Fire Safety in Tunnels and the Effects of Ventilation - Literature review Example

FDS Modeling Literature Review Few years ago, rapid and fast growth in computer technology and hardware development has lad to simulation of hectic and complex technological and scientific problems. In this paper, we will discuss the performance investigation of FDS used in simulation of fire in tunnels. The main aim will be to address the main issues that are involved in tunnel fires. This will be an insight into the modes of ventilation and the workability of these ventilation systems in making the process of saving lives and evacuating victims simplified. Ventilation velocity for control of smoke and the influence of ventilation on the sizes of fire, spread and growth of fire are also discussed. The effects of ventilation will be looked into as a part of the integrated system for tunnel fire safety. FDS Modeling means Fire Dynamic Simulators. This is a modeling that was improved after a research. The research was done to know the relationship between the properties of fuels, sensitivity of the grid, dynamics, and temperature of plume. The model is also used to show that, an engineering consultant on fire protection may effectively predict results using computer model (Forney, 2004). This cannot be effectively achieved when using a full size scenario of simulation. Fire process has complex and complicated phenomenon. There are chemical processes involved, turbulence and combustion. Research also shows that fluid dynamic and radiation processes are also involved (Kenyon, 2006). A number of catastrophic events involving fire in tunnels have caused mass destruction and damage of valuable things and los of lives. For a number of years, simulation of fire using computers has become very successful in saving of lives and resources in tunnel fires. It is used in rescue in a specific area. They help in knowing how fire is spread and how it started. People can also know the condition of the fire i.e. how the heat is released, the temperature, the speed of the air, and how the smoke moves. They are also used to analyze how effective the suppression of fire is to fire wardens and fire fighters (Gao-shang, 2006). FDS helps to know thermal driven flow of smoke and heat from the combusting objects. It is therefore, a form of computerized fluid dynamic that uses flow of fluid driven by fire. It aims at providing solutions to fire problems especially in burning and combustion. It is very effective to fire protection engineers. The Fire Dynamic Simulation has been developed to assist in management of different operating systems. They can be run in series or in parallel form or even multiple. It uses an interface called ‘message passing” which runs a single Fire Dynamic Simulation work in computers. In FDS, there are many meshes that allow the flow of fluid. The interface allows the sending of data between the processes. Every mesh has individual interface process. This allows the large meshes to compute on the processors needed (Forney, 2004). The accuracy of fire that is simulating depends on the grid size resolution. This makes the researchers find out the effect of the size of the grid on fire features. The features of the fire include the height of the fire, distribution of the temperature and the heat (Jin Xu-Hui, 1999). When something is burning, it produces smoke and heat. Somebody can easily note the presence of fire at a distance from the appearances of smoke or feel of heat. It is there impossible to do a study of fire without discussing about the smoke and heat. Various researches have been done on smoke and heat in tunnels by different scientists. The scientists have not yet rested and are still doing more researches on the ways of reducing tunnel fires. They are also analyzing the ways in which lives and resources can be rescued in cases of fire in tunnels. As discussed earlier in the text, they have come up with technologies as part of their study. Development of Fire Dynamic Simulations is one of them. It is used in carrying out of researches on smoke and heat (Linteris, 2004). In this world of development, people have started developing and making of smoke management systems in times of emergencies or when there is incidental fire. They are dependent on model and their designs. There are various methods of tests e.g. the hot smoke test. They use fire conditioning stimulations to analyses the use in constructed buildings. They also use installed systems that does not cause any harm or destruction to the structures. A number of scientists and engineers did experiments in different buildings using hot smoke test. Their test recorded air temperatures, optical density of smoke and the speed of the air in several areas (Australian standard, 1999). According to Gelder Bedford, 2003, predictions of simulation can be used to analyze or to find out whether current arrangement of a place can be improved to hold the smoke well spread in tunnels. Apart from the system of water mist, planned for a place and that would mark a point in improving a safety of a place, new fire resistance doors can be used. Ventilation methods can also be used to improve on safety in tunnels. In 2005, NIST used Fire Dynamic Simulation code to perform CFD modeling. They found out that fire used 75% of the oxygen available in the tunnel. But, according to the author, this was an overestimation. The model uses a combustion model called ‘mixed is burnt’. The real combustion processes are very complicated and inefficient in an enclosed place like the tunnel. The model overestimated the combustion percentage because most of the fuel was used in the tunnel or was never used at all. It could be concluded that, computer based models especially Fire Dynamic Simulation is very crucial in assisting fire safety decision making. However, many models can bring undesired results and therefore, misleading (McGrattan, 2004). The data that is collected globally shows that, the departments in charge of fire are frequently involved in fire fighting. In U.S it has become very difficult to control tunnel fires. The have been trying day and night to manage fire invents and this is followed by a lot of difficulties. Almost half of the tunnels in U.S reports that they low truck services for emergencies. They own some and the rest are available to individual people. Internationally, a few of the agencies reported on the strength of their fire management programs. With the use of fire dynamic stimulation model, the agencies could effectively manage the tunnel fires (Beard, 2006). Consequences of tunnel fires have been very catastrophic. Some of the well known cases are the “Mont Blanc tunnel”, 1999; “Swiss St. Gotthard tunnel”, 2001 and “Austrian Kaprun funicular fire”, 2000. Various researches have been done to provide guidelines for proper design of ventilation systems so as to support life during the evacuation processes. Miclea et al (2007) looked at the various design practices that are internationally acclaimed and used in the design of fire safety mechanisms in tunnels. In this research focus was on the design practices in use in various places according to geographic localities like Europe, Asia and Northern America. Kashef (2008) performed a research on a case study that looked into the control of smoke and fire in road tunnels. This research looks into the various designs that are applied in enhancing effective ventilation strategies during an emergency. Scientific methods are applied here. Ricky (2009) looked at ventilation systems as well as suppression systems in road tunnels. Focus has been given on these two technologies; suppression and ventilation as the most important fire safety mechanisms in tunnel fires. The works done by these authors are so deep and pertinent in this research and can be hailed as great. However, in this paper, there will be focus on filling the gaps that have been left by these researches. The concept of the ventilation systems and the magnitude that they plays in reduction of threats during emergencies, various design procedures for the systems and the importance to which these systems should be accorded in the tunnel design process. This will serve to enhance fire safety and then expound on the effects of the ventilation systems to all stakeholders who might be involved in enhancement of this safety. Today, research is still needed to evaluate the fire test data available added to Computational Fluid Dynamics modeling. This will help in understanding the dynamics of tunnel fires. The problem is to ensure that, the fire dynamic simulations are valid to induce the rate of heat released and the rate at which the flame is spreading or moving. The valid tunnel fire model will help in designing of ventilation in tunnels. For very large fires used in testing the suppression systems of tunnels fires, the variability of fire is greater than the small scale fires (Huijben, 2005). There is a big problem to give the performance measures of fire that evaluate the importance of suppression system. The performance can only be left to the authorities that think that fire behaves in a certain manner. Many roads tunnels have ventilations that control smoke in fire emergencies. The air can flow longitudinally by the help of fans. When it moves in such a manner, the water particles from the fixed suppressions of the fire will be interfered with. This shows that the Fire Dynamic Simulations are efficient for fire fighting (Ernst S, 2005). Fire safety in tunnels poses a variety of safety issues. This is more so due to the increasing number of tunnels, lengths of the tunnels and the number of people who are constantly using them. There are some main fire issues which are involved in this case which include; evacuation of trapped people, rescue operations, effects to the environment as a result of the combustible materials involved and lastly minimization of the property loss. Threats to life in tunnel occur mainly due to poisonous gases inhalation, high temperatures exposure and also heat fluxes. To safely evacuate victims in a tunnel, it is pertinent that there is viability in the temperatures, visibility and the quality of air in the tunnels. Underground spaces and tunnels give a unique problem for life and fire safety. Effective fire strategies should be developed and then adopted to ensure safe operation (MacDonald, 2010). In year 2006, San Pedro de Anes in Spain a research was done where a computational fluid dynamic model was used to a number of fire tests. Very large fires of wood and plastic pallets were used to carry out a test. They required the heat release rate under controlled conditions. Thermocouples were placed at different distances from the fire. They recorded temperatures all through the test. The test was to be used to give valuable information about the interaction between water mist and large fires in the tunnels. There was also the importance of evaluating the performance of water systems in comparison to indicators used during fully test. The Fire Dynamic Simulator and Computational Fluid Dynamic models were used to activate Marioff San Pedro fire safety in the tunnels. The computational fluid dynamic is not 100% effective. It has some short comings. There are accuracy and discipline problems associated with it. Computational fluid dynamic model is a strong tool needed for understanding the importance of water mist systems (Mawhinney, 2006). There is a common thing about all the fire test programs done in recent years- the tests are very long in scale compared to the norm of performance of testing the fire protection systems in industrial applications of old days. A research done in the Runehamar tunnel, Norway in year 2003 shows that, the rate of heat released in heavy vehicles fuel loads is about 75 to 200 Mega Watts. Very large fires used in testing bring about problems during approval of test programs. The sources of large fires made of wood and plastic pallets are not specific. Confinements in the tunnels can bring these complications. It is difficult to do comparisons between tests because of the condition brought about by the huge and large fires. With an assumption that the materials used for testing have almost the same burning properties, the ventilations can be modified. This can be done using obstructions on heat release rate and the rate at which the fire grows. The shapes and sizes of fuel packages are altered as the fire burns causing variations in reading. In the test done by IMO (International maritime Organization), fire with 10 Mega Watts was considered to be large within 15 minutes (Annex B, 2006). The organization is in charge of mist water systems for aquatic machineries especially ships. The test done by the organization expected the fire to extinguish within 15 minutes. This is a good time because the water mist test protection method of fire cannot extinguish heavy goods vehicle fires. The importance of water mist system is to control the fire temperatures of the fire in the tunnels. It controls water from exceeding and to prevent propagation of fire. The fire controlled is sensitive to slight changes in the ventilation. It is very crucial to identify the dynamic nature of the fire in order to know the performance of the fire protection systems. The events followed by controlled large fire in tunnels do not strictly remain the same. It can be confirmed by several calibrations (Ingason, 2005). A review of literature on tunnel safety shows that, the computational fluid dynamic modeling is used in investigation of tunnel safety issues. The model provides a way of analyzing the phenomena involved in fires in the tunnels. At this level, the use of fire dynamic simulator is simulated by San Pedro tunnel fire tests. It is confirmed that the model can forecast conditions which are like the ones used during the scale test. It is therefore a useful tool for analyzing the performance of water mist systems. The model can be tested effectively. Fire dynamic simulator is developed for fire engineering and science studies. Fire dynamic simulator, version 4.0.7 was first developed followed by Version 5. The first fire dynamic simulator was based on the distribution of spray, sprinklers of high standard (Mawhinney, 2006). At NIST, Fire dynamic simulation is still used for research purposes. It is very effective because it solves equations which are fundamental in conservation. It gives fewer errors. However, the users must follow manuals provided for guidance (Mowrer, 2001). Studies in validation have shown that the transport of heat and smoke are predicted vey well by the use of Fire Dynamic Simulations (Jason, F., 2010). The model has been recommended for turbulent and laminar flow in narrow channels which have smooth and rough walls. It is able to reproduce friction factors. The research that is done by various engineers, technologists and institutions show a tremendous improvement of Fire Dynamic Simulation (Vauquelin, 2006). This will help curb fire damages and loss of lives in tunnels. People around the world will be at a lower risk of suffering from tunnel fires. In addition, fire protection agencies will come up with effective fire protection methods. This will be achieved when they stay abreast with development of safety measures. References Allan M (1999). Hot Smoke Testing In Tunnels: Melbournes Citylink. Australia pp.22-24 Annex B. (1996). Amendment to The Test Method For Equivalent Fire Extinguishing Systems. International Maritime Organization. Carvel, R.O Beard, An Jowitt P (2005). Fire Spread between Vehicles In Tunnels: Effects Of Tunnel Size, Longitudinal Ventilation And Vehicle Spacing. Fire tech. Francisco. CarvelR, Guillermo,R,(2009). Ventilation and Suppression Systems in Road Tunnels: some issues regarding their appropriate use in fire emergencies .Tunnel Forum for Road Rail. Francisco. Emmerish S.J. (1998). Application of a Large Eddy Simulation. Model to Study Room Air Flow, Francisco. Floyd J.D. (2001). Mixture Fraction Combustion Model for Fire Simulation. Engineered Fire Protection Design. Francisco pp. 211-226. 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Simulation Analysis for Peoples Escape in Public Building Fire. Fire Safety Science. Read More