Effect of Wind in Small Compartment Fire - Literature review Example

Name Institution Instructor Course Date Effect of Wind in Small Compartment Fire Introduction In this part, the dissertation discusses the research that is related to the topic of discussion. The literature review disc uses the effects of the small scale compartment on fire and the effects of wind in these small compartments (Kumar and Naveen 1558). In fact, the literature review contains the works on the topic that was conducted by other researchers and their findings. The literature review focuses on the stages of fire development and the effects of wind on the stages of fire development. In addition, the paper focuses on the characteristics of flames and smoke during the approaching wind models in small compartments (Takahashi et al., 1026). This forms the background information on this research paper. This will also form the basis of future research works since it helps to identify the research gap and focus on ways in which the research gap can be filled. This is through the background information on the effects of wind in compartment fire. Compartment Fire Development According to Chen et al (2008), the development of fire in a compartment is influenced by many properties including the proportion the fuel, quantity of fuel, natural and mechanical ventilation, the geometry of the compartment, location of the fire and ambient condition in the compartment. Therefore, the combustion of fire in the compartment can be divided into the following stages of development. It is crucial to investigate the features of fire development in each stage of fire development in order to establish the effects of compartment in fire development. Fire Ignition Stage: this is the initial stages in combustion which is initiated by the combustion of fuel. Hence it is the beginning of fires in the compartment. The Fire Growth stage: this is the stage in which the fire in the compartment grows as a function of fuel and has little influence from the features of the compartment. This means that the fire in the growth stage can be described in terms of the rate of energy and combustion energy. However, the continued growth of fire is dependent on certain factors such as fuel availability and oxygen presence. In the presence of oxygen, the growth of fire will continue and spread to other areas of the compartment and building. This is because oxygen supports combustion and keeps the fire growing. Flashover Stage: this is the transition stage from fire growing stage to full fire development in the compartment. During this stage, the combustible items in the compartment are also involved in the compartment fire. This means that all the available flammable materials used in the construction of the compartment acts sources of fuels in the flashover stage of fire development. Hence, various changes in the environment of the compartment occur during g the transition stage from growth stage to fully developed fire in the compartment. However, flashover is not a precise term since various scholars define the stage differently. Most scholars define the stage on the basis of temperature. According to Walton and Thomas (n.d), this stage involves the ignition of combustible items in the compartment in which there is a change in radiation from the hot gases in the compartment. The onset of flashover stage is characterized by temperatures of between 3000C to 6000C. However, temperatures of 500-600 degrees Celsius are mostly used. This stage is affected by external factors such as wind and temperatures of the compartment. In windy or more ventilated compartments, the rate of combustion is high. This means that the flash over stage is shortened since the rate of burning the fuel in the compartment is increased (Walton and Thomas 377). Fully Developed Fire: at this stage, the amount of heat released from the combustible items in the compartment is at its greatest. During this stage, more fuel is pyrolized than with the oxygen that is present in the compartment. This means that the fire is controlled by the ventilation of the compartment. This implies that when the compartment has some openings, it is possible for the unburned gases to escape from the compartment and burn outside the compartment. Therefore, the compartment environment has a direct effect on the pyrolysis rate of the combustible items in the compartment. Decay Stage: as the fuel used in the combustion of compartment t items become used, the rate of fire also slows down. This means that the rate of heat produced in the fire is also declining. This implies that the fire in the compartment is no longer controlled by the ventilation of the compartment but controlled by the fuel used in the fire. Figure 1. Illustration of stages in fire development (Hartin 2009). Fire Behaviours in Small Compartment The behaviour of fire in a compartment is affected by the compartment boundaries and feature in the compartment. The compartment size determines the building up in smoke in the compartment (Carvel & Beard 233). This implies that the materials in the compartment boundaries are influential in heat transmission from one compartment to another. Hence depending on the materials used in the compartment heat is conducted from one compartment to another through the boundaries of the compartment. Moreover, the growths of fire in a compartment are influenced by the size and location of ventilation as well as the environmental conditions such as temperature and wind. The circulation of wind in the compartment is also affected by the size of the compartment. Large compartments are able to accommodate large amounts of air hence wind sweeps the compartment with ease. In addition, the fire behaviours in the compartment are subject to other external factors, and factors such as size and location of ventilation is in the compartment. However, in smaller compartment, wind is not able to circulate easily resulting in the build yup of smoke in the small compartment. According to Quintiere (2002), the behaviours in the compartment fire are affected by both thermal and oxygen processes. Hence the fire behaviours in a compartment are affected by wind and heat of the compartment. In addition, the compartment fire behaviours are affect6ed by the location of ventilation in the building. Compartments that have ventilation on the ceiling and walls have different fire behaviours and growth rate compared to compartments whose ventilation is on the ceilings alone. The compartment fire has different fire zones in the compartment Fire Growth and Compartment Ventilation According to Huang et al (2009), the location of ventilation in a reduced compartment is crucial in determining the fire growth rate and flashover process in fire development. In order to establish the effects of wind and ventilation on smaller compartment, Huang et al (2011) conducted a series of experiment using different scenarios in which the ventilation were placed at a different location in a model compartment. In this experiment, the wind velocity was set at various velocities. The growth of fire is high in smaller compartments that have more than two openings. This is because there is available oxygen, which supports the burning of the fire (Huang et al., 316). In addition, a well-ventilated compartment allows the smoke to escape from the compartment hence ensuring an exchange of air with smoke with the outside environment. In smaller compartments, the walls of the compartment are in proximity to the sources of fire. This means that the walls of the smaller compartment burn faster and easily. As the walls burn, the fire spreads to other location of the compartment. The behaviour of the flames was also investigated such that flames were observed to follow the ventilation (Saito 312). The transfer of heat in compartment walls can be expressed using the equation qcond =kA ∆T/∆x q = Conducted thermal energy (kW). k = Coefficient of thermal conductivity. A = Area of surface in question (m2). T = Absolute temperature of surface in question (K). x = Thickness of material in question (m). Figure 2: Fire Characteristic in different ventilation locations (Huang et al 314). In addition, the rate of burning in reduced compartments is influenced by the size and shape of ventilation. This means that larger openings make the burning process independent hence the rate of burning becomes dependent on the surface area of the compartment. This means that ventilation of a compartment is crucial in determining the direction and velocity of wind in a small compartment. In addition, ventilation size and location determines the direction of the flame and smoke of the building. This is crucial in influencing the compartment temperatures (Kerber and Madrzykowski 2009). Wind Effect on Compartment Fire The growth of fire and spread of fire in a small compartment is influenced by wind and ventilation. The location of ventilation in a compartment also determines the direction of flame flow in a compartment fire. According to Chen et al (2008), experiment of cross ventilation indicated a difference in flow of flames in cross ventilated compartments. In investigating g the effect of wind, ventilation was made in various locations in a compartment model using different wind velocities. In addition, the materials of the compartment were also varied such that glass materials and board material were used. From the experiments, the velocity of wind influences the rate of fire growth rate. This means that as the velocity of the wind is increased, there is an increase in the∆ rate of heat generated since the rate of combustion is also increased. Hence, strong wind drives in the compartment a lot of fresh air. This means that increasing the ventilation of a compartment while increasing the ambient wind into the compartment will increase the rate of combustion. This causes an increase in the temperature of the compartment (Takahashi et al., 1028). In addition, there is a decrease in the transition flashover stage. This is because the wind conditions increase the rate of fire growth which shortens the flashover transition stage of fire development. According to Quintiere (2006), the effects of wind were also investigated where smaller model compartments are made with cross ventilation. In the absence of wind, the hot gases and flames in the compartment is observed to flow in two different directions. This means that the o gases were light making them flow on the upper ventilation while the ambient air was flowing towards the lower ventilation of the compartment models. However, with an increase in the velocity of wind, the hot air is forced to flow towards the windward side ventilation as the ambient air outflows towards the leeward openings (Prétrel & Such 2155). According to Chen et al (2011), the behaviour of fire differs under different environmental conditions in the small compartments. In compartments where there is no wind, the flames of the fire appear symmetrical and still. This means that there are not external forces affect the direction and flow of wind in the compartment. During a compartment fire, the compartment is divided into the flame zone, smoke zone, which is the upper part of the compartment and the lower air some which is adjacent to the floor of the compartment. These zones have different temperature during various stages of fire development. Apart from ambient wind, approaching wind also has different effects on the compartment fire (Chen et al., 1028). The approaching wind provides a cooling effect on the hot gases in the compartment causing a decrease in compartment temperatures. In addition, the approaching wind provides more oxygen to the fuel to burn in the compartment hence increasing the temperatures of the compartment. Chen et al (2009) argues that the wind drives the fire to the sides of the walls where it comes into contact with the walls of the compartment. This causes the fire to ignite the walls of the compartment causing the fire to spread in the compartment. The flames are forced near the ventilation of the compartment such that it flows outside of the compartment. The effects of wind affect other factors and variables such as mass lost from the fuel, radiant heat, external features of the flame and wall heat loss. Mass Loss Rate of Fuel Under normal burning conditions, there is low mass loss as compared to compartment fire burning. This means that in a smaller compartment fire, there is a great loss of mass of the fuels. In addition, the ignition is increased in the presence of ventilation and wind hence making it to occur at a faster rate than under normal fire conditions. This means that wind affects the ignition process and the mass of fuel and different cases. Increasing the speed or velocity of approaching wind in a compartment through certain ventilation in the compartment increases the rate of fire ignition thus increasing the rate of losing the mass of the combustion fuels. External Flame Feature in Compartment Fire Wind influences the features of the flames in compartment fires. When flames are burning in a still environment it is still and steady. However, in the presence of wind, the flames are wavering and unsteady. This implies that in windy cases, the flames from a compartment fire occupy the whole size of the compartment ventilation. Quintiere (2006) argues that the velocity of the wind also determines the thickness of the flames. This suggested that flames in which the velocity of the wind is high are thinner than those compartment flames which are affected by low speed winds. Hence flames that are outside the compartment are puffing within seconds after ignition. This is because wind affects the thickness and size of the flames. In addition, the velocity of the wind on outside flames is influencing the oxygen concentration that reaches the ignition surfaces. This implies that wind causes extinction rate on the flames outside the compartment (Utiskul et al., 369). The external flame equation that demonstrates the dimensions of the flame can be summarised as follows. Q=Cpmout∆T Where the ∆T0 is the temperature which is at the arbitrary position, Cp is the specific heat, and mout is the outflow of flame. Radiant Heat Loss This is termed as the heat which is lost from the combustion gases that are hot inside a burning compartment. This heat is lost to the outside environment through the ventilation of the compartment. This affects the temperatures of the compartment during combustion (Carvel 571). Wall Heat Loss Smaller compartment has walls which are in proximity. The compartment fire is affected by the size of the compartment and the boundaries of the compartment. Apart from the walls the compartment has boundaries such as the ceilings. These walls of the compartment have the ability to transmit heat. Wind increases the rate at which fire comes into contact with the boundaries of the compartment such that it increases the rate at which fire grows in the compartment. As heat is transferred from one wall to another, some of it is lost, hence reducing the temperature of the compartment. This decreases the rate of fire growth (Drysdale 54). Conclusion Wind has different effects on the behaviour of fire in a compartment. Compartment fire development has different stages. The crucial stages in fire development include the ignition stage. This is the stage at which fire in a compartment begins. In the fire growth stage, the fire spreads to the walls of the compartment. The other stages include flashover stages, fully developed fire and decays stage. In the decay stage, the fire begins to decrease. Ventilation in a compartment affects the direction of fire and flames in the compartment. The effects of wind were also investigated where smaller model compartments are made with cross ventilation. In the absence of wind, the hot gases and flames in the compartment is observed to flow in two different directions. This means that the gases were light making them flow on the upper ventilation while the ambient air was flowing towards the lower ventilation of the compartment models. Wind velocity affects the rate of fire growth and development. Work Cited Carvel, R. O., Beard, A. N., Jowitt, P. W., Drysdale, D. D., Variation of Heat Release Rate with Forced Longitudinal Ventilation for Vehicle Fires in Tunnels. Fire Safety Journal, 36.1(2001): 569– 596. Carvel, Richard., & Beard, Alan. The Handbook of Tunnel Fire Safety. London: Thomas Telford Chen, H.X., Liu, N., & Chow, W. Wind effects on smoke motion and temperature of ventilation-controlled fire in a two-vent compartment. Building and Environment, 44.12 (2009):2521-2526 Chen, H.X., Liu, N., & Chow, W. “Wind tunnel tests on compartment fires with cross flow ventilation”. Journal of Wind Engineering and Industrial Aerodynamics, 99 (2011): 1025–1035 Chen, H., Liu, N., Zhang, L., Deng, Z. and Huang, H. Experimental Study on Cross-ventilation Compartment Fire in the Wind Environment. Fire and Safety Science 9 (2008): 907-918 Drysdale, Douglas. “An Introduction to Fire Dynamics”. New Jersey: John Wiley & Sons, 2011 Hartin, Ed. Positive Presure ventilation. (Online). Available at http://cfbt-us.com/wordpress/?tag=positive-pressure-ventilation. Accessed on 21-06-2013 Huang, Hong., Ooka, Ryozo,. Liu, Naian., Zhang, Linhe., Deng, Zhihua., and Kato, Shinsuke. “Experimental study of fire growth in a reduced-scale compartment under different approaching external wind conditions”. Fire Safety Journal 44 (2009): 311–321 Kerber, S. and Madrzykowski, D. NIST Technical Report 1629 - Wind Driven Fire Tests. U.S.A.: National Institute of Standards and Technology. 2009 Kumar, R. and M. Naveen. Compartment fires: CALTREE and cross-ventilation, Combustion Science and Technology, 179.8 (2007): 1549-1567 Quintiere, James. “Fire Behaviour in Building Compartments”. Proceedings of the Combustion Institute, Volume 29 (2002): 181–193 Quintiere, James. Fundamentals of fire phenomena. New Jersey: John Wiley & Sons, 2006 Prétrel, H., & Such, J. Effect of ventilation procedures on the behaviour of a fire compartment scenario. Nuclear Engineering and Design, 235.20 (2005): 2155-2169 Saito, Kozo. Progress in Scale Modelling: Summary of the First International Symposium on Scale Modelling (ISSM I in 1988) and Selected Papers from Subsequent Symposia (ISSM II in 1997 Through ISSM V In 2006). New York: Springer. 2008 Takahashi, Y., Hayashi, Y., Kodama, N., & Omiya, Y. “An experimental study on compartment fire affected by external wind”. Summaries of Technical Papers of the Annual Meeting of Architectural Institute of Japan, (2006): 241–24 Utiskul, Yungyong., Quantiere, James., Rangwala, Ali., Ringwelski, Brian., Wakatsuki, Kaoru., & Naruse, Tomohiro. “Compartment fire phenomena under limited ventilation”. Fire Safety Journal, 40.4 (2005): 367-390 Walton, W., & Thomas, Philip. Estimating Temperatures in Compartment Fires. (n.d). Retrieved From fire.nist.gov/bfrlpubs/fire02/PDF/f02082.pdf‎ Read More