Smoke Movement in High Rise Building - Report Example

Smoke Movement in High Rise Building Name Date Course Table of Contents Table of Contents 2 Smoke Movement in High Rise Building 3 Introduction 3 Dynamics of fire spread 5 High rise fires 5 Compartment fire 6 Smoke spread on exterior walls 7 Smoke toxics and smoke products 8 Windows and external walls 10 Effects of balcony to avoid the spread of smoke in high rise building 11 Smoke studies 12 Numerical studies 13 Previous studies of smoke movement in high rise building 15 Air flow network model 15 Conclusion 17 List of References 18 Smoke Movement in High Rise Building Introduction Smoke that is caused by fire in high rise building is a potential threat to life and it has resulted to many fatalities in the world. It is also important to note that the fire and temperatures in the high rise building is not the main cause of deaths. Smoke is usually responsible for the deaths in such situations. Due to the modern construction techniques of high rise buildings, measures have been put in place to prevent the spread of fires from one floor to the other. This has been achieved through the use of fire resistant materials during the construction process. However, although the spread of fire can be prevented as it can easily be confined within one floor; it is difficult to prevent the spread of the smoke from one floor to the other. This is because of the structural features of the high rise building. Smoke usually penetrates in the spaces that are found in the buildings. In most instances, the high rise buildings usually have elevators and other open spaces like the fire exit and stairs. These are the potential areas that the smoke usually penetrates as it spreads from one floor to the next. The spread of smoke in most cases occurs in a vertical movement in the high rise building. This means that the smoke that is generated by fire from the ground floor will easily spread to the other floors (Cui, 2012). Air movement in a high rise building, similar to path taken by smoke cmhc-schl.gc.ca The mechanism of the spread of the smoke in high rising building is guided by a mechanism referred to as stack action. Through thus mechanism, it has been established that air usually flows upwards in a high rise building. Smoke thus follows the same path and hence its vertical flow leading to the spread of the smoke to the floors in the upper part of the building. The number of casualties resulting from ingestion of smoke in a high rising building may be high as compared to the other buildings. This is because the smoke usually occupy the fire exit and hence the difficulty of people moving downwards in order to exit the building. The characteristic of smoke is also responsible for the deaths that it causes in a high rising building. Smoke contains toxic substances and hence the risks that it poses when ingested. On the other hand, smoke reduces visibility and hence making it difficult for the people to move incase the fire exit is full of smoke. It is also important to note that the density of the smoke determines the effects that it may have. The denser the smoke, the more toxic it is and the more it hinders visibility. The mechanism of smoke movement is also an important factor that determines its spread in a high rise building (Ohmiya, 2007). The control of smoke should thus be considered during the design of a high rise building. The paper thus discusses the concepts of smoke movement in a high rise building. Dynamics of fire spread High rise fires Heat and mass transfer in solids and gas faces are the dynamics behind the spread of fire in high rise building. Other factors may also affect the rate of fire spread in a high rise building. The concentration of oxygen, pressure and radiation intensity are also responsible for the spread of fire (Hall, 2001). It is also important to note that oxygen is a component of fire as it supports combustion. This means that the high concentration of oxygen leads to a high rate of fire spreading. During the heat transfer process, the chemical kinetics plays an important role in terms of determining the spread of the fire. The con-current flame spread model is also responsible for explaining the dynamics of the fires spread. According to this model, the direction of the flame spread is also responsible for determining the rate at which the fire will flow in the high rise building. This also determines where the fire has started in the high rise building. It is easier for the fire to spread easily if it has started from the ground floor as compared to the top floors. This is due to the effects of gravity which also has impacts on the spread of fire in a high rise building. It is for this reason that fire emanating from the ground floor will easily spread to the upper floors as compared to the fire that emanates from the top floors of a high rise building. However, it is also important to note that the materials in the building play an important role in determining the spread of the fire. This is because some of the materials are highly combustible while others are not. Compartment fire In high rise buildings, the spread of fire may cause extensive damage to properties as well as loss of life. A fire compartment is thus required for the purposes of controlling the spread of the fire. The fire compartment is usually constructed of materials that are resistant to fire and hence preventing its spread (Liang, 2002). The fire compartments usually have unique features that are designed to ensure that the fire is contained within a high rise building. This includes a fire resistant door which always close whenever a there is a fire. This plays an important role in terms of controlling the spread of the fire to the other sections of the building. It is however dependant on the intensity of the fire. Although the fire compartment is built of fire resistant materials, it is not completely fire proof. Confining the fire to one area is important in terms of preventing its spread. However, the spread of the smoke cannot be controlled by the fire compartment. This means that the smoke can still spread to the other sections of the building despite the confinement of the fire. The harmful effects of the smoke can thus lead to deaths due to its characteristics. It is however recommended that high rise buildings be installed with fire compartments so at to control its spread which may result to the total destruction of the building. This act as a measure top control the spread of fire in a high rise building and most of the insurance companies also recommend for its installation. Compensation may not be granted if a building lacks a fire compartment. Smoke spread on exterior walls The spread of the smoke is usually determined by the stack action. The vertical spread of the smoke is a characteristic taken by the smoke while spreading on the exterior walls in a high rise building. This is derived from the movement of the air within the high rise building. In most of the instances, the air moves in a vertical direction in the high rise building. This therefore means that the smoke pattern is the same and hence its vertical movement along the exterior walls. The characteristics of the exterior walls are also a factor that determines the movement of the smoke. Leakages on the exterior walls cause the vertical movement of the smoke to increase on the exterior wall. This is responsible for the air moving to the upper parts of the building. However large openings can have an advantage as it may decrease the movement of the smoke on the exterior walls. This is because it allows a high amount of air to enter the fire area and hence limit the smoke movement. This is however applicable in the initial phases of the fire. The density of the fire also determines the movement of the smoke and its spread on the exterior walls. Depending on the prevailing weather condition, the spread of the smoke in the exterior walls may be high or low. The temperatures and pressure are also factors that determine the rates of the spread of the smoke in the exterior walls (Bong, 2000). Smoke toxics and smoke products Smoke is mainly composed of airborne solids, liquid particulates and gases and it is usually emitted when a material undergoes combustion. In a high rising building, several materials could be present in the building. This leads to the generation of smoke which is toxic and responsible for suffocation leading to death. The composition of the smoke is also dependant on the materials that are undergoing combustion. The intensity of the fore also determines the chemical composition of the smoke. In high temperature fires, nitrogen and hydrogen are the main composition of smoke. Nitrogen oxide and sulfur dioxide are also the products of smoke after a complete combustion. Inhalation of these substances is harmful and it also results to death if the victim is exposed for a long period of time. In the case of a high rise building, the fire usually burns under low concentration of oxygen. This is because the building is confined and the oxygen is consumed during the combustion. This results to the production of a highly toxic smoke that causes death when inhaled. Carbon monoxide is usually produced as a result of partial oxidation of carbon. This is a highly toxic gas that causes suffocation when inhaled. Hydrogen cyanides and oxides of nitrogen are also produced incase the materials undergoing combustion have nitrogen products. The plastics can also result to production of toxic smokes when it undergoes combustion. Hydrogen chloride is a toxic gas that is contained in the smoke when plastics undergo combustion under low concentration of oxygen. This is because the plastics are products of polyvinyl chloride (Nijenhuis, 2009). The production of hydrocarbons is also a by product of smoke. This is as a result of lack of complete combustion of materials under low concentration of oxygen. The condensation of the smoke always results to the production of tar. Such kind of smoke is highly toxic and it is characterized by a yellow to brown smoke. The presence of sulphur in the materials burning can result to the production of toxic gases like the sulphur dioxide. The gases produces as a result of burning sulphur has a strong odor that is also harmful. Irritation may occur when victims are exposed to the smoke of the materials burning from sulphur. Carbon is also a major component of smoke and it is sometimes referred to as soot. This is usually present in most of the smoke and it is equally toxic incase of long exposure to it. The materials containing metals also result to the production of metal oxides when it undergoes combustion. The smoke particles could either be visible or non visible depending on the materials that are undergoing combustion. It is also important to note that most of the high rise building are usually painted on the inside part of the wall. The paints contain different chemical substances which also lead to the release of toxic gases when combustion occurs. Trace elements are some of the products of the smoke and usually occur after the combustion of the materials. It is thus important to note that the nature of the burning materials determines the contents of the smoke (Milke, 2002). Windows and external walls The movement of smoke in high rise building is dependant on the leakage characteristics of the building. This is due to the stack action which determines the movement pattern of the smoke in the building. The higher the leakage area in the building, the higher the rate of smoke contamination. The tightness of the building reduces the smoke contamination in a high rising building. The windows are sections within the building that can contribute to the spread of the smoke to the other floors. During the fire, the high temperatures may cause the glass windows to melt. This increases the spaces within the building and hence contributing to the increase in the leakage areas. This in turn leads to the spread of the smoke to the other floors of the building. Incase of open windows, it may take less than fifteen minutes for the smoke to spread up to the eighth floor incase the fire has started in the first floor. On the other hand, it is important to note that increasing the tightness of the building reduces the spread of the smoke. In a high rise building, the number of windows is usually high as compared to the other buildings which are not high rising. This is a disadvantage in terms of containing the movement and spread of the smoke. This is because the windows increase the amount of open spaces and hence supporting the spread of the smoke (Klote, 2003). It is however important to note that the windows could offer and advantage to the building in the initial phases of the fire and if the intensity of the fire is not high. This is because it provides ventilation and hence the expulsion of the smoke from the building. The conditions of the external walls also contribute to the spread of the smoke within the high rise building. The exterior wall may have cracks and thus allowing the air to move in the building. This contributes to the spread of the smoke in the high rise building. On the other hand, it is also important to note that the exterior wall may be composed of spaces for pipe work or other installations this reduces the tightness of the building and hence increasing the smoke contamination. The conditions of the external walls also determine the rate of the heat transfer. This is because the heat loss reduces the temperatures and hence determining the movement of the smoke. The spread of smoke on the external walls be vertical or horizontal. This is dependant on the amount of air. It is thus important to note that the conditions of the external wall also affect the movement of smoke across the building. The external walls are also in direct contact with the weather conditions. The prevailing conditions also influence the spread and movement of the smoke within the high rise building (Bahnfleth, 2001). Effects of balcony to avoid the spread of smoke in high rise building The spread of some in a high rise building is dependant on the stack action and the expansion of gases. Other external factors such as temperature, wind and the mechanical air handling system. These factors in most instances cause the spread of the smoke to behave in either a horizontal or vertical manner. The presence of the balcony plays an important role in reducing the stack action and hence the reduction in the spread of smoke in the high rise building. The presence of a balcony plays an important role in breaking the pattern that is taken by the smoke as it spreads from one floor to the other (Kumar, 2010). This therefore avoids the spread of the smoke in high rise building. On the other hand, it is also important to note that it provides room for combating the effects of the expanding gases which leads to the spread of the smoke. The balcony provides ventilation and it controls the amount of air entering and leaving the high rise building. This is important in terms of reducing the spread of the smoke. The balcony can also be used as a temporary point for evacuating the victims inside the building. This ensures that they do not open the doors as the people struggles to move downwards. This is one of the factors that usually contribute to the spread of the smoke. The balcony therefore ensures that the movement of the victims is limited and hence preventing the spread of smoke from one floor to the other. Smoke studies Experimental Several experimental studies have been carried out to determine the movement of smoke in high rising building. However, most of the experiments have been limited to buildings with several storeys. This is due to the cost implications and the damage that may be caused by fire. One such experiment was done on a multi-floor and multi room to determine the movement of smoke in a five storey building. According to the experiment, the temperature of the smoke varies from the point of the fire to the other areas that the smoke has spread. The difference in temperature also contributes to the spread of the smoke from one floor to the other. The airspaces within the building were also responsible for the spread of the smoke to the other floors. This includes the elevators, doors, cracks on the walls and the windows. During the experiment, the main combustion materials that were used were timber and kerosene. The experiment also indicated that the toxic gases are usually produced and it is responsible for the deaths of the occupants. Sulphur dioxide, carbon monoxide and nitrogen oxides are the toxic gases that are composed in the smoke and they have negative impacts on the health of the occupants when inhaled. During the experiment, it was also noted that balconies plays an important role in terms of controlling the spread of the fire and smoke from one storey to the other. This is because it breaks the vertical movement and hence avoiding the spread of the smoke (Zhong, 2004). Heat diffusion also has an impact on the spread of the smoke from one area to the other. This is caused by the difference in pressure between the point of the fire to the upper floors. However, according to the experiment, the pressure is usually the same before the burst of the fire making it intense. This therefore indicates that the spread of the smoke in a high rise building is also dependant on the pressure. According to the experiment, the distribution of the smoke in usually high in the areas away from the fire. This explains why the smoke usually spreads to the upper floors easily even after the fire is confined to a particular floor within the high rise building. The fluctuation rate and the frequency of the air pressure also determines the movement of the smoke in a high rise building (Sun, 2009). The experiment on the five storey building also indicates that the open spaces greatly contribute to the movement of the smoke in high riser building. On the other hand, the experiment also indicated that the materials used for combustion determines the type of gases that are released. The smoke is thus responsible for the deaths of occupants as compared to the fire in a high rise building. This is due to the toxic substances and gases that are composed in the smoke. Numerical studies Several numerical studies have been conducted to determine the stack effect and how it affects the movement of smoke in a high rise building. A numerical study was carried out in a forty storey building in South Korea. The building had two main elevator shaft and five basement floors. The numerical studies were mainly based on the stairwell and the elevator of the building. This is considering that these areas are the main zones that allow the internal movement of smoke from one storey to the other. According to the numerical study, the movement of smoke in the building through the elevator and the stairway is controlled by various factors. Buoyancy is one of the factors that control the smoke movement (Zou, 2009). This combined with the stack effect pressure is responsible for the temperature difference in the interior of the building. This in turn leads to contributes to the spread of the smoke in the interior of the building. Mathematically, this can be represented by the following equation: _PSO = −gPatm/ R (1 /TO- 1/ TS) z Where: Subscript s and o refers to the shaft and out side corresponding temperatures TO and TS refers to the corresponding temperatures and are absolute units. z refers to the distance above or below the neutral plane. g refers to the gravitational acceleration. Patm refers to the atmospheric pressure. R refers to the specific gas constant for the air The sum of the pressure difference across the elevator or the stairwell is the total pressure difference. The differences in the stack effect pressure and the buoyancy of the hot gases provides the means of distribution of the smoke in the high rise building across the stairwell and the elevator (Beasley, 2009). According to the study, the pressurization systems in the stairwell and the elevators can be used for the purposes of preventing the flow of smoke in the building. The entry of smoke in the shaft which is responsible for the movement of the smoke in the interiors of the building can be prevented by creating a positive pressure. The pressurization process can be achieved through the use of fans to blow outside air into the shafts. This is considering that the air being blown is of different a temperature which is also a factor that affects the spread and distribution of smoke in the interior of a storey building (Fu, 2000). It was also established from the numerical experiment that the principles of heat transfer has an effect on the pressure and hence the distribution of the smoke. The height of the building also determines the spreads of the smoke and hence determining the average height that the smoke can move in the building. However, the numerical study of the distribution of the smoke did not take into account some of the factors like leakages which were also established as factors that affects the smoke distribution. The principles of thermal modeling were also considered in the numerical study due to he effects of temperature on the movement of smoke. Previous studies of smoke movement in high rise building Air flow network model The airflow network movement is mainly concerned with the study of the movement of the smoke in a high rise building under fire. The main concept that is analyzed in the model is the room temperature as well as the pressure. According to the model, the heat transfer rate is also an important factor that determines the rate of spread of the smoke in a high rise building (Chow, et al, 2001). The shape and volume of the building is also a factor that affects the movement of smoke in a high rise building. The compartment patterns as well as the geographic and atmospheric factors also determine the movement of smoke in a high rise building. This model is usually used to predict the movements of smoke incase of a fire hazard in a high rise building. A mass balance equation is usually used for the purposes of determining the movement of smoke. According to this model, the mass flow rate through the openings is usually equated to the mass production rate of the smoke. The letters I and j are usually used in the model to signify two separate rooms. M+ signifies the smoke leaving the room while M- signifies the air entering the room. This model therefore explains that the mass flow rate through each opening in a high rise building is dependant on several factors. However, the main factors are the temperature difference, the pressure difference and the position of the neutral plane between the adjacent rooms of the opening. The movement of the smoke between two adjacent buildings can be explained through the use of the following equations in relation to the model. mij = f(Pij, Ti, Tj, B, μ) mji = f(Pji, Ti, Tj, B, μ) The first equation is the movement of smoke from room I to room j while the second equation n signifies the movement of smoke from room j to room i. In both equations, μ signifies the coefficient of the opening. B on the other hand is the width of the opening and it is measured in meters. Pij and Pji signify the pressure difference at the openings of both rooms. The equations are also referred to mass balancing. The flow rate of the smoke from one room to the other can thus be obtained by solving the equation. The heat absorption also has effect is on the spread of the smoke. This is because it may lead to the increase in temperature. According to the model, the rate of the heat absorption can be expressed in terms of the thickness of wall. However, the presence of openings on the wall may result to heat loss which is also a factor that influences the movement of smoke in the high rise building. The model therefore highlights the factors that contribute to the movement of smoke in a high rise building. The analysis of the factors is also important in terms of determining the flow rate as well as the movement of smoke in the building (Kim, 2007). Conclusion In conclusion, the movement of smoke in high rise building is influenced by various factors. The temperatures, pressure as well as the prevailing weather conditions are the main factors that influence the movement of smoke in high rise building. On the other hand, it is also evident that the effects of smoke are usually fatal. In a high rise building, smoke is usually responsible for the death of the occupants as compared to the fire. This is due to the toxic substances and gases that smoke has. The gases released are however dependant on the materials undergoing combustion. It is also common for the smoke to spread to other parts of the building even after the fire has been confined to a particular floor or room. This is mainly attributed to the stack action which is responsible for the movement of the smoke. Experiments have also shown that the open spaces and leakages are also responsible for the movement of smoke within a building. The amount of smoke moving from one room to the other can also be calculated using the formulas derived in the airflow network model. Numerical experiments also have some formulas that can be used to calculate the movement of smoke in the high rise building. However it is also important to note that the windows as well as the exterior walls may increase the rate of the spread of the smoke. However, this is dependant on other factors. The balcony plays an important role in terms of reducing the spread of the smoke from one floor of the building to the next. List of References Nijenhuis, K, 2009, Properties of Polymers: Their Correlation with Chemical Structure; Their Numerical Estimation and Prediction from Additive Group Contributions. Elsevier. p. 864. Chow, W, et al, 2001, A network model of simulating smoke movement in buildings, International Journal on Engineering Performance-Based Fire Codes, Volume 3, Number 4, p.151-157. Bong, F, 2000, Fire spread on exterior walls, New Zealand: University of Canterbury, 206 p. Zou, G, 2009, Numerical simulation of pressure changes in closed chamber fires, Building and Environment, 44(6): 1261-1275. Kumar, S, 2010, Air entrainment into balcony spill plumes, Fire Safety Journal , 45(3): 159-167. Liang, F, 2002, Preliminary studies on flashover mechanism in compartment fires, Journal of Fire Sciences, 20(1): 87-112. Fu, Z, 2000, A two-zone fire growth and smoke movement model for multi-compartment buildings, Fire Safety Journal, 34(3): 257-285. Zhong, M, 2004, China: some key technologies and the future developments of fire safety science, Safety Science, 42(7): 627-637. Sun, Q, 2009, Smoke and control research in vertical high- rise building channel, University of Science and Technology of China, Hefei. Bahnfleth, P, 2001, A validation study of multizone airflow and contaminant migration simulation programs as applied to tall buildings, ASHRAE Transactions 107(2). Milke, A, 2002,Principles of Smoke Management, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, Georgia. Beasley, D, 2009, Stairwell and Elevator Shaft Pressurization for Smoke Control in Tall Buildings," Building and Environment, 44, 1306-1317. 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