Definition and experimental evaluation of the smoke “confinement velocity” in tunnel fires

An experimental study is carried out on a reduced scale tunnel model (scale reduction is 1:20). The main objective is to evaluate the longitudinal velocity induced into a tunnel when a fire plume continuously released is confined and extracted between two exhaust vents located on both sides of the fire source. For the experimental simulations, fire-induced smoke is simulated by an air and helium mix release. Smoke flow is symmetrical as regards the fire location and experiments are realized for an half tunnel with only one vent activated downstream the source. The vent extraction flow rate is step by step increased and the length of the stratified smoke layer downstream the vent as well as the longitudinal fresh air flow induced, are measured. A confinement velocity is then associated to the minimum value of the longitudinal air flow needed to prevent the smoke layer propagation downstream the vent. This velocity is evaluated for several values of the fire heat release rate and finally compared with the corresponding critical velocity obtained for a longitudinal ventilation system.     

纵向通风与竖井自然排烟下隧道火灾烟气特性实验研究

中国逐渐发展成为世界上隧道和地下工程最多的国 家,其长隧道数量和长度跻身世界前列。据统计,火灾中85%的 人员死亡是由热烟气造成的,目前隧道中采用较为广泛的排烟系 统有纵向排烟系统、集中排烟系统和横向排烟系统,而针对长隧道 来说,我国广泛采用的是竖井式纵向通风,因此,研究纵向通风与 竖井排烟综合效应下隧道火灾烟气流动特性及温度分布规律具有 重要意义。本文建立了1：10 缩尺寸竖井隧道模型,主隧道长度 16.5 m,宽度1.3 m,高度0.65 m;竖井通过排烟横通道与主隧道 连接,排烟横通道设置在主隧道侧面中部,尺寸为1.2 m 长、0.6 m 宽、0.4 m 高;竖井横截面为半径0.6 m 的1/4 圆,高4.6 m。在 竖井隧道模型中开展了一系列油池火实验,选取2 种方形燃烧池 （20 cm×20 cm、23 cm×23 cm）作为火源,设置2 个纵向火源位置 （位置A：火源中心线与排烟横通道中心线距离0.375 m;位置B： 火源中心线与排烟横通道中心线距离1.375 m）,7 种纵向通风风 速（0,0.18,0.27,0.35,0.44,0.52,0.69 m/s）,定量分析不同工 况下温度分布及烟气逆流长度。研究结果表明：当无纵向通风时, 火焰与隧道地板垂直,且呈轴对称形态;当有纵向通风时,火焰向 下游偏移,且纵向通风风速越大,火焰向下游偏移越明显;当纵向 通风风速为0 m/s 时,由于竖井的存在,火源上、下游两侧烟气温 度分布并非对称,火源下游（竖井侧）烟气温度下降速度较快,与单 洞隧道烟气温度分布明显不同;随纵向通风风速增加,烟气逆流长 度和烟气温度减小,而最大温度偏移距离整体呈增加趋势;当无量 纲纵向通风风速v′＜0.19 时,主隧道最大温升△Tmax 与Q2/3/ Hef 5/3 呈正比,而当无量纲纵向通风风速v′＞0.19 时,主隧道最大 温升△Tmax 与Q? /(vb1/3Hef 5/3)呈正比,但常数系数均小于Li 等预 测模型中的常数系数;竖井隧道内无量纲纵向烟气温度分布符合 Fan 和Ji 等建立的纵向温度衰减模型,衰减系数k′在1.36~1.63 范围内变化,但其值明显大于单洞隧道纵向温度衰减系数k′;另 外,当火源位于位置A 时,最大烟气温度低于火源位于位置B 时 的最大烟气温度,无量纲纵向烟气温度衰减速度慢于火源位于位 置B 时衰减速度。     

公路隧道纵向通风对火灾烟气分层影响研究

纵向通风目前是我国长隧道使用最多的通风排烟方式。通过1∶ 10隧道模型火灾排烟试验,利用激光片光观测火灾烟气分层结构,分析了纵向通风对火灾烟气分层结构的影响;通过数值模拟,研究了隧道采用纵向通风排烟的效果。结果表明:在无风情况下,火灾初期烟气能够较好地维持在隧道顶部,与空气分层界限明显;开启纵向排烟后,能够有效抑制火灾烟气向火源上游蔓延,但烟气分层结构遭到破坏并随着风速增加逐渐消失,火源下游区域能见度下降;纵向排烟风速维持在临界风速及以下,可降低纵向风对烟气分层的影响。     

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.     

海底特长隧道利用横通道控烟技术研究

摘 要：为了解决特长海底隧道发生火灾时的排烟问题,提出利用服务通道和联络横通道辅助送风的通风方案。利用火灾动力学模拟软件（FDS）,建立隧道火灾通风模型,通过研究通风排烟时服务隧道内补风量与横通道开启数量对火灾烟气的控制效果,确定通风系统的技术参数。结果表明：火灾发生时,事故隧道内纵向通风风速2 m/s,同时开启火源上游3 个横通道,并在服务隧道两端各施加1.3 m/s 纵向通风风速,既可将烟气控制在火源一侧,同时不影响人员安全疏散,其控烟效果与通风网络解算结果一致。采用横通道辅助送风的通风方案,控制特长海底隧道内火灾烟气蔓延是具有理论可行性的。     

Influence of tunnel width on longitudinal smoke control

The objective is to carry out experiments on scale models and CFD calculations in order to study the influence of tunnel width W on critical velocity (for a given tunnel height H). By definition, the critical velocity is the minimum longitudinal velocity needed to prevent smoke back flow when a fire occurs in a tunnel. Two different experimental reduced scale models are used: the first one is a thermal model using a propane gas flame to simulate the fire and the second one is a densimetrical model in which the fire-induced- smoke is represented by a continuous release of an isothermal buoyant mixing. In both approaches, for aspect ratios W/H greater than unity, it is noticed that the critical velocity decreases when the width increases, as predicted by theory, but for low values of the aspect ratio (i.e. when W<H) and for high enough fire heat release rates, the critical velocity significantly increases with tunnel width. This can be associated to a change in the transverse flow pattern close to the buoyant source. Complementary CFD calculations are also presented in order to describe the influence of the lateral confinement on smoke plume spreading and then, on critical velocity.     

Experimental study of the effectiveness of a water system in blocking fire-induced smoke and heat in reduced-scale tunnel tests

A water system, consisting of several water mist nozzles, has been installed in a reduced-scale tunnel. Its effectiveness in blocking fire-induced smoke and heat is tested, with and without longitudinal ventilation. A total of 14 fire tests have been carried out, with 250 ml methanol in an iron tray (25 cm × 20 cm) as fuel. Temperatures have been measured by 30 thermocouples, located upstream and downstream of the fire location. The aim is to assess the effectiveness of the water system in preventing smoke spread and in reducing the temperature in the tunnel. Interaction of the water with the fire is avoided. The impact of water pressure, ventilation velocity and nozzle arrangement on the effectiveness in smoke blocking and temperature reduction is discussed. The result confirms that the water system effectively reduces the temperatures and prevents smoke spreading in the absence of longitudinal ventilation. However, strong longitudinal ventilation (0.8 m/s ventilation velocity in the reduced-scale tunnel, corresponding to critical velocity in full-scale (1:10) tunnel) reduces the effectiveness in blocking the smoke spreading by the water system, although the temperature reduction downstream the water system remains in place. Higher water pressure makes the cooling effect stronger, because more and smaller water droplets are injected into the tunnel. For a given level of water pressure level, the impact of the nozzle row configuration is small in the tests.     

设排烟道隧道的烟气逆流长度与临界风速研究

隧道火灾是运营公路隧道的主要灾害。为有效控制隧道火灾,采用理论分析和数值模拟相结合的方法研究了设排烟道隧道的火灾烟气逆流长度与临界风速。以国内常见的双车道隧道尺寸建立模型,分析了排烟速率和纵向通风速率对烟气逆流长度的影响,提出了临界风速的预测模型。并将其通风效果与常规未设排烟道的纵向通风做了比较。结果表明:未设排烟道时,纵向风速还未达到临界风速时,火灾下游烟气的层化状态就已破坏。设排烟道能及时排出火灾产生的烟气,有利于保持烟气的层化状态,有效改善火灾时的隧道环境,为火灾下游人员的疏散救援提供了有利条件。同时,设置排烟道有利于减小逆流长度和临界风速。随着排烟速率的增大,相应的临界风速呈指数函数递减的特性。     

Longitudinal ventilation for smoke control in a tilted tunnel by scale modeling

Longitudinal ventilation systems are commonly installed in new tunnels in large cities of the Far East including Mainland China, Hong Kong and Taiwan. Many tunnels are found in big cities and some of them are inclined at an angle to the horizontal. However, smoke movement in tilted tunnels is not fully understood. In some of the tunnels, the ventilation system was designed based on presumed smoke movement pattern without experimental demonstration. Smoke movement pattern in a tilted tunnel model was studied by using a scaled model. A 1/50 tunnel model of length 2 m with adjustable angle to the horizontal was constructed by transparent acrylic plastics. A small 0.097 kW propanol pool fire was used as the heat source combined with burning pellets generating smoke. A fan placed at the upstream end was used to create longitudinal ventilation. Different ventilation rates were set using a transformer to control or adjust the fan speed. Experiments were performed with the tunnel angle varying up to 30° to the horizontal. Effect of smoke screens was also studied. The observed smoke movement patterns indicated that the shape of the buoyant plume inside the tunnel depends on the tilted angle. Smoke would flow along the tunnel floor due to gravity. The bending angle of the plume depends on the tunnel angle. Tunnel inclined at greater angles to the horizontal would give larger amount of smoke flow. Smoke movement pattern for a tilted tunnel with smoke screens was observed to be very different from some design projects. All results will be reported in this paper.     

Performance of the smoke extraction system for fires in the Busan–Geoje immersed tunnel

A new partial smoke extraction system for the Busan–Geoje immersed tunnel was investigated experimentally using simulated tunnel fires. The tests were performed in a 1:20-scale model tunnel with a smoke extraction duct between two traffic tubes. The fire corresponded to a 5-MW full-scale fire, based on Froude modeling. Isothermal and thermal experimental models were considered. The performance of the partial smoke extraction system was quantified under natural and longitudinal ventilation conditions. The results showed that the smoke extraction efficiency of the natural ventilation was 30% better than with longitudinal ventilation, because of smoke stratification in the tunnel. Additionally, the efficiency obtained from the thermal model was comparable to that from the isothermal model under both ventilation conditions. The results suggested that the use of a partial smoke extraction system without longitudinal ventilation improved the initial visibility during tunnel fires.     

着火列车驶入隧道停靠救援站烟气控制研究

为研究铁路隧道救援站火灾烟气蔓延的规律并为火灾情况下铁路隧道救援站内控烟方案设计提供技术依据,笔者建立了几何比尺为1∶50的铁路隧道列车行驶模型试验平台。通过室内模型试验,对自然通风以及3种轴流风机风速影响下铁路隧道救援站火灾烟气蔓延规律展开研究。同时,用Flunet数值模拟软件建立了动网格模型,计算了2种火灾工况结果并与模型试验进行对比分析。试验结果表明:隧道内活塞风大小受列车车速的影响,两者成正相关。未开启风机时,离火源较近的前后横通道均会被烟气侵入;开启右线主隧道两端风机进行2 m/s送风后,仅有7号横通道有烟气侵入。     

火灾时隧道内烟流流动状态试验研究

通过大比例火灾模型试验,研究火灾时隧道内烟流流动状态、烟流速度变化以及通风对烟流流动状态的影响。试验模型隧道长100m,内径1.8m。火源采用燃烧床盛放油料模拟,试验中设定了A、B、C三个火灾规模用以模拟实际隧道火灾场景。试验结果表明,点火后,隧道内火区、火区下游烟流速度在2～8min内增加很快,明显大于点火前风速,且其增幅随通风风速、火灾规模的不同而变化。同时,随着火势的逐渐减弱隧道内烟流速度也逐渐减小,并趋于初始风速。试验结果建议对于一般的限制或禁止油罐车通行的隧道,火灾时,隧道内应尽快建立起2～3m/s的纵向风流以抑止烟气的逆流。     

Smoke spreading characteristics during a fire in a shallow urban road tunnel with roof openings under a longitudinal external wind blowing

A series of fire experiments was conducted using a 1:12 scale model of a shallow urban road tunnel with roof openings to clarify the flow structure of smoke and fresh air during a fire with a longitudinal external wind blowing above the roof openings. The model tunnel consisted of two road tubes separated by a pillar-type median structure. Five fire test cases were conducted by changing the heat release rate as the experimental parameter. When the smoke produced by a fire in the tunnel tube was exhausted by natural ventilation through the roof openings of the tunnel tube, fresh air was sucked in from the roof openings of the opposite tunnel tube. The flow of exhausted smoke and sucked-in fresh air created a complex three-dimensional flow structure inside the tunnel tubes. Stratified smoke that had formed under the ceiling of the tunnel tube was disturbed by the flow of sucked-in fresh air and was diffused on the upstream side of the fire. Compared to the condition without a longitudinal external wind, when a longitudinal external wind blew over the tunnel with the pillar median structure, the smoke spreading distance on the upstream side was longer than that without the external wind due to the diffusion of smoke. On the other hand, the smoke spreading distance on the downstream side of the fire was shorter than that without the external wind due to the improved smoke extraction performance by the Venturi effect of the longitudinal external wind. Furthermore, the smoke spreading distance on the downstream side was nearly constant and independent of the heat release rate of the fire, within the scope of our experimental conditions.     

Enclosure Smoke Filling and Management with Mechanical Ventilation

Enclosure smoke filling and management are addressed from the standpoint of the volumetric flow rates commonly used for mechanical ventilation system design. In this context, fire-induced gas expansion is treated as a volumetric source term. A two-layer analysis developed previously for enclosure smoke filling without mechanical ventilation is extended to consider the impact of mechanical ventilation on smoke layer descent rates and conditions within the smoke layer. A spreadsheet-based model of enclosure smoke filling developed in conjunction with the previous unventilated analysis is also extended to consider both mechanical extraction and injection systems. Some implications of mechanical ventilation on the development and descent of a smoke layer in an enclosure fire are discussed.     

通过模型试验与数值模拟对隧道火灾烟气控制策略的研究

为满足隧道火灾安全体系研究方面的需要,本文以中国科学技术大学火灾科学国家重点实验室的隧道试验台为对象,进行了比例模型隧道火灾试验,并利用Fire Dynamics Simulator(FDS)软件对该实验在不同纵向风速控制条件下的火灾烟气层沉降速度进行了计算机模拟,通过试验与模拟结果的对比,给出了不同纵向通风速度下,隧道火灾时烟气层沉降速度的变化规律,并提出了烟气分层化临界风速这一概念,为隧道火灾的控制、救援和人员疏散提供了一定的参考价值.     

Driving Forces for Smoke Movement and Management

The movement of smoke in buildings and tunnels is governed by a number of driving forces, including fire-induced buoyancy and expansion, stack effect, wind effect and mechanical ventilation. To manage smoke movement in buildings and tunnels, these driving forces need to be considered individually and collectively so that appropriate strategies and systems can be implemented to achieve desired smoke control objectives. This paper provides an overview of the driving forces for smoke movement in buildings and tunnels and for the current methods used to manage smoke movement in structures.     

Experimental studies on fire-induced buoyant smoke temperature distribution along tunnel ceiling

Twelve tests were conducted to study the distribution of smoke temperature along the tunnel ceiling in the one-dimensional spreading phase, two tests in a large-scale tunnel and the other ten in full scale vehicular tunnels. The fire size and the height above the floor, the tunnel section geometry and longitudinal ventilation velocity varied in these tests. Experimental results showed that when the fire size was larger, the smoke temperature below the ceiling was higher, but it decayed faster while traveling down the tunnel. The longitudinal ventilation velocity seemed to take much influence on the smoke temperature decay speed downstream. A “barrier effect” was shown for the smoke temperature distribution of the upstream back layering. The smoke temperatures measured were higher upstream than downstream before the “barrier”, and were much lower and decreased faster along the tunnel ceiling after the “barrier”. The temperature and the traveling velocity of the upstream smoke flow decreased largely when the longitudinal ventilation velocity increased a bit. The dimensionless excess smoke temperature distributions along the tunnel ceiling in all tests fell into good exponential decay. But the decay speed along the tunnel seemed to be much larger in the large-scale tunnel than that in full-scale tunnels. The measured data on ceiling jet temperature decay along the tunnel was compared with predictions of Delichatsios's model, a model built based on small-scale tests, with hydraulic diameter introduced. Results showed that Delichatsisos’ model over estimated the decay speed of ceiling jet temperature for the downstream flow. However, good agreement was achieved between the measured data and the model predictions for the upstream back layering. All the experimental data presented in this paper can be further applied for verification of numerical models, bench-scale results and building new models on ceiling jet temperature distribution.     

Analyzing fire-induced dispersion and detector response in complex enclosures using salt-water modeling

The current investigation examines suitability of the hydraulic analog for analysis of fire-induced dispersion within a complex enclosure. This analog has been implemented using salt-water modeling and planar laser induced fluorescence (PLIF) diagnostics providing quantitative visualization of simulated fire-induced flows. The non-intrusive PLIF diagnostics are used to temporally and spatially characterize dispersion from a buoyant source within a 1/7th scale room–corridor–room enclosure. This configuration is geometrically similar to a full-scale fire test facility, where local fire conditions were characterized near five ionization type smoke detectors placed throughout the enclosure. The full-scale fire and salt-water model results were scaled according to the dimensionless fundamental equations that govern source dispersion.An evaluation of the local conditions and dispersive event times for both the systems was used to explore the ability of the hydraulic analog to predict smoke detector response times. The dispersive event (front arrival) times predicted by the salt-water model, which represents a necessary event for detector activation, were in excellent agreement with the fire test data. A methodology using these front arrival times along with local conditions at the detector location is introduced in this paper. However, the complex nature of detector response and fidelity limitations of the analog make precise predictions of detector response time challenging. The predicted dimensionless response times were within 25% for all detector locations, with the exception of the first-room ceiling detector location. For this latter, a shorter dimensionless response time by less than 40% of that in the actual fire was predicted.     

灭火救援专业知识智能匹配算法

摘 要：基于当下灭火救援领域中的突发事件,提出灭火救援专业知识智能匹配算法,该算法基于自然语言处理和注意力机制计算案件描述和消防预警信息之间的语义关系,从而实现相关灭火救援专业知识的匹配。首先基于自然语言处理的方法学习句粒度级别的语义信息,然后基于注意力机制学习词粒度级别的语义信息,最后基于两个级别语义信息的交互,根据信息之间局部差异推断两个句子之间的关系。试验结果表明：该算法具有优异的性能,能够同时从词和句两个粒度上更准确地理解句子,实现基于案件描述的灭火救援专业知识智能匹配。     

Numerical studies on evaluation of smoke control system of underground metro rail transport system in India having jet injection system: A case study

The rail based urban transport system is being developed for national capital of India, New Delhi. The smoke control using ventilation in case of fire inside the tunnel, similar to Delhi Metro corridor has been investigated using computational fluid dynamics technique. A section of tunnel having dimensions 400 m long, 5.5 m wide and 6 m high is considered for simulation. The analysis has been carried out by assuming a variable fire source with a peak heat release rate (HRR) of 16 MW, located at the center of the tunnel. Ventilation ducts are located in the ceiling near the tunnel portals and are inclined at 10 degrees to the plane of the ceiling through which fans discharge air. The influence of the fire HRR curve slope on the smoke flow dynamics in a realistic tunnel model fitted with jet injection type longitudinal ventilation system has been investigated. In case of fire two cases are studied: (1) fans activated immediately after detection, (2) fans activated at delayed times to take into account the response time for the fans to achieve its maximum speed. The velocity of supply and exhaust fans necessary to remove smoke in 30 s from the upstream direction is determined. The velocities of fan required to produce desired critical velocity in the longitudinal direction for different HRR of fire is predicted.