锥形量热计研究木材临界辐射能流和点燃温度

锥形量热计不但可以直接测量出材料的某些燃烧特性数据（如热释放速率、质量损失率、点燃时间等），而且可以根据所测得的数据间接得出材料的其它燃烧特性数据。笔者介绍了一种从锥形量热计测得的数据推导临界辐射能流和点燃温度的方法。     

Burning Characteristics of Automotive Tires

The ignition and burning characteristics of individual un-mounted automotive tires are presented including heat release rate and heat flux. The propensity for ignition at various locations on the tire is discussed. The burning characteristics of the tire are discussed for both accelerated and non-accelerated fires along with the effects of tire orientation on burning behavior. Ignition by non-accelerated means was only successful at the tire bead. Ignition location was found to have an effect on time to fire growth and overall burning duration with times ranging from 16.5 min to 47.5 min. Duration of significant burning was 25 min to 30 min for the sidewall orientation and 10 min to 15 min for the on-tread orientation. Tires in the on-tread orientation provide a substantially greater heat release rate (350 kW to 450 kW) and corresponding radiant ignition hazard (20 kW/m² to 35 kW/m²) than the sidewall orientation (200 kW and 10 kW/m² to 13 kW/m²).     

Fire Performance Properties of Solid Wood and Lignocellulose-Plastic Composite Deck Boards

Traditionally fire performance properties of externally located deck boards have been characterized by their flame spread index (FSI) as determined by UL 723/ASTM E 84. In this test a nominal 0.6 m wide by 7.3 m long array of deck boards is exposed to an approximately 90 kW ignition source fire for 10 min in the Steiner Tunnel. More recently the University of California Forest Products Laboratory developed a new fire test protocol based the principles of oxygen consumption calorimetry, California SFM 12-7A-4, Part A: Under-Deck Flame Test. This protocol addresses the potential ignition of a deck from underneath as may occur during a wildfire. In this protocol a nominal 0.44 square meter deck-system of deck boards mechanically fastened to wood joists is subjected to an 80 kW ignition source fire for 3 min. For this study the fire performance characteristics of more than thirty-five deck board types were evaluated by the above two methods and by a smaller-scale material-based test, ASTM E 1354 cone calorimeter. Deck boards were selected to represent a range of materials (untreated wood, lignocellulose-polymer composite), structures (solid, voided, microcellular foam), and cross-sectional profiles (width, thickness, presence of hidden fastener system longitudinal edge grooves). The results from this study were used to: 1. Develop correlations for deck boards between the material-based cone calorimeter tests and system-based under-deck tests. 2. Develop correlations for deck boards between the small-scale cone calorimeter tests and large-scale Steiner Tunnel tests. 3. Estimate the significance of ASTM D 2898 Method A accelerated weathering on fire performance.     

Material fire properties and predictions for thermoplastics

Ignition and burning rate data are developed for nylon 6/6, polyethylene, polypropylene and black polycast PMMA in a cone calorimeter heating assembly. The objective is to examine a testing protocol that leads to the prediction of ignition and burning rate for thermoplastics from cone calorimeter data. The procedure consists of determining material properties, i.e. thermal inertia, specific heat, thermal conductivity, ignition temperature, heat of gasification and flame heat flux from cone data, and utilizing these properties in a model to predict the time to ignition and transient burning rate. The procedure is based on the incident flame heat flux being constant in the cone calorimeter which occurs for flames above the top of the cone heater. A constant net flame heat flux of approximately 20 kW/m² for nylon 6/6, 19 kW/m² for polyethylene, 11 kW/mP² for polypropylene and 28 kW/m² for black PMMA is obtained for irradiation levels ranging from 0 to 90 kW/m². The burning rate model is shown to yield good accuracy in comparison to measured transient burning in the cone assembly.     

Heat release rate measurements of thin samples in the OSU apparatus and the cone calorimeter

The Ohio State University (OSU) apparatus and the cone calorimeter are two devices commonly used to measure the heat release rate (HRR) of materials and products in forced flaming combustion. Each operates on a different principle but is calibrated in the same way. However, HRR results from these two test methods do not agree in most cases. For the present study, the OSU was modified to measure oxygen consumption and sensible enthalpy (temperature rise) of the apparatus in addition to the usual sensible enthalpy of the exhaust gases during the test. After calibration, total sensible heat (exhaust gases+apparatus) and oxygen consumption methods gave similar results for thin samples in the OSU. However, OSU results for thin samples did not agree with results from the cone calorimeter (ASTM 1354/ISO 1556) unless the HRR history in the cone calorimeter was corrected for smearing that results from dilution of the combustion gases with air in the sample chamber, exhaust duct, and scrubbers and the response time of the oxygen analyzer.     

Benchmarking the Single Item Ignition Prediction Capability of B-RISK Using Furniture Calorimeter and Room-Size Experiments

This paper benchmarks B-RISK’s capability to predict item ignition in multiple object compartment fire simulations. A series of fire experiments have been conducted which measured single item ignition times under the furniture calorimeter and in the ISO 9705 room. These experiments used mock-up armchair, TV and cabinetry furniture items created from three common materials found in most households in New Zealand exposed to a 100 kW gas burner flame. B-RISK uses the flux-time product (FTP) method as the criterion to predict ignition of items, based on radiation received using the point source model (PSM). This paper presents an analysis of the B-RISK predictions compared to the experimental measurements. Due to the mathematical formulation of the PSM and FTP method, it is found that the predicted ignition time is sensitive to the distance between the radiative source and the item. Predicted ignition times of armchairs constructed of polyurethane foam were within 14% of the ISO 9705 room experimental results. However, for the furniture calorimeter experiments it is found that to get reasonable predictions of the ignition times for the mock-up armchair and TV items there is a need to account for the burner flame movement by adjusting the radial distance by 10–30 mm. Direct flame contact was required to ignite the mock-up cabinetry items and B-RISK was unable to successfully predict this ignition time.     

Evaluating the flammability of wood-based panels and gypsum particleboard using a cone calorimeter

This study examined the combustion characteristics of wood-based panels and gypsum particle board (GPB) made from wood particles using a cone calorimeter according to the ISO 5660-1 specifications. The combustion characteristics of the wood-based panels and GPB were measured in terms of the time to ignition (TTI), heat release rate (HRR), smoke production rate (SPR) and CO yield under a fire condition. The results demonstrated variations in the burning characteristics between the wood-based panels and a significant influence of the surface materials and construction elements on the HRR and SPR. The HRR, SPR and the CO yield of GPB were significantly lower than those of the wood-based panels.     

Radiant smoldering ignition of plywood

This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m² in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m². This compares favorably to predictions made using classical self-heating theory. The role of self-heating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased.     

EcoSmart Fire as Structure Ignition Model in Wildland Urban Interface: Predictions and Validations

EcoSmartFire is a Windows program that models heat damage and piloted ignition of structures from radiant exposure to discrete landscaped tree fires. It calculates the radiant heat transfer from cylindrical shaped fires to the walls and roof of the structure while accounting for radiation shadowing, attenuation, and ground reflections. Tests of litter burn, a 0.6 m diameter fire up to 250 kW heat release under a Heat Release Rate (HRR) hood, with Schmidt-Boelter heat flux sensors in the mockup wall receiving up to 5 kW/m² radiant flux, in conjunction with Fire Dynamic Simulator (FDS) modeling verified a 30% radiant fraction, but indicated the need for a new empirical model of flame extinction coefficient and radiation temperature as function of fire diameter and heat release rate for use in ecoSmartFire. The radiant fluxes predicted with both ecoSmartFire and FDS agreed with SB heat flux sensors to within a few percent errors during litter fire growth. Further experimental work done with propane flame heating (also with 30% radiant fraction) on vertical redwood boards instrumented with embedded thermocouples validated the predicted temperature response to within 20% error for both models. The final empirical correlation for flame extinction coefficient and temperature is valid for fire diameters between 0.2 and 7.9 m, with heat release rates up to 1000 kW. From the corrected radiant flux the program calculates surface temperatures for a given burn time (typically 30 s) and weather conditions (typically dry, windy, and warm for website application) for field applications of many trees and many structural surfaces. An example was provided for a simple house exposed to 4 burning trees selected on a Google enhanced mapping that showed ignition of a building redwood siding. These temperatures were compared to damage or ignition temperatures with output of the percentage of each cladding surface that is damaged or ignited, which a homeowner or a landscaper can use to optimize vegetation landscaping in conjunction with house exterior cladding selections. The need for such physics-based fire modeling of tree spacing was indicated in NFPA 1144 for home ignitability in wildland urban interface, whereas no other model is known to provide such capability.     

基于CONE的超高温耐火电缆火灾危险性分析

利用锥形量热仪对超高温耐火电缆在不同辐射功率下的点燃时间（TTI）、热释放速率（HRR）、质量损失速率（MLR）和燃烧残余物进行了研究。研究表明,随着辐射功率增加,耐火电缆的TTI逐渐缩短,HRR和MLR逐渐增大,火灾危险性逐渐增加。超高温耐火电缆在35 kW/m2和50 kW/m2辐射功率下火灾性能指数相比于25 kW/m2分别增加了44.4%和176.5%,火灾增长指数分别增加了30.4%和83.0%。结合理论分析可以得出,耐火电缆的临界辐射功率为3.61 kW/m2、零辐射平均热释放速率为36.5 kW/m2,表现出较低的火灾危险性。     

Combustibility Parameters for Enclosure Lining Materials Obtained During Surface Flame Spread Using a Reduced Scale Ignition and Flame Spread Technique

A reduced scale ignition and flame spread technique, RIFT, was implemented in the cone calorimeter system to obtain thermocombustibility properties of enclosure lining materials during flame spread over the sample surface. Previously, a thermal model of ignition and opposed flow flame spread was used to analyze flame spread data obtained using RIFT. Here, a framework is discussed for deducing critical material combustibility parameters from the measured heat release and mass loss rates as the spreading flame proceeds to the point of flame extinction. The nature of the data and analytical framework allows users to deduce spreading flame flux from the heat release rate (HRR) and mass loss rate (MLR) data relatively economically and directly. The anomalies highlighted by comparing flame spread data in the RIFT system compared to data from the BS 476 Part 7 apparatus indicates that the RIFT system is well-suited for developing and refining models describing ignition, flame spread, and mass burning.     

典型汽车内饰材料的燃烧特性研究

采用锥形量热仪实验对涤纶面料丙纶玻璃纤维板、涤纶面料丙纶麻纤维板和 PVC 革丙纶麻纤维板 3 种典型汽车内饰材料在 25、35、50 kW/m2 热辐射强度下的点燃时间、质量损失率、热释放速率等燃烧特性参数进行研究,并选取点燃预测模型计算材料的临界热辐射强度,使用轰燃倾向指数和热释放总量评价其潜在火灾危险性。结果表明,在实验热辐射强度下,涤纶面料丙纶麻纤维板质量损失百分率最大,结构完整性最差;涤纶面料丙纶玻璃纤维板平均点燃时间最短,临界热辐射强度最小,最容易被引燃;PVC 革丙纶麻纤维板热释放速率峰值最大,火灾性能指数最小,发生轰燃的可能性最大。     

Flammability assessment of fire-retarded Nordic Spruce wood using thermogravimetric analyses and cone calorimetry

Experimental techniques such as the cone calorimeter, representing realistic fire conditions, and the thermogravimetric analyser (TGA) combined with evolved gas analysis (EGA) can be used to determine flammability and degradation properties of materials. The desire is to correlate the flammability properties measured in the cone calorimeter for samples of size 100 mm×100 mm with those measured or deduced from TGA combined with EGA for milligram samples. Such an achievement will allow the design of fire-safe materials by quickly assessing (a) the fire safety of materials in their earliest milligram formulation and (b) the dependence of their flammability properties on the molecular structure of the material. In the present study, a cone calorimeter and TGA investigation is conducted for commercial Nordic Spruce wood impregnated by mono-ammonium phosphate (fire retardant, FR) through a vacuum pressure method. Experiments in the cone calorimeter with increasing FR concentrations indicated that (a) the char yields increased, (b) the apparent ignition temperature increased, (c) time to piloted ignition increased, (d) the total amount of heat released was reduced, (e) the peak heat release rate was reduced and (f) the carbon monoxide and smoke yields increased especially before ignition occurred. By comparison, char yields also increased with FR content in the TGA degradation experiments in nitrogen. The increase in the char yield with FR content explains quantitatively the decrease in the heat release in the cone calorimeter. By contrast, the onset temperatures measured in TGA decreased, whereas the ignition temperature deduced in the cone calorimeter increased with FR content. This difference is attributed to reduced yield of levoglucosan (reported in recent literature using TGA/EGA) with increased char yield as well as to the presence of phosphorous containing moieties in the volatiles, which both can quench piloted ignition. Finally, the TGA measurements showed that the FR concentrations decreased for milligram samples at different distances from the surface of the wood used in the cone calorimeter measurements. The variation of FR retardant with depth needs to be considered when using TGA data to interpret cone calorimeter measurements and the fire performance of the FR wood in approval tests such as the single burning item (SBI).     

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.     

Improved fire resistance test method for belt materials

A moderately scaled apparatus was developed for determining the fire resistance characteristics of mice conveyor belts and similar type materials. The test method overcomes the limitations of existing laboratory-scale methods and provides a measure of both ignitability and flammability in quantitative terms. Data are presented for nine belt materials, and fire resistance ratings are proposed in terms of the flame spread rate, heat release rate, and critical ignitor heat flux.     

Effects of nanoclay and fire retardants on fire retardancy of a polymer blend of EVA and LDPE

The effects of nanoclay (organoclay) and fire retardants (aluminium tri-hydroxide and magnesium hydroxide) on the fire retardancy of a polymer blend of ethylene-vinyl acetate (EVA) and low-density polyethylene (LDPE) were assessed using thermogravimetric analysis (TGA) and the cone calorimeter. TGA measurements were conducted in nitrogen and air atmospheres at different heating rates (1–20 °C/min), whilst in the cone calorimeter square samples were tested under various external heat fluxes (15–60 kW/m²). The TGA results indicate that the nanoclay (NC) alone has little effect on the degradation of the polymer blend, whereas aluminium tri-hydroxide (ATH) and magnesium hydroxide (MH), used as fire retardants (FRs), generally decrease the onset degradation temperature and also reduce the peak mass loss rate. However, it was found in the cone calorimeter that, though having negligible effect on ignition, the nanoclay reduces the heat release rate (HRR), and increases smoke and CO yields. In comparison, FRs (ATH or MH) were found to delay ignition owing to loss of water at lower temperatures, reduce the HRR, and have similar smoke and CO yields compared to the polymer blend. The reduced HRRs for both the nanoclay and FRs can be attributed to the formation of a surface layer (a nano layer for nanoclay and a ceramic-like layer of Al₂O₃/MgO for FRs), which acts as mass and heat barriers to the unpyrolysed material underneath. The global effect of the surface layer for the polymer blend nanocomposite was examined using a previously developed numerical model, and a methodology for predicting the mass loss rate was subsequently developed and validated.     

Ignition of wood under time-varying radiant exposures

Many studies have utilized a small-scale experimental apparatus such as the cone calorimeter to investigate the piloted ignition of wood exposed to constant levels of incident heat flux; however, there is a deficiency of similar studies related to the non-piloted ignition of wood exposed to time-varying heat fluxes which might represent more realistic fire exposures. In this study, a method was established for producing well-controlled, time-varying exposures using the conical radiant heater of a cone calorimeter. Experiments were conducted in which the incident flux, time to non-piloted ignition, and back-surface temperature of spruce wood were measured. Measured data were used in combination with a numerical heat transfer model to compute the time-dependent temperature distribution through each specimen, and thereby deduce the surface temperature at ignition. From the 30 specimens tested, the average surface temperature for non-piloted ignition of wood was determined to be 521±10 °C. From this surface temperature range, the heat transfer model was used to predict the range of time over which non-piloted ignition was likely to occur for a given time-varying exposure. This procedure was found to produce excellent predictions of ignition time for the time-varying exposures considered in this study. In addition, several existing ignition models were considered, and their suitability for predicting the non-piloted ignition of wood was assessed.     

典型变压器油燃烧特性及烟气危害性研究

利用锥形量热仪及傅里叶变换红外光谱仪,测试了典型变压器油在3种不同外加热辐射通量下的燃烧特性和烟气危害性。重点对比了凝固点不同的KI25X和KI50X变压器油的燃烧过程和火灾危险性。结果表明,外加热辐射通量和变压器油的类型均会对燃烧特性和火灾危险性产生影响。随着外加热辐射通量的增加,两种变压器油的点燃时间均缩短,HRR、生烟率及CO的浓度峰值随之增加。当外加热辐射通量提高至35 kW/m²时,KI50X变压器油火灾的蔓延速度更快,释放出的毒性气体浓度更大,此时其火灾热危险性和烟气危害性相较更大。     

Technological breakthroughs in material flammability evaluations

A number of major innovations have recently been achieved using techniques that employ small-scale flammability measurements to predict full-scale end-use applications. The principles used couple ignition characteristics with combustion characteristics to assess fire performance. These techniques have been developed to classify the flammability of aerosol products; characterize liquid fuel spray fires, such as those involving hydraulic fluids; evaluate the fire propagation behavior of electrical cables; classify conveyor belts; and determine the fire propagation behavior of wall/ceiling materials.This paper was originally presented at National Fire Protection Association 97th Annual Meeting, May 23–27, 1993, Orlando, Florida.