Fires in Underground Transport Systems - Essay Example

? Fires in Underground Transport Systems Introduction Underground transportation systems planned and built these days are obviously very complex and vulnerable to fire accidents. Evidences show that fire accidents in the recent past caused extreme damages to people and property alike. Due to the spatial limitations of an underground transportation system, tunnel fires hinder all ‘rescue and repair’ operations and hence add to the intensity of the catastrophe. In addition, unlike other accident scenarios, passengers are less aware of the sources of danger and may not have clear and coherent information. This situation will also become a barrier to evacuation measures and increase the magnitude of the disaster. As Julga (1984) argues, technical defects and accidents are the two fundamental causes of fires in underground transportation systems. Although a variety of fire resisting tunnel transportation technologies have been developed recently, none of them is potential enough to completely eliminate the danger of fire. This paper will discuss the causes and effects of tunnel fires or fire accidents in underground transportation systems. It will also make recommendations to mitigate the impact of such types of disasters in future. Description of Major Incidents Some of the recent fire accidents in underground transportations systems are described below. They would help one to understand the seriousness of the issue. King’s Cross fire The King’s Cross fire was a destructive fire occurred at the underground rail transportation system in London. The disaster occurred on 18th November 1987 and stole 31 lives. This fatal incident happened at the King’s Cross St. Pancras station which comprised of two parts; a subsurface station and a deep level tube station. The fire developed from an escalator shaft connecting the Piccadilly Line and reached the top of the deep level tube station; hence, the strength of the fire was unimaginable even at its initial stages. The forensic investigation connected the disaster to a fluid flow phenomenon. As Allinson (2005, pp.223-225) points out, although the real cause of this fire still remains unrevealed, careless use of fire by travellers, staleness of the escalator, and other technical reasons were thought to be the causes of the disaster. Invisible flames and clean wood smoke caused misinterpretations among emergency response teams. In addition to 31 deaths, more than 60 people got hurt ranging from smoke inhalation to severe burns. Kaprun fire disaster The Kaprun fire disaster occurred at the Gletscherbahn 2 railway tunnel in Austria on 11th November 2000. The disaster killed 155 people; 12 people including 10 Germans and 2 Austrian were the only survivors of the catastrophe. As Carvel et al (2005, p. 6) claim, the unscientific infrastructure of the railway car greatly added to the disaster. To illustrate, the unit had kept its fire extinguishers out of the travellers’ reach and there were no smoke detectors on the board. The fire was ignited by an electric heater at the lower end of the train evidently due to a faulty design. The braking system pipes containing flammable hydraulic fluid were quickly melted and this condition resulted in an unexpected halt of the train. The intense fire damaged the emergency exit systems of the train and therefore majority of the passengers were trapped in the train. Prior to the Kaprun disaster, designers had held a general view that fire would not occur in a funicular cabin. 1995 Baku Metro fire According to Fridolf (2010), the fire occurred in the subway system in Baku, the capital city of Azerbaijan, on 28th October 1995 claimed the lives of 289 people. Electrical malfunction is believed to be the ultimate cause of the disaster even though there alleged to have a deliberate sabotage. Although 95% of the passengers survived the disaster, it remains the world’s deadliest fire in the underground transport system (ibid). Firstly, passengers observed white smoke, which was quickly turned to thick black smoke and caused irritation. The putative electrical malfunction halted the train and hence the tunnel was full of smoke. Although the driver realized the emergency and demanded immediate power cut, burning of synthetic materials caused lethal carbon monoxide emissions which affected travellers quickly. The disaster also damaged the ventilation system of the train and this condition raised the number of deaths and injuries. Similarly, the intense smoke and failure of exit systems greatly challenged all rescue operations. A critical analysis on chemical explosions (or fires) There are two fundamental causes for fires in underground transportations systems: technical defects and accidents. Evidences suggest that technical defects are the main causes of majority of underground tunnel fires. The technical defects may include “accumulation of combustible debris along the roadway and within vent shafts; fuel spills and oils on the road surface; flammable materials carried as cargo; short circuits or electrical malfunctions in control or power cables; and ventilation and air handling equipment” (Protectorwire, n.d). Generally, fires caused by technical defects develop at a slower pace and hence such disasters are not detected before the fires reach its peak levels. Experiments and other real disaster experiences show that tunnel fires may reach a distance ranging from 4 to 8 metres. In case of fires caused by an accident, spilled petrol causes rapid spread of the fire, and this situation would probably result in the burning of nearby vehicles. If fire occurs on heavy goods vehicles, it would uncontrollably pass to other vehicles due to large volume of loads and ventilation conditions. It has been identified that increased usage of plastic materials in automobile manufacture causes high smoke production during a fire accident. If there is no thick traffic, fires on cars can be easily extinguished without much effort. Statistical calculations indicate that the probability of a fire in underground rail transport to underground road transport is 1:20 to 1:25. Although the sources of fire in a passenger train are only a few, a disaster would claim the lives of hundreds of people. Burns (2005, p. 438) points out that deaths and injuries in underground transport fires result from direct exposure to heat and toxic gas emissions. Limited access for fire workers to accident scenario, inadequacy of water supply, and insufficient ventilation facilities usually increase the adverse impacts of fires in underground transport systems. In addition, development of advanced technologies today lead to the construction of further lengthy tunnels, and this condition also hampers the emergency response efforts. The heat produced during underground transportation fires is very dangerous as tunnels are closed systems and the heat remains in the tunnel itself for long hours. Scientific studies point out that the thick soil and rocks nearby the fire accident place slow down the process of heat dissipation. Therefore, a high gas temperature is quickly developed in the accident area. However, it must be noted that the intensity of the tunnel fire disaster may largely vary with the degree of heat evolved during the fire. The mass of the evolved heat in tunnel fires or fires in underground transport systems is different for different kinds of vehicle. For instance, the mass of the evolved heat for an underground railway wagon is higher than any other vehicle. According to Blennemann and Girnau, the mass of the heat evolved in a total burn out of a NF 10 underground railway wagon generates nearly 91,592,854 kJ energy (given that wagon length is 40m and width 2.4m) (cited in Fehervari, 2008). The equivalent heat load for different types of vehicles is illustrated below. (Source: Fehervari, 2008). From the figure, it is clear that the equivalent heat load produced is directly proportional to the size of the vehicle. The diagram indicates that the equivalent heat evolved during the burn out of a small car is 2.5mW whereas it is 5mW in the case of medium car and 8mW in the case big car. Similarly, a bus burn out will produce an equivalent heat load of 15mW while it reaches 20mW in a coach burn out. The figure clearly depicts that that a total burn out of a railway wagon is dreadful as compared to other vehicles as it generates an equivalent heat load of 100mW. Nowadays, designers try to minimise the total mass of flammable materials in vehicle assembly so that the heat evolved during a fire accident would cause less harm to human organisms. Although it is possible to calculate approximately the equivalent heat load produced during the burn out of different vehicles, the rate of spread of fire cannot be measured using these data. There are different standardised fire characteristics curves used to describe the common characteristics of an average tunnel fire. As Fehervari (2008) describes, among the developed models, the RWS, RijksWaterStaat illustrates the highest maximum temperature than any other curve; and this curve describes a case scenario of a road tunnel accident in which a container with 50 m3 gasoline explodes. The explosion releases energy of 300 MJ in 180 minutes. “The behaviour of the curve shows rapid increasing duding the ignition period, deceleration in rate of temperature increase in the second period, a significant maximum point, slight recession and stagnation” (Fehervari, 2008). In addition, it has been also identified that the temperature will be the maximum at the roof of the tunnel during a fire while it will be relatively lower at the tunnel walls. The water which is chemically and physically bound inside concrete walls is released during a tunnel fires due to the effect of quickly rising temperature and these water molecules change to gaseous state; and when the water transforms to gaseous state, its volume will be increased by a factor of 1,100 (Fermacell, 2010). The smoke produced during an underground transport fire also plays an inevitable role in causing deaths and injuries. Hence, it is necessary to analyse the rate at which smoke is generated and its movement in tunnel fires. Lee and Ryou (as cited in McGrattan, 2006) carried out a study using Fire Dynamics Stimulation (FDS) code to assess the effect of the aspect ratio on smoke spread in underground transport fires. From the study, they found that the growth and development of the smoke during a tunnel fire notably varies with the aspect ratio of the tunnel cross section (ibid). Empirical evidences and experience results show that large eddy stimulation affects the smoke movement during a ventilated tunnel fire. In addition, the visibility of the smoke is heavily dependent on the components used in the manufacture of vehicles involved in fire accidents. As we discussed earlier, white smoke is difficult to be identified quickly and hence it would add to the dreadfulness of the disaster. The magnitude of a tunnel disaster is greatly determined by the critical velocity of the smoke, which can be “defined as the minimum longitudinal ventilation velocity needed to avoid the upstream smoke flow” (Yucel et al, 2008). The critical velocity of the smoke in turn relates to the rate of fire heat release. In other words, the critical velocity significantly varies with the cross-sectional geometry of tunnels. Toulouse chemical explosion The chemical explosion occurred at Toulouse in France on 21st September 2001 claimed the lives of 29 people. The explosion dreadfully hit the AZF fertiliser factory, a subsidiary of AtoFina. According to Arens and Thull (2001), a total of 2,400 people were injured including 34 severe injuries. There were more than 600 employees working in the factory in several shifts (ibid). Since the chemical explosion occurred unexpectedly and intensely, the workers had no chance to escape. The pressure of explosion threw automobiles into the air and severely damaged the nearby buildings and surrounding area. The intensity of the explosion was sufficient enough to damage things at a distance of 5 kilometres from the factory. In addition, it also damaged hundreds of vehicles and the traffic system due to high volume of dust and bricks. The detonation resulted in the release of cloud like gas, which totally collapsed the telephone network in the city centre and nearby areas. It was estimated that the chemical explosion caused the loss of several billion francs. As Arens and Thull (2001) reported, the Institute for Geophysics at Strasbourg recorded the blast at 3.4 on the Richter scale and hence this disaster became one of the deadliest chemical explosions in the modern industrial history. Even though the dangerous conditions in the factory were well known prior to the detonation, concerned authorities could not prevent the catastrophe. However, many people including French chemical workers were of the opinion that widespread cost cutting in the chemical industry contributed to the Toulouse disaster. Investigations reported that nearly three thousand tons of ammonium nitrate was kept in the factory at the time of the explosion. Official enquires pointed that mishandling of ammonium nitrate was the central cause of the explosion (UNEP, 2001). At the same time, some people still suspect a terrorist attack as it occurred just ten days after the World Trade Centre attack. It is obvious that ammonium nitrate is sensitive to heat and organic materials such as coal and oil. Anyhow, enormous level of heat and smoke raised challenges to the evacuation activities and fuelled the after-effects of the disaster. Consequences of explosions Empirical evidences show that either fires in underground transports systems or other chemical explosions cause devastating impacts. As compared to other chemical detonations, underground transport fire accidents kill more people as tunnels are closed systems and it would be difficult for passengers to escape during a fire. To illustrate, Mont Blank, Gotthard, Kaprun, and Tauern tunnel fires which occurred over a time period of just two years led to the death of 221 people. The smoke generated during a chemical explosion contains a component called carbon monoxide, inhalation of which may even cause death (Lbfdtraining.com). When a person inhales carbon monoxide, it combines with haemoglobin to form carboxyhaemoglobin which hampers effective delivery of oxygen to body tissues. Even a low concentration of 667 ppm carbon monoxide is able to convert 50% of the body’s haemoglobin to carboxyhaemoglobin. A 50% presence of carboxyhaemoglobin in body may result in seizure, coma, and sometimes death. Medical researchers have identified that confusion and visual disturbance are two major neurological signs of carbon monoxide poisoning (Hopkins & Bigler, 2001, pp.41-42). These neurological troubles physically weaken an individual during a tunnel fire disaster and hence lessen his possibility of a survival. Carbon monoxide combines with other molecules in the human body including myoglobin and mitochondrial cytochrome oxidase. Several studies indicate that carbon monoxide exposure may lead to heart failure and damages to central nervous system. In addition to human tragedy, such fire accidents heavily damage the infrastructure of the underground transport system in general. Hence, human and material losses are identified to be the major consequences of tunnel fires. It must be noted that even though tunnel fires and other chemical explosions involve many serious socio-economic losses, academic literatures have not sufficiently discussed this aspect yet. Underground transport fire accidents often lead to closure of tunnels and this condition adversely affect the economy in total. For instance, the channel tunnel fire caused a financial loss of ?200 million as a result of direct damages and lost revenues. As Khoury et al (2009) point out, the Italian economy’s socio-economic loss due to the three year closure of Mont Blanc tunnel was estimated to be ?2.6 billion according to the Industry Ministry. Generally, socio-economic costs associated with a tunnel fire include maintenance costs, user benefits-costs, and internal returns. Hence, human and socio-economic losses are the major consequences of a chemical explosion or underground transport fire. A critical appraisal From the above discussion, it is obvious that a high level of heat and smoke is generated during every chemical explosion regardless whether it is in an underground transport system or in an open infrastructure. Smoke and heat evolved cause fatality to humans while the heat damages the surrounding structures. Technical defects together with mishandling of equipments cause explosion in majority of the cases. It is very difficult for humans to walk in thick smoke and this situation reduces the effectiveness of rescue operations. In case of chemical explosions, it is a cumbersome task to stop the fire before the building or wagon is completely burned out as it contains different flammable materials. While analysing railway tunnel fires, it is evident that they have some similarities. Most of the railway tunnel fires damage the emergency exit system of the wagon and it increases the number of deaths and injuries. In addition, tunnel fires develop gradually and last for several hours whereas other open place explosions happen in seconds. The intensity of the disaster often depends on the responsiveness and courage of passengers in the burning building or wagon. Likewise, it seems rescue workers take relatively long time to reach tunnel fire spots due to the closed nature of tunnel structures. In short, rescue teams have to take extra care to stop further spread of fire while responding to a chemical explosion. Recommendations Fire-resistant boards have been developed to prevent the explosive reaction of concrete walls to heat and smoke. They are potential enough to protect underground transport structures even against a high peak temperature of 1,350o C. This technology also prevents concrete spall and slough. In addition to technology applications, fire extinguishers and other safety equipments have to be kept at people’s reach. In the case of tunnel transport, it must be ensured that the vehicles are free from technical defects before each journey. Furthermore, the vehicle driver or other officials must ensure that passengers do not involve in any activity that may cause fire. Conclusions The discussion altogether indicates that fires in underground transport result in dreadful impacts including human and material damage and immeasurable socio-economic losses. Normally, technical defects and accidents are the root causes of tunnel fire. The smoke and heat produced during the chemical explosion pose barriers to rescue activities and hence add to the intensity of the disaster. Carbon monoxide, a component of the smoke, is extremely toxic and can cause immediate death. Chemical explosions are difficult to be addressed due to the quick spread of fire. Underground transport fire accidents can be reduced to a considerable extent if passengers are well aware of the activities that may cause fire. References Allinson, RE 2005, ‘The king’s cross underground fire’, Saving Human Lives: Lessons in Management Ethics, Springer, Netherlands. Arens, M & Thull, F 2001, ‘Chemical explosion in Toulouse, France leaves at least 29 dead’, World Socialist Web Site, Viewed 20 January 2012, Burns, D 2005, ‘Emergency procedures in road tunnels: Current practice and future ideas’, in A Beard & R Carvel (eds), The Handbook of Tunnel Fire Safety, Thomas Telford Publishing, London. Carvel, R, Marlair, G & Beard, A (Ed) 2005, ‘A history of fire incidents in tunnels’, The Handbook of Tunnel Fire Safety, Thomas Telford Publishing, London. Fehervari, S 2008, ‘Characteristics of tunnel fires’, Concrete Structures, pp. 56-60, Viewed 20 January 2012, Fermacell 2010, ‘AESTUVER: Fire safety concepts for underground transport systems’, pp. 1-27, Viewed 20 January 2012, Fridolf, K 2010, ‘Fire evacuation in underground transportation systems: A review of accidents and empirical research’, Department of Fire Safety Engineering and Systems Safety, pp. 1-52, Viewed 20 January 2012, Hopkins, RO & Bigler, ED 2001‘Pulmonary disorders’, in RE Tarter, M Butters & SR Beers (eds), Critical Issues in Neuropsychology: Medical Neuropsychology, Springer, USA. Julga, G 1984, ‘Problems of operational planning for fires connected with an underground rail transport system: The Hamburg high speed railway’, Fire Safety Journal, vol. 8, no. 1, pp. 53-61. Khoury, GA, Walley, D & McWilliams, D 2009, ‘New methods for road tunnel fire safety evaluation and upgrading', Proceedings of the Institution of Civil Engineers Structures and Buildings, vol. 162, no. 3, pp. 183-197. Lbfdtraining.com n.d, ‘Fire behavior and chemistry’, Viewed 20 January 2012, McGrattan, K 2006, ‘Fire dynamics simulator (version 4) technical reference guide’, NIST: National Institute of Standards and Technology, pp. 1-99, Viewed 20 January 2012, Protectowire: Fire Systems n.d, ‘Overheat and fire detection in tunnels’, Special Hazard Application, Viewed 20 January 2012, UNEP: United Nations Environment Programme 2001, ‘Ammonium nitrate explosion in Toulouse – France’, Disaster, Viewed 20 January 2012, Yucel, N, Berberoglu, MI, Karaaslan, S & Dinler, N 2008, ‘Experimental and numerical simulation of fire in a scaled underground station’, World Academy of Science, Engineering and Technology, pp. 309-314, Viewed 20 January 2012, Read More