Numerical investigation of smoke exhaust mechanism in a gymnasium under fire scenarios

The Fire Dynamics Simulator code is used to investigate the smoke filling process in a large building. Initially, the model is used to simulate the smoke descending process in an atrium under fire scenarios. By comparing with experimental data, reasonable model constants of _Cs$C_{\mathrm{s}}$ and _Prt${\mathit{Pr}}_{\mathrm{t}}$ are determined for simulating smoke movement in buildings with large space. The performance of different smoke exhaust methods in a real gymnasium is then studied. Smoke filling processes are investigated under different natural and enhanced smoke exhaust methods. Simulated results show that natural smoke exhaust method is preferred when the smoke exhaust vents are located at the ceiling of the gymnasium. On the other hand, when the smoke exhaust vents are located on the walls of the gymnasium, enhanced smoke exhaust methods are preferred. In addition, the influence of ceiling temperature in the gymnasium on the smoke spreading process is presented in this paper. Results indicate that high ceiling temperature slows down the so-called smoke ceiling jet moving horizontally at the ceiling, whereas low ceiling temperature accelerates such smoke ceiling jets.     

Numerical model and validation experiments of atrium enclosure fire in a new fire test facility

The use of computational fluid dynamics (CFD) as a tool for buildings, warehouses or factories design requirements fulfilling about fire safety is becoming more common and reliable. Performance-based fire safety assurance procedures make use of the CFD fire modelling to anticipate the evolution of fire, but they need always to be validated. This is especially difficult for big structures, with great clear volumes, where effects of natural and forced ventilation can be very scale dependent. A good opportunity to check the prediction capability of CFD codes to establish temperatures and velocities fields is the new full-scale fire test facility of the Technological Metal Centre in Murcia, Spain. It is an aluminium prismatic squared base building of 19.5 m×19.5 m×20 m, with several vents arranged in its walls and four exhaust fans at the roof. Series of experimental tests have been carried out using several heptane normalized pool-fires placed at the centre of the atrium. The data obtained from these experiments have been later used in a validation study of two CFD simulations implemented for temperature wall, ambient temperature prediction and exhaust fan assessment. The results show good agreement between experimental and numerical predictions and allow concluding that for a fire test of 1.6 MW of average heat release power, the exhaust and ventilation system is not enough to extract the hot combustion products. There is an excessive and dangerous accumulation of hot gases at the upper part of the atrium and the exhaust capacity of the roof fans must be increased. The CFD models can give the answer to that question.     

Numerical simulations on fire spread and smoke movement in an underground car park

The Fire Dynamic Simulator code is used to investigate fire spread and smoke movement in a large underground car park under different fire scenarios. Initially, by comparing with experimental results of heat release rate of a single car fire, the development of car fire is designed by letting surface densities of the fuel over the car. Fire spread and movement of smoke are then investigated under different ventilation conditions. Simulated results show that the development of car fire in the underground car park can be classified into four stages; namely an initial stage, a developed stage, an extinction and re-burning stage and another fast-developed stage. Affected by ventilation systems, fire develops rapidly resulting in consuming most oxygen quickly followed by early extinction of the fire. After extinction of the fire, with more ambient air drawn into the car park due to ventilation, re-ignition takes place with accelerated development. In addition, detailed field distributions of temperature and velocity vectors are given. It is found that the smoke layer decent to the top of the car after 15 min and the hot smoke flows in a disorderly manner resulting in the spread of fire more rapidly.     

地铁车站火灾烟气蔓延数值模拟分析

分析了地铁火灾特性。利用FDS对天津地铁某站在发生火灾时的烟气温度与能见度分布情况进行了数值模拟,并对模拟结果进行分析,结果表明,360s时最不利点温度小于45℃,能见度为6～7m,完全满足火灾工况下的人员安全疏散对温度和能见度的要求,故该车站设计满足火灾时人员安全疏散的要求。     

酒店中庭自然排烟方式的数值模拟

分析青海某庭院式酒店中庭区域的烟气蔓延,通过模拟得到排烟口高度处烟气层内热流、质量流、体积流随时间变化的情况,分析建筑自然排烟系统的有效性,并对比排烟口布置位置对排烟效果的影响。通过计算得出排烟窗面积为内庭院面积的10%时能够保障建筑的消防安全。在4.0 MW的火源功率下,火源稳定之后150s左右烟气层稳定在30～32m高度处;自然排烟口位于庭院中心处的排烟效果优于排烟口位于四周。     

Influence of fire ignition locations on the actuation of smoke detectors and wet-type sprinklers in a furnished office

Experiments were conducted in a full-scale model office equipped with movable and fixed fire loads to explore the influence of ignition source (movable fire load(s)) conditions on smoke detector and sprinkler actuation. The interior plan dimension is 5.7 m × 4.7 m and the net ceiling height is 3.3 m. Both northeast and southeast wings have a 2.1 m × 0.9 m single door to be opened. Seven fire scenarios (seven different ignited fire load configurations) under natural ventilation were investigated experimentally. The results show that the amount of fire load at the initial stage in a room fire does not markedly affect smoke generation and does not significantly impact the actuation time of the smoke detectors. When the fire source is located near a corner, the plume corner effect greatly increases; smoke detectors and sprinklers can activate quickly and effectively actuate the fire suppression. When the fire source is located in the room's center, given the uncertainty regarding smoke detector and sprinkler actuation, it may not be possible to control the fire spread.     

中庭火灾烟气流动的大涡模拟

采用大涡模拟的方法,对中庭火灾烟气的流动过程进行了模拟,了解了中庭烟气的蔓延过程,得到了烟气的速度场和温度场、顶棚射流的速度和温度的详细结果。模拟结果表明,大涡模拟能比较准确地预测中庭内烟气的流动状态,可用于指导中庭建筑的防火设计。     

Full-scale experimental studies on mechanical smoke exhaust efficiency in an underground corridor

Full-scale burning tests were conducted in a full-scale underground long corridor with beamed ceiling and smooth ceiling. The influence of air-supply opening position on the smoke exhaust efficiency was studied. The operation time of the smoke exhaust fan was also discussed to obtain a better smoke exhaust. Results showed that the smoke exhaust would be more efficient when air-supply openings were some distance away from the smoke exhaust openings. When the air-supply opening was near the smoke exhaust opening, even with larger smoke exhaust rate, it still gave poor smoke control results. Two comparing tests on the effects of operation time indicated that it would give poor smoke control ability when the smoke exhaust system operated too early. Finally, some future research topics were also discussed in this paper.     

低位排烟作用下小室火灾的数值模拟研究

采用数值模拟的方法,结合某装配有低位排烟系统的实体小室,分析了低位排烟作用下小室火灾的发展过程.结果表明,在低位排烟模式下,烟气层高度的界面比较低,通常都处在连续火焰区;大量的空气被排烟风机从下层空气层直接抽走,使得机械排烟效率大大降低;机械排烟效率随着火源功率的增加而增加;通过模拟得到低位排烟时的平均机械排烟效率约为27.3%.     

盾构机外部失火隧道内烟气传播数值模拟

用FDS模拟不同通风条件及水幕开启/关闭状态的火灾过程,分析盾构机外部配电箱失火时隧道内的烟气传播规律,通过比较隧道内关键位置处的烟气体积分数、温度、二氧化碳体积分数、氧气体积分数及能见度,评估对隧道内工作人员安全的影响。结果证明,水幕可起到一定的阻烟作用和很好的隔热作用,能降低盾构机一侧的二氧化碳体积分数,并使得掘进面附近工作区域内的能见度变化很小;在通风条件下,风流会阻隔烟气到达掘进面附近;水幕的阻烟效果及通风充足使得隧道内的氧气体积分数基本不变。     

On the bidirectional flow across an atrium ceiling vent

Sizing of horizontal ceiling vent in a tall atrium is usually based on vent flow models with unidirectional flow. This is only good for natural vents with large pressure differences between inside and outside. For low pressure differential across the horizontal ceiling vent as experienced in some atrium fires, bidirectional smoke flow rates were observed. The extraction rate through the vent would be reduced, giving poor performance of the smoke exhaust system.     

高层建筑走廊机械排烟的数值模拟研究

采用场一区复合模型模拟起火层内的烟气运动过程，分析了走廊通道内三种机械排烟方案的烟气控制效果。模拟结果表明，与排烟量相比，排烟口的位置和数量对排烟效果的影响更大；排烟口应尽量远离疏散出口。     

多层建筑火灾烟气运动的数值模拟

阐述了烟气运动的数学模型．应用CFD技术对多层建筑火灾产生的烟气运动进行了模拟，分析了烟气的运动状况，初步论述了CFD技术的优缺点。     

隧道火灾烟气运动的数值模拟

对不同入口风速和隧道高宽比情况下隧道内的烟气运动进行模拟,分析隧道内的烟气分布情况.结果表明:随着入口风速的增大,隧道内整体的烟气浓度会逐渐降低.入口风速过大,加强了气流的湍流程度,使烟气层较早降至路面,隧道断面提前充满烟气,使火源附近近地面处的烟气浓度过高.当入口风速较小时,火源上部的部分烟气会逆着风向流动,产生回流现象,所研究工况下烟气不发生回流的临界入口风速为2.2 m/s左右.横截面积相同的情况下,隧道高宽比越小,烟气上升高度越高,隧道下部烟气量越少,利于救援和人员疏散.     

Influence of different make-up air configurations on the fire-induced conditions in an atrium

In this paper, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. In the experiments, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke-layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. These data could be used as benchmark for future numerical validation studies. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDSv4). In the experiments, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. In the numerical simulations, the predictions agree well with the experiments for the cases with larger make-up air openings. Poor agreement has been found for the case with the smallest inlet openings.     

A small-world network model for the simulation of fire spread onboard naval vessels

This work is devoted to the development of a small-world network model to predict real-time fire spread onboard naval vessels. This model takes into account short-range and long-range connections between neighboring and remote network compartments. Fire ignition and flashover, as well as fire transmissions through the walls and ventilation ducts are simulated using time-dependent normal probability density functions. Mean durations of fire transmission through the walls and ducts are determined by a three-zone model and a one-dimensional CFD code, respectively. Specific experiments are conducted in a steel room, representative of a naval vessel compartment, in order to validate the zone model. Then a proof of concept is developed by applying the network model to a full-scale vessel mockup composed of 113 compartments on 7 decks. A statistical study is conducted to produce fire risk maps, classifying the vessel compartments according to their propensity to burn.     

地铁站台火灾烟气蔓延数值模拟分析

采用FDS对地铁站站台层火灾进行数值模拟,分析其火灾情况下地铁站内的烟气蔓延、温度分布、能见度分布、CO浓度分布情况,研究地铁火灾时人员疏散的安全性。研究表明：火灾情况下,烟气温度、CO浓度的变化主要集中在火源区域附近。站台层其他区域的温度和CO浓度均得到很好的控制。但能见度下降较明显,不利于人员疏散。     

Laboratory evaluation of smoke detectors for use in underground mines

Laboratory experiments were conducted to determine the responses of a prototype smoke detector and a commercially available photoelectric smoke detector to smoke particles generated from various combustion sources. The prototype smoke detector combines optical scattering measurements with ionization chamber measurements in order to reduce/eliminate nuisance alarms due to the presence of airborne dusts or diesel exhaust particles. The commercially available smoke detector is designed for use in harsh environments where airborne dust represents a major problem due to both nuisance alarms and detector contamination. In the experiments, the responses of the two detectors were measured when exposed to smoke particles from the exhaust of a diesel engine and from a variety of fire sources, including wood, coal, styrene butadiene rubber, and No. 2 diesel fuel. For the solid fuels, data were obtained for both smoldering and flaming combustions. This report describes the experiments, their results, and the use of these results as they apply to early-warning fire sensors capable of the rapid and reliable detection of fires in atmospheres that may or may not be contaminated by either airborne dust or the products produced from diesel engines.     

Experimental measurements,integral modeling and smoke detection of early fire in thermally stratified environments

Building fires go through a series of stages. They start with a fire plume period during which buoyant fire smoke rises to the ceiling. A second stage is the following enclosure smoke-filling period. In this paper, the first stage is the subject, especially for the fire plume behavior in thermally stratified environments in large volume spaces. In NFPA 92B, Morton's integral equation was introduced for calculating the maximum plume rise, and beam smoke detectors were recommended for smoke detection design. In this work, experiments and CFD simulations were conducted in a small-scale enclosure and a large space to investigate early fire movements in temperature-stratified ambients. The results show that in a thermally stratified environment, the axial temperature and velocity of a fire plume decrease more quickly along the vertical axis than in uniform environment, and in some cases the fire plume ceases to rise. The previous integral equation was shown to underestimate the actual maximum height of a fire smoke plume, and also was unable to explain the differences of the maximum heights of low-density and high-density smoke plumes with the same stratification and outlet conditions. The integral equation was improved by introducing two correction factors, and extended for non-linear temperature stratified environments. A light section smoke detection method with three space-protected area was suggested and discussed.     

Experimental and numerical evaluation of the influence of the soot yield on the visibility in smoke in CFD analysis

Experimental and numerical analysis have been performed to evaluate the influence of the soot yield parameter on the results of advanced engineering analysis, in regards to visibility. After identifying soot yield as the most influential factor on the results, fuels with various values of Ys have been analysed in a fire chamber and then compared to numerical data. The numerical analysis has been performed using two different CFD packages, ANSYS® Fluent®, and Fire Dynamics Simulator. The numerical analysis itself show an apparent hyperbolic trend of the visibility when changing the soot yield with clear consequences on the ASET (Available Safe Egress Time). Below a cut-off point, that exists at a soot yield value close to Ys =0,10 g/g, a small change in the parameter causes a substantial shift in the results (visibility or ASET time), while above this value an increase to soot yield does barely influence the results. Qualitative assessment of the results shows a need for use of conservative values of Ys in engineering analysis if detailed and precise material data is not available. Additionally to the full-scale experiments, a real case study has been included to show how this research can be translated into the Fire Safety Engineering design process. In this study, change of Ys value below 0,10 g/g caused a significant change of the qualitative assessment of the results of CFD.