Formation of Smoke Layer in Industrial Building - Essay Example

Formation of Smoke Layer in Industrial Building Principles governing Smoke Layer Formation On the outbreak of fire, there is a marked difference in the principle of formation and spread over of smoke layers in an open large industrial building when contrasted with that of a closed compact space in a residential house. The closed space usually found in a residential house suffocates the fire and reduces its fast growth. Whereas in an open industrial building due to the abundant availability of oxygen fire rages and grows rapidly generating a huge plume of smoke which initially shoots up to the roof and then starts logging all over the space available. During this period if sufficient extraction mechanism is not provided to ooze out the smoke from the confines of the industrial building then the extent of damage it could cause to the occupants of the building can be colossal. The characteristics of smoke is such that it can spread with a velocity of up to 5m per second whereas an occupant can walk only 1-2 m per second and can manage to run at 7.5 m per second. So if proper exit access routes are not available for the occupants to make their way in the event of a raging fire the ensuing smoke layer, containing toxic substances and asphyxiates, could disorientate them in seconds and even kill them in minutes by engulfing them all over. Typically studies have shown that in a situation where there is no ventilation even a space spanning a volume of 10, 000 cubic meter can be smoke logged within minutes. A smoke layer study made within an area of 13, 000 cubic meters resulted in smoke logging of the whole area in less than two minutes. The three figures in the following page shows three successive stages depicting how even large buildings get smoke logged within few minutes of a raging fire. 1. Smoke rising to roof. 2. Smoke travels laterally. 3. Smoke-logged in minutes. Controlling Smoke Layer Smoke can be controlled by limiting the spreading of smoke throughout the industrial building and by providing means of extracting heat and smoke. This requires that there be openings or fans at higher levels in the building to extract and exhaust the smoke out of the building. It also requires the existence of effective barriers to prevent the smoke from spreading through the building. Further well positioned inlet ventilators are required to supply replacement air in place of the extracted smoke layer. Care should be taken that all such inlet ventilation takes place below the smoke layer failing which it could mix with the smoke layer causing it to cool down and getting deepened inside the building itself instead of getting extracted or exhausted. Ideally the smoke layer should be designed not to be less than one-tenth of the height between the floor and the ceiling. Also if the smoke layer is at a very low level then replacement air will be sucked into the middle of the ventilator rather than the smoke thereby reducing its efficiency. The containment of smoke is essential for effectiveness of smoke ventilation systems. If the lateral flow of smoke is not restricted then the ventilators might be rendered less effective in driving out the hot smoke. This may cool the smoke and deepen their levels towards the ground which would stifle escape roots and endanger life. To prevent this smoke reservoirs have to be created by the use of smoke curtains resulting in the containment of smoke. The smoke reservoirs help in increasing the time available for occupants to flee the building since they reduce the travel distances. They are a cost-effective mechanism for dividing the building to zones. It also aids the emergency services by containing and channeling the smoke into predetermined areas. Smoke reservoirs limit the travel and cooling of smoke thereby preventing their descent downwards which could lead to obscuring of vision. The three figures below show how smoke curtains help contain the smoke layer. Studying Demonstration of Smoke Layer Formation – Purpose and Strategic Objectives Smoke is a major hazard in the event of a fire breaking out. It has been observed statistically that about 70% of death during fires is due to smoke. It is not just a threat to life but also to property. In a fire 95% estimated loss of property pertained to smoke. So it is essential to understand the behavior of smoke layer by modeling fire growth and the resultant temporary development of smoke plumes and layers. Several methods including hand calculations, zone models and computational fluid dynamics can be followed to obtain detail on smoke conditions like smoke temperature, toxicity and visibility. This could result in assessment of effective smoke control strategies or alternative design parameters. For simple designs a steady state calculation can be the guiding factor wherein the assumption is that the output heat from the fire has reached a steady value, invariably the maximum heat expected, and hence the volume of smoke produced by the fire is constant. However as the complexity of design grows the calculations may need to be more detailed enough. Here the assumption is that the heat output increases as fire grows in size and hence there is a corresponding increase in smoke volume and temperature. By means of detailed and advanced modeling of smoke (i.e. the study of demonstration of its behavior) it is possible to evolve effective smoke control strategy. Also the areas prone to risk from smoke can be identified and suitable control methods to protect those areas can be devised. The very features of the industrial building can be involved in the smoke control method giving stability to the building design. Another way of demonstrating smoke layer formation and studying its impact to control it ultimately is the computational fluid dynamics model. A simulator which is used to study the dynamics of fire and the resulting flow of heat and smoke can be deployed for studying large scale fires in industrial buildings with high reliability. It has been observed practically that when tested under different conditions it continually predicts flow velocities and temperature falling within a range of 10-20% of experimental measurements under controlled conditions. The specific advantages of using such a simulation model leads to identification of critical locations within a building or structure, choice of most effective safety solution through integration of ventilation and fire suppression system into the model, clarity in smoke behaviour to clients with presentations using pictures and animations and finally assessment of the available escape times for the fire-stuck occupants. The techniques just discussed allow with ease the demonstration of performance targets such as tenability limits and smoke control system requirements. This helps expedite approval process of statutory authorities instantaneously rather than relying on the relatively inaccurate traditional hand calculation methods. Let us also consider the zone model. As compared to the model of computational fluid dynamics, in the zone model two zones are purported to exist within a compartment during a fire. The lower zone is relatively clear while the upper zone contains all the hot combustion products emanating from the raging fire. Strategic Direction of Smoke Layer Formation and its ensuing impact on fire safety The major aim of demonstration of smoke layer formation and its study is to understand the fire resistance of constructional elements and total structures within the building exposed to extreme heat conditions. The involved strategy must take into account the verification of experimental results and the theoretical model to make the results as reliable as possible. Evacuation of occupants from a smoke engulfed industrial building should address the requirements of providing a justified approach for determining the needs and ability of human beings to escape and evacuate the building. Considerations of model include the prediction of rate of escape and evacuation in the event of fire and smoke, and an influence on such predictions of the ability of occupants to present a response in terms of their free mobility and efficient conduct. Currently safe evacuation from buildings is provided mainly through prescription, in terms of regulations and codes, of adequate means to escape by specifying for example requirements for protected routes for escape and maximum escape distances. Under a more fundamental approach to the evacuation process, evacuation may be defined as “the process whereby people by themselves or assisted by other people inside the building are moved to a place where they are safe from the fire. Design of buildings play a major role in fire safety. The potential of growth of fire in an open industrial building is much greater than otherwise due to the vertical movement of the raging fire up the racks. So for effective fire safety strategies the usage of sprinklers is recommended to keep the fire under control. The combination of an effective smoke control system and sprinklers can assist emergency services while controlling the fire and removing the smoke thereby reducing the resulting damage that is likely to be caused. In most of the modern day industrial buildings an in rack sprinkler system is present to control fire growth. The major considerations for industrial buildings, especially warehouses are (a) the nature of goods stored in the building (b) the type of materials used in packaging (c) the manner of storage of goods (d) the surface area of goods that are exposable to combustion and last but not the least (e) the type of sprinkler system installed. After thoroughly examining the behaviour of fire / smoke in the industrial or any other building / open space and the readiness of infrastructure to deal with safety of occupants, building and goods there still persists an increasing need for research into providing safe and easy access for fire fighting and rescue teams especially within large and complex smoke-filled buildings in relation to the very operations, building design as well as internal communication and guidance systems. Development of appropriate design criteria and concepts for means to escape, inclusive of stairways and corridor spaces, fire lifts and other internal protected areas, the ability to use fire and smoke control systems as part of fire fighting are all significant areas that need to be addressed in totality in future for an effective understanding of fire safety and smoke layer formation and its resulting lasting impact. Works Cited Awbi, H.B., 1991, Ventilation of Buildings, Taylor & Francis, ISBN 0419210806, 9780419210801 Barham, Ronald, 1996, Fire Engineering and Emergency Planning: Research and applications, Edition: illustrated, Taylor & Francis, ISBN 0419201807, 9780419201809 Bilington, M.J., Ferguson, Anthony, Copping, Alexander G., 2002, Means of Escape from Fire, Blackwell Publishing, ISBN 0632032030, 9780632032037 Carvel, Richard, Beard, Alan N., 2005, The Handbook of Tunnel Fire Safety, Thomas Telford, Edition: illustrated, ISBN 0727731688, 98780727731685 Combustion Science and Technology, 1993, Gordon and Breach Science Publishers Hughes, Phil, Ferret, Ed, 2007, Introduction to Health and Safety in Construction: The Handbook for Construction, Butterworth-Heinemann, Edition 2: illustrated ISBN 075068111X, 9780750681117 Quintiere, James G., AIAA, Cooper, Leonard Y., American Society of Mechanical Engineers Heat Transfer Division, 1990, Heat and Mass Transfer in Fires: Presented at AIAA/ASME, Thermophysics and Heat Transfer Conference, June18-20, 1990, Seattle, Washington, University of Michigan, Digitized Dec 5, 2007 Rasbash, D, 2004, Evaluation of Fire Safety, John Wiley and Sons, ISBN 0471493821, 9780471493822 Smoke Control in Single Storey Buildings and Warehouses, Smoke_Control_in_Single_Storey_Buildings_and_Warehouses.pdf, Stollard, Paul, Johnston, Lawrence, 1994, Design Against Fire: An introduction to Fire Safety Design, Edition: illustrated, E & FN Spon, University of Michigan, Digitized Dec 5, 2007 The Architect’s Journal, 1986, The Architectural Press ltd. 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