A numerical model for flame spread along combustible flat solid with charring material with experimental validation of ceiling flame spread and upward flame spread

This paper gives a numerical model for flame spread along combustible flat solid with charring materials. The presented model consists of a one‐dimensional flame spread model coupled with a one‐dimensional pyrolysis model. The existing experimental data (the ceiling flame spread beneath medium density fibreboard) are used for comparison to validate the model. In addition, the model can also be used to predict upward flame spread; only some expressions are changed. A comparison with full‐scale experimental data on the upward flame spread over plywoods from the literature is performed. The results obtained from numerical simulations using the model are consistent with these two kinds of experimental tests. Thus, the presented model is appropriate for modelling not only the ceiling flame spread, but also the upward flame spread. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental study of vertically upward flame spread over polymethyl methacrylate slabs at different altitudes

Experiments of vertically upward flame spread over polymethyl methacrylate slabs were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). Measurements were taken for the flame heights, the flame heat flux to the fuel surface and the flame spread rate. Two regions were identified for the dependence of the flame height on the heat release rate per unit width . When is less than 22 kW/m, the flame height scales as while it scales as , when is greater than 22 kW/m. The flame heights in Lhasa are approximately 1.34 and 1.25 times, respectively, of those in Hefei for these two regions. The flame heat flux to the fuel surface decreases significantly from the pyrolysis front to the flame tip, whereas it decreases slowly above the flame tip. In both regions, it can be correlated reasonably well with (x ? x_p)/(x_f ? x_p) using the form of . The flame heat flux to the fuel surface in Lhasa is approximately 0.75 times of that in Hefei. The flame spread process can be divided into three stages, which correspond to a flow region of laminar, transitional, and turbulent, respectively. The transition to a turbulent flow is delayed in Lhasa compared with Hefei. The flame spread rate in Lhasa is about half of that in Hefei because of the lower flame heat flux caused by the lower ambient pressure. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of vertical upward flame spread on charring materials—Part II: Numerical simulations

Simulation results, obtained by means of application of an enthalpy‐based pyrolysis model, are presented. The ultimate focus concerns the potential of the model to be used in flame spread simulations. As an example we discuss vertically upward flame spread over a charring material in a parallel plate configuration. First, the quality of the pyrolysis model is illustrated by means of cone calorimeter results for square (9.8 cm × 9.8 cm exposed area), 1.65 cm thick, horizontally mounted MDF samples. Temperatures are compared at the front surface and inside the material, for different externally imposed heat fluxes (20, 30 and 50 kW/m²), for dry and wet samples. The mass loss rate is also considered. Afterwards, vertically upward flame spread results are reported for large particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face‐to‐face, for different horizontal spacings between the two plates. The simulation results are compared to experimental data, indicating that, provided that a correct flame height and corresponding heat flux are applied as boundary conditions, flame spread can be predicted accordingly, using the present pyrolysis model. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of pyrolysis and upward flame spread on charring materials—Part I: Experimental study

In this paper, we describe the results from an experimental campaign, focused on vertical upward flame spread over a charring material. First, for validation purposes of simulation tools, we report on cone calorimeter results for square (9.8cm×9.8cm), 1.65 cm thick, medium density fibre samples, mounted horizontally. Temperature is shown at the surface and at different depths. The mass of the sample is continuously measured. From the raw data, we derive the temporal evolution of the mass loss rate due to pyrolysis. Different externally imposed heat fluxes are investigated (20, 30 and 50kW/m²), onto dry and wet material. Afterwards, for the configuration of two particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face to face is considered. Two different horizontal spacing distances between the two plates are studied (30.5 and 10.5 cm). The purpose of this set‐up is to investigate the vertical upward flame spread with strong radiative heat feedback. To that purpose, the temporal evolution of surface temperature is measured over the height of the plates. The measurement data are used to test a pyrolysis model in numerical simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

乳胶泡沫引火位置对火蔓延特性的影响

利用自行搭建的小尺寸实验平台,开展了对不同点火位置的乳胶泡沫材料燃烧过程的对比实验,通过对火蔓延过程中的部分重要参数（如最大火焰高度、火蔓延速度和蔓延过程中样品表面温度变化等）的测定,分析了点火位置不同时,乳胶泡沫材料的火蔓延特性。结果表明：边缘点火和中间点火条件下,最大火焰高度分别为397和491 mm,火蔓延速度分别为1.8和0.97 mm·s^-1;边缘点火时的乳胶泡沫材料表面火蔓延过程中的温度低于中间点火情况下。     

Relative humidity versus moisture content relationship for several commercial wood species and its potential effect on flame spread

Recently, measured flame spread indices on commercial wood species tested per ASTM E84 were found to be lower than previously published data. One reason for this may be that the hygrothermal conditioning of the red oak calibrant required by the test standards for measuring flame spread was changed between 1973 and 1981. This paper examines how much variability there is in the moisture content of commercially important wood species at 50% relative humidity by collecting water vapor sorption isotherms. Additionally, the effect of moisture content on the flame spread was evaluated after conducting 14 tests with eastern white pine in accordance with CAN/ULC‐S102 and four in accordance with ASTM E84 at four commercial test laboratories. For the sorption isotherms, it was found that the moisture contents at 50% relative humidity ranged from 6.8% to 11.4% moisture content and depended on the species and whether the specimens had been conditioned in absorption or desorption. The flame spread indices, as measured as different laboratories, also varied from 37% at 10.4% reported moisture content to 200% at 6.5% reported moisture content. The findings suggest that the wood moisture content and conditioning requirements of the standards are important test variables that affect the flame spread results.     

Experimental study of horizontal flame spread over rigid polyurethane foam on a plateau: effects of sample width and ambient pressure

The effects of sample width and ambient pressure on horizontal flame spread over horizontal rigid polyurethane foams are experimentally studied. A series of comparative experiments are conducted at two places with different altitudes in China. The sample surface temperature, spread rate, and height of flame are measured over a range of sample widths from 4 to 16 cm. Experimental results show that the horizontal flame spread rate decreases as the sample width increases in a negative power law at both two altitudes and the flame spread rate in the Hefei plain (at an altitude of 30 m) is larger than that on the Tibetan plateau (at an altitude of 3658 m) of the same width. The horizontal flame spread mechanism on the rigid polyurethane foam is analyzed qualitatively in comparison with the results of the flame spread rate of expanded polystyrene foams. The relationship between the dimensionless flame height (H_f/W) and the sample width (W) is obtained by using Froude number similarity. It is found based on the experimental data under two different ambient pressures that the average value of the exponent of the ambient pressure in the power law for the horizontal flame spread rate is about 1.9, which is in good agreement with the theoretical value 2.0. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental study on flame spread along fuel cylinders in high pressures

Flame spread over solid fuels in high‐pressure situations, such as nuclear containment shells during a pressurized period, has potential to result in catastrophic disaster, thus requiring further knowledge. This paper experimentally reveals the flame spread behaviors over fuel cylinders in high pressures. Polyethylene and polymethyl‐methacrylate cylinders with the diameter of 4.0 mm are used in this study. Ambient gas is air, and total pressures are varied from naturally normal pressure (100 kPa) to elevated pressure (500 kPa). Flame characteristics including flame appearance and flame size and burning rate and flame spread rate are investigated. Results show that in high pressure, the flame appearance is significantly affected. As the pressure increases, the blue flame disappeared, and the color of flame tip changes from luminous yellow to orange as well the orange part extends down towards the base of flame. The dimensionless flame height increases with pressure for pressure below 150 kPa and then decreases with pressure above that level. The burning rates show increasing trend with pressure and are proportional to P^0.6 and P^0.79 for polymethyl‐methacrylate and polyethylene, respectively. Besides, flame spread rates for polymethyl‐methacrylate and polyethylene both were found to be proportional to P^0.5.     

The effects of transient heat release rate and crosswind on flame length and tilt angle of flames at different positions in the spread of fire over a diesel pool

The spread of fire over liquid fuel is a common phenomenon, and it has been demonstrated experimentally that the flame length and tilt angle change with the transient heat release rate and different positions of the flame. The coupling relationship between these factors is studied in this paper. The experiments are composed of a rectangular pool with dimensions of 80 cm × 6 cm × 5 cm and crosswind with speeds of 0.8 to 2.4 m/s. Diesel is used as the fuel, and a new method is applied to ensure that the initial temperature of the diesel is constant during ignition. The results show that the traditional method of luminous flame intermittency may not be suitable for studying the geometric characteristics of the spread of fire over a pool, and a new method is proposed. In addition, the transient variation of flame length in different positions of the pool is shown to fluctuate around a mean flame length. The evolution of flame tilt angle along the longitudinal direction of the pool exhibits a U‐shaped curve. Moreover, the multivariate nonlinear relationships of mean flame length and tilt angle among the heat release rate, fire position, and wind speed are established, and relevant coefficients are determined.     

Estimation of heat release rate based on analysis of flame spread behavior in mattresses

To investigate the fire danger of mattresses, combustion experiments were conducted with a mattress installed at different heights above the floor to better understand their combustion behavior. The installation height was varied because the height of a mattress varies depending on the bed frame, and the combustion behavior is expected to change with the installation height. Experiments with a mattress installed at 0–515 mm above the floor revealed that the fire growth was faster, and the maximum heat release rate (HRR) increased with installation height. In contrast, in a series of experiments where a mattress was installed above a water pool, the flame spread rates and HRR histories were comparable for all installation heights. This demonstrate that the combustion behavior of the mattress was affected by the combustion of the molten mattress material that dropped to the floor, and this effect was influenced by the mattress installation height. Furthermore, we analyzed the HRR per unit area of mattress construction material using cone calorimeter tests to mimic the combustion taking place on the floor. Combining these results with the relation between the length of the burning part of a mattress at the front of flame spread and the HRR, we proposed a model for predicting the HRR history of mattress for a flame ignition at the center of its longitudinal side. The derived predictive model for the HRR history of mattress combustion emphasize that it is necessary to understand factors such as the intense radiant heat from the pool fire.     

Bedding ignition,vertical flame spread and subsequent thermal impact on underlying mattress

The ignition of bedding and subsequent vertical spread of fire along the side of a noncombustible surrogate bed set was investigated. One‐hundred‐eight (108) tests were conducted to assess the ignition timeline and subsequent vertical flame spread of bedding up the side of a bed along with the thermal impact of the bedding fire on the underlying bed set. The ignition source for all tests was comprised of the flame from a book of matches placed on bedding at floor level at the base of the bed. The bedding consisted of combinations of a cotton/polyester blend sheet and bedspread. Ignition occurred in 3 to 10 seconds for the majority of the test. The speed of subsequent vertical flame spread, assessed through video frame analysis tools, was dependent on the exposed bedding material with an exposed sheet exhibiting faster spread. Thermal exposure from the burning bedding to the vertical sides of the bed set was assessed with an array of thermocouples embedded at the surface of the sides of the underlying bed set. The time to thermal exposure was found to be a function of the vertical flame spread and thickness of the bedding material(s).     

Survey of small‐scale flame spread test results of modern fabrics

The flammability of apparel worn on a person has one of the highest ratios of fire fatalities per fire, and there are few statutory requirements. A series of evaluations was conducted on the flammability of 50 fabrics (both cellulosic and thermoplastic) using the (now withdrawn) NFPA 701 small‐scale test. The fabrics covered a broad range of areal densities (weights) and many were not intended for apparel. A series of conclusions were reached. In particular, it is apparent that the following primary correlation exists between fabric weight and flammability: the heavier the fabric the better it behaves in a fire. Secondarily, however, the type of fabric also strongly affects this conclusion. This paper presents the results of the testing and offers an analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

阻燃硬质聚氨酯泡沫塑料垂直火蔓延特性研究

通过一步合成法制备了阻燃硬质聚氨酯泡沫,自主搭建保温材料火蔓延实验台,采用中小尺寸实验对比研究了阻燃及非阻燃硬质聚氨酯的垂直火蔓延特性,分析了火焰结构特性、火蔓延速度、火焰温度、质量损失速率等参数的变化规律。结果表明,火蔓延过程中,材料表面均出现了炭化现象,垂直双面燃烧过程中聚氨酯纯样RPUF燃烧最剧烈,阻燃剂膨胀石墨(EG)、次磷酸铝(AHP)和二乙基次膦酸铝(ADP)的加入,抑制了材料的燃烧和蔓延,使材料燃烧的火蔓延速度、质量损失速率及温度等参数都相应降低。RPUF/AHP5垂直双面火蔓延过程中,火焰稳定性差,在20 s后出现熄灭现象,原因是阻燃剂次磷酸铝(RPUF/AHP5)受热挥发出难燃气体。AHP降解后形成的含磷化合物可促进聚氨酯分子链成炭,导致产生熄灭现象。而RPUF/ADP5火蔓延过程中,同样出现了熄灭现象,其熄灭的程度低于阻燃剂次磷酸铝(RPUF/AHP5)试样。RPUF/EG5火蔓延过程中试样表面温度存在两个峰值,由于RPUF/EG5燃烧生成的炭层不稳定所致。当温度高于400℃时炭层被迅速氧化,热量穿透炭层使内部未燃样品热解,生成温度的第二个峰值。     

倾斜角对液体燃料润湿条件下砂床表面火蔓延的影响

利用纹影系统、CCD相机以及K型热电偶对正丁醇润湿条件下不同角度的砂床表面火蔓延特性进行了研究,分析了不同砂床表面倾角对火蔓延的影响机理。研究结果表明:正丁醇润湿条件下变角度砂床表面火焰是稳定匀速蔓延的,向上蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而增大;向下蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而减小;蔓延火焰前方存在预热区,且预热区随表面倾角的增大而增大:砂层内部存在热边界层,且砂床热边界层厚度随表面倾角的增加而减小。得到的火蔓延特性及燃烧机理为此类液体燃料的储存、使用以及环境保护提供了一定的科学依据。     

Experimental evaluation of flame and flamelet spread over cellulosic materials using the narrow channel apparatus

Originally conceived as an apparatus to study near‐limit flames and their breakup into flamelets and later modified to function as a microgravity simulation apparatus, the narrow channel apparatus serves also as a facility for examining long time flame spread and material flammability in on‐earth (terrestrial) applications. These applications include flame spread in narrow gaps, persistence of flame in heat‐loss environments, and flame‐to‐flamelet front transition. The narrow channel apparatus tests described here measure behavior of the spreading flame and features of the flame‐to‐flamelet transition. Measured quantities include flow, flame and flamelet velocities in normal and inverted tests, flow deceleration and acceleration rates with associated flame or flamelet response, flame‐to‐flamelet transition times, and influences of fuel thickness. The principal goal of this research was to ascertain the capacity of the narrow channel apparatus to produce data for phenomena observed in both (1) simulated microgravity flame spread and (2) terrestrial flame spread in narrow gaps and channels. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical behavior of masonry materials at high temperatures

An experimental campaign is presented to determine the effects of high temperatures on the mechanical properties of several materials for masonry walls (blocks and mortars), testing a series of cylindrical specimens (diameter of 100 mm and height of 200 mm). After compression tests at 20 °C, an experimental procedure was designed for high‐temperature testing. The cylindrical samples were heated in a muffle furnace, then were inserted into a specific apparatus (called ‘thermos’) for maintaining the prescribed temperature, and finally were subjected to a mechanical compression test. The results obtained by applying this procedure show a common variation of the strength, reduction of modulus of elasticity, and corresponding increments of the ultimate strain with temperature enhancement. Specific diagrams and discussion on the results are performed for each material. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental investigation into the influence of ignition location on flame spread and heat release rates of polyurethane foam slabs

This study presents the results from a set of 11 large‐scale open fire tests performed on flexible polyurethane foam slabs/mattresses. The purpose of the study was to investigate the influence of the ignition location on the fire behaviour of the foam slabs and to generate data on a highly characterised material that could be used for modelling work in the future. A method for obtaining spatially resolved flame spread data for this type of material was presented using a gridded array of 5 × 10 thermocouples placed on the underside the foam slab and from this, flame spread was examined using three different approaches. The heat release rate (HRR) results showed clear shapes forming that were dependent on the ignition location, with two distinct behaviours being observed between the various different ignition locations, this was also observed in the calculated flame spread rate (FSR) data. Results within an individual test, showed the calculated range of FSRs over the geometry of the slab varied between approximately 1 and 8 mm/s depending on the ignition location. The average FSR values between tests varied between 3 and 7 mm/s and the maximum and minimum values were calculated to be approximately 11 and 2 mm/s respectively.     

点火位置对乳胶泡沫水平火蔓延规律的影响

为研究点火位置对乳胶泡沫材料水平方向火蔓延规律的影响。搭建小尺寸实验平台,在距离材料中心点0（x1）、3.54 cm（x2）、7.08 cm（x3）、10.62 cm（x4）、14.16 cm（x5）、17.70 cm（x6）位置处点火,研究了试样表面温度、质量损失、火焰高度、火蔓延速度等特性参数的变化规律。结果表明,随着点火位置由材料中心点向边缘点移动,平均火蔓延速度分别为0.24、0.23、0.19、0.31、0.42、0.51 cm·s^-1,呈现先减小后增大的规律;x3点火位置时的平均火焰高度较低,燃烧时间较长,平均质量损失速率较低,主要与火蔓延过程中的热量传递方式有关。研究结果显示了乳胶泡沫的火蔓延过程,得到了点火位置对火蔓延的影响规律。     

Study on downward flame spread over extruded polystyrene foam in a vertical channel: Influence of opening area

Experimental methods and theoretical analysis are employed to investigate effects of channel opening area on downward flame spread characteristics of extruded polystyrene (XPS) thermal insulation materials on building facade. The average flame height first drops and then rises as dimensionless opening area (the ratio of sidewall opening area to sidewall area, ie, S^*) increases. As S^* rises, both the average and maximum temperature of the curtain wall decrease, and the decreasing of the average temperature is linear. XPS surface temperature history can be divided into four stages, ie, inapparent rising stage (preheating), significant rising stage (melting), dropping stage (pyrolysis), and rerising stage (ignition). The preheating length first rises and then drops as S^* increases. The XPS flame spreads steadily at the early period while acceleration occurs at the later period. For different opening areas, the difference in spread distance history is not apparent in the early stage while this difference is significant in the later stage. The flame spread rate (V_f) first increases and then decreases as S^* rises. A downward flame spread model for XPS in vertical channel with openings is built. The varied trend of V_f predicted using this model corresponds to the experimental result.     

The effects of angular orientation and ultraviolet aging on ETFE wire flame spread

This paper considers the solid phase heat conduction along with the effect of ultraviolet (UV) aging on the flame spread and separately discussed the upward and downward flame spread. The 0.15‐mm‐thick ethylene‐tetrafluoro‐ethylene (ETFE) insulated with a 0.5‐mm‐diameter copper core used in the paper. The flame spread was measured at various inclined angles (vertical ± 90^○, to horizontal 0^○) in the directions of gravity assistance (up) and gravity opposition (down). The ETFE was categorized into two groups: the unaged ETFE (ETFE‐U) and the UV aged ETFE (ETFE‐A). The kinetic parameters of samples were obtained from thermogravimetric analysis (TGA) test. The flame spread experimental results showed that the bigger the absolute inclined angle, the higher the flame spread rate. Besides, the effect of UV aging on the upward spread is greater than that of the downward spread. A theoretical system was established through the flame spread experiments and TGA test. The heat flux and the flame spread rate of upward and downward equations were presented to reveal the effects of solid conduction, orientation, inclination, and UV aging on wire flame spread.