation plans in an underground MRT station.