Pressure rise due to a fire in an enclosure

Can temperature and pressure rise resulting from a fast developing fire in an enclosure be predicted? Toward that end, the authors developed equations, the results of which were compared with the few available experimental data and with the Apollo accident pressure record.     

Full scale experimental and numerical studies on effect of ventilation in an enclosure diesel pool fire

The compartment fires have been studied through full-scale experiments, which were conducted in a compartment of size 4 m × 4 m × 4 m with a door of size 2 m (height) × 1 m (width). Four different experiments were performed, in which the width of the door was varied. The diesel fuel pan of 60 cm diameter was placed in the center of compartment. The maximum heat release rates measured were 502, 564, 446 and 124 kW for Exp. 1, Exp. 2, Exp. 3 and Exp. 4 respectively. The average hot gas temperature in Exp. 1, Exp. 2, Exp. 3 and Exp. 4 were found to be 266, 328, 314, and 174 °C respectively. In Exp. 3, highest heat flux was found to be 13.6 kW at ceiling. Further, the numerical simulations were performed for Exp. 1 and Exp. 2 experimental condition using Fire Dynamics Simulator incorporating different mesh sizes.     

油池燃烧中油面上的热反馈分析

油池燃烧时 ,油面所接受的热反馈将决定着燃烧的发展。本文将实验研究得到的一些现象和数据进行了比较 ,并应用热平衡原理分析了油池燃烧时 ,油面上所接受的热反馈与物质燃烧速率的变化以及直径为 0 .3米的油池燃烧时 ,辐射热在热反馈中所起的重要作用。本文旨在通过分析进一步认识油池燃烧的过程 ,从热反馈这一主导因素出发为控制油池火灾提供理论依据。     

Incident radiation from an engulfing pool fire to a horizontal cylinder — Part I

A three-dimensional formulation has been utilized to determine the incident radiant heat flux on a cylinder surface which is engulfed in flames. The model has been developed as part of a study concerned with thermal protection systems for rail tank cars carrying hazardous materials. The circumferential and longitudinal variation of heat fluxes on the cylinder surface are determined.The effect of wind on the inclination of the flame and the location of the points of maximum radiant heat flux on the cylinder have been determined.     

Risk analysis of unburnt gas ignition in an exhaust system connected to a confined and mechanically ventilated enclosure fire

The main purpose is to focus on the assessment of an ignition risk due to a large amount of unburnt fuel gases accumulated in the extraction duct connected to a confined and mechanically ventilated enclosure fire combining numeric and experiment. The current numerical study includes the initial well ventilated fire, spreading of flame in the enclosure, subsequent decay during under-ventilated conditions and exhaust of unburnt gas ignition in an extraction duct. Globally, Large Eddy Simulation (LES) combined with an Eddy Dissipation Concept (EDC) combustion model shows the feasibility for simulations of the air vitiation effect on transient combustion events occurring in a closed environment. A particular effort is undertaken to properly predict the pressure level inside a confined facility, and consequently, air inflow supply rate by using a HVAC system. Overall, the numerical results are in fair agreement with the experimental data for the minor species production (CO, H₂), and good agreement for pressure pulse, temperature peak, the major species and heat release rate. In spite of results for minor species that could be improved, the current work confirms the feasibility of a numerical treatment of under-ventilated fire phenomena. The possibility of simulating an ignition risk in an extraction duct connected to a very under-ventilated enclosure fire, has been demonstrated with success in medium-scale facility.     

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.     

Effect of scale and fuel type on the characteristics of pool fires for fire fighting training

This paper examines the effects of pool size and fuel type on the characteristics of pool fires. The fuels studied include hydrocarbon solvents, alcohol and their blends. The large-scale experiments were conducted on 0.445 and 1 m diameter pools in two enclosures: 41 m long×5.4 m wide×2.4 m high and 25 m long×2.7 m wide×2.4 m high, under a ventilation rate of 1–1.2 m/s. In these tests, measurements of the fuel pyrolysis mass loss rate, heat release rate (from CO₂ and CO concentrations as well as oxygen depletion), smoke extinction area (from laser attenuation), total heat flux emanating from the flame, and the yields of CO₂ and CO were made. Bench-scale tests were conducted using the same fuels and fuel blends on 100 mm× 100 mm pool fires in a Cone Calorimeter—a well-known fire test method.

The hydrocarbon+alcohol fuel blends are used to create large pool fires for fire fighting training. The aim of this study was to: (1) Formulate a fuel blend which will produce a “hot” fire for realistic fire fighting training while generating a minimal quantity of smoke to comply with the pollution regulations. (2) Investigate the effect of fuel type and scale on the properties of the pool fires. (3) Make comprehensive measurements on pool fires in tunnels which can be used for validating mathematical fire models.

This study has resulted in the formulation of a fuel blend which satisfies the requirements of fire fighting training as well as Environment Protection Authority of New South Wales. The bench and the large-scale results correlate well showing good agreement between the heat of combustion, smoke extinction area (SEA) and the yields of CO₂ and CO. The SEA increases with the CO and CO₂ yields which in turn increase with the carbon fraction and the aromatic content of the fuel/fuel blend. The SEA correlates strongly with the CO and CO₂ yields and in both the correlations, the entire data collapse on a single curve. These correlations indicate that the SEA and the CO₂ and CO yields vary mainly with the fuel type, and not so much with the pool size. The flame heat flux increases with the carbon content in the fuel.     

A comparison of gas velocity measurements in a full-scale enclosure fire

Gas velocity measurements were conducted in the doorway of an enclosure containing a natural gas fire. Two independent measurement techniques, Stereoscopic Particle Image Velocimetry (SPIV) and bi-directional impact-pressure probes, were utilized for comparison – the first such comparison for a fire-induced flow in a full-scale structural fire. Gas velocities inferred from the bi-directional probe measurements were consistently greater than SPIV measurements in a region of the flow between the floor and the flow interface. The comparison revealed that a measurement bias exists in the bi-directional probe technique. Estimates of the relative magnitude of the bias were inferred from the results.     

Numerical study of under-ventilated fire in medium-scale enclosure

In an enclosure, as all the air inflow is consumed in burning with the excess fuel, the internal fire enters the decay phase, and such process is said flame exhaust. The complicated multistage process from an initial fire growth up to a flame exhaust followed by an external burning is investigated by means of a Large-Eddy-Simulation (LES). Turbulent combustion process is modelled by an Eddy Break-Up concept by using two sequential, semi-global steps for CO prediction. The numerical model solves three dimensional, time-dependent Navier–Stokes equations, coupled with submodels for soot formation and thermal radiation transfer. The critical fuel supply rate needed for flame to exhaust and the time period from the fuel ignition to the appearance of an external flaming in medium-scale facilities are previously obtained experimentally by Chamchine AV, Graham TL, Makhviladze GM, et al. [Experimental studies of under-ventilated combustion in small and medium-scale enclosures. In: Proceedings of the fourth international seminar on fire and explosion hazards; 2003. p. 97–107.], and the general trends predicted by the numerical model follow closely their experimental observation. This model is capable of adequately describing the essential simultaneous phenomena (flame height, soot generation, CO production, convection and radiation) occurring in a room fire. The distinct transient stages of fire development prior to flame exhaust and scenarios of the exhaust are analysed. An external burning is followed after the flame exhaust inside enclosure, and the flame height, H_f, past the ceiling is approximately in an order of the opening height. Even though the flame exhaust takes place under the critical conditions, the heat transferred from the hotter gases and the external fire source poses significant threat to people inside enclosure, and potentially induces an ignition of fuel package exposed near the opening of an enclosure.     

饰面材料对火灾冷热气层分界面的影响

采用ISO 9705标准全尺寸单室火灾实验方法,对3种常用的饰面装饰材料的单室火灾进行实验研究,实时测量地面辐射强度、室内和开口部位不同高度的温度随火灾变化的情况,分析装修材料对室内火灾的影响,测算轰燃时间以及冷热气层界面位置的变化,为火灾预防和扑救提供参考。     

封闭空间火灾中燃料烟尘对墙体所受热通量的影响

尽管在封闭空间内已经做过很多关于气体温度和燃烧率的研究,但目前仍然缺乏封闭空间内墙体上热通量及其分布方面的信息。该热通量数据是确定墙体材料特别是玻璃的热反应及性能的必要输入参数。试验用封闭空间墙体上的热通量是通过多块薄钢片(25.4mm×25.4mm×3mm)以及钢片周围隔热材料的温度推算出来的。另外,笔者还测量了热流计附近墙体的质量损失率和温度。试验用封闭空间是ISO标准墙脚火试验的1/3,有六个开口,燃料为甲醇、IMS(工业用甲基化酒精)以及甲苯,装在大小不同的三个方形油盘里,油盘放置在封闭空间的内外拐角处。在选择燃料方面,笔者的依据是燃料燃烧产生的烟尘应越来越浓。试验发现,与以前对地板的研究结果有所不同的是,墙体上的热通量不仅仅取决于烟气温度,还取决于热释放速率的强弱以及燃料所产生的烟尘的多少。另外,对甲醇、IMS以及甲苯所产生的热通量的比较发现,对流热可以与辐射热通量(热烟气流以及封闭墙体造成)以及来自烟羽流的辐射热通量分开。     

壁面对池火燃烧特性影响

调节圆形油盘距壁面的距离,分别对直径为15、30、40、50 cm的油盘进行了池火燃烧实验,探讨油盘直径、油盘距壁面的距离对热释放速率、火焰高度和火焰温度的影响.结果表明:火源靠近壁面燃烧时,各燃烧参数均值约是自由燃烧状况的1.14倍;油盘直径越大,燃烧参数随着L/D的增大,下降趋势越大.     

单一空间火灾三维场模拟

对单一空间火灾烟气流动作三维场模拟，采用了P-1辐射模型，将火源设定为放热量随时间变化的热源，并对由室内外温差所引起的热压边界条件设定作了详细论述。     

Comparison of different combustion models in enclosure fire simulation

In this study, three combustion models, the volumetric heat source (VHS) model, the eddy break-up model and the presumed probability density function (prePDF) model, are examined in enclosure fire simulation. The combustion models are compared and evaluated for their performance in predicting three typical enclosure fires, a room fire, a shopping mall fire and a tunnel fire. High Reynolds number turbulence k–ε model with buoyancy modification and the discrete transfer radiation model (DTRM) are used in the simulation. Corresponding experimental data from the literature are adopted for validation. The results show satisfactory prediction in flow patterns and features in the complex enclosure fires. However, it is shown that these combustion models are not able to show consistent performance over the different locations and enclosure fires. The needs for adequate turbulent combustion models in enclosure fires are discussed.     

On wall fire interaction in a small pool fire: A large-eddy simulation study

Large-eddy simulation (LES) with stochastic fields (SF) method is used to simulate a pool fire in a compartment for different distances from the compartment sidewalls. In our previous work (Jangi et al., 2016) [24], we have formulated and validated LES-SF method for modeling pool fires. Here we use the same approach to study the wall-fire interaction. For this purpose, two cases are presented. In one case the pool is located at the center of the compartment floor far from all sidewalls, referred to as case C. In another case the pool is in the vicinity of a sidewall, referred to as case W. In both cases, it is shown that pool fires are not a fully non-premixed flame but they can involve some levels of premixed combustion, especially in the form of ignition process in fuel-lean mixtures. This is more evident in case C when the pool is far from the walls. Results in case C show that flow is mainly driven by crosswise vortices, whereas for the case W, the flow is driven by longitudinal vortices. Depending on the distance for the sidewall, two mechanisms for the fire intermittency are identified: in case C the intermittency is mainly due to quenching and re-ignition, whereas in case W, it is essentially due to the interaction between flow and the sidewall.     

Extinction limit of a pool fire with a water mist

This work describes an experimental investigation of fire extinction limit and enhancement for a gasoline pool fire interacting with a water mist. A downward-directed nozzle produces a fine water spray over a small-scale opposed pool fire. The fire extinction limit is obtained from minimum nozzle injection pressure measured when the fire extinguish takes place. The burning rate of the fuel is also measured using a verified technique. For the conditions tested, it is shown that there are two distinct regions in the relationship between the distance from the nozzle to the fuel pan and the injection pressure, i.e. a fire extinction region and a fire enhanced region. The effective water flux is shown to be a more useful parameter than the injection pressure for the fire extinction limit. It is also revealed that the larger the spray thrust the larger the burning rate is in the fire enhanced region.     

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.     

依托单位消防水池建设公共消防取水口研究

针对部分市、县不能保证市政供水管网24 h 供水,停水期间,消防水鹤、市政消火栓均无法使用,现有规范标准不便于使用且防冻效果不好、建设成本较高等问题,提出了依托消防水池建设公共消防取水口的技术措施,并就建设公共取水口的水池选择、建设形式和建设要求进行了研究,表明该措施具有建设周期短、建设成本低、防寒、取水方便等特点,可有效解决部分城区公共消防供水能力不足的问题。     

燃料载荷和含水率对平坡地表火蔓延影响实验研究

燃料载荷和含水率是森林火灾中地表火蔓延的重要影响因素.选取香樟叶和云南松松针作为研究对象,开展了不同燃料载荷和含水率条件下平坡地表火蔓延实验.研究结果表明:同一燃料载荷下,随含水率增大,火焰长度、火蔓延速率、火线强度和辐射热流减小,滞留时间增大;同一含水率下,燃料载荷增大,火焰长度、火蔓延速率、火线强度、辐射热流和滞留...