Natural and Mechanical Ventilation on Corridors of the Apartment Buildings - Coursework Example

Title: Review of natural and mechanical ventilation on corridors of the apartment buildings Name Institution Date of submission Introduction The project of a smoke ventilation system in the apartment blocks is taken as the essential part of Fire Safety Framework in organizations. During in the situation of fire, smoke is normally regarded as liquid or solid particles that are produced from the combustion of fuels. In other fire situations/context such as gaseous combustion, their products are toxic gases. The most common toxic gases in building fires are the carbon II oxide and hydrogen cyanide. It is evident that the smoke can be hazardous to people and the whole environment as well (Lougheed, 2000). Some severe hazards from smoke include poor visibility and effect on the respiratory systems of people. Smoke ventilation systems in corridors and apartment blocks ensure that there is safe and good access to the buildings when it comes to fire services. In this report, we focus on the natural and mechanical systems and its benefits on the apartment when it comes to the fire situation. According to Shi & Gao, (2013), the apartment design often determine the appropriate ventilation system. The British Standards vary depending on the height of the building and the distance between the two apartment entrances and escape route (Lougheed, 2000). Most requirements regarding smoke ventilation systems states that with the apartments with four storeys and more up to the height of 11 metres, the maximum of 7.5 metres are allowed for the travel distance. On the other side, the corridor compliance should be allowed with a 1.5 square metres of the automatic opening vent (AOV) opening or 1.5 square metres for the natural smoke shaft. This provides a safe and efficient escape route for residents by ensuring that there is a good protection on corridors from reduced visibility. This report examines the use of natural and mechanical smoke ventilation systems in apartment blocks and corridors. Smoke control and ventilation systems in apartments and corridors It is important to control smoke in corridors and apartments due to the following reasons: 1. The central escape route in large apartments is the corridors towards the protected stairs. 2. When the smoke is left for a while to spread around, it may go beyond the open doors to corridors that will reduce the visibility if the occupants thus making escape route difficult. 3. Smokes on the stairs make it difficult for the escape of the residents in the higher storeys 4. In taller apartments, smoke can obstruct the rescue services on the stairs and corridors thus forming a bridgehead for procedures of rescue. Smoke ventilation systems are developed for each corridor and stair in the apartments to stop the smoke from spreading to other stairs. Therefore, natural or mechanical ventilation systems can be used. Natural ventilation systems A natural ventilation system often uses the resilience of the smoke to compel the exhaust. In this case, smoke’s depth and temperature determine the compelling force of the exhaust. There are two advantages gained from the natural ventilation system: they are reliable and simple to install. With the buildings of the height more than 18 metres, or with the basement more than 10 metres, there is a unique requirement. However, in the case of the residential apartments with higher heights, the fire fighting lobby is only required for the natural ventilating system (British Standards, 2002). As mentioned, the natural ventilation system is simple, and it is developed with low cost, it is the most effective choice for apartments. The system often has ventilated corridor that extend to the outside wall. The natural ventilators and wind effects It is important to position in the right place the smoke exhaust relative to the wind when the natural ventilation is installed in the apartments. In some instances, it is okay when the natural ventilation is developed vertically by arranging the inlets to face a region that is sheltered from the wind. This will enable the smoke not to be interfered with the movement of the wind. This type of erection can also boost the positive pressure by converting the excess pressure to suction. The power exhaust in the system, however, may be a problem in the case of poor positioning. The smoke may idle and may call for its extraction through a wide ductwork system. Therefore, it is important to consider a negative wind pressure when installing natural ventilation. The figure below shows effective natural ventilation installed relative to the wind pressure. Figure 1 (Adapted from BS: Lougheed, 2000) From the above figure, the natural ventilation installed can overcome negative wind pressure since the windows of the apartment can release suction even when the wind changes its direction. Regarding the application of natural ventilation, it is intended that the driving force should be the buoyancy of the hot smoke that is emitted from the fire. Given that the buoyancy of the forces sometimes is smaller compared to the forces of the wind, the performance of the natural ventilation can be affected by the wind. Therefore, for natural ventilation to function effectively there must be an exhaust, the inlet of air and a mounted vented wall. The mounted vent wall will help the system by ensuring that it has an inlet at the bottom as well as the exhaust at the top. The vent is also needed at the head of the corridor to assist any smoke that enters the corridor (Morgan, Ghosh, Garrad, Pamlitschka & Smedt, 1999). The universal standards of the natural ventilation the right angles are set at the direction in which the air flows. In this case, the free area that is measured for the natural ventilator should be done on the plane and the area set at a minimum as shown in the figures below. Figure 2 (Adapted from: Sun, Fang & Chen, 2013) From the above figure, the angle minimum of the opening should be 140° should be designed to mitigate the adverse effects of the wind in case it will be experienced. The free are is calculated by multiplying the length of the corridor that is opposite the pivot mechanism (a) by the ventilator’s open distance (d) that is measured at 90° relative to the opened window as shown in figure 2 (British Standards, 2002). This is often done where the outward opening corridor vent is used. The general principles underlying natural ventilation system Air in the apartment blocks will try to move from a region of higher pressure to a region of low pressure. As a result, the pressure increases in the protected region (the escape routes) which is located above the region where there is the likelihood of fire occurrence in the apartment. This system sill thus prevents the smoke from spreading into the escape routes. The escapes routes in the natural ventilation systems are pressurized to achieve the efficiency of the overall system. Despite the possibility of achieving the same efficiency through depressurizing the apartment, there is no apparent action of the positive results especially when the speed of the wind high (Sun, Fang & Chen, 2013). The movement of the smoke in an apartment is often restricted by the fabric of the building. This only occurs when the fabric of the building is leak free, and this could maintain the pressure difference. Since the fabric allows leaks, air needs to blow constantly to maintain the pressure difference as well. A difficulty is when the doors of the apartments are opened during the escape. People will be escaping through the corridors thus making the fire service attendance difficult to maintain the pressure difference. It is highly recommended therefore that the natural ventilation system should have a design of spacious corridors that will achieve maintenance of pressure difference even when the doors are open. Shi & Gao (2013) found that too much pressure, when the apartment blocks are closed perhaps, will make difficult the functioning of the natural ventilation system. Mechanical smoke ventilation system The general principle of the mechanical smoke ventilation system The mechanical ventilation system can be used as n alternative of the natural ventilation system. The option of choosing mechanical ventilation as an alternative came as an assumption that the shaft system are used, and the floor of the apartment should have a power system (British Standards, 2002). It is important to note that mechanical ventilation system in apartments is only used when its measures offer the equivalent performance to the 1.5 square metres natural counterparts. The mechanical ventilation has the following benefits: 1. It has a specified extraction rate 2. The sensitivity of wind is low 3. Well known capability when it comes to overcoming the resistance, and 4. The system’s shaft cross sections are reduced. The requirements of the mechanical system include: 1. Constant power source, 2. Standby fans 3. Resting wiring 4. Classified temperature equipment The mechanical smoke ventilation system operates efficiently when the internal pressures of the apartment are considered, and the doors leading to the corridors remains operable. Like the natural ventilation system, it is important to provide an air inlet to prevent the destruction of the system. This also ensures that the pressure difference is maintained to avoid either more pressure or depressurization in the ventilated rooms within the apartment. In this case, the smoke will be prevented from being drawn from the fire origin but rather elevated by the pressure difference (Lougheed, 2000). The mechanical ventilation system in an apartment that has a reservoir of up to 0.5 metres deep needs smoke higher containment practices (British Standards, 2002). To achieve the containment of the in an apartment with the use of the mechanical system, it is necessary to use a system reservoir with a depth greater than 0.5 meters. From the figure 3 below, the total height of the mechanical reservoir’ should be .5 meters. Figure 3: Mechanical smoke ventilation system (British Standards, 2002) From the above system, the smoke shafts are constructed from the non-combustible materials and the corridors are smoke resistance at least equivalent of E30S fire door. Normally, the mechanical ventilation system is activated upon approval from the authorities (Shi & Gao, 2013). But is some cases, the system is activated when there is a detection of the smoke on the apartment corridors or stairs. According to Sun, Fang & Chen (2013), the mechanical system can be developed to provide higher performance through extending the distance travelled in the corridors. However, care should be enhanced in deciding to remove the sub-divisions doors in the corridors. The removal of these doors will reduce the travel distance and also limiting the efficiency of evacuation procedures by the fire services. Removal of these doors can compromise the efforts of the fire safety services in the apartment in case of fire outbreak. The installation equipment and the design process for the mechanical ventilation system All the air conditioning in the mechanical ventilation system is normally contracted with steel or aluminum materials. All these materials should be adequately supported, and the duct covering should be non-combustible. From the figure 4 below, the ventilation ducts do not pass through the corridor. In this case, the region of the ventilation duct is enclosed during the construction of the apartment. The concealed space between the floor and the ceiling has a sheltered metal cable. The concealed spaces will provide a medium for fire and smoke transfer. Therefore, in building up the dust, it is important to use reduced number of combustible materials. Figure 4 (adapted from: British Standards, 2002) The above figure shows that the components of the mechanical smoke ventilation system are installed in such a way that the mechanical exhausts do not discharge the smoke to the adjacent building. From the analysis point of view, the design of the system considers the safety of the adjacent apartment. Conclusion Mechanical systems are the equivalent of natural systems where both systems can be installed in the apartments that have travel distance in the corridors that extend more than the recommended 7.5 meters. The reason for installing these systems is because they offer effective performance during the escape and assisting in clearing the smoke in the whole apartment. Both natural and mechanical smoke ventilation system offer the apartments advantages not only in terms of smoke clearance but also it saves costs. Therefore, the choice of whether to install a natural or mechanical ventilation system depends on the factors such as the design of the apartment and the objective of the developer. The experience fire fighting services often provide the best results in designing n appropriate smoke control system for the apartment. References British Standards,. (2002). Application of fire safety engineering principles to the design of buildings —. Part 2: Spread Of Smoke And Toxic Gases Within And Beyond The Enclosure Of Origin (Sub-System 2), 31-43. Lougheed, G. (2000). Considerations in the Design of Smoke Management Systems for Atriums (pp. 2-6). Ottawa: Institute for Research in Construction. Retrieved from http://irc.nrc-cnrc.gc.ca Morgan, H., Ghosh, B., Garrad, G., Pamlitschka, D., & Smedt, J. (1999). Design methodologies for smoke and heat exhaust ventilation. Garston: CRC. Shi, W., & Gao, F. (2013). Simulation and Analyzing of Mechanical Smoke Exhaust in a High-Rise Building. AMR, 726-731, 3596-3599. doi:10.4028/www.scientific.net/amr.726-731.3596 Sun, J., Fang, Z., & Chen, J. (2013). Full-Scale Experiment of Longitudinal Ventilation Smoke Control System and Central Smoke Exhaust System in City Underwater Tunnel. Procedia Engineering, 52, 330-335. doi:10.1016/j.proeng.2013.02.149 Read More