The Smoke Ventilation System - Case Study Example

REPORT ON THE SMOKE VENTILATION SYSTEM By (Student Name) Course Tutor University City/State Due Date Table of Contents Content Pg Introduction 4 Natural smoke ventilation system 5 Advantages of natural smoke ventilation system 5 Installation of natural smoke ventilation system 6 Components of natural smoke ventilation system 8 Mechanical smoke ventilation system 9 Ways of achieving mechanical smoke ventilation system 10 Advantages of using mechanical smoke ventilation system 13 Disadvantage of using mechanical smoke ventilation system 13 Continuous fluid dynamics (CFD) modeling of the smoke control 13 Recommendation 17 Bibliography 18 List of Figures Content Pg Figure A. Share of fire death by smoke inhalation 4 Figure B. Opening- clear opening width degree cellulous 6 Figure C. Opening- opening angle 7 Figure D. Openings- used for natural smoke ventilation system 9 Figure E. Mechanical ventilation circulation system 10 Figure G. System overview 11 Figure H. Scenario A- fire initiates at the left area at the fourth floor 15 Figure I. Scenario B - Fire begins at the right end just adjacent to the two corridors16 Figure J. Scenario C- the location of fire is next to the escape route 17 List of Tables Table A. CFD Modeling parameters 14 INTRODUCTION Smoke ventilation system refers to a combination of parts such as heat and smoke vents, fans, and draft curtains which work together to help in keeping smoke confined in one place and consequently evacuate the smoke out of the building. According to Approved Document B (2006), more often than not it is not fire that kills people during a fire incidence but rather it is the smoke1. This document acknowledges the importance of having good smoke ventilation practices. Literature review reveals that the primary danger which is associated with fire during its early stages is usually not the fire flames but rather the noxious gases and smoke produced by the fire. Smoke usually causes most of the casualties in a fire incident. They also obscure way for victims to the escape routes or exits in the building. The smoke also makes it difficult for the fire fighters to get into the building to extinguish the fire. Statistics show that out of the 300 fatalities that result from home fires, nearly 70 % are due to smoke inhalation. (Source of image: SFPE Handbook of Fire Protection Engineering 2016) It is therefore imperative to come up with measures that are designed to offer safe escape routes or exits and also provide appropriate arrangements that will limit rapid spreading of smoke as well as fumes. There are a number of systems which architects, consultants, contractors and the building control officers have been using over the years to carry this important role. What is important is having a system that looks good, offers value for money and is also compliant with the Building Codes within the area of jurisdiction2. In the United Kingdom, there are a number of companies that offer assistance in design, supply, install, commission and maintain smoke ventilation systems. Generally, according to the British Standards (BS 9999:2008), a ventilation system should be reliable, have near unseen smoke vents while in non-fire mode and increase confidence in the Engineered Solution designs. Broadly there are two types of smoke ventilation systems, they are; 1. Natural Smoke Ventilation System. 2. Mechanical Smoke Ventilation System. NATURAL SMOKE VENTILLATION SYSTEM Natural Smoke Ventilation System is usually designed in a way to make a smoke free zone directly above the floor of the building. The system utilizes natural buoyancy to perform its role. Hot air is usually lighter than cold air, it therefore, rises and exhaust via the high level vents while fresh air enters the building via the low level vents to replace the hot rising air. This in turn significantly makes the condition within the building safer for escape and permits the fire to be fought while still at an early stage. Natural smoke ventilation systems open automatically specific doors, windows, roof lights or louvers upon the detection of smoke in the building. The system is normally made up of a combination of control panels, actuators, manual control points and detectors. A natural smoke ventilation system can either stand alone in a building or it can be interfaced with the fire alarms or it might be integrated with the Building Management System (BMS) so as to obtain maximum control. Advantages of Natural Smoke Ventilation Stysem 1. EFFECTIVE AND SAFE: Controlling smoke using natural ventilation is particularly an effective means to protect escaping fire victims, those waiting to be rescued and the fire fighters from direct dangers of smoke and fire. In principle, the high and low-level vents automatically open to allow entry of cool air and exit of hot air and smoke from the building. In the absence of a ventilation system, the smoke in the building might fill up the room as it is being drawn down via convectional currents leading to potential, and specifically dangerous 'flashover.' 2. COMPLYS WITH THE BUILDING REGULATIONS: The guidance to building regulations in England and Wales include specific deployment of the smoke ventilation systems. According to the Approved Document (AD B), there are a number of situations whereby Automatic Opening Vents (AOVs) are appropriate in applying natural ventilation. These situations include; Basement areas, enclosed car parks, common escape routes in large buildings and the single stair blocks. 3. Natural Smoke Ventilation System can be used on a day to day basis in buildings for the purpose of providing routine natural ventilation. Hence, the system offers affordable and complete solutions. INSTALLATION OF NATURAL SMOKE VENTILATION SYSTEM There are different types of heat and smoke ventilation openings. They type chosen depends on the type of building and also the architecture. Buildings with flat roofs the smoke ventilation openings can take the shape of dome lights, glass pyramids or rows of windows. Buildings that have pitched roofs can be made with hung ventilators. The openings of natural smoke ventilation system are frequently installed on the exterior walls. So as to achieve optimum level of natural smoke ventilation, one should consider the following aspects; -Size of the opening elements. -Type of opening elements. -Arrangement of opening elements. (Figure B. Opening- clear opening width degree cellulous. Source of image; Proceedings of the 9th International Conference on Structures in Fire, 2016) The smoke and the noxious gas should be able to flow out of the building into the open air without facing any hindrance. The direction of the outflow should at no point collide with the window sashes, stairwells, projecting walls and stairwells. During the installation of the natural smoke ventilation system, it is fundamental for an Engineer to establish a distinction between the geometric and aerodynamic opening area. Requirements relating to smoke removal systems such as stairwells generally need a geometric opening. The aerodynamic area is significant since it the one that presupposes which ventilation system is appropriate for a given building. Geometric opening area is determined by obtain direct measurements as shown in figure B. above. Geometric Area=Clear Opening Width (C)*Width clear. Where the opening angle exceeds 60 degrees, the geometric area at that point can be used as the maximum value. It is important to calculate the aerodynamic opening area for a smoke vent installed in a natural smoke ventilation system. This needs an experimental determination of the coefficient of flow rate which is then used in calculating the aerodynamic opening area. Aerodynamic Area= Wclear*Hclear*Cw Where Cw= experimentally determined flow rate coefficient. The coefficient depends on the widow geometry and the opening angle. This must be followed so as to comply with the regulations. (Figure C: opening angle obtained from RWA update. Source of image: Proceedings of the 9th International Conference on Structures in Fire, 2016) (Source of image: Proceedings of the 9th International Conference on Structures in Fire, 2016) Terminology Definitions; It is important to understand the following areas before installing a natural smoke ventilation system; 1. Smoke Section Area A- The building is divided into several sections. These are partitioned into smoke section areas as where it is possible and also necessary. According to the British Standards, the maximum smoke section area should be 1600 square meters3. The smoke section areas obtained are usually seperated using smoke aprons as specified in AD B. 2. Low-smoke layer d- The low-smoke layer should be approximately 2.5m. 3. Fire development time- Refers to the time from when the fire is created to the time it is detected and the time from detection to real fire fighting activities. 4. Fire spreading rate - Entails an evaluation of expected probability of occurrence of fire and relies on the types of materials which are present in the given room. 5. Smoke ventilation area – It is this that is normally divided into a number of natural smoke ventilators (facade openings) based on the standards set by the guidelines. The openings should be totally inside the smoke layer. 6. Air Supply Area - Must completely fall within the low-smoke layer. Should be at least 1 meter below the smoke layer. At any instance, one should make sure that the incoming fresh air does not collide with the smoke layer since the impulse might result in eddying effects. COMPONENTS OF THE NATURAL SMOKE VENTILATION SYSTEM; The system is made up of a number of components. They include; 1. Ventilators- These are purposed to ventilate hot gases and smoke on the occurrence within a building. Ventilators also offer inlet as well as extract ventilation and also entry of natural day light. Ventilators achieve high thermal, acoustic and aerodynamic performance. Some ventilators are controlled manually whereas some are electrical. There are different types of ventilators, and they include; See fire louvered ventilator, Kameleon casement ventilator, coltlite louvred ventilator and airlite louvred ventilator. 2. Openings – There are different types of openings used for natural smoke ventilation systems as shown in figure D. below (Figure D: Openings- used for natural smoke ventilation system. Source of image: SFPE handbook of fire protection engineering,2015) 3. AOV Roof Units- Fit at the roof to allow exit of smoke from the building. This should be thermally broken. 4. AOV Vertical systems-Developed to be used particularly in external walls. It can be thermally broken as per the requirements set by regulations. Offers average area of ventilation of approximately 1.5 square meters hence complying with the Building Regulations AD B. MECHANICAL SMOKE VENTILATION SYSTEM Mechanical smoke ventilation systems offer an alternative means to the natural smoke ventilation. On the occurrence of fire, the mechanical smoke ventilation systems offer ultimate smoke control as it extracts smoke from the setting to allow occupants an escape route and also offer clear access to allow firefighting services. The advantage of deploying mechanical smoke ventilation system is that one is guaranteed that it will perform; the system will extract a per-determined volume of air after every minute at a consistent rate4. However, mechanical ventilation is expensive to install and maintain. There exist a range of circumstances which might cause one to choose mechanical over natural smoke ventilation. Such situations include; 1. When the apartment is too deep to offer ventilation from its perimeter. 2. Where the quality of local air is poor, for example, a building which is located next to a busy road. 3. Noise levels in the area mean that windows should remain closed. 4. The area has dense structures and the building is sheltered from direct wind by other structures. 5. Security or privacy requirements prohibit opening of windows. 6. The internal partitions block the air path. Mechanical ventilation can be achieved in a number of ways; 1. A circulation system might be used; the system can be a ceiling fan. It creates internal movement of air but fails to introduce fresh air into the building. (Figure E. Mechanical ventilation circulation system; Source of image; SFPE handbook of fire protection engineering, 2015) 2. A pressure system whereby fresh air from outside gets blown into a room via inlet fans. This creates higher internal pressure compared to the external one. Schemes which are correctly designed and installed can offer high protection standards for evacuation as well as fire fighting activities. (Figure . F. System overview. Source of image; SFPE handbook of fire protection engineering, 2015) 3. A vacuum system whereby stale internal air gets extracted out of the building via exhaust fan. This as a result will create lower internal pressure that the outside one. 4. A balanced system which uses inlet and extract fans to maintain internal air pressure at a level similar to the external one and by doing so effectively reduces draughts and air infiltration. 5. Local exhaust system which extracts local heat sources or contaminants at the point of origin, such as fume cupboards, cooker hoods and so on. 6. Mechanical Extract System; Protect the escape routes by extracting smoke from a room before accumulating. It is particularly appropriate in buildings where space is limited hence one cannot use simpler and cost effective uneven solutions. In most (Figure G. System overview.) (Source of image: SFPE handbook of fire protection engineering, 2015) commercial buildings, mechanical smoke ventilation systems are typically run by air handling units (AHU) which are connected to a ductwork that is within the building and supplies fresh air to and extracts smoke from the interior. Typically, the systems are made up of insulated box that houses chambers or filter racks, a blower or a fan, and at times heating and cooling elements, dampers and sound attenuators Generally, the MSVS normally works like a depressurization system. It removes heat and smoke from an area consequently depressurizing the space. Air will be entrained from a region with high pressure and move towards the smoke shaft hence preventing the flow of smoke into neighboring regions. It is imperative to make provision for additional inlet air into the room being depressurized so as to prevent a case of excessive depressurization. Excess depressurization can cause damages to the smoke venting apparatus or the smoke might be pulled actively from the fire room. Pressure differentials might also increase to a point at which the door might be difficult to open or it might be pulled to open as it lies in the region between the fire area and the depressurized area. Advantages of using MSVS 1. It optimizes space and it is therefore more usable. 2. It is more efficient when compared to a code compliant solution since it's not affected by external factors such as wind conditions. 3. The MSVS is not complex like the pressurization system. Disadvantages of using MSVS 1. To be approved, the system efficiency has to be proven through calculations or the CFD modeling. 2. Most non-specialists fail to understand its working. 3. It is not cost-effective for certain types of buildings such as the small buildings. In relation to saving of property and lives, smoke ventilation systems are indispensable necessity. The only means to avert the dangers posed by conflagration gases and smoke is by installing a smoke ventilation system. It is with a good reason that you find the requirements for a smoke ventilation system stipulated in all building regulations in England and Wales. PART TWO The second part of the assignment involves Continuous Fluid Dynamics (CFD) modeling of the smoke control system of the 15-storey building whose plan is provided. The building is to constructed at Leicester City in England The key issues which the CFD modeling will involve are; 1. Time of escape once smoke is detected. 2. Structural response and the resistance to fire. 3. Space separation and heat radiation. 4. Fire characteristics. 5. Smoke and heat transport. 6. Effectiveness of smoke control. In a situation whereby fire begins at the 3rd floor of the 15-storey building whose plan is provided, the first thing to do is to find out the heights of the exit doors and corridors. The corridors is three meters high in the third floor and since the plan is similar in all floors, all the floors have a height of three meters. It is to be considered in this CFD modeling that the exit doors are single-leaf fire doors that measure 2 meters in height, and 0.8 meters wide at a 20 degrees Celsius ambient temperature5. Therefore, fire is spreading from a 9 square meter area within 12 meter perimeter and at the centre of the third floor of the 15-storey apartment. Note that in the simulated CFD model employed (See Table A), the heat flux is considered to be 702 Kilowatts per square meter; this means that the overall size of fire thinning out in different directions is equal to 6,318kW5. Suppose there is a fast fire growth rate of approximately 0.231kJ/s3, the assumed values to determine rate of heat travel will be as given below; Table A: CFD model parameters Parameter Assumed value Heat flux 6318kW Heat growth rate 0.231kJ/s3 Travel time travel distance = 30 meters or the walking speed of1meter per second equals to 300 seconds. Travel distance 30 meters to the exit Surface thickness 25 millimeters Fire flat External façade=1.8 meters wide by 1.2 meters high; Lobbies and straight corridors are modeled. The front door of the fire flat is less than or equal to 22 meters from single stairway Corridor breadth 1.8 meters Staircase There are 15 storeys and it is single case for all the floors Smoke detection time 60 seconds Maximum projected temperature in fire plume 3000C (Source of image: SFPE handbook of fire protection engineering, 2015) The total lost rate of fire per unit area is determined and obtained at a cone heat flux equal to 702kW/m2.At the genesis of the fire, approximately five minutes or 300 seconds the lost rate was consistent. Conversely, as fire grew in later stages the boundary conditions also change. The reaction characteristics are linked to heptane that started the original fire and also for mass loss measurements. The provision of vertical smoke shaft ensures that the common areas the staircase are protected from the extremely high temperatures and cases non-visibility because heavy smoke occupying the corridors. In the scenarios provided below smoke visibility is capped at 8 meters whereas temperature is 550C in all the three scenarios SCENARIOS CFD modeling is accomplished by conducting an investigation involving three scenarios while the location of the vertical smoke shaft and that of the location of fire source is varied and designed to account for worst situations of fire. The movement of smoke in the corridors is also evaluated and calculated. The approach deployed to control smoke in the fifteen storey apartment building is clearly demonstrated in the three cases shown below; SCENARIO A In scenario A, it is assumed that fire initiates at the left area at the fourth floor of the residential apartment just adjacent to the main corridor Figure H. Scenario A- fire initiates at the left area at the fourth floor In the case portrayed above, it is assumed that fire begins at fourth floor's left wing of the 15 storey apartment house having a width of 1.8 meters and a distance of 25 meters from the staircases. Due to the strong winds outside, smoke within the building drifts to the right area of the building at a speed of 1/s. The location of the smoke detector is approximately 25 meters away as well as the smoke shaft. In the case considered it will thus take twenty-five seconds for the smoke detector to detect presence of smoke within the building and hence start the alarm. The occupants within the right section of the building response time will be about 30 seconds while running at a speed of 2 meters per second in order to escape using the mid staircases. In addition, movement shall also be made possible at the lesser volume corridors so as to make available buffer for the smoke at both the staircases and vents. SCENARIO B Fire begins at the apartment's right end just adjacent to the two corridors while the smoke shaft's location is within the same corridor at the second floor. Figure I. Scenario B - Fire begins at the right end just adjacent to the two corridors In state B above, fire begins seven meters from the main corridor, the smoke moves at a speed of 1meter per second towards the left. It will therefore take approximately ten seconds so that the smoke is detected by a smoke detector, and in the next six minutes smoke will have get to the exit of the smoke shaft. In scenario B, smoke is sensed early enough and tenants residing at leftwing as well as the upper floors within the apartment have sufficient time about ten minutes to escape via the central staircases hence there need to be offered emergency stairs at the right wing. Extinguishing the smoke will be done at an appropriate time since the mechanical system location is adjacent to the source of fire and also the smoke detector. SCENARIO C In this scenario, the location of fire is next to the escape route, that is, the central stairs and at the twelfth floor of the building. The location of smoke detector is about five meters from the source of fire and it takes almost five seconds before the smoke gets detected. The fire alarm starts, hence alerting all the residents. Figure J. Scenario C- the location of fire is next to the escape route In setting C above, fire starts close to the exit route. The Smoke shaft exits the smoke after six minutes because the travel distance is about 35 meters. Occupants at the 11th floor and below can escape downwards via the staircases. Whereas the twelfth floor residents will escape using the emergency exits. Fire is easily put out in this case because the smoke vents' location is just over the source of fire. Because smoke is apparently the greatest killer even than the fire itself, saving over 98 percent of residents is possible in case there is increased fire intensity. RECOMMENDATIONS The Continuous Fluid Dynamics modeling above as well as the three cases considered above reveal that smoke control can be made possible by; a) Installing mechanical and natural smoke shafts at the ends of the corridors and also at the staircases b) Surface and boundary conditions should be maintained at all parts of the apartment which enable evacuation through the central staircases c) The owner should install mechanical smoke shafts at the staircase as well as extreme points of the fifteen-storey building CFD Simulation results consents smoke control system while demonstrating aspects like natural ventilation, ducts, vents and the deployment of smoke detectors. Hence ensuring the occupants are aware of safe evacuation in the event of occurrence of fire. Bibliography Alkhazaleh, A., & Duwairi, H.( 2015), Analysis Of Mechanical System Ventilation Performance In An Atrium By Consolidated Model Of Fire And Smoke Transport Simulation. Ijht, 33(3), 121-126. http://dx.doi.org/10.18280/ijht.330318 Banjac, M. and Nikolic, B.( 2009), Computational study of smoke flow control in garage fires and optimization of the ventilation system. Thermal Science, 13(1), pp.69-78. Carlsson, (2005), Flame spread and fire growth-Modeling capabilities in various room configurations, Swedish defense research agency. www.foi.se/ReportFiles/foir_1579.pdf. Gubeau, N & Zhou, XX ( 2004), Evaluation of CFD to predict smoke movement in complex enclosed spaces, Health and Safety Laboratory, http://www.hse.gov.uk/research/rrpdf/rr255.pdf. Meacham, B. J., Charters, D., Johnson, P., & Salisbury, M. (2016). Building fire risk analysis. In SFPE Handbook of Fire Protection Engineering (pp. 2941-2991). Springer New York. Gernay, T., & Franssen, J. M. (2016, June). Towards a standard measure of the ability of a structure to resist a natural fire. In Proceedings of the 9th International Conference on Structures in Fire. Hurley, M. J., Gottuk, D. T., Hall Jr, J. R., Harada, K., Kuligowski, E. D., Puchovsky, M., ... & Wieczorek, C. J. (Eds.). (2015). SFPE handbook of fire protection engineering. Springer. BSI British Standard (BS 9999:2008)- Code of practice for fire safety in the design, management and use of buildings. Read More