Thermal characteristics of fires in a combustible corner

Three full-scale fire tests were performed with an area initiating fire in a combustible lined corner with a ceiling. In each of the three tests, the mock corner was lined with a different combustible material, plywood and two different composite materials. The area initiating fire was one of the ISO 9705 recommended standard ignition sources, a 0.17 m square propane sand burner with a heat release of 100 kW for 10 min followed by 300 kW for 10 min. Measurements of flame fronts, surface temperature, gas temperature, total heat flux, and total heat release rate were made during each of these tests. Heat flux and gas temperature data were found to be well represented by correlations developed from noncombustible fire tests.     

Models for calculating flame spread on wall lining materials and the resulting heat release rate in a room

An extensive research programme, dealing with fire growth on combustible wall lining materials, has been ongoing in Sweden over the last decade. Several lining materials were tested in bench-scale fire tests in order to derive basic material flammability parameters. The same materials were also tested in a full scale room test and a 1/3 scale room test for two different scenarios, A and B. Scenario A refers to the case where walls and ceiling are covered by the lining material, Scenario B where lining materials are mounted on walls only.

This study utilises the results from these experiments and presents a mathematical model where material properties derived from standardised bench-scale tests are used as input data. The model predicts fire growth in the full- or 1/3 scale tests, in two different scenarios (A and B), and consists of sub-models for calculating the rate of heat release, gas temperatures, radiation to walls, wall surface temperatures and flame spread on the wall lining material.

A thermal theory of wind-aided flame spread on thick solids is examined and solutions are given and analysed for flame spread velocities under ceilings. Both numerical and analytical solutions are discussed.

The analytical solutions can be used to evaluate the flame spread propensity of materials and thus, whether a certain material is likely to go to flashover or not in the Room Corner Test. More generally, the solutions can be used to estimate whether a material will spread flame in a variety of concurrent flow flame spread scenarios. Results from the analytical solutions are compared with experimental flashover data for 22 materials, showing a good agreement.

The numerical solutions are incorporated into a simple room fire model. The results from the numerical model are compared with experiments on 22 materials tested in the full scale room for Scenario A. Comparisons for Scenario B are made with 10 materials tested in the 1/3 scale room. The results show reasonably good agreement for most materials between the model and the experiments.     

Fire development in a 1/3 train carriage mock-up

To study what parameters that control the initial fire spread and the development to local flashover in a metro carriage, a total of six fire tests were conducted in a mock-up of a metro carriage that is about 1/3 of a full wagon length. They were carried out under a large scale calorimeter in a laboratory environment. The focus was on the initial fire development in a corner scenario using different types of ignition source that may lead to a fully developed fire. The ignition sources used were either a wood crib placed on a corner seat or one litre of petrol poured on the corner seat and the neighbouring floor together with a backpack. The amount of luggage and wood cribs in the neighbourhood of the ignition source was continuously increased in order to identify the limits for flashover in the test-setup. The tests showed that the combustible boards on parts of the walls had a significant effect on the fire spread. In the cases where the initial fire did not exceed a range of 400–600 kW no flashover was observed. If the initial fire grew up to 700–900 kW a flashover was observed. The maximum heat release rate during a short flashover period for this test set-up was about 3.5 MW. The time to reach flashover was highly dependent on the ignition type: wood cribs or backpack and petrol. A full developed carriage fire was achieved as a result of intense radiation from the flames and ceiling smoke layer. This was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was, leading to a ceiling flame. In such cases, the seats alone did not contain sufficient fuel for the fire to spread within the train, and additional fuel (luggage) is required near the seats. For fully developed carriage fires, the fire starting on the seat in the corner spread to the opposite seat on the same side of the aisle, then horizontally spread to seats on the other side of the aisle, and finally a longitudinal flame spread along the carriage was observed. When and where the fire stopped or whether it reached a fully developed stage was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was.     

Application of field model and two-zone model to flashover fires in a full-scale multi-room single level building

This paper presents a comparison of the results from a computational fluid dynamics (CFD) model and a two-zone model against a comprehensive set of data obtained from one flashover fire experiment. The experimental results were obtained from a full-scale prototype apartment building under flashover conditions. Three polyurethane mattresses were used as fuel. The CFAST two-zone model (version 2.0) was also used to predict results for this flashover fire test. The mass release rate, gas temperature, radiation heat flux and gas compositions (O₂, CO₂ and CO) were measured. A CFD program, CESARE-CFD Fire Model, has been developed and was used also to predict results for polyurethane-slab fire. A simple flame spread model was incorporated into the CFD program to predict the mass release rate and heat release rate during the fire instead of providing it as an input as is required for most zone and CFD models. It was found that the CFD model provided reasonable predictions of the magnitude and the trends for the temperatures in the burn room and the species concentrations, but over-predicted the temperatures in the adjacent enclosures. From a life safety perspective, the CFD model conservatively predicted the concentrations of CO and CO₂. The predicted temperatures from the CFAST fire model agreed well with the experimental results in most areas. However, the CFAST model under predicted the temperature in the lower layer of the room of fire origin and the concentration of CO in most areas.     

The contribution of flames under ceilings to fire spread in compartments

An experimental investigation has been made of flames spreading beneath both combustible and non-combustible ceilings. Experiments were performed in a model representing the ceiling of a corridor with a fire at one end: a gas burner was used to represent the fire, this was replaced by wooden cribs in experiments to be described in later part of this report.

The flames rising vertically from the fire in effect drew air up into the horizontal layer of flames and gases beneath the ceiling. Depending on the rate of flow of fuel gas (or rate of burning of the cribs) this air could be sufficient for complete combusion of the fuel gases and the flame length was then apparently determined by mixing processes within the layer. When this air was not sufficient, the remaining air for combustion was entrained vertically into the horizontal layer from the cool air beneath and the flames became much longer.

Correlations of lengths of horizontal flames beneath non-combustible ceilings have been derived and related to the much shorter lengths of vertical flames. Relationships have been derived from the experimental data from which it is possible to estimate the radiation downwards from a hot non-combustible ceiling and the gases beneath it to the floor with a view to estimating the contribution to fire spread on the floor. A heat balance of the ceiling gases was satisfactory, so confirming the validity of the calculations. Horizontal flames radiate more of the heat produced at a level sufficient to assist fire spread than do vertical ones.

A combustible ceiling lining results in longer flames, an increase in the distance over which heat radiated downwards at an intensity sufficient to promote fire spread and a faster rate of increase of radiation than a non-combustible one with similar thermal constants.

The aspect of performance which best related to the results of BS 476 tests was the rate of increase of radiation downwards in the early part of the experiments. The radiation downwards was apparently partly determined by extraneous factors such as the detachment of the board from its holding nails and whether the decomposition products were emitted as jets.

The rate of spread of fire along a narrow strip of wood on the floor beneath a burning ceiling lining has been calculated and the results related to the index of performance on the Fire Propagation Test.     

Influence of substrate on fire performance of wall lining materials

This study assessed the fire risk of attaching a qualified surface wall lining to an unqualified combustible substrate. Experimental materials were gypsum, magnesium oxide, calcium silicate board and fire-retardant plywood, which were attached to a non-fire-retardant plywood panel. The CNS 6532 Surface Test and the ISO 5660 Cone Calorimeter Test were applied. The former simulates the heating environment in the early fire stage and the latter simulates a fully developed fire. Experimental data show that when a qualified surface material was attached to a non-qualified substrate, the temperature rise in the Surface Test decreased. The substrates consequently enhance fire safety performance in the early stage of fire growth mainly due to crake prevention and a decrease in the amount of heat stored in surface materials for subsequent ignition. Additionally, the heat release rate in the Cone Calorimeter Test increased or decreased when a qualified surface material was attached to a non-qualified substrate. Therefore, the existence of substrates enhances or reduces a material’s combustibility rank when a fire is fully developed. The key mechanism is the crake or flame penetration of surface wall lining, which can lead to substrate ignition. The change of combustibility rank depends on the time at which a crake develops or flames penetrate a substrate.     

Investigating the contribution to fire growth of combustible materials used in building components

Recent work at the UK Fire Research Station has provided a measure of the possible contribution to fire growth from the combustion of such components as wall or ceiling panels rather than the well-known contribution from surface spread of flame on wall and ceiling linings.

The oxygen depletion technique is used to assess the rate of heat release from panels with a range of facing materials and different cellular polymer cores. The paper discusses how such an experimental approach may be adapted to direct validating modelling techniques with certain components but must take account of the variablity in existing building practices.     

Thermal characteristics of fires in a noncombustible corner

A series of fire tests were conducted in a full-scale open corner with a ceiling to measure the thermal field generated by fires located in a corner. Fires were produced using different size (0.17, 0.30, and 0.50 m) square and line propane burners with heat release rates ranging from 25 to 300 kW. Burner distance below the ceiling was also considered. Measurements included flame length, gas temperatures, and total incident heat flux onto the noncombustible corner boundaries. Flame lengths were related to Q*, with the burner dimension as the length scale, and were found to be similar to those measured in studies with no ceiling. By dividing the corner into three regions (corner walls (z/H<0.8), top of the walls (z/H>0.8), and ceiling, empirical relations for estimating the gas temperatures and incident heat fluxes were developed. Incident heat fluxes on the corner walls were measured to be similar to those in other studies.     

Effectiveness of vertical barriers in preventing lateral flame spread over exposed EPS insulation wall

Insulation panels made of organic, combustible materials are frequently used in the exterior thermal insulation systems (ETIS) for buildings. Such combustible insulation panels have been involved in several catastrophic building fires in recent years in China. One potential strategy to mitigate this fire hazard is to limit fire spread over the ETIS. The present work evaluates the effectiveness of vertical fire barriers in inhibiting fire spread over exposed insulation walls made of expanded polystyrene (EPS) panels. Reduced-scale experiments were carried out indoors using EPS panels with or without two vertical barriers made of non-combustible mineral wool, the fire started at the bottom center of the middle panel. The interval and width of the barriers were varied systematically, while the temperature distribution on the wall, the radiation heat flux from the fire, and the infra-red (IR) images were recorded. To demonstrate the validity of the concept, an outdoor, full-scale experiment was carried out using a 7-floor building. Our reduced-scale experiments showed that the installation of two vertical fire barriers successfully stopped the lateral flame spread, decreasing the peak temperatures of the two side panels by about 300 °C for all barrier configurations tested. When barrier width was fixed at 5 cm, an increase of the barrier interval from 30 to 90 cm led to increases in the peak temperatures, radiation heat flux, and the maximum rate of upward flame spread. By contrast, when barrier interval was fixed at 90 cm, an increase of the barrier width from 2 to 5 cm had little influence on the combustion dynamics of the middle panel but the peak temperature on the side panels dropped, consistent with the smaller heat transferred with wider fire barriers. In the regions of the side panels next to the barriers, pyrolysis and deformation could be observed with barrier widths of 2 and 3 cm, but not 5 cm. Finally, our outdoor, full-scale experiment demonstrated that a 30 cm wide vertical barrier made of air-filled cement successfully stopped the lateral flame spread over exposed EPS wall. The study highlights the effectiveness of vertical fire barriers in preventing the lateral flame spread over the exposed EPS insulation wall and provides another option for enhancing the fire safety of the combustible insulation systems.     

Effect of ignition conditions on upward flame spread on a composite material in a corner configuration

This paper focuses on the issue of fire growth on composite materials beyond the region immediately subjected to an ignition source. Suppression of this growth is one of the key issues in realizing the safe usage of composite structural materials. A vinyl ester/glass composite was tested in the form of a 90° corner configuration with an inert ceiling segment 2.44 m above the top of the fire source. The igniter was a square propane burner at the base of the corner, either 23 or 38 cm in width, with power output varied from 30 to 150 kW. Upward flame spread rate and heat release rate were measured mainly for a brominated vinyl ester resin but limited results were also obtained for a non-flame retarded vinyl ester and a similar composite coated with an intumescent paint. Rapid fire growth to the top of the sample was seen in replicate tests for the largest igniter power case; the intumescent coating successfully prevented fire growth for this case.     

A simulation model for fire growth on materials subject to a room-corner test

A mathematical model has been developed to simulate fire growth on wall and ceiling materials when subject to a room-corner fire test exposure. The model predicts the area of burning, the upper layer gas temperature, and the rate of energy release as a function of time. Material fire property data are developed from apparatuses described in ASTM E 1321 and E 1354. The results compare favorably to experimental data generated in Sweden for 13 materials tested. Furthermore, the model shows the sensitivity to ‘flashover’ for thin materials relative to small variations in their property data.     

砖木结构古建筑不同风速下火灾蔓延规律研究

为探明砖木结构古建筑火场下火灾蔓延的变化规律,从火灾蔓延特性、热释放速率、温度的变化等方面探究不同风速影响下的火灾蔓延变化情况.选取中国典型砖木结构三原城隍庙为实例,通过古建筑BIM参数化建模,合理设置火灾场景进行火场模拟分析.结果表明:风速作用下,火焰蔓延过程变化波动较大,呈现一定的周期性,在一定范围内,风速越大,古...     

Experimental investigation on transverse ceiling flame length and temperature distribution of sidewall confined tunnel fire

This paper presents an experimental investigation on the transverse ceiling flame length and the temperature distribution of a sidewall confined tunnel fire. The experiments were conducted in a 1/6th scale model tunnel with the fire source placed against the sidewall, 0 m, 0.17 m and 0.35 m above the floor, respectively. Experiments of fire against a wall without a ceiling, 0.35 m above the floor in a large space, were also conducted as a control group. Results shows that for small heat release rate (HRR), the flame is lower than the ceiling and extends along the sidewall. With the increase of HRR and elevation of burner height, the flame gradually impinges on the ceiling and spreads out radially along it. The flame impingement condition and the flame shapes of the wall fire with and without ceiling are presented. From the viewpoint of the physical meaning of flame impinging on the ceiling, the horizontal flame length should be a function of the unburned part of the fuel at the impinging point. Based on the proportional relation between the flame volume and HRR, the effective HRR (Q_ef) at the ceiling is determined and the effective dimensionless HRR, Q^*_ef is defined to correlate the horizontal ceiling flame length. Additionally, predictive correlations of transverse ceiling temperature distribution are proposed for the continuous flame region, the intermittent flame region and the buoyant plume region under the ceiling, respectively.     

隧道列车火灾的顶棚射流平均温度分布

列车着火并停留在隧道内时,容易产生夹带火焰的顶棚射流.通过建立列车中部着火时火焰顶棚射流的一维单元控制体模型,考虑火焰烟气与隧道壁面和列车壁面之间的换热,导出列车火灾火焰顶棚射流平均温度的迭代计算公式.并通过隧道列车火灾的1:8缩尺模型实验和数值模拟计算,确定了迭代公式中的待定系数.由该公式经过迭代运算后得到的平均温度...     

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.     

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO₂ and H₂O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.     

地铁隧道列车火灾的火焰顶棚射流温度特性研究

以地铁隧道火灾为研究对象,通过1∶8缩尺模型试验和数值模拟分析夹带火焰的烟气顶棚射流的温度特性,为地铁隧道火灾的防灾减灾提供参考。假定火源位于列车中部,燃烧强度是经过相似变换的等量荷载。火焰直接撞击顶棚并向上、下游扩展。考虑隧道内热辐射效应,得到在不同燃料用量下火焰顶棚射流温度的时变规律与空间分布特征。结果表明:燃料的多少对火焰顶棚射流在燃烧时间内的温度时变曲线的变化趋势影响不大,燃烧达到稳定的时间非常接近,但稳定状态的温度明显不同;火焰区上方顶棚射流烟气的最高温度与燃料液面的高度有关,试验中出现在距隧道顶0.18H处,而不是纯烟气顶棚射流给出的0.01H的区域内;列车上方及列车首尾附近的火焰顶棚射流温度沿隧道纵向呈线性衰减,且衰减速率不随时间变化,而不是纯烟气顶棚射流的指数衰减形式。在一定的高度以下,火焰顶棚射流的温度迅速降低,存在温度较低的安全区域适合于人员疏散。     

Position of Maximum Ceiling Temperature in a Tunnel Fire

The position of the maximum ceiling gas temperature indicates how far the fire plum could be blown away by a ventilation flow. It could be applied to estimate the activation of a detection system or a sprinkler system, or to estimate the range of damage to the tunnel structure. An equation for predicting the position of the maximum ceiling gas temperature in a tunnel fire is proposed based on a theoretical analysis and validated using both laboratory test data and full scale test data. A flame angle has been defined based on the position of the maximum ceiling temperature in a tunnel fire. The flame angle is directly related to the dimensionless ventilation velocity, and it becomes insensitive to the heat release rate for a large tunnel fire. Further, it is found that a constant critical flame angle exists, defined as the flame angle under the critical condition when the backlayering just disappears. For a given tunnel and fire source, the flame angle under critical conditions is the same value, independent of heat release rate, and the maximum ceiling temperature under critical conditions always corresponds to the same position. Generally the horizontal distance between the position of the maximum ceiling temperature and the fire source centre is around 1.5 times the effective tunnel height under the critical condition.     

Runehamar tunnel fire tests

Five large-scale fire tests, including one pool fire test and four HGV mock-up fire tests, were carried out in the Runehamar tunnel in Norway in year 2003. New data and new analyzes are presented in this paper, together with a short summary of previous work on these tests. Heat release rate (HRR), radiation, fire spread, gas production, backside wall temperature, visibility, backlayering, fire growth rate, gas temperature, flame length, ventilation and pulsation are investigated. Simple theoretical models are developed to estimate and predict these parameters. The correlations developed can be used by engineers working on fire safety in tunnels.     

单室墙角火壁面烟熏痕迹特征研究

为研究单室墙角火火灾壁面烟熏痕迹特征，采用1/3尺寸火灾试验还原单室墙角火火灾，测定壁面不同点的温度及烟气蔓延速度，研究火源在不同位置时的壁面烟熏痕迹特征；利用PyroSim软件模拟烟气蔓延过程。结果表明：火源位于房间中间时，在屋顶呈现圆形痕迹；火源在墙角时，两边侧墙和墙角顶部形成明显烟熏痕迹；墙角火在墙角位置的温度和烟气蔓延速度高于房间中间起火；试验结果与模拟结果吻合。试验结果可为调查墙角火火灾提供理论及试验依据。