Thermal response characteristics of fire blanket materials

The thermal response characteristics of over 50 relatively thin (0.15–3.7 mm) fire blanket materials from four different fiber groups (aramid, fiberglass, amorphous silica, and pre‐oxidized carbon) and their composites have been investigated. A plain or coated fabric sample was subjected to a predominantly convective or radiant heat flux (up to 84 kW/m²) using a Meker burner and a cone heater, respectively. In addition to conventional thermal protective performance ratings for protective clothing, two transient thermal response times (for the fabric back‐side temperature to reach 300 °C and for the through‐the‐fabric heat flux to reach 13 kW/m²) and a steady‐state heat‐blocking efficiency (HBE) were introduced for both convective and radiant heat sources. For most woven fabrics, the HBE values were approximately 70 ± 10% for both convection and radiation and only mildly increased with the fabric thickness or the incident heat flux. Nonwoven (felt) fabrics with low thermal conductivity exhibited significantly better insulation (up to 87%) against convective heat. Highly reflective aluminized materials exhibited exceptionally high HBE values (up to 98%) for radiation, whereas carbon and charred aramid fabrics showed lower HBEs (down to 50%) because of efficient radiation absorption. A relatively thin fire blanket operating at high temperatures can efficiently block heat from a convective source by radiative emission (enhanced by its T⁴‐dependence and high surface emissivity) coupled with thermal insulation and from a radiant heat source by surface reflection while the aluminum surface layer remains. Copyright © 2013 John Wiley & Sons, Ltd.     

Simulating the thermal response of the flame manikin with different materials exposed to flash fire by CFD

To investigate the differences of thermal response between heat flux sensors and human skin on the flame manikin, a three‐dimensional heat transfer model was developed and validated by the flame manikin system. The initial temperature of the model with sensor material was set to 300 K, and the model with skin material was set as the real condition. Simulated results validated the effectiveness of heat flux measured by the sensor. The incident heat flux through the measured surface was influenced by the different emissivity of the human skin and experimental sensors. Significant difference was found for the temperature response of these two kinds of materials within 4‐s fire exposure. The heat flux measured by sensor or the simulated results with actual human skin parameters could be used as the input boundary condition of the skin heat transfer model for Henriques's skin burn prediction. It is necessary to study the actual skin thermal response by experiments, where the 3D model established in this study could be used as the supplementary means for skin simulant sensor development. These findings will also be adopted in our following study of skin burn prediction module in the 3D full‐scale simulation platform. Copyright © 2016 John Wiley & Sons, Ltd.     

表面温度测量方式对喷雾冷却表面传热特性的影响

喷雾冷却在工业过程中应用广泛,制冷剂喷雾是激光皮肤手术中实施表皮冷保护的必要手段。为提高冷却效率,需要通过表面温度的测量反推表面传热特性。为探索不同表面温度测量方式对实验结果的影响,搭建了瞬态喷雾冷却实验台,分别使用磁控溅射薄膜热电偶（TFTC）、丝状热电偶（FTC）和片状热电偶（STC）研究了R404A制冷剂喷雾环氧树脂表面传热特性的差异。实验结果表明,磁控溅射薄膜热电偶（TFTC）热响应性能最佳,能准确及时地反映表面温度的瞬态变化且可与热通量变化准确对应。丝状热电偶（FTC）和片状热电偶（STC）属于间接测温,温度变化存在明显滞后,影响热通量、对流传热系数等表面传热特性的精确分析。薄膜溅射热电偶测温是准确研究瞬态喷雾冷却表面传热过程的可靠手段,可为临床治疗提供理论指导。     

Mechanical properties of fire‐damaged glass‐reinforced phenolic composites

Changes to the mechanical and physical properties of a glass‐reinforced resole phenolic composite due to intense radiant heat and fire are investigated. Fire testing was performed using a cone calorimeter, with the composite exposed to incident heat fluxes of 25, 50, 75 or 100 kW/m² for 325 s and to a constant flux of 50 kW/m² for different times up to 1800 s. The post‐fire tensile and flexural properties were determined at room temperature, and these decreased rapidly with increasing heat flux and heat exposure time due mainly to the chemical degradation of the phenolic resin matrix. The intense radiant heat did not cause any physical damage to the composite until burning began on exposure to a high heat flux. The damage consisted of cracking and combustion of the phenolic matrix at the heat‐exposed surface, but this only caused a small reduction to the mechanical properties. The implication of the findings for the use of glass‐reinforced resole phenolic composites in load‐bearing structures for marine craft and naval ships, where fire is a potential hazard, is discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

The use of the ISO/TC92 test for ignitability assessment

The ignitability of solids, including fire-retardant-containing polystyrene, is reported using results of a small-scale thermal radiation exposure test (a modified ISO ignitability test procedure). Additional information is provided from the results of exposure to convective heating and from oxygen index determinations. The use of a permanent sample mask and smaller samples than described in the ISO procedure proved convenient. The ISO procedure was found useful for determining the response of ignition time to changes in radiant flux. Good agreement was found with the analysis of Quintiere and Harkleroad for most samples but not with polystyrene, with and without halogen fire retardant. The increase in ignition resistance with fire retardant concentration suggested by the oxygen index is not always consistent with the ignition delay times under radiative or convective assault.     

Ignition performance of new and used motor vehicle upholstery fabrics

This paper examines the standards for fire safety in transport systems and in particular the test method for the flammability of materials within passenger compartments of motor vehicles. The paper compares data from ignition tests conducted in the cone calorimeter and the FIST apparatus with tests conducted using the FMVSS 302 horizontal flame spread apparatus. Ten materials were selected as representative of those used as seat coverings of private and commercial passenger vehicles. The time to ignition of new and used materials subject to exposure heat fluxes between 20 kW/m² and 40 kW/m² was measured. The results from the ignition tests were analysed using thermally thick and thermally thin theoretical models. The critical heat flux for sustained piloted ignition was determined from the time to ignition data using the thermally thin approach. Derived ignition temperatures from both the thermally thick and thermally thin methods were compared with measurements using a thermocouple attached to the back surface of materials in selected tests. The flame spread rates in the FMVSS 302 apparatus were determined and a comparison was made between the performance of the materials in the flame spread apparatus, the cone calorimeter and the FIST. The results suggests that a critical heat flux criterion could be used to provide an equivalent pass/fail performance requirement to that specified by the horizontal flame spread test although further testing is needed to support this. Copyright © 2004 John Wiley & Sons, Ltd.     

Cracking behavior of glazings with different thicknesses by radiant exposure

Fourteen experiments on cracking behavior of glazings with thicknesses of 3, 6, 8, and 10 mm by radiant exposure were carried out with a new experimental apparatus. The radiant power was controlled proportional to time square to simulate a time‐squared growth fire. An infrared thermal imaging camera was employed to monitor the temperature field of the unexposed glazing surface. Other important parameters including incident heat flux, local gas temperature, exposed surface temperature, and time of the first cracking were obtained. The relationship between the cracking behavior and glazing thickness was analyzed based on the experimental results. The results show that the protected edge temperature of glazing has a considerable rise when the first cracking occurred, which should be included in further modeling. It was also shown that thicker glazings have smaller surface temperature during the heating process and induce longer time to first crack. However, the critical temperature difference approximately remains constant for all glazings studied. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of cone and OSU calorimetric techniques to assess the flammability behaviour of fabrics used for aircraft interiors

Two test methods for measuring the heat release rate, HRR have been compared on fabric composites used for aircraft interior materials as side‐wall panels. These methods are based on the principles of direct measurement of the convective and radiant heat by thermopiles using an Ohio State University (OSU) calorimeter, and oxygen consumption using a cone calorimeter. It has been observed when tested by standard procedures, cone results at 35 kW/m² incident heat flux do not correlate with OSU results at the same heat flux. This is because in the cone calorimeter, the sample is mounted horizontally whereas the OSU calorimetric method requires vertical sampling with exposure to a vertical radiant panel. A further difference between the two techniques is the ignition source—in the cone it is spark ignition, whereas in the OSU it is flame ignition; hence, samples in the OSU calorimeter ignite more easily compared to those in the cone under the same incident heat fluxes. However, in this paper we demonstrate that cone calorimetric exposure at 50 kW/m² heat flux gives similar peak heat release results as the 35 kW/m² heat flux of OSU calorimeter, but significantly different average and total heat release values over a 2 min period. The performance differences associated with these two techniques are also discussed. Moreover, the effects of structure, i.e. type of fibres used in warp/weft direction and design of fabric are also analysed with respect to heat release behaviour and their correlation discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Steady‐state heat flux measurements in radiative and mixed radiative–convective environments

The steady‐state responses of four heat flux gauges (Schmidt–Boelter, Gardon, directional flame thermometer (DFT) and hemispherical heat flux gauge (HFG)) were examined under various radiative and convective heating conditions. In radiative environments, Gardon measurements were up to 8% higher than Schmidt–Boelter measurements, but in mixed radiative–convective environments, Gardon measurements were 8–18% below those of the Schmidt–Boelter gauge. This difference increased as the convective portion of the total heat transfer increased, due to discrepancies between the radiation‐based calibration environment and the application environment. The DFT data in radiative environments were comparable with the Schmidt–Boelter and Gardon values (within 12%), with the difference largely attributed to natural convection losses from the DFT. In mixed environments, the DFT values were significantly lower than those of the Schmidt–Boelter gauge due to differences in the surface temperatures of the gauges, resulting in the convective flow cooling, rather than heating, the DFT. The HFG heat flux estimates were 35–48% lower than the Schmidt–Boelter measurements under radiative conditions, influenced by large conduction losses from the sensor plate to the gauge housing. Lateral conduction due to a mismatch between the experimental convective flow outlet diameter and the gauge width also affected results from the DFT and HFG. Copyright © 2009 John Wiley & Sons, Ltd.     

航空煤油不同尺寸池火热流及温度特性研究

为研究航空煤油池火燃烧过程中热流与温度特性,搭建了油料燃烧模拟实验台架。通过分析实验图像与数据,发现航空煤油池火辐射热通量随径向距离和高度的增大逐渐减小,其中辐射热通量对高度增加更为敏感,随高度升高下降幅度更快;热辐射先于热对流达到强度最大值,随后在稳定燃烧阶段后期热对流强度存在跃升现象,强度超过热辐射强度,成为该阶段主要传热方式;航空煤油池火中心线上,下部区域火焰连续燃烧、氧气浓度低,上部区域油火卷吸空气、氧气浓度较高,是导致不同高度最高温度到达时刻不同的主要原因;对不同尺寸油池火来说,其热通量峰值随着油池尺寸增大而增大,同时方形油池热通量峰值显著高于圆形油池。     

Impuls‐, Wärme‐ und Stofftransport in Abgassensoren bei motorischen Betriebsbedingungen

Knowledge of all relevant parameters affecting function and load is a precondition for optimal engineering of exhaust gas sensors. Access to those parameters by measurement is difficult and often impossible. Thus the development of a validated model to simulate operating behaviour of exhaust gas sensor was the aim of this work. Coupling of a 1D‐engine simulation with a 3D‐CFD simulation is done to predict convective momentum, heat and mass transfer to the sensor surface. Being results from coupled simulations, transient boundary conditions are applied to a further 1D‐model to predict mass transfer inside the sensor. Signals of two exhaust gas sensors were simulated.     

Effectiveness of pre‐applied wetting agents in prevention of wildland urban interface fires

The purpose of the work described in this paper is to investigate the effectiveness of pre‐wetting structures, dead fuels, and landscaping plants in preventing fire spread from wildland fires to structures. Critical fluxes for fire growth were determined using intermediate‐scale testing for three wetting agents (water, type A foam, and gel) applied to 10 landscaping plants conditioned to 20% moisture, a mulch material, and four external structural materials (vinyl siding, plywood siding, asphalt shingle roofing, and cedar shake roofing). The critical flux for fire growth values was determined at 3‐min heat radiation exposure and simultaneous 300‐mm long flame exposure. Test specimens were exposed to various durations and intensities of drying prior to exposing them to heat radiation. Application of water or foam provided no noticeable protection. Gel was effective in providing protection even after 60 min of laboratory condition drying but was less successful when exposed to fire weather simulating accelerated drying. Some uncertainty is associated with the results of this work because of the variability of landscaping plants and gel wetting agent application uniformity. The intermediate‐scale test results were verified using full‐scale testing. Copyright © 2012 John Wiley & Sons, Ltd.     

Heat transfer coefficient for a single coke piece

The heat transfer coefficient for a single coke piece is determined experimentally, in the case of convective heat transfer with coolant gas. The experimental method and apparatus are described. A mechanism is proposed for the convective heat transfer of the coke piece with inert gas. The heat transfer coefficient in the coke bed is considerably increased on account of additional turbulization of the flux.     

Actively Cooled Calorimeter Measurements and Environment Characterization In a Large Pool Fire

Quasi-steady-state heat fluxes absorbed on the calorimeter surface in ten vertical 0.1 m high×1 m wide zones were measured by means of water calorimetry. The calorimeter surface also included an array of intrinsic thermocouples to measure surface temperatures, and an array of Schmidt – Boelter radiometers for a second, more responsive, method of heat flux measurement. The pool fire environment characterization was done with measurements from velocity probes, directional flame thermometers (DFTs), and thermocouples. The initial measurements with a 1 m×1 m water cooled vertical flat plate calorimeter located 0.8 m above and inside a 6 m×6 m JP-4 pool fire are described. Water calorimetry measured absorbed surface heat fluxes of about 65–70 kW m⁻² with a gradual decrease with increasing height above the pool. Intrinsic thermocouple measurements recorded typical calorimeter surface temperatures of about 500°C, with spatial variations of ±150°C. Gas velocities across the calorimeter face averaged 3.4 m s⁻¹ with a predominant upward component, but with an off-vertical skew. Analysis of data collected in the fire environment in the vicinity of the calorimeter was performed to characterize the fire environment and to determine the input parameters required to calibrate analytical models. For this test, the emissive power distribution near the plate was essentially linear. Flux measurement in the fire environment ranged from 75 kW m⁻² to 175 kW m⁻². With temperature and heat flux data, effective absorption coefficients were determined by using a two-flux method to solve the inverse problem. The results show that the optical thickness increases with increasing distance from the calorimeter surface. The effective absorption coefficient is approximately 0.8 m⁻¹ in the vicinity (0 – 1.85 m) of the calorimeter and is approximately 2 m⁻¹ in the vicinity (1.85 – 2.8 m) of the plume centerline. The observed decrease in heat flux on the calorimeter surface with increasing vertical height is consistent with analytical fire models derived for constant temperature surfaces. Results from several diagnostics also indicated trends and provided additional insight into events that occurred during the fire. Some events are correlated, and possible explanations are discussed.     

高压可燃气体泄漏动力学过程与喷射火热灾害分析

以高压可燃气体泄漏诱发的喷射火为研究对象,对泄漏过程中喷口处稳态气流状态参数变化及其被点燃之后的喷射火火焰形态与辐射热流场预测模型研究进展进行了综述。归类分析了基于理想气体状态方程和Abel-Noble状态方程的高压气体泄漏模型及其适用情况,并对不同浮力控制和动量控制范围的几种喷射火火焰几何尺寸模型进行了概括性总结,同时对不同火焰形态下的点源、多点源、固体以及线源4种热辐射模型进行了汇总,最终提出将3种模型耦合联用以建立适用于不同泄漏条件下喷射火热灾害分析预测方法。分析表明,该分析预测方法具有很好的适用性。     

Crack evolution process of window glass under radiant heating

Window glass breakage has a significant impact on the compartment fire development being sometimes a weak link for fire safety design. This work focuses on the process of crack evolution of window glass in a fire environment. A total of 11 experiments were conducted in a box apparatus by changing heating rate of a heat source. The box apparatus is an enclosed compartment, which includes the heat source, assembled boxes, and glass pane. Crack time, temperature field, breaking stress, crack evolution, and fall‐out of the glass panes are presented. Main and secondary fractures are defined and illustrated in the process of crack evolution. Average time to the first, second, and third main fractures decreased as the heating rate of heat source increased. The average breaking stress was 71.14 MPa for float glass at the time of first main fracture. The crack evolution process was very complicated. Cracks initiated at an edge and propagated towards other edges for main fractures. Multiple cracks were joined together to form cracked glass islands. The fall‐out of cracked glass islands under radiant heating was more difficult than that under real fire scenarios.     

Heat release rates from samples of polymethlmethacrylate and polystyrene burning in normal air

Results are presented for mass generation rates of major combustion products (CO₂, CO, total hydrocarbons and smoke particulates) and heat release rates from samples of polymethylmethacrylate and polystyrene burning in normal air under varying magnitudes of externally applied radiant heat flux. In the experiments mass generation rates of products and convective heat release rates are measured and, from heat and mass balance, actual and radiative rate of heat release, as well as heat that is not released due to incompleteness of combustion, are calculated. From the data, 99% of the rate of the theoretical heat release for complete combustion can be accounted for. In some cases the experimentally derived heat release rate was less than half that predicted from mass loss rate (assuming complete combustion). This ‘combustion efficiency’ decreased strongly with increasing externally applied radiant flux, and was always much lower for polystrene than for polymethylmethacrylate. At the ‘deal’ condition, defined as a condition where heat losses have been compensated and where the mass burning rate of polystyrene is 1.44 times the rate for polymethylmethacrylate, polystyrene generates 6.60 times more CO, 7.83 times more smoke particulates, and the radiative rate of heat release is 1.75 times more than that of polymethylmethacrylate.     

A radiant heat flux apparatus for measuring the thermal response of polymeric materials to high temperatures

An efficient and economical experimental apparatus has been designed and built which delivers a known radiant heat flux and simultaneously measures the in-depth temperature profiles in polymeric materials. Test samples are maintained in a controlled environment and are heated radiantly by a silicon carbide heating element capable of producing heat fluxes up to 7.0 cal/cm²-sec. The experimental data produced by this device are extremely accurate and therefore are suitable for use in verification of numerical models. The utility of the apparatus was demonstrated by measuring temperature profiles to approximately 1000°C in a glass-filled phenol-formaldehyde resin.     

Effect of flame heat flux on thermal response and fire properties of char‐forming composite materials

This study evaluates the effect of flame heat flux on the prediction of thermal response and fire properties of a char‐forming composite material. A simplified two‐layer flame model was developed and incorporated into a heat transfer thermal model to predict the thermal response and fire reaction characteristics of a burning material. A typical char‐forming material, E‐glass reinforced polyester composite, was used in the study. A cone calorimeter was used to measure the fire reaction characteristics of the composite. The flame heat flux in a cone calorimeter test setup was estimated using the simplified flame model. Thermal response and fire property predictions with and without the effect of flame heat flux were compared with experimental data obtained from the cone calorimeter tests. Results showed that the average flame heat flux of the composite in a cone calorimeter was 19.1 ± 6 kW/m² from model predictions. The flame had a significant effect on the thermal response and fire properties of the composite around the first heat release peak but the effect decreased rapidly afterwards. Copyright © 2012 John Wiley & Sons, Ltd.