Atrium İçeren Çok Katlı Binalarda Duman Dağılımının Sayısal İncelenmesi

Abstract

Yangınlarda, insan hayatı için en önemli tehlike kaynağının duman olması, günümüzde duman kontrol sistemlerinin gelişmesine, bu konu üzerinde çalışmalar yapılmasına neden olmuştur. Gelişen yapılanma ile birlikte atrium, alış-veriş merkezi, konferans salonu, sergi salonu, depo, hangar, vb. geniş hacimlerin kullanımı artmış, buna bağlı olarak duman kontrol sistemi gerekliliği doğmuştur. Tasarım kriterleri bina kullanım amacına göre farklılık göstermektedir. Bu tür geniş hacimlerde meydana gelebilecek bir yangın sonucu açığa çıkan duman hareketleri, sonlu hacimler yönteminin esas alındığı bir akış analiz programı kullanılarak incelenebilmektedir. Günümüzde sıkça kullanılan çok katlı, atrium yapısına sahip binalara örnek bir yapının bir kısmı baz alınarak bir model tasarlanmış ve bu yapıda duman hareketi incelenmiştir. Bina kuyum atölyeleri içermekte ve kullanım amacı nedeniyle yangın için elverişli bir ortam sunmaktadır. Bu tür binalarda doğal havalandırma, mekanik havalandırma veya her ikisi birden kullanılabilmektedir. Yanma sonucu oluşan duman, genel olarak yükselerek atrium kısmında biriktirilip dışarı atılmaktadır. Ele alınan binada atrium üst kısmında doğal havalandırma yapılmadığı, en alt kat ve en üst katlarda egzoz fanları olduğu kabul edilmiştir. Bu tip bir binada yangının kuyum atölyelerinde çıkabileceği düşünülmüş ve bu nedenle 3 farklı kattaki atölyede yangın havuzu oluşturulmuştur. Binada duman egzozuna ve taze hava girişine izin verilen farklı açıklıklar tanımlanmış ve dumanın bina içinde hareketini incelemek için farklı yangın senaryoları oluşturulmuştur. Tasarlanan 2 çözüm senaryosu ile bina içinde, yangın kararlı hale geldiğinde, diğer yangın senaryolarına göre daha düşük duman kütle oranını sağlamak hedeflenmiştir. Bina içindeki duman hareketi, Fluent adlı CFD programı kullanılarak incelenmiştir. Oluşturulan yangın senaryolarında yangın büyüklüğü sabit olarak alınmıştır. Bununla birlikte; taze hava miktarı, taze havanın sağlandığı yer, duman egzoz fan adeti ve konumu, duman tahliyesine izin verilen açıklıkların adeti ve konumu değişken parametrelerdir. Yangının en alt kat olarak alınan 5. kat atölyesinde bulunan yangın havuzunda çıkması durumunda 7 adet farklı yangın senaryosu incelenmiştir. 5. kat atrium alt yüzeyi taze hava girişi olarak kabul edilmiştir. Buradan gelen hava debisinin alt katlardaki taze hava menfezlerine ait debilerin toplamı kadar alındığı durumlar ile hava debisi miktarının serbest bırakıldığı durum karşılaştırıldığında, serbest debili taze hava girişi olmasının bina içindeki duman kütle oranını oldukça düşürdüğü görülmüştür.

Since smoke is the most significant threat to human life in fires; today, this has lead to improve of the smoke control systems and studies on the subject. The smoke and toxic gases that occurs by combustion causes significant part of loss of human lives. Generally, people who are in a burning building don’t lost their lives due to a crash caused by the fire or due to direct fire. They lost their lives due to exposed of smoke and toxic gases. Panic and reduced visibility that caused by smoke plays a vital role that increase the danger. With toxic gases there are tear gas and irritant gases in the smoke. These gases extend the length of time exposed to the smoke and the risk of death increases. In smoke control, fires are investigated in two different cases. Fires, which occur in houses, offices that have small base area and hotel rooms, are investigated as room fires. Add to that fires, occurs in places that have huge base area and volume like malls, atriums, conference halls, exhibition halls, warehouses, aircraft hangars are investigated as large space fires. The basic logic of the smoke management systems that applied to large volumes is, collecting the smoke in the specific regions with the help of the devices like smoke curtains and smoke booths, then exhausting the smoke from the opening at the top of this collection region with natural or forced convection. The main issue for the smoke control system designer is to determine the flow of the fan used in forced convection or determine the ventilation opening area for natural convection. In both condition, the smoke amount must be known to design the smoke control system. The smoke amount can be calculated by the empirical correlations produced by the experimental studies. Thus the minimum flow rate that must be exhausted can be calculated and this amount can be taken as the flow rate of the fans of mechanical exhausting system. Atriums and circulation areas are commonly using in malls. These are the discharge ways for people to exit a secured place out of the building. Generally, covered, a few floors or higher gaps are called atrium. Atriums are around by the usage areas. Atriums are connection gaps between the floors therefore it has a serious risk to spread the fire and the smoke It is very important and critical part to prevent smoke spread over the building and to clean the air from smoke. It effects the life safety, damage to property and easy intervene to fire. On the other hand safe egress time and flashover terms are very important parameters for the fire. It is technically known that the temperature of the smoke layer must be at least 18 °C higher than the ambient temperature. Otherwise the smoke layer come closer to the floor. Also the temperature gap between the smoke layer and the ambient make it is easy to discharge the smoke. However if the smoke layer temperature is higher than 200°C, the heat radiation becomes very high, it becomes very dangerous for the people who are trying to escape from the fire. As technological developments in the construction sector gain acceleration, nowadays the high-rise buildings become popular. As a result of this trend, the control volumes of the buildings reach great values and smoke control systems become essential. Atriums, shopping centers, auditoriums, showrooms, warehouses, hangars are the examples for constructions that has necessity for the smoke control systems for different usage purposes. The design criterions of smoke control systems depend on usage purposes. The smoke movements occur during a fire in high-rise buildings can be analyzed by a program, which based on the finite difference volume method. A construction model designed by taking as an example part of a high-rise building, which contain atrium. In this model, smoke movements are investigated. The building contains jeweler workshops, which have very conducive environment for fire. In such buildings, natural ventilation, mechanical ventilation or both of them can be used. Smoke as a consequence of the fire, rises and is collected at the top of the atrium and exhausted. As a assumption, at the top of the building, there is no natural ventilation and at the top and bottom floors of the building there are exhaust fans available. It is assumed that the fire starts in the workshops. Therefore, the fire pools are placed at the three different floors in the workshops. There are some openings which allow smoke outlet and fresh air inlet are defined. Some fire scenarios are build up to investigate smoke movements. On the other hand two solution scenarios are iterated. It is aimed to obtain with these two solution scenarios lower mass fraction of the smoke than the other solutions when the smoke flow become stable. The smoke movements are analyzed with the CFD programme named Fluent. The heat release rate is taken constant for the fire scenarios. However, fresh air rate, fresh air opening locations, number of exhaust fans and locations, number of openings and the locations are the variable parameters. In the case of fire in the atrium, in the corridor that opens to the atrium or workshops the smokes moves in two directions. Mainly, because of the high temperature of the smoke and chimney effect, smoke rises. However if there is unsteady and undirected fresh air inlet, It makes a second direction which is parallel to the surface of the floor. This situation is an undesired phenomenon to have second movement direction. When the smoke reach to the places which are far away from the fire by the horizontal movement, it becomes dangerous for the people. In case of fire start at the workshop which is placed at the fifth floor of the building which is assumed bottom floor of the model, 7 different scenarios are investigated. 5. floor, bottom surface of the atrium is assumed as the fresh air inlet. There are two situation for the fresh air flow rate. In the first situation, the fresh air flow rate is equal to sum of the flow rates of fresh air vents at below the fifth floor. In the second situation there is no restriction for the fresh air flow rates. If these two situations are compared, it can be seen that in the second situation mass fraction of the smoke is lower than first situation. Smoke source is the workshop which is in the below floor for all the reference cases and third case. In the reference cases, smoke movement can be investigated and minimum air inlet is provided, discharge of the smoke is allowed. In the lowest part of the atrium, there is an air inlet, which carries equal air to the air carried by the all culverts up to the fifth floor. It is assumed that there is no fresh air inlet in the fort he modeled floors. Smoke is exhausted by the two discharge fans, which are placed in the fifth floor and top floor. In addition to these fans, in the third case, smoke is sucked by two linear discharge fans, which are placed in the fifth floor of the atrium. Case 7 and case 8 are the solution for the fire situation in the multi storey building which has a atrium is investigated. As a result of these investigations low smoke mass ratios are obtained. The combustion phenomenon and the wind pressure are neglected. In the scenarios which are for the fire situations on the 5. floor, smoke-mass ratios are investigated for the 6. and 10. floors. It is assumpted that the air is a mixture which has %21 oxygen. Therefore the oxygen amount on the 6. and 10. floors are calculated and compared to requirements for the health conditions. Aim of this calculations is to decide whether oxygen amount is critical or not. It is advised in this thesis that for the similar buildings different fire size scenarios should be investigated. It can provide useful information for the different situations.