Knowledge of the Behaviour of Fires - Research Proposal Example

1.1 Background of the Study Though fires are never a desire thing in buildings but this does not prevent their occurrence and when they occur often will result to injuries, death and property being lost [1]. It is due to this that the fire community has increasingly paid attention to addressing this issue [2] [3]. Also the fire and rescue authorities have persistently sought ways of improving their ability of managing and extinguishing fires in a more efficient manner so as to reduce levels of injuries and property damage [4]. In order to improve the management of fire it is critical to understand the way the fire will behave in various prevailing conditions that are likely to be encountered. This has fueled undertaking of many studies as a step of increasing knowledge of the bahaviour of fires, in particular improvement in prevention means, containment and effective management of fire [1] [4]. There has been continuous attempt by researchers to establish what could be the most appropriate means of preventing and containment of fires with the factors influencing the behaviours of fires being put into consideration. [5]. These factors have substantial effect on the control, spread and rate of growth of fire as well as having influence on Heat Release Rate (HRR), the Mass Loss Rate (MLR) and the duration of the fire. While it is common knowledge that fires will exhibit different behaviours ranging from those that burn slowly and evenly to those fires which are extremely hot and burning rapidly, for compartment fires the dynamics are affected by some major factors one of which being the wind influence on the fires [6]. In the resent past wind effect in ventilated compartment fire has been a subject that has attracted many studies with researchers attempting to come up with models describing behavior of fires in various conditions [7] [8] [9]. With construction of multi-story buildings becoming more common, the need to put into consideration the influence of wind in fires occurrence in such buildings has become a priority. The combustion process and movement of smoke in multistory buildings is greatly influenced by the stack effect of these buildings in addition to exposure to wind whereby wind velocity and direction will have effect of the course of the fire [10]. It is with this background that we have had many ongoing studies directed towards having a better understanding of how fire will behave in such structures, which are categorized as compartment fires owing to the fact that they are usually closed. From studies it has been established that the level of influence of wind on a building is proportional to the height, where the dynamics of the fire are affected and smoke dispersion characteristics are very important ingredients in fire safety. In addition studies that have been made about the effect wind has on compartment fires have shown that ambient wind have two effects on compartment fires which are seen as contradictory. One being an increase in the level of severity of fire when there is an increase in the oxygen supply and two is the cooling effect of the wind as a result of heat being removed and the combustible gases being diluted [11] [12]. The thermal behavior of the flame/plume ejection in compartment windows is also found to be significantly affected by ambient wind pressure [13]. Studies have also established that configuration of ventilation in a compartment has influence on the manner in which the flames will behave [8] [14]. Understanding the influence of wind on behavior of fires by improvement in knowledge of the important factors which are vital with regards to the behavior of fire is very necessary. The factors include Mass Loss Rate (MLR), Heat Release Rate (HRR) fire spread and smoke movement as these are likely to contribute to better management and controlling of the fire. 1.2 Need for the Study As a way of gaining more understanding with regards to the management requirement for ensuring fire safety in buildings understanding and being able to make prediction of compartment fires has proved to be very important [8]. This is also very important in placing one at a position of making prediction with regards to fire growth dynamics and the impact the fire will have on the structural elements of the building. There has been some overviews on empirical studies which have been undertaken in the recent past that were aimed at shading light on behavior of fires and this has shown that a lot has already been done with regards to understanding the general issues underlying flying properties, the process of combustion and materials behavior. Also much has been done concerning compartment fire dynamics with ambient wind and varied configurations of compartment vents. However, it has been seen that there is a lot that is yet to be accomplished so as to have a full examination with regards to horizontal ventilation in compartment fires and the possible influence of wind on the behavior exhibited by the wind [8]. It is with this regard that the current study has its focus on the assessment on how behavior of compartment fire with one vent may be affected by wind. The study involve a close look at the wind influence on HRR of the fire, the impact on MLR and the impact on smoke temperature. Wind may be taken to be a natural phenomenon and thus making it to be a common feature of muilti-storey buildings. With careful examination of the influence of wind on various compartment configurations, there can be substantial improvement on many existing theories with regards to power performance [10]. From discussions it has clearly come out that it is not easy to discern the level of risk to life paused in compartment fires owing to the existence of many factors interacting with each other in the occurrence of fire [12]. However, examination of each individual factor may prove to be a useful means of gaining understanding on the influence the factor has on fire behavior and combustion parameters. This will ensure that fire safety practices are to be in a manner of ensuring increased fire management efficiencies in addition to realizing improvement in structural elements design. 1.3 Research Aim and Objectives This research aims at determining how wind velocities affect the behaviour of fire in a compartment where there is only one horizontal ventilation, by employing Computational Fluids Dynamics (CFD) in simulating the fire cases. This is to be achieved by addressing the following specific objectives 1. To determine the effect of wind with different velocities on the heat release rate and mass loss rate of the combustion process. 2. To identify how the presence of one and two ventilation points in a compartment influences the movement of air within a compartment and the associated behaviour of fire. 3. To determine the variation of smoke temperature at different wind velocities across the compartment. 4. To comparing the result between one and two ventilation points in a compartment influences the smoke movement within a compartment and the effect of its movement 1.4 Research Methodology For methodology of choice, the main objective is to come up with the needed solutions so as to be able to provide answers to the stated objectives. This in essence means that any methodology of choice need to ensure that the data collection and analysis process should be able to provide results that can pass the reliability test while research studies on the same subject should be able to validate the results. Use of Fire Dynamics Simulation (FDS) is important in the execution of this research as the program is seen as a leading computer modeling technique in the fire dynamics field owing to its effectiveness in numerical simulation. Specifically CFD model will be used in simulation process of this research [16]. In addition the smokeview programme will be used as it will serve an important role in visualizing the results of numerical calculations which will be helpful in obtaining the required dynamic details in the compartment fire. 1.5 Main Achievements Through this study there has been new understanding on the impact of wind on fire behavior in the context of fire engineering design. This has been attained by undertaking experimental case study research aimed at examining the effect wind has on compartment fires. The following are the main achievements of this research are: 1. When the velocity of wind increases, the combustion process increase interns the heat release rate and the mass loss rate increases. 2. Wind velocity between 4 to 5.5 m/s helps in achieving maximum heat release rate. 3. The temperature inside the compartment increased due to the increasing supply of oxygen. In this study there is modeling of the impact of six wind velocities (0, 2, 4, 6, and 8 m/s) using FDS simulations for the case where only the window is open. The other case involving on open door in addition to an open window three wind velocities (1, 2 and 3m/s) are looked at. The aim is to explore the flow field, temperature field, and the rate of heat transfer. The analysis considers the effect of wind on the fire behavior including the MLR, the HRR and gas temperature. 1.6 Limitations This study has a limitation of giving analysis of the effect of wind velocity in compartment fires where wind velocity effect is investigated with regard to HRR, gas temperature, and MLR. In this study there is no analysis on effect of wind at different locations of ventilation. The study also does not put into consideration the way the compartment fire is affected by smoke visibility and behavior of flame. 1.7 Layout of Dissertation The organization of this study is such that we have five chapters each chapter addressing specific issues. The introduction of the dissertation is addressed under chapter 1 where there is the background of the study, the need of the study, aim and objectives, methodology, main achievements and study layout. Review of literature related to this study is addressed in chapter 2. In chapter 3 there is explanation of the methodology and answering the aim and objectives through description of methods used in conducting the research. There is a highlight on the motivation for choosing FDS as the methodology in conducting this study. This is also the chapter where CFD model is validated which serves to ensure the results obtained is reliable and efficient. The analysis of the obtained results and overall discussion in done under chapter 4 while in chapter 5 there is presentation of main conclusions and presentation recommendation for further research related to the current topic. References [1] Whelan, R. J. (1995). The Ecology of Fire, Cambridge: Cambridge University Press. [2] Lo S. M.(1999). “A Fire Safety Assessment System for Existing Buildings,” Fire Technology, vol. 35, no. 2, pp. 131-152. [3] Rein G., et al. (2007). “Multi-story Fire Analysis for High-Rise Buildings,” Edinburgh Research Archive, London. [4] BRE, “Fire Risk Assessment Protecting People, Property and the Planet,” BRE Global, Watford, 2010 [5] Clancy J. (2002), “Strategies For Managing Fire Risks,” Building Operation Management. [6] Chen H., Liu N. and Chow W.(2011). “Wind tunnel tests on compartment fires with crossflow ventilation,” Journal of Wind Engineering and Industrial Aerodynamics, vol. 99, no. 1, pp. 1025-1035. [7] Utiskul Y., et la.(2005). “Compartment fire phenomena under limited ventilation,” Fire Safety Journal , vol. 40 , no. 4, pp. 367-390. [8] Himoto K., Tsuchihashi T., Tanaka Y. and Tanaka T. (2009). “Modeling thermal behaviors of window flame ejected from a fire compartment,” Fire Safety Journal , vol. 44, no. 2, pp. 230-240. [9] Hadjisophocleous G. and Yung D. (1992). “A Model for Calculating the Probabilities of Smoke Hazard From Fires in Multi-Storey Buildings,” Journal of Fire Protection Engineering , vol. 4, no. 2, pp. 67-79. [10] Chen H., Liu N. and Chow W.(2009). “Wind effects on smoke motion and temperature of ventilation-controlled fire in a two-vent compartment,” Building and Environment , vol. 44, no. 12, pp. 2521-2526. [11] Richardson K.(2000). “Fire Safety in High-Rise Apartment Buildings,” Ken Richardson Fire Technologies Inc, Canada. [12] Chen H. , Liu N., Zhang L., Deng Z. and Huang H., “Experimental Study on Cross-ventilation Compartment Fire in the Wind Environment,” Fire Safety Science, vol. 9 , pp. 907-918, 2009. [13] Pitts, W. M. “Wind effects on fires,” Progress in Energy and Combustion Science , vol. 17, no. 2, pp. 83-134, 1991. 14 Takeda H. and Akita K., “Critical phenomenon in compartment fires with liquid fuels,” Symposium (International) on Combustion , vol. 18, no. 1, pp. 519-527, 1981. Read More