Fire simulation in road tunnels

The catastrophic tunnel fires since the year 1999 and a series of accidents in some tunnels in the summer of 2001 triggered extensive discussions and proposals relating to tunnel safety. When a fire occurs in a tunnel, and in absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Unless a strong flow is created and maintained, hot gases and smoke migrate in all directions. With a weak airflow, smoke forms a layer along the tunnel ceiling and can flow against the direction of forced ventilation, interfering with personal evacuation. This paper shows the results of a computer fire simulation in a tunnel and the results of this simulation: air velocity, air temperature and wall temperature in the case of fire. The simulation started before the emergency ventilation system is activated and continued with the fans activated to control the smoke.     

隧道式建筑火灾的消防对策

Tunnel is type of long and narrow underground building. Common tunnels are city metro tunnel, railway tunnel and motorway tunnel. These tunnels are for the commuting of vehicles. Some go through mountains, others go under the sea and many are over thousands meters long. In recent years, there have beeu many tunnel fires home and abroad. Based on the theory el tunnel fire smoke movement, the arlicle analyzes the features el tunnel fire and proposes directional lirelightiflg schemes in tunnel fire design.     

阻塞效应下隧道火灾顶棚最高温度的实验分析

隧道火灾时拱顶最高烟气温度的预测对于隧道防火安全设计具有很重要的意义。通过1/10隧道火灾缩尺模型实验得到了不同火源热释放率、不同通风速度下隧道顶棚最高温度测试值,并与现有的温度模型预测值进行了对比,发现现有模型对于无风及风速较小的情况,或多或少存在缺陷。另外在实际情况中车辆通常占据一部分的隧道断面积,所形成的阻塞效应不可忽略。为此,进行了不同阻塞比情况下的实验,发现现有的温度模型与不同阻塞比下的实验数据相差较大。最后,基于本文实验数据对Kurioka温度模型进行了修正,所提出的修正模型与已有的其他实验数据吻合也较好。     

Critical ventilation velocity for multi-source tunnel fires

Ventilation is an effective method for controlling smoke during a fire. The “critical ventilation velocity” u_cr is defined as the minimum velocity at which smoke is prevented from spreading under longitudinal ventilation flow in tunnel fire situations. All previous studies on this topic have simulated fire scenarios in which only one fire source exists. This study conducted small-scale experiments and numerical simulations to investigate u_cr for cases in which two tunnel fires occur simultaneously. The tunnel was 4 m long, 0.6 m wide and 0.6 m tall. Three cases of two variously separated fires were experimentally explored and six cases were examined numerically. Both the experimental and simulation results indicated that for two identical fires, u_cr declines with separation. When the two fire sources are separate completely, u_cr can be determined by considering only a single fire. When the larger fire is upstream of the smaller downstream fire, u_cr also decreases with the separation. When two such fires sources are completely separate, u_cr can be evaluated by considering only the larger fire. The concurrent ventilation flow and flow of downstream smoke from the larger fire are strong enough to suppress the smoke flow from the smaller fire. However, when the smaller fire is upstream of the larger fire, the decrease in u_cr becomes insignificant as distance increases and the flow at u_cr must overcome the flow from both fires.     

A survey of vehicle fires in Norwegian road tunnels 2008–2011

Norway is one of the countries that constructs most road tunnels, and there are well over 1000 in the country today. The aim of this study is to map the prevalence and describe the characteristics of vehicle fires in Norwegian road tunnels 2008–2011. The average number of fires in Norwegian road tunnels is 21.25 per year per 1000 tunnels, and the average number of smoke without fire (SWF) is 12.5 per year per 1000 tunnels. The study provides four main results. The first is that the fires generally did not involve harm to people. This has also been reported in previous Norwegian research. The second finding is that heavy vehicles are overrepresented in fires in Norwegian road tunnels. This is in line with international research. The third main finding is that the causes of road tunnel fires involving heavy and light vehicles are different. This is also in accordance with international research. The fourth important and unique finding of the study is that subsea road tunnels are overrepresented in the statistics of fires in Norwegian road tunnels.     

隧道火灾中火羽流特性的数值模拟

利用F luen t软件对隧道火灾中火羽流特性进行了模拟分析,研究了隧道坡度对火羽流的影响,与前人所进行的数值模拟进行了比较,为隧道火灾的研究提供了一种有效的研究手段,为进一步研究隧道火灾临界通风速度奠定了基础。     

纵向通风下公路隧道双火源火灾烟气扩散研究

采用试验与数值模拟研究隧道双火源火灾临界风速变化,重点研究双火源功率和火源间距对临界风速的影响。结果表明：随着火源间距增加,临界风速逐渐降低,当两火源间距达到极限距离时,临界风速不再变化;当进风口侧火源功率确定时,在极限间距内出风口侧火源功率增大时,临界风速增大,说明出风口侧的火源对进风口侧的烟气回流有促进作用;在极限间距内,临界风速随火源间距增加呈二次方递减到一个稳定值;两火源总功率越大,临界风速随着间距增加降低的幅度越明显。并得到了临界风速的预测公式。     

Effect of cross section and ventilation on heat release rates in tunnel fires

Model scale fire tests were performed in tunnels with varying tunnel widths and heights in order to study the effect of tunnel cross-section and ventilation velocity on the heat release rate (HRR) for both liquid pool fires and solid fuel fires. The results showed that for well ventilated heptane pool fires, the tunnel width nearly has no influence on the HRR whilst a lower tunnel height clearly increases the HRR. For well ventilated solid fuel fires, the HRR increases by approximately 25% relative to a free burn test but the HRR is not sensitive to either tunnel width, tunnel height or ventilation velocity. For solid fuel fires that were not well ventilated, the HRRs could be less than those in free burn laboratory tests. In the case of ventilation controlled fires the HRRs approximately lie at the same level as for cases with natural ventilation.     

Experimental evaluation of the heat flux induced by tunnel fires

Traffic tunnel closures are highly undesirable and some of the lengthiest are attributed to structural failures. Historical data shows that these failures are closely linked to fire. Furthermore, the parameters necessary for proper thermo-mechanical analysis of structural members are poorly defined or absent from literature. The energy transferred to the structure (i.e. heat flux) is the fundamental parameter for determining structural performance in fire. However, current research focuses on identifying heat release rates and temperature histories which are difficult to use for structural analyses. In this study, full-scale experiments were undertaken on passenger vehicles resulting in heat fluxes between 20 and 70 kW/m². The analyses show fire duration is linked to a vehicle’s mass and small vehicle fires can be scaled as a function of the ratio between the tunnel diameter and the characteristic height of the desired vehicle. Appropriate design values are outlined for engineers to undertake informed thermo-mechanical analyses to minimise the risk of structural tunnel failure in fires.     

The Influence of Tunnel Geometry and Ventilation on the Heat Release Rate of a Fire

It has occasionally been observed that fires in tunnels appear to be significantly more severe than fires in the open air. A literature review has been carried out, comparing heat release data from fires in tunnels with heat release data from similar fires in the open air. A Bayesian methodology has been used to investigate the geometrical factors that have the greatest influence on heat release rate. It is shown that the heat release rate of a fire in a tunnel is influenced primarily by the width of a tunnel; a fire will tend to have a higher heat release rate in a narrow tunnel rather than in a wide tunnel. The observed relationship between heat release rate and tunnel width is presented. Results from a study investigating the variation of heat release rate with ventilation velocity for fires in tunnels are also presented. A method for making realistic estimates of the heat release rates of fires in tunnels, based on these results, is presented.     

The international FORUM of fire research directors: A position paper on future actions for improving road tunnel fire safety

Fire safety in tunnels has come in focus owing to numerous catastrophic fires and extensive monitoring in media. Casualties can be counted in hundreds and the economic damages have been enormous not only for tunnel owners but also for users and bordering communities. The recent increase in serious road tunnel fires is closely associated with the increase in the traffic volume as well as in the large number of tunnels being built in recent years. In particular, volumes transported on heavy goods vehicles have increased by 40–80% over a decade in many European countries. Today, about 75% of all goods traffic is by road, and is expected to increase by 40–60% over the next 10 years [Thamm B. The new EU directive on road tunnel safety. In: Proceedings of the international symposium on catastrophic tunnel fires (CTF), SP Swedish National Testing and Research Institute, SP Report 2004:05. p. 19–30].This FORUM position paper discusses some aspects on how to improve the design of road tunnels in order to obtain a higher level of fire safety. It discusses briefly design principles of tunnels as well as of fire safety of vehicles, use of forced ventilation systems and of active fire suppression.     

Automatic Data Generation Method for Precise Ceiling Temperature Prediction of Cables Fire in the Utility Tunnel and Full-Scale Experimental Verification

Fire Technology - Being impossible to carry out ceiling temperature prediction in tunnel fires, the specific fire scene (fire type, fire location, number of fire sources, etc.) are unknown in the...     

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.     

隧道横向偏置火源顶棚温度纵向分布特性研究

为研究隧道横向火源位置对隧道顶棚温度沿纵向分布过程的影响,采用数值模拟与全尺寸模型实验相结合的方法,分析3 种火源功率多种横向偏移位置火源燃烧产生的顶棚温升与对应中心火源工况沿隧道纵向不同位置的温度分布特性。结果表明：对于多种横向偏置火源位置,火源所处纵向的顶棚温升衰减仍可用指数形式描述,越靠近隧道侧壁,温升衰减速度越快。火源与横向中心的偏距和纵向距离的耦合影响对温升衰减规律可以用相对独立的公式形式进行描述。火源功率越大,不同偏距火源下影响温升纵向衰减的范围越小。     

南京过江隧道中部火灾风机失效模式的安全疏散研究

以长江南京段上游过江隧道为研究对象，分析了隧道火灾的特点，介绍了隧道安全疏散救援的思路和方法，设定了火灾场景，通过火灾时人员所需安全疏散时间与可用安全疏散时间的比较分析，探讨了隧道疏散口间距和逃生滑梯通行能力的初步设计方案。     

The critical ventilation velocity in tunnel fires—a computer simulation

In ventilated tunnel fires, smoke and hot combustion products may form a layer near the ceiling and flow in the direction opposite to the ventilation stream. The existence of this reverse stratified flow has an important bearing on fire fighting and evacuation of underground mine roadways, tunnels and building corridors. In the present study, conducted by the National Institute for Occupational Safety and Health, a CFD program (fire dynamics simulator) based on large eddy simulations (LES) is used to model floor-level fires in a ventilated tunnel. Specifically, the critical ventilation velocity that is just sufficient to prevent the formation of a reverse stratified layer is simulated for two tunnels of different size. The computer code is verified by checking the computed velocity profile against experimental measurements. The CFD results show the leveling-off of the critical ventilation velocity as the heat release rate surpasses a certain value. At this critical ventilation, the ceiling temperature above the fire reaches a maximum for both tunnels. The velocity leveling-off can be explained from this observation. An extended correlation of Newman (Combust. Flame 57 (1984) 33) is applied to the temperature profiles obtained by CFD. At the critical ventilation, temperature stratification exists downstream from the fire. The computed critical ventilation velocity shows fair agreement with available experimental data taken from both horizontal and inclined fire tunnels. The CFD simulations indicate that the Froude modeling is an approximation for tunnel fires. The Froude-scaling law does not apply to two geometrically similar fire tunnels. The CFD results are compared with two simple theories of critical ventilation by Kennedy et al. (ASHRAE Trans. Res. 102(2) (1996) 40) and Kunsch (Fire safety J. 37 (2002) 67).     

黄河公轨合建隧道火灾人员疏散安全研究

以济南黄河公轨合建隧道为研究对象,分别对公路隧道和轨道交通发生火灾时,纵向疏散楼梯和横向疏散门的间距对人员疏散时间的影响进行分析,获得必需疏散时间。结果表明：疏散楼梯间距为60 m和75 m时,均满足安全疏散要求;轨道交通发生火灾,在通风有效情况下,人员可用安全疏散时间TASET为2 700 s;疏散门间距为150 m和300 m时,均满足安全疏散要求。从安全和运行成本考虑,推荐疏散楼梯间距设置为75 m、下层疏散门间距设置为300 m。     

高海拔隧道全尺寸火灾烟气及温度场特征试验研究

通过对海拔为4100m的高海拔隧道进行全尺寸火灾试验,揭示高海拔隧道火灾烟气下沉及温度场变化特征。试验采用三种不同尺寸火源(0.8m2、1.0m2、2.0m2),对隧道火灾烟气蔓延特征、火区最高温度、隧道拱顶纵向温度分布进行研究。试验研究结果表明：隧道火灾试验初期及燃烧稳定阶段,火源附近隧道上层烟气与下层冷空气分界明显,火灾后期烟气下沉严重;较小风速有利于高海拔隧道小规模火灾烟气逆流层纵向和垂向蔓延的控制。隧道火灾温度场研究表明：隧道火灾温升速率随火源热释放率增大而增加;火源附近20m范围内温度衰减速率较快,远火源区域隧道拱顶纵向温度衰减较慢,趋于平缓;通过对火源上方拱顶烟气温度分析,发现隧道火灾探测采用差温报警模式较定温报警模式更加有效,并得出10℃/min的温升速率可基本满足高海拔隧道小规模火灾的初期报警;隧道拱顶纵向温度分布规律导致火源远场烟气下沉严重而近火源区域烟气层化较好的特征。高海拔隧道火灾温度分布特性试验研究,可为高海拔隧道火灾动力特性研究提供依据,为高海拔隧道人员疏散逃生提供指导及建议。     

隧道火灾研究现状与展望

隧道火灾往往会造成严重的人员伤亡和巨大的社会影响及经济损失,是威胁隧道运营安全的主要灾害之一。本文指出了隧道火灾的诱因、频率及其特点,介绍了隧道火灾的主要研究方法及研究内容,并重点介绍了隧道火灾的两个主要影响因素——火源释热率和临界风速,最后提出了今后有待研究的内容。     

移动式微滴喷雾灭火系统应用

利用已获专利设计的双模式喷嘴产生的微滴喷雾灭火装置，可有效地扑灭灌木火灾、汽车火灾、建筑火灾等。该喷嘴可以在2MPa压力下产生射程达15m的微滴喷雾，消除了以往高压系统中的射流阻力问题，尤其是低速射流确保了喷射时不产生挟带气流，避免了出现降低灭火效果的副作用。该装置可装载在消防车、抢险救援车、摩托车等轻便运载车辆上，作为移动式系统迅速抵达火场扑救初期火灾。