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.     

The impact of atrium shape on natural smoke ventilation

The performance efficiency of natural smoke ventilation in atria spaces are influenced greatly by several design decisions such as atrium shape, height, size and openings location. This paper investigates the impact of atrium shape (horizontal profile) on smoke ventilation performance in naturally ventilated atria. Three different configurations (square, rectangular and triangular prism) with the same area, height, and hence, volume were tested. The smoke ventilation performance is being assessed in terms of smoke filling time using a computational fire dynamic simulator (FDS). FDS is used to simulate the natural smoke filling resulting from atrium fire in the three configurations. The smoke layer interface height as a function of time and soot mass fraction and temperature as a function of height have been registered during the simulation. The predicted transport lag time for initial formation of the smoke layer beneath the ceiling (ceiling jet) was compared for the three tests. In order to test sensitivity of the shapes, all other parameters were designed to be similar in the three tests, and the same fire scenario was applied including inlet and outlet area, and fire size and location. The results showed that the rectangular configuration contributes better to smoke ventilation, and that the triangular configuration is the most critical in terms of smoke filling time, followed by the square configuration.     

Numerical study on smoke movement driven by pure helium in atria

The hot smoke test is often used for commissioning fire smoke management system in atrium buildings, in which liquid fuel is burnt to generate a buoyant plume mixed with artificial tracer smoke to model a fire smoke. The method is usually costly and often causes safety concerns. This paper studied an alternative method of using a cold smoke test, in which pure helium is used to create the buoyant plume. A method was developed to determine the supply rate of pure helium necessary to achieve the same buoyancy effect as that of the corresponding hot smoke test. Computational fluid dynamics (CFD) simulations of the helium smoke tests were conducted and compared to the measured hot smoke tests in a full-scale naturally ventilated atrium and a sub-scale atrium with mechanical ventilation. A new method was added in the CFD model to track the smoke layer height for the simulations of helium smoke based on the concentrations of smoke and helium. It is found that the predicted smoke layer heights based on the mass fractions of the tracer smoke are generally close to the measured ones in the hot smoke tests of different heat release rates. A non-dimensional temperature in the hot smoke test is also found closely related to the dimensionless helium concentrations in the helium smoke test for the atria modeled. Although the consumption of pure helium for a full-scale helium smoke test can be very high, it is promising to use the pure helium smoke test in the lab-scale experiments as the preliminary tests of full-scale and/or lab-scale testing of real fires.     

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。     

Prediction of fire and smoke propagation in an underwater tunnel

Different models and solvers are used to calculate the spread of fire and smoke in a tunnel. The methodology for obtaining the numerical solution of this fire dynamics problem involves commercial software and a research program. Both can handle geometries described in three dimensions. Particular emphasis was placed on road tunnels in which vehicles are present. The specific application of this work is a study of a fire scenario in the Louis-Hippolyte-Lafontaine Tunnel which runs under a river in the Montreal area. Besides standard representation, visualization is also used, with elements which consider the optical properties of the phenomenon for a realistic rendering of smoke and fire.     

商业厨房火灾烟气蔓延数值模拟研究

通过实地调研得到典型商业厨房物理模型。设置8种工况,利用CFD模拟商业厨房不同火灾事故场景下的烟气、温度、能见度等参数的变化规律,得到不同火灾事故场景的演化特点。分析结果可知,商业厨房发生火灾约30~40 s后,厨房内2 m高度处截面的能见度降到10 m以下,影响人员疏散;发生火灾约50~150 s后,门口1.8 m高度处测点温度达到60 ℃,影响人员的生命安全。     

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。     

某室内商业步行街火灾烟气控制研究

为了研究室内商业步行街的火灾烟气控制效果,以某城市综合体为例,模拟室内商业步行街火灾,在中庭位置设置1.5 MW酒精火源,点火后分别联动开启排烟设施和手动开启自然排烟设施,观察两种工况下室内步行街内烟气蔓延情况,并测量试验区域温度等参数.试验发现,相较于顶部自然排烟,采用联动机械排烟的烟气沉降速率低17％,烟气层高度高...     

A study of an optimal smoke control strategy for an Urban Traffic Link Tunnel fire

An Urban Traffic Link Tunnel (UTLT) is a novel type of underground transportation system consisting of a main tunnel in a loop shape and several linked tunnels. It has a higher level of fire risk compared to other common road tunnels. In this study, numerical study was conducted to investigate the smoke control strategies for a designed fire scenario in the Beijing Center Business District (CBD) UTLT. An optimal smoke control strategy was developed and evaluated using three criteria: critical velocity, minimal smoke spreading area and available safe evacuation time. In developing the optimal smoke control strategy, six different smoke control strategies for the UTLT were evaluated initially by the criterion of critical velocity, and one of those control strategies was chosen as the primary strategy by steady simulation. This strategy was then modified according to the dynamic simulated results of smoke movements to satisfy the other two criteria. Consequently, the optimal smoke control strategy for the UTLT based on the primary strategy was obtained. The transient distributions of the smoke spread, smoke temperature and CO₂ concentration, were analyzed.     

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。     

Experimental study on heat exhaust coefficient of transversal smoke extraction system in tunnel under fire

Heat exhaust coefficient of transversal smoke extraction system in tunnel under fire is studied by experimental means with a 1:10 model tunnel using Froude scaling. Heat exhaust coefficient is defined as the proportion of the heat exhausted by individual exhaust inlet, smoke duct and exhaust fans in total heat released by the fire in the tunnel, respectively. Results of a series of fire tests in a model tunnel are presented. Heat exhaust coefficient of single exhaust inlet and the smoke duct are strongly influenced by the configuration of the exhaust inlets. Heat exhaust coefficient of the exhaust fans varies in the range of 13–20% and is smaller than the heat exhaust coefficient of the smoke duct which varies from 17% to 83% and tends to be about 35% with the increase of the total area of the exhaust inlets. Activating small number of the exhaust inlets is beneficial for enhancing the heat exhaust coefficient of the smoke duct. The heat exhaust coefficient of the smoke duct and exhaust fans is high when the exhaust inlets are set close to the fire. Due to the cooling effect of the solid boundaries on the smoke while traveling in the tunnel and smoke duct, the heat exhaust coefficient of the exhaust fans in unilateral exhaust mode is slightly smaller than that in bilateral exhaust mode.     

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%.     

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.     

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.     

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。     

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。