Ignition and Opposed Flow Flame Spread Using a Reduced Scale Attachment to the Cone Calorimeter

A reduced scale ignition and flame spread technique (RIFT) was implemented in the cone calorimeter test system to generate thermal and combustibility material response parameters normally associated with an intermediate scale test, LIFT. The magnitude of the parameters derived using RIFT compare favorably with those obtained using the standard LIFT apparatus. The results of the modified cone calorimetric system or RIFT can be used to generate more specific material combustibility characteristics associated with materials burning over time, helping to create and refine engineering models of solid phase combustion. When validated, such models would help us predict and control flame spread with more certainty.     

Fire Spread and Flame Length in Large-Scale Tunnel Fires

An analysis of fire spread during four large-scale fire tests that were performed in the Runehamar tunnel in Norway is presented. The fire loads consisted of mock-ups simulating a Heavy Goods Vehicle (HGV) trailer. The fire spread downstream of the HGV trailer mock-ups was studied, both to large targets with the same type of commodities as used in the trailer mock-up for each tests, and to small pieces of wood and plastic poles placed at different distances from the fire. The purpose was to determine a critical distance for fire spread between HGV trailers for different heat release rate histories. The time to ignition of a second object and fire spreading distances were estimated from post-visual observations and temperature measurements. Correlations for flame length were developed from the experimental results. Since the average temperature of the cross-section often is used to estimate fire spread, results from a model for the average temperature were compared with the measured temperatures.     

粘合剂对火蔓延的影响

1．前言 目前，各种天然及合成高分子材料已被广泛用于建筑、室内装潢以及家具等行业。尤其值得注意的是，粘合剂是其中不可缺少的高分子物质，在日本各类粘合剂的年总产量约110万吨1），其中属于热固性树脂（脲醛树脂）和热塑性树脂（水溶性聚醋酸乙稀，PVAC）的粘合剂各占10％左右。然而，一旦建筑发生火灾时，可以想像这些材料中所含有的高分子物质将对燃烧的过程与现象产生影响。     

Upward Flame Spread Over an Array of Discrete Thermally-Thin PMMA Plates

Experiments and theoretical analysis were conducted to investigate the upward flame spread over a homogenous PMMA plate and an array of discrete thermally thin PMMA elements. In the experiment, a digital video camera was used to record the flame spread process. An electronic balance and thermocouples were adopted to monitor the mass loss and pyrolysis front position, respectively, as a function of time. In the theoretical analysis, the mass loss rate of PMMA was correlated to the heat transfer during flame spread. The experimental results show that the flame spread rate peaks in the case of discrete PMMA elements with a fuel coverage around 80% rather than 100% (the homogenous case) because the gap with an appropriate spacing between neighboring elements accelerates the flame spread. However, the flame cannot spread over an array of discrete fuels at a coverage of 50% or smaller where the gap is too large to allow effective heat transfer required for flame spread. A smaller coverage of PMMA results in a larger mass loss rate per area since the gaps between elements can entrain more air to promote the burning. A logarithmic relation, that can well describe the mass loss rate as a function of PMMA coverage, was proposed based on the theoretical analysis and the fitting of experimental measurements.

     

Ignitor and Thickness Effects on Upward Flame Spread

The effects of a material's ignitor characteristics and burning duration on upward wall flame spread are investigated. The ignitor is represented as an energy line source. Its energy release rate and its duration after ignition are considered. The material is represented as a finite, thick noncharring material with properties representative of polymethylmethracrylate (PMMA). A Volterra integral equation is solved for upward flame speed by numerical methods, and a transient, noncharring burning rate model is included. Results show the influence on propagation of ignitor effects and material thickness. A propagation map is computed showing the domains of flames that spread and flames that stop. Criteria for propagation and how propagation affects fire growth are considered in a standard room-corner test.     

Correlation of Burning Rate with Spread Rate for Downward Flame Spread Over PMMA

Burning rate of solid fuel and laminar flame spread rate are both well studied topics for flame spread in downward configuration. Yet, despite well-developed theories, not much experimental data is available to correlate the two. In this work, experiments are performed under ambient conditions in downward spread configuration for a wide range of thicknesses (2 mm to 24 mm) for flat samples of Poly-Methyl Methacrylate (PMMA). The samples are held by two ceramic plates in order to obtain a two-dimensional propagation that is independent on the sample width. By analyzing videos of the experiments, the instantaneous spread rate is obtained using a recently developed MATLAB based tool. The shape of the pyrolyzing fuel is carefully measured after extinguishing the flame during a steady propagation. The spread rate and the burn angle, which is defined as the angle subtended by the pyrolyzing surface with respect of the fuel surface, are correlated, producing an expression for the burning rate in terms of the burn angle and flame spread rate. As the fuel thickness is increased, the burn angle and burning rate decrease and reach asymptotic limits for thermally thick fuels, in analogy with the spread rate limit. The comparison with data from literature suggests that in the thick limit the value of mass flux for PMMA (about 10 g/m² s) tends to the one of non-spreading flames. The presented geometrical approach to study the downward spread problem avoids the use of the B number and local gradients in order to calculate the mass burning rate of the fuel.     

Influences of Talc on Fire Performance of Low Density Polyethylene

In this paper the effects of talc on the ignition time, the burning rate and the downward flame spread rate of low density polyethylene were studied through the cone calorimeter test, the modified UL 94 vertical burning test and a designed downward flame spread experiment. Cone calorimeter tests show that the mass loss rate (MLR) and the heat release rate (HRR) decrease with increasing the talc content, which is ascribed to the residue formed by talc. When the loading of talc is low, talc powders aggregate to form separate talc tablets during burning, leading to the slight decrease of MLR and HRR. When the mass fraction of talc is higher than 20%, possibly the percolation threshold for barrier effect of talc, an integral crust covering the whole specimen surface is generated to act as a good heat and mass barrier, resulting in the significant drop of MLR and HRR. However, no evidence of char in the residue is found. The ignition time in both the cone calorimeter test and the modified UL 94 test initially decreases and then increases with increasing the talc content. It is supposed that the wick effect of talc aggregations reduces the ignition time while the dilution effect and the barrier effect delay the ignition time. The downward flame spread rate initially increases and then decreases with increasing the talc content, which is suspected to be related with the reduction of ignition time and melt flow rate during burning caused by talc.     

Lateral Flame Spread over PMMA Under Forced Air Flow

Fire Technology - In wildland and other flame spread scenarios a spreading fire front often forms an elliptical shape, incorporating both forward and lateral spread. While lateral flame spread is...     

A Theoretical Model of Major Fire Spread in a Tunnel

A model of major fire spread in a tunnel is described. It employs the concepts of non-linear dynamical systems theory and identifies the onset of instability with major fire spread in a tunnel. In particular, the model associates the existence of a fold bifurcation with dramatic fire spread from an initial fire to a ‘target object’. The purpose is to identify the thermo-physical and geometrical conditions which lead to instability and sudden fire spread. Flame impingement on the target object is assumed not to exist; fire spread is assumed to be by spontaneous ignition only. The case considered assumes the existence of a longitudinal forced ventilation and predicts the critical heat release rate needed for a fire to spread from an initial fire to an item with a given assumed shape. The target object may be taken to approximate a vehicle. The illustrative case approximating fire spread from an initial fire to a heavy goods vehicle (HGV) within the Channel Tunnel is presented; it is not restricted to this case, however. The model is identified with the name FIRE-SPRINT A3, which is an acronym of Fire Spread in Tunnels, Model A, Version 3. It is a development of an earlier model, FIRE-SPRINT A2. The current model takes greater account of thermal radiation than was done in the earlier work and also assumes a more extensive flame volume for a downstream flame section.     

铺层结构对碳纤维/环氧层压板火反应特性的影响

利用锥形量热仪,垂直/水平燃烧速度测试仪、极限氧指数测定仪研究了单向、织物两种铺层结构对碳纤维/环氧层压板火反应特性的影响.结果表明,随热辐射强度的增加,不同铺层结构碳纤维/环氧层压板的点燃时间均缩短,质量剩余率降低,热释放速率、产烟速率峰值均增加,达到峰值时间变短,总热释放量和总烟释放量增加;在相同热辐射强度下,相比...     

Flame Spread Modelling of Complex Textile Materials

Flame spread in textile materials was modelled using two different simulation programs: the semi-empirical area-based code ConeTools, and the computational fluid dynamics, CFD, code Fire Dynamics Simulator, FDS, (version 5). Two textile products developed within the EU-project Flexifunbar were selected for study. The two products show a large difference in composition and application area, one material is developed to function as a protecting layer for the underlying structure in case of fire while the other is an insulating material with no requirements on fire performance. The products represent materials for which fire test results indicate a classification on either end of the rating scale for wall materials according to EN 13501. Two FDS-models were developed for the simulations. The first FDS model was a relatively simple model of the small scale Cone Calorimeter test (ISO 5660) which served the purpose of a first preliminary validation of the model for pyrolysis of the material. In the second FDS model, a model of the intermediate scale Single Burning Item, SBI, test method (EN 13823), the fire scenario was expanded to simulate flame spread over a surface. The work included determination of the necessary material properties. In ConeTools, the option to predict an SBI test was used. The results from the two simulation methods were compared to real SBI tests. Neither model was able to fully predict the heat release rate for these complex products. However, the results from both codes were accurate enough to correctly predict the fire rating class for wall linings according to EN13501.     

Numerical model of upward flame spread on practical wall materials

The focus of this paper is the development of a thermal, finite difference numerical model to describe one-dimensional upward flame spread on practical wall materials. Practical materials include composite materials and those that char, in addition to clean burning, homogeneous materials. A set of equations used in the model is developed and the methods for obtaining necessary “fire properties” are discussed. Some of the particular features of the model include the use of a correlation for flame heat feedback and the use of an experimentally measured mass loss rate to incorporate the burning characteristics of practical materials. A comparison of the numerical predictions with the experimental results for flame heights and temperatures are shown for Douglas fir particle board. The model correctly predicts trends but underpredicts the flame heights and pyrolysis height in the cases tested. Two additional cases are shown for materials for which experimentally measured heat release rate data are used in place of the mass loss rate data. The flame and pyrolysis height predictions are in much better agreement for these cases. Further efforts to obtain material property data that is appropriate for flame spread modeling is indicated by this work.     

燃料覆盖率对非连续分布固体竖向火蔓延的影响

非连续分布固体燃料是指多个固体可燃物非常靠近但被气隙隔开的状态,与连续分布燃料相比,非连续分布燃料更能够代表一些现实的火灾情况,以往的研究中较少涉及.笔者通过实验的方法分析不同燃料覆盖率下固体燃料竖直向上火焰蔓延的特点.所选用的浇筑型聚甲基丙烯酸甲酯(简称"PMMA")材料广泛应用于高层建筑外立面中,呈现出一种非连续分...     

Evaluating Models for Predicting Full-Scale Fire Behaviour of Polyurethane Foam Using Cone Calorimeter Data

Two models that can be used to predict full-scale heat release rates of polyurethane foam slabs were evaluated in this study. Predictions were compared with results of furniture calorimeter tests of 10 cm thick polyurethane foam specimens which were ignited in the centre or on the edge. Furniture calorimeter results indicated that peak heat release rates and fire growth rates were higher during centre ignition tests than edge ignition tests. For both situations, the growth phase of the heat release rate curves measured in the full-scale tests was successfully predicted using t ² design fires; the choice of a specific t ² fire depended on the surface area of the specimen and ignition location. A model originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project was also evaluated using heat release rate data from cone calorimeter tests and flame area burning rates measured using infrared video records of the furniture calorimeter tests. This model was able to successfully predict the initial growth phase of the fires and predictions of peak heat release rates were within 17% of measured values. The model had less success in predicting heat release rates later in the growth phase and during the decay phase of the fires, and did not appear to capture all of the physics of the full-scale tests, in particular foam melting and subsequent liquid pool burning. As the model did show promise, future work is planned to address these shortcomings and to develop improved flame spread models for polyurethane foam.     

Ignition,Heat Release Rate and Suppression of Elastomeric Materials

The focus of this paper is to determine flammability characteristics of rubber materials that are common to vehicle tires, conveyor belts, and electrical power cable insulation and to compare the thermal magnitude of cargo quantities of these materials to other fuels that are publicly transported. Although a literature review was performed, very little data was found on this topic. Standard flammability test procedures were used to measure the critical flux for ignition, critical ignition temperature, and heat release rates (HRR) of rubber compounds common to tire tread materials and conveyor belt covers. Both the intermediate scale calorimeter: ISO 14696, ASTM E-1623 (ICAL) and the cone calorimeter: ISO E-5660, ASTM 1354 (Cone) provided the bulk of the data. Critical ignition flux and vertical flame spread data for rubber based electrical insulations were determined using a radiant panel from a modified ASTM flame spread apparatus: ASTM E-162. thermogravimetric analysis was also used to evaluate thermal decomposition progression of selected test materials. Further, suppression tests were conducted on tire piles to evaluate agents to extinguish and control tire fires. Also, the HRR of the tire piles were measured and compared to work performed by others. Results confirm that the area heat release rate of rubber materials is directly proportional to exposure flux intensity. The critical exposure flux for ignition of a variety of rubber-based materials is approximately 20 kW/m² to 30 kW/m² and the critical temperature for piloted and non-piloted ignition were independent of exposure intensity at ~400°C and ~600°C respectively. In large quantities, rubber tire loads have total HRR comparable to the heat released from similar areas of liquid hydrocarbon spills.     

Modeling fire growth in a combustible corner

A fire growth model was developed to predict the flame spread and total heat release rate of a fire in a corner configuration with a combustible lining. Input data for the combustible lining were developed using small-scale test data from the ASTM E1354 cone calorimeter and ASTM E1321 LIFT. The fire growth model includes a flame spread model linked with a two zone compartment fire model, CFAST Version 3.1.2. At a user selected time interval, the flame spread model uses the gas temperature from CFAST to predict the heat release rate of the fire at that time interval, and then provides CFAST with a new heat release rate to predict conditions during the next time step. The flame spread model is an improved version of the flat wall flame spread model previously developed for the US Navy. The model is capable of predicting flame spread in a variety of configurations including a flat wall, a corner with a ceiling, flat wall with a ceiling, unconfined ceiling, and parallel walls. The model has been validated against ISO 9705 test data and was used in this study to simulate conditions that develop in three open corner tests each with a different lining material. The model was able to predict the heat release rate of the fire and provide a reasonable estimate of the flame fronts and flame lengths during the growing fire.     

CFD Simulations of Fire Propagation in Horizontal Cable Trays Using a Pyrolysis Model with Stochastically Determined Geometry

In this paper, a pyrolysis model for a PVC cable is constructed using results from thermogravimetric analysis, microscale combustion calorimeter and cone calorimeter experiments. The pyrolysis model is used to simulate fire propagation in horizontal cable trays. The simulated arrangement corresponds to a cable tray fire experiment from OECD PRISME 2 project. As laying the cables loosely along the horizontal trays is a random process, a novel stochastic method is developed for making the simplified cable tray geometries for the computational fluid dynamics model. In addition, as the simplified cable tray geometry has significantly smaller surface area than a real tray full of cables, the surface area was parametrically adjusted. In contrast to most of the earlier published numerical approaches for simulating cable tray fires, the presented approach does not use empirical correlations for predicting fire propagation and does not require any results from full-scale experiments for calibrating the model. The simulation results are compared to experimental results in terms of heat release rate, mass loss, tray ignition times and lateral flame spread rates. The maximum heat release rate was overpredicted by 8% on average.

     

不同影剧院座椅连排燃烧特性试验研究

利用10 MW 大尺度量热计对不同影剧院座椅进行连排燃烧试验研究。建立座椅燃烧试验台，将15 把影剧院座椅分3 排台阶布置，通过对多人影剧院软质座椅排列在一起进行燃烧试验，提供燃烧产生的热释放速率、总热释放量、产烟速率、总产烟量相关特性信息。试验中，分别选取普通影剧院座椅与阻燃影剧院座椅分别进行连排燃烧试验，并将燃烧测试得到的热释放速率、总热释放量等燃烧性能参数进行了对比分析，同时对火焰传播速度进行了计算。结果表明：同样点火方式条件下，普通座椅连排燃烧在8 min 内发生轰燃，热释放速率峰值高达9.204 MW，总热释放量为1 957.2 MJ，经阻燃处理后，热释放速率峰值为83.6kW，总热释放量为27.33 MJ，其他燃烧性能指标均显著下降；普通影剧院座椅连排燃烧时，火焰规模大，火焰扩散速度快，经计算火焰传播速度为0.65 m/min。     

A study of non-flashover and flashover fires in a full-scale multi-room building

Realistic fire environments in a prototype multi-room apartment in a multi-storey building are studied. The fires are designed as non-flashover and flashover types, using standard polyurethane mattresses as fuel. A comprehensive set of experimental data is presented. The measured results include flame spread velocity, mass release rate, gas temperature, radiation heat flux and gas analysis. A computational fluid dynamics (CFD) model, called a CESARE-CFD fire model, has been used to simulate these polyurethane slab fires. The CFD model is described by three-dimensional transport equations for mass, momentum and enthalpy. The turbulence flow was modelled using the k−ϵ model. A soot formation model and a flame spread model were incorporated into the CFD model. The flame spread velocity and the mass release rate of the polyurethane slab fires were predicted in this study. It was found that the CFD model provided reasonable predictions of the magnitude and trends for the experiments both in the non-flashover and flashover fire cases.     

Spread and burning behavior of continuous spill fires

Spill fire experiments with continuous discharge on a fireproof glass sheet were conducted to improve the understanding of spill fire spread and burning. Ethanol was used as the fuel and the discharge rate was varied from 2.8 mL/s to 7.6 mL/s. Three ignition conditions were used in the experiments; no ignition, instantaneous ignition and delayed ignition. The spread rate, regression rate, penetrated thermal radiation and the temperature of the bottom glass were analyzed. The experiments clearly show the entire spread process for spill fires. Further, the regression rate of spill fires at the quasi-steady burning was lower than that of pool fires and the ratio of the spill fires’ regression rate to the pool fires’ regression rate was found to be approximately 0.89. With respect to the radiative penetration and the heat conduction between the fuel layer and the glass, a regression rate expression for spill fires was developed based on some modifications on existing expressions for pool fires. In addition, a complete phenomenological model for spill fires was developed by combining the characteristics of spread and burning. The model was verified by the experimental data and found to predict the spread process for spill fires with reasonable accuracy.