On the maximum smoke temperature under the ceiling in tunnel fires

Maximum smoke temperature under the ceiling in a tunnel fire was studied experimentally and numerically. Full-scale burning tests in two vehicular tunnels of length 3.27 and 1.032 km with and without operating the longitudinal ventilation system were carried out. Smoke temperatures at selected positions under the ceiling were measured under different longitudinal ventilation velocities. Two different pool fires of 1.6 and 3 MW were set up. Computational Fluid Dynamics (CFD) simulations with Fire Dynamics Simulator (FDS) version 3.10 were carried out on those scenarios. CFD predicted smoke temperatures were firstly verified by comparing with the measured values at those selected positions, and then compared with the calculated values using the empirical equation due to Kurioka et al. Fairly good agreement was achieved, though the slope of the tunnel was not considered in this empirical equation.     

Fire Dynamics Simulator (Version 4.0) Simulation for Tunnel Fire Scenarios with Forced,Transient, Longitudinal Ventilation Flows

In this study, a series of sensitivity analyses were conducted to evaluate a computational fluid dynamic (CFD) model, Fire Dynamics Simulator (FDS) version 4.0, for tunnel fire simulations. A tunnel fire test with a fire size on the order of a 100 MW with forced, time-varying longitudinal ventilation was chosen from the Memorial Tunnel Ventilation Test Program (MTVTP) after considering recent tunnel fire accidents and the use of CFD models in practice. A careful study of grid size and parameters used in the Large Eddy Simulation (LES) turbulence model—turbulent Prandtl number, turbulent Schmidt number, and Smagorinsky constant—was conducted. More detailed analyses were performed to refine the smoke layer prediction of FDS, especially on backflow (i.e., a reversed smoke flow near the ceiling). Also, energy conservation was checked for this scenario in FDS. A simple guideline is given for smoke layer simulations using FDS for similar tunnel fire scenarios.     

New approach to estimate temperatures in pre-flashover fires: Lumped heat case

This paper presents a model for estimating temperatures in pre-flashover fires where the fire enclosure boundaries are assumed to have lumped heat capacity. That is, thermal inertia is concentrated to one layer with uniform temperature and insulating materials are considered purely by their heat transfer resistance. The model yields a good understanding of the heat balance in a fire enclosure and was used to predict temperatures in insulated and non-insulated steel-bounded enclosures. Comparisons were made with full scale experiments and with other predictive methods, including CFD modeling with FDS and the so called MQH relationship. Input parameter values to the model were then taken from well-known literature and the heat release rates were provided from the experiments. The fire temperature predictions of the model matched very well with experimental data. So did the FDS predictions while the original MQH relationship gave unrealistic results for the problems studied. Major benefits of using the model in comparison with CFD modeling are its readiness and simplicity as well as the negligible computation times needed. An Excel application of the presented pre-flashover fire model is available on request from the author.     

基于CFD的开放空间油池火燃烧速率和热辐射研究

采用混合组分燃烧模型和有限体积辐射模型,通过液体表面蒸发模型对液态燃料和火羽流进行耦合,建立开放空间油池火模型.利用CFD方法分别对不同直径的庚烷油池火进行模拟,研究其燃烧速率、热释放速率随直径的变化以及火焰中轴上的温度和单位体积热释放速率(HRRPUV)分布,并得出油池表面的热辐射反馈以及油池外部水平和垂直方向的热辐射强度分布规律.部分模拟结果与实验进行对比,验证该模型的适用性和有效性.     

Determinations of the fire smoke layer height in a naturally ventilated room

According to the case-based reasoning of natural ventilation designs in recommended Green Buildings, an investigated model space was proposed in this study. FDS simulations and full-scale experiments were carried out to measure the impact of natural ventilation conditions and the installation of a natural ventilation shaft on smoke layer descent during different fire scenarios. The feasibility of using the N-percentage rule to determine the fire smoke layer height in a naturally ventilated space was also investigated.In a non-fire room, the smoke descent curve determined from the FDS simulated temperatures is consistent with the experimentally measured temperatures and visual observation of the smoke layer. However, the thermocouples in the fire room are affected by direct burning and fire radiation, and the experimentally measured temperatures cannot be used to determine the smoke height. Under these conditions, FDS simulations can be used to compensate for the lack of experimental measurements. In fire scenarios without outdoor winds blowing into the building's interior, FDS simulations can reliably model the fire smoke layer height. When outdoor air blows into the interior, it causes the smoke layer temperature to become unstable. Thus, the temperature will not be thermally stratified, and the use of the N-percentage rule is not recommended.     

Correlation equations on fire-induced air flow rates through doorway derived by large eddy simulation

Air flow rates through a doorway are important in modelling compartment fires. The ventilation factor is regarded as a key parameter and numerous efforts have been made on deriving the correlation of air flow rates with it. Most of the correlation expressions reported in the literature were derived empirically from experiments. The results might be different if the fire geometry, fuel type and ambient conditions are changed. Further, the heat release rates measured in most of the experiments were based on the mass loss rate of fuel, not by the oxygen consumption method. There might be some deviations from the actual heat release rates.Computational fluid dynamics (CFD) is now a practical tool in fire engineering. Aerodynamics through a doorway induced by a compartment fire can be simulated accurately. Factors which are difficult to control in experiments but affecting the doorway flow can be studied.The Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology, USA, is one of such CFD software. This is a product achieved from long-term research on developing a CFD model capable of carrying out fire simulations. This model is different from the others based on the Reynolds Averaging Navier–Stokes equations method. Physical processes occuring at small length and time scales were modelled by large eddy simulation (LES). Larger length scale on buoyancy-induced turbulence flow structure was computed directly from the set of equations with acoustic waves filtered out. The new version of this CFD package, FDS version 3.01, is now applied to derive equations on doorway flow rates induced by a fire. Results will be compared with those reported in the literature.     

A simple two-layer zone model on mechanical exhaust in an atrium

Provision of make-up air is essential in designing mechanical exhaust system in a compartment. There are always problems in determining the inlet positions for supplying make-up air. In this paper, a zone model for studying the effect of different positions of make-up air supply on the performance of a mechanical exhaust system in an atrium will be developed. Traditional two-layer approach with an upper smoke layer and a lower air layer will be assumed.Three scenarios of extraction with different relative positions of the air inlet are studied. These are scenarios with the smoke layer interface lying above, within, and below the air inlet. Conservation of mass and energy are considered for each scenario to study the smoke filling process. Transient variations of smoke layer temperature and interface height will be predicted under different fire sizes, exhaust rates and make-up air conditions.Full-scale burning tests in an atrium were conducted to justify the predicted results. In addition, results predicted by this zone model will also be compared with those predicted by Computational Fluid Dynamics (CFD) with the software Fire Dynamics Simulator FDS version 3.1; and another zone model CFAST version 5.0.1. It is observed that the predicted results from this new zone model agreed well with experiments and CFD results. However, results predicted by CFAST deviated from experiments for the scenario with the smoke layer interface lying below the air inlet.     

Experiments and Numerical Simulations of Pressure Effects in Apartment Fires

The fire induced pressure and its influence on ventilation flows within a compartment have not been studied in detail previously. In this research work, we have investigated the development of gas pressure and the resulting flows in compartment fires first experimentally, by burning a series of heptane pool and polyurethane mattress fires inside a real, 58.6 m\(^2\) by 2.57 m high, apartment and then by carrying out numerical simulations of the experiments with the FDS code. The experiments were conducted with three different ventilation duct configurations to simulate three different airtightness conditions. The peak heat release rates were less than 1 MW and the burning times were about 180 s. The experimental results indicate that the gas pressure in relatively closed apartment can become high enough to revert the flows of the ventilation system, prevent escape through inwards-opening doors, and even break some structures. The peak gas temperatures under the ceiling of the burn room were about 300°C. The pool fires remained well-ventilated. The pressure ranges encountered in the experiments were between 100 Pa to 1650 Pa and the pressure occured within 50 s of ignition. We also report the FDS validation for this type of simulations and discuss the process of modelling the ventilation system and leakages.     

Modellierung des Single Burning Item Tests

Modelling the Single Burning Item Test Harmonisation in Europe led to new standards, tests and classification of building products in fire safety. The Single Burning Item (SBI) test is the new reaction to fire test for the intermediate level. In the test a developing fire caused by a single burning item, e.g. a burning waste paper basket, is simulated. Numerical investigations of the SBI test have been performed by the Federal Institute for Materials Research and Testing (BAM) in cooperation with Technical University Berlin. Two CFD (Computational Fluid Dynamics) codes, Fluent and FDS, have been used to develop models of the SBI test. Data of our own experiments and literature has been used to validate the numerical models. Variation of ventilation in the burning room and variation of ambient air temperature lead to significant changes in temperatures and flow velocities in the burning room. The SBI standard EN 13823 allows the ventilation and ambient air temperature to be in a range. New experiments are necessary to show the effect of one single parameter like ambient air temperature. But the used data and the numerical results give reason to think about narrowing the ranges for ventilation and ambient air temperature in the standard.     

Burning rate of a pool fire with downward-directed sprays

The present study investigates how water sprays affect fire intensity, the burning rate of fuel and the relationship between droplet size and degree of water penetration. Downward-directed sprays which interact with a small-scale opposed gasoline pool fire are experimentally investigated in an open environment. It is shown that the burning rate of fuel is always greater under this opposed spray-fire plume arrangement compared to the freely burning condition, i.e. without water sprays, when fire extinction does not arise. These results imply that water sprays are able to enhance an oil fire. Furthermore, very small droplets are shown to be ineffective for fire extinction by cooling because they do not reach the fuel surface through fire plumes. Therefore, within a small-scale gasoline pool fire in an open environment, the mechanism of the fire extinction by water sprays is concluded to act via the cooling of the fuel surface, which will lead to the suppression of fuel evaporation, rather than the cooling of the fire plume itself.     

Comparison of FDS Prediction of Smoke Movement in a 10-Storey Building with Experimental Data

In this study, the Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) model developed by National Institute of Standards and Technology (NIST) is used to simulate fire tests conducted at the National Research Council of Canada (CNRC). These tests were conducted in an experimental 10-storey tower to generate realistic smoke movement data. A full size FDS model of the tower was developed to predict smoke movement from fires that originate on the second floor. Three propane fire tests were modelled, and predictions of O₂, CO₂ concentrations and temperature on each floor are compared with the experimental data. This paper provides details of the tests, and the numerical modelling, and discusses the comparisons between the model results and the experiments. The 10-storey experimental tower was designed to simulate the centre core of high-rise buildings. It includes a compartment and corridor on each floor, a stair shaft, elevator shaft and service shafts. Three propane fire tests were conducted in 2006 and 2007 to study smoke movement through the stair shaft to the upper floors of the building. The fire was set in the compartment of the 2nd floor. Thermocouples and gas analyzers were placed on each floor to measure temperature and O₂, CO₂ and CO concentrations. Comparisons in the fire compartment and floor of fire show that the FDS model gives a good prediction of temperature and O₂ and CO₂ concentrations. In the stair shaft and upper floors there are some small differences which are due to the effect of heat transfer to the stairs that was not considered in the model. Overall the study demonstrates that FDS is capable of modelling fire development and smoke movement in a high rise building for well ventilated fires.     

综合管廊内防火隔板对电缆火蔓延的影响

以苏州城北路综合管廊标准段为参考建立FDS全尺寸火灾数值仿真模型,模拟分析综合管廊电力电缆舱室发生火灾时的火势发展形势、温度分布。在管廊左、右两侧设置了4层电缆,分有、无防火隔板两个场景研究防火隔板对火势发展及温度分布的影响。结果表明：未设置防火隔板时,管廊内发生火灾时火势的发展方向首先以横向蔓延为主,顶部电缆随着火势的扩大及烟气聚集传热发生燃烧最后向管廊的其他区域蔓延。设置防火隔板后,竖向火的蔓延时间延缓了约40%,管廊内最高温度降低约18%。     

Assessment of the Fire Dynamics Simulator for Modeling Fire Suppression in Engine Rooms of Ships with Low-Pressure Water Mist

Water mist-based fire-extinguishing systems are gaining acceptance for the protection of ship machinery spaces. The use of simulation tools presents a great potential for taking a performance-based design (PBD) approach to these fire scenarios. The Fire Dynamics Simulator (FDS) is the most frequently used and validated fire modeling software; however, studies of low-pressure water mist fire suppression modeling in ship engine rooms are rare. This paper contributes to the current literature by using the FDS to model a series of fire suppression scenarios defined by the International Maritime Organization (IMO) Circulars, including spray and pool fires with heptane and diesel oil, as well as exposed and obstructed fires. The simulation results are compared to data from full-scale tests conducted at recognized fire testing laboratories. Furthermore, an analysis of both the experimental and model uncertainties is carried out to assess the simulations performance. In general, a good agreement in compartment temperature evolution and fire extinguishing time is found for the modeled fire scenarios. The results support the application of FDS in a PBD approach for the design of water mist fire extinguishing systems for machinery spaces in ships. In this way, designers and engineers could model different machinery volumes and nozzles spacings that differ from those prescribed for a one story square engine room of the IMO, and, thus, predict the evolution of temperatures and extinguishing times for get the authorities approval.     

Experimental study and numerical simulation for a storehouse fire accident

Full-scale experiment and numerical simulations are carried out on a shelf fire in a storehouse to study the ignition manner, the fire spread and the combustion characteristics. A computational fluid dynamics (CFD) model of fire-driven fluid flow, FDS (Fire Dynamics Simulator), is used to solve numerically a form of the Navier–Stokes equations for fire. Ignition manner experiments with both cigarette ends and lighter are conducted first. Then a full-scale experiment on a shelf fire is performed. The temperatures are measured and the fire growth and spread process is analyzed. A numerical model is used to simulate the experiment; the temperatures, fire growth and heat release rate are studied. In numerical simulations, the grid size resolution is analyzed. The experimental results of temperatures and the fire growth and spread process are compared with the results of numerical simulations. It shows that the numerical results are in good agreement with the experimental results. The chimney effect is also observed in both the experiment and the simulation. These useful data can be helpful in the numerical reconstruction of the whole storehouse fire accident.     

Burning behavior of sedan passenger cars

Four full-scale fire experiments using 4-door sedan passenger cars were carried out. The cars were ignited either at the splashguard of the right rear wheel or at the left front seat in the passenger compartment with a gasoline spill. The temperature inside the burning car and the mass loss rate were measured. The burning of the 4-door sedan was composed of three compartmental fires: the engine compartment, the passenger compartment, and the rear part inclusive of the fuel. In the experiments where ignition was initiated at the splashguard, the flame spread in the following order: to the rear part of the car, to the passenger compartment, and to the engine compartment. Breakage of the window glass markedly affected the spread of fire into the passenger compartment. The quantity of gasoline in the fuel tank also affected the speed of spread of the fire, because the gasoline ignited at an early stage of the fire. In the experiment where ignition was initiated in the passenger compartment, the fire gained force after the windshield was broken entirely. The flame spread in the following order: to the passenger compartment, to the engine compartment, and to the rear part of the car. The temperature within the passenger compartment peaked at 1000 °C. The heat release rate (HRR) curves showed several peaks depending on the burning of the three compartments. The HRR increased markedly when the fire spread to several different parts of the car at the same time. The HHR peaked at 3 MW when the passenger compartment and fuel (gasoline) burned simultaneously. The measured HRR curves were characterized by superposition of a Boltzmann curve and a Gaussian curve in order to obtain a model, which allowed us to make a more precise prediction of the fire spread probability from a burning car to nearby structures. The HRRs of burning cars were described by the sum of HRR from each compartment.     

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on façades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m³ lower compartment of a two levels high concrete structure. External flames develop in front of the façade from the fire compartment through windows with dimensions 1?×?1.5 m (W?×?H). In order to predict the fire exposure of a façade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested façade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the façade during calibration tests and can be used for further evaluation of combustible material on façade.     

Full-scale experiment and CFD simulation on smoke movement and smoke control in a metro tunnel with one opening portal

Three full-scale model experiments were conducted in a unidirectional tube, which is a part of a metro tunnel with one end connected to an underground metro station and the other end opened to outside in Chongqing, PR China. Three fire HRRs, 1.35 MW, 3 MW and 3.8 MW were produced by pool fires with different oil pan sizes in the experiments. Temperature distributions under the tunnel ceiling along the longitudinal direction were measured. At the same time, CFD simulations were conducted under the same boundary conditions with the experiments by FDS 5.5. In addition, more FDS simulation cases were conducted after the FDS simulation results agreed with the experimental results. The simulation results show that the smoke temperature and the decay rate of the temperature distribution under the tunnel ceiling along the longitudinal direction increase as HRR increases. The smoke exhausts effectively from the tunnel under mechanical ventilation system, whether the emergency vent is activated as a smoke exhaust or an air supply vent. The operation mode of the mechanical ventilation system depends on the evacuation route.     

Assessment of the Use of Fire Dynamics Simulator in Performance-Based Design

This paper discusses a procedure for the use of fire modelling in the performance-based design environment to quantify design fires for commercial buildings. This procedure includes building surveys, medium-and full-scale experiments and computer modelling. In this study, a survey of commercial premises was conducted to determine fire loads and types of combustibles present in these buildings. Statistical data from the literature were analysed to determine the frequency of fires, ignition sources, and locations relevant to these premises. Based on the results of the survey and the statistical analyses a number of fuel packages were designed that represent fire loads and combustible materials in commercial buildings. The fuel packages were used to perform medium- and full-scale, post-flashover fire tests to collect data on heat release rates, compartment temperatures and production and concentration of toxic gases. Based on the experimental results, input data files for the computational model, Fire Dynamics Simulator (FDS), were developed to simulate the burning characteristics of the fuel packages observed in the experiments. Comparative analysis between FDS model predictions and experimental data of HRR, carbon monoxide (CO), and carbon dioxide (CO₂), indicated that FDS model was able to predict the HRR, temperature profile in the burn room, and the total production of CO and CO₂ for medium- and large-scale experiments as well as real size stores.     

在受限和通风防火分区内对燃烧速率特性的试验研究

在核安全研究框架内对在受限和通风防火分区内油池火燃烧速率进行了试验研究。在实体火灾试验基础上，此研究为在受限和通风火灾场景下的燃烧速率机理提供了新的信息。描述了在自由条件和空气受限条件下所进行的试验，对试验装置、仪器以及火源进行了详细叙述。在相同场景（0．4m^2TPH油池火）下，对自由条件和空气受限条件的试验情况下的燃烧速率进行了对比。在空气受限情况下，燃烧速率与时间的变化曲线显示出三个不同阶段：自由条件和受限燃烧速率相同；不稳定阶段，空气受限条件下燃烧速率高于自由条件下的燃烧速率;稳定阶段。从图像分析看，不稳定阶段显示，动荡和间歇火焰大大提高了燃烧速率。介绍了通风速率和油池面积对此现象的影响。试验结果为理解有限区域内燃烧速率提供了新的试验信息。     

高速列车起火车厢位置对火灾发展趋势的影响

运用FDS软件建立高速列车火灾模型,设置4种工况分析热释放速率及温度的变化,探究火源所在车厢位置对列车内火势发展的影响.结果表明:起火车厢位于列车前列时,车厢内发生的轰燃现象作用范围大、破坏力强,救援困难;随着起火车厢位置的后移,车内气流抑制轰燃现象的发生并有效稀释车厢内的可燃气体及热量,人员逃生可能性增大.