Using CFD to Assess the Smoke Control System in Corridor - Case Study Example

Assessment of smoke control system in corridor using СFD STUDENT NAME: STUDENT NO: COURSE: FACULTY: UNIVERSITY: SUPERVISOR: DATE OF SUBMISSION: PART 1 (2049 words) NATURAL AND MECHANICAL SMOKE VENTILATION SYSTEMS IN COMMON CORRIDORS OF APARTMENT BLOCKS ABSTRACT Until lately, normative paperses like British Standards and Approved Document B (ADB) did provide guidelines on design of smoke control systems that primarily work using natural means. This is to mean that these systems use natural smoke shaft and external automatic opening vents (AOV’s) as well as the difference in the system pressure. Nevertheless, BS 9999 is the alternative that can be used instead of ADB on fire safety, since BS9999 is more flexible than ADB in matters that pertain a building design. If the building does not follow the ABD regulations, BS9999 regulations can be use in the building design. It allows for a provision that door widths can be decreased as well as final exits, while escape distances can be increased. As part of performance testing based on the design theory and design factors of a fire management system, MSVS can be incorporated in different building designs and in specific building areas to help in smoke management system. INTRODUCTION Every building must have a set of approvals. Therefore, ADB provides a set of recommendations that help in the fitting for the building regulations. Smoke control system internalization is the most significant way in which safety of the building can be improved. As the smoke control systems are made of different designs, they have a wide range of complexities, that is, natural smoke venting, mechanical smoke ventilation systems and pressurization systems. Irrespective of the system design, objective of each system remain constant in providing the smoke control purpose intended to. However, the ADB does not work well with the complex structures, but it fits well in simple structures and buildings. Therefore, BS 7974 or BS 9999 can be the most appropriate recommendation to use in complex buildings. Although BS 7974 is more flexible to use, it requires high skill in operation and use. In addition, BS 9999 targets to provide simplified operation to provide sophisticate solutions. Design guidelines provided in the documents ADB are intended to abide by the set standards and regulations that are set for buildings. However, it is not necessarily that the recommendations in ADB and BS 9999 be met but, fire engineers should ensure the building is code compliant. Based on performance of a given design fire engineer may issue a normative on the design requirements that would help in designing a cost effective, flexible life safety system that would not comprise the design of the building(Francis, & Steven, 2012, 188). Therefore, the fire engineers will have to consider a number of factors when planning on the best design that would suit the appropriate safety plan. Some factors that ought to be considered for performance testing in a smoke control system include: The objectives of the design The risks that might face the occupants and contents in case of a fire event, Geometry of the building and the floor geometry; Size of fire that might be expected Objectives Some of the objectives for the smoke safety control system are: To ensure the evacuation routes are free from smoke; To determine a means by which smoke can be eliminated from fire area to prevent fire spread to other areas; To ease the process of fire fighting procedures Operation of Natural and MSVS System In general, design of mechanical smoke venting can be made to serve two purposes other than dilution intentions. For instance, it can help in creating tenable conditions in case there is fire in the compartment or in corridors. In addition, smoke can be sufficiently buoyant and hence released through high-level vents in the corridors and ensure that at low level there is fresh air to replace it. In addition, mechanical smoke venting can help in depressurizing the space along the corridor that has smoke creating differential smoke pressure scheme. To the centrally, in particularly in UK there has been proposals to have smoke shafts. With sufficiently buoyant smoke, Natural ventilation is expected to draw smoke out through the shafts and the vent at the top. However, the passage of smoke in still or cool weather can either be downwards or upwards, which might not be clear due to stack pressures (Klote, 2002, p. 112). As far as the NMSVS is concerned, effectiveness and increased performance efficiency in containing the occurrences the system must work as a depressurization system. This system generally extracts heat and smoke from the affected place, which lower the pressure tin that area thus depressurizing the area, which creates higher pressure at the surrounding areas. Higher pressure in these regions generally prevents flow of smoke to these regions by simply entraining the air around these areas and directing the smoke to the extracting vents. However, it is necessary to maintain the in flowing air to prevent over depressurization in the areas as this can damage the smoke extraction vents. Therefore, in case such a case occurs and there is over depressurization in the building, the following can be done to balance pressure in the building; Ensure the building staircase has Natural inlet via (AOV); Ensure that there is inlet of external air to the building; Design shaft for Natural inlet; and Design a shaft for Mechanical inlet Residential Buildings Natural and Mechanical Smoke Ventilation Systems The cornerstone for smoke control system in all buildings is to preclude flow of smoke from entering in corridors and staircase as these are the major escape route for the occupants. In addition, fire fighters can use these regions as the areas that they easily reduce the risk of damage by the fire. Recommendations by ADB are given that for all residential buildings that have over 11m floors or they are more than 3-storey building; the design dictates that every flat ought to be separate from any common staircase or common corridor. Further, this regulation recommends that for common corridor ought to have a ventilation of approximately 1.5m2 AOV that is directly accessible to the outside or, have 1.5m2 natural smoke shaft. As a NMSVS actively ‘extracts’ smoke and heat from corridors and solely does not rely on the natural buoyancy of the smoke, then the shaft area is significantly reduced to fit for the entire extraction system. Therefore, such factors as size of the corridor, extraction rate, fire loading and AOV shaft size must be a consideration when designing such NMSVS. Thus, a computation fluid dynamic (CFD) must be done for these factors to be considered in the smoke management system. Generally, the range of most NMSVS shafts is between 0.25m2 to 0.6m2. It is recommendable therefore, when planning on the smoke management system to consult a fire engineer, who will provide relevant information on how to design the smoke management system and provide guidance as to what will be required. Using the NMSVS system different factors are incorporated in the arrangement to meet the system requirements. Thus on planning on the design of the NMSVS space in the building is most critical and must kept into consideration to ensure that there is enough floor space. System performance may be heightened to ensure that justifiable distance along which smoke may travel in a corridor. This improves NMSVS smoke extraction capacity to ensure that all corridors have tenable space for the occupant to evacuate from the building safely. Depending on the design of the building the occupant can evacuate the building using this strategy with no casualties on any injuries. Designing other residential buildings such as hotels and student accommodation, which purpose group B to residential standards, then all the principles applies to the same structures as well Fire Fighting Shafts N MSVS BS 9999:2008 and ADB give provisions that when designing for the fire fighting shafts and how they should be included in any given building. Generally, the ADB governs that, for any fire-fighting shaft there should be shaft that are provide in the building and should be 18m or more. This recommendation applies to both office and residential building. Further, the regulation are clear on the outline of the given provisions for firefighting shafts that must meet the required criteria the purpose groups 4, 5 and 6, (which include commercial, assembly shops, & recreation and industrial buildings). ADB recommends that in any given building that has as fire fighting shaft that serves residential accommodation, which may include flats and massionettes, then the planning of for this system is equivalent to a corridor for smoke control. This further, dictates that the system must follow the firefighting regulations on the design of the shafts, which must follow the 1.5m2 AOV design parameters to directly face the outside and have 1.5m2 natural smoke shafts. Therefore, to have the regulations set to offer more and better cost effective solutions, it is ideal to have the buildings follow the provisions that relate to MSVS in residential buildings. Fire fighting shafts regulations for other buildings such as offices, industrial buildings and retail offices are all provided by the ADB regulations. ADB regulations recommend that all the buildings should have ventilations that are constructed in accordance to the BS 5588:2004, which has been replaced by BS 9999:2008. Regarding that, it is not always possible to have fire fighting shaft that is always on an external wall, which would allow for the provision of the AOV direct to outside this regulation, BS 9999:2008 advocates that the design of the smoke shaft to be in conformity with BRE Study 79204. This regulation provides a guide for the design of the smoke shaft to have a cross sectional area of at least 3m2. Further, this regulation allowed for the lobby ventilator are to have an area that has at least 1.5m2. Thus, from the BRE report, the shaft area should be large to allow for enough space that might be required for the fire load. From the simulations made to test the functioning of the shafts, the 3m2 shaft provided positive results that would be required as a necessity in fir fighting in an external AOV. However, MSVS system is able of drawing out more smoke and heat out of any area. Nevertheless, the MSVS will only be capable of functioning efficiently depending on the system design parameters, which range from the size to the direction of the airflow. Further, such factors as accommodation of the fire load, rate of extraction of fans and AOV size of the opening to the shaft, can be reduced to a minimal size of 0.6m2, which can as well function without failing the system. Thus, comparing the two systems with different sizes is clear that, for a smaller system there is reduced cost of installation, which act as the best approach when designing the smoke management system for buildings. MERITS AND DEMERITS OF USING MSVS MERITS Allows for more free space thus it optimizes space; it is a cost friendly design; Compared to code of compliant the MSVS system in more efficient than the natural system; It is a simple design to make DEMERITS The system must use CFD modeling for computational purposes and analysis to prove its functionality; The design might not be cost friendly for smaller; It requires one to have knowledge on the design procedures when planning to use this design CONCLUSION It is insightful to use MSVS on smoke management system design as they can render a cost effective answer when implemented and used in certain buildings that would have cost higher when installing smoke management systems. It is clear that alternative approaches are possible when planning to use this design for the fire safety in the residential buildings. Further, most of the approaches that are used in assessing the performance of a design are ideal in cost saving and provide effective in reducing the fire risk in residential buildings. However, it is notable that all building has different geometrics that must be followed when planning on the best smoke management plan. Hence, consulting a fire engineer is always the best approach to have a successful plan that would give a recommendable design. Therefore, this would ensure that proper planning and safety measures are made a priority when design the corridors and well as access points to the residential buildings. PART 2 (1052 words) CFD MODELING IN PERFORMANCE OF THE SMOKE CONTROL SYSTEM AND CORRIDOR ARRANGEMENT ABSTRACT Computational Fluid Dynamics (CFD) models are used in this section to cover the general study on the effectiveness of smoke system in a building that is design to have a complex picture. Fire Dynamics Simulator (FDS) in CFD is used in this study for the purpose of analysis on the system. Fire load expected in the building are in the simulator with a selection that is fit for the lobby area of the given 15-storey building. Further, using this simulation of the lobby area, to exhaust the system design, smoke movement was studied. Smoke movement study was carried out for the analysis of the interconnected corridors used to represent the expected fires that may arise and spread in the lobby area. INTRODUCTION Inhaled smoke in the building fires leads to most of the reported injuries as well as the fatalities in these buildings. This is from the fact that smoke is combination of irritant gases and toxic gases, which cause these injuries and fatalities that, may eventually lead to death of the victims. Moreover, as smoke increases in the building corridors, it lowers the visual ability of the occupant when evacuating from the building thus it becomes difficult for them to escape from the building. For instance, escaping from a 15-storey house is very difficult considering that, the occupant must move smoothly without congestion along the corridors. Therefore, a better corridor design would facilitate such evacuation without confusion and congestion. Due to smokes’ buoyancy, it rises up in the building from the origin. When the smoke rises up it entrain the air filling the upper region reducing the breathing air in the building creating a layer of hot gases in the air. As the hot is layer is formed and more gases continue to form, fire plume releases gases that enter into the hot layer (McNew, 2013, 122). Therefore, when designing the building a smoke management system is the most critical factor that must be considered to prevent smoke accumulation. OBJECTIVES To design CFD model that will provide smoke managing system to control spread of smoke in the corridors in a 15storey building. PROBLEM STATEMENT Poor fire safety smoke management systems have over time caused injuries and fatalities in the buildings in the event of evacuation. Thus, increased congestion and concentration of smoke in the evacuation areas are a major alarm that has lead to the design of this CFD model on fire safety and smoke management. CFD MODELING DESIGN THEORY A 15-storey apartment block that has identical floor plan at each level is considered and it includes corridors at each level. Simple models and simple correlations are not ideal when designing fire protection systems. Therefore, this makes it difficult to design complex geometries of a building. CFD models are used in such designs since they provide the most appropriate model necessary for predicting smoke movement therefore determining the smoke impact in the exhaust systems. Thus, using CFD computer modeling on planning and designing the smoke exhaust system for the 15-storey building is the most ideal safety measure. Further, this design aims at making a smoke exhaust system set to provide well-founded environment in the corridors that will ensure safety across the building in case of an outcome of fire event. MODEL DESCRIPTION This design is made in such manner that the spaces and corridors provided must conform to the rectangular grid. This is made to ensure that building design must improve the model efficiency, which is made to ensure that system performance is maintained without altering operations in the building. Fig. 1 depicts the building escape-route geometry, while Fig. 2 is the geometry of the model common areas. From fig. 2, common areas are the major areas in the building that in case of fire event smoke may accumulate causing damage and injuries and they need safety of 2 people per m², who should be at a speed of 1.25 m/sec while walking, and having 5 mm/person as per the demand of the Approved Document B. Figure 1: Building escapes route geometry Figure 2: smoke view in a corridor SMOKE MOVEMENT From the recent works by BRE, it has been affirmed in ADB, states that, the possibility of maintaining lobbies and corridors in a building free from smoke is hard, except for system that use pressurization. Moreover, it also clears out that protecting the stairs is most essential thing since people trying to vacate use the stairs more than the corridors. Further, it should be clear that the temperature should not exceed 600C and the visibility should be not less than 10m. Figure 3: fire spread in a corridor JUSTIFICATION The most appropriate time to do selection of the recommendable performance criteria for evaluating a fire engineered system design should be instituted at the commencement of the design process. This is the qualitative review of the design. Thus, in this fire system performance is engineered system is measurable against an ADB related system, where the assessment fundamentally compares the smoke and thermal conditions rendered by the two systems. TIME DEPENDENT DESIGN Generally, a system will depend on timely analysis, for instance one system can require time dependent analysis or steady state analysis. Either way the system can be termed as more appropriate to function or perform a given task. Since time dependent analysis uses computer models, while steady state analysis use hand calculations, then this system uses time dependent analysis since it is made of computer model. Figure 4: time dependent fire analysis CONCLUSION Essentially, the use of computer modeling design in fire safety in building is critical and simulations are necessary to determine the ideal way that may be used to reduce the occurrences. Therefore, CFD design used in this model is ideal and provides a visualization expected in demonstration of smoke management systems. Further, the model evaluated CO concentrations, temperature and visibility in the corridors of the entire model. This ensured that the entire model gave the exact expectations for a building under such conditions. RECOMMENDATIONS It is important to design any system to have stairs free from the smoke in case of fire outbreak. When designing any system it is necessary to consider tenable conditions that will allow space for travelling via corridors/lobbies when escaping. References Klote, J. H. 2002. Principles of smoke management, American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. Francis, D. & Steven R., 2012, Building Codes Illustrated: A Guide to Understanding the 2012 International Building Code, John Wiley & Sons, New York. McNew, R., 2013, Emergency Department Compliance Manual: 2013 Edition, Aspen Publishers, New York. Read More