Comparison of three test methods for measuring rate of heat release

Three test methods for measuring the rate of heat release, RHR, have been compared on the same building materials. The test methods are the OSU-box modified for O₂-consumption, the STFI open arrangement and the NBS cone calorimeter. All methods are based on the oxygen-consumption technique. Radiation intensities up to 50 k Wm^?2 have been applied. Thirteen different materials were tested. The results obtained using the three methods seem to be quite similar in spite of the different equipment used. The minor deviations observed in the results seem to be systematic and may be due to the different testing arrangements. There is a good correlation between results, e.g. total heat release up to 1min after ignition, obtained by the different methods. Additional information about the time to ignition is obtained simultaneously. Heat-release rates in the vertical and horizontal orientations are also compared in the NBS cone calorimeter.     

Flammability evaluation of clean room polymeric materials for the semiconductor industry

A new methodology, identified as the 4910 Test Protocol, has been developed to evaluate the fire propagation and smoke development behaviour of polymeric materials for use in clean rooms for the semiconductor industry. This paper reviews the scientific basis of the concepts and criteria contained in the 4910 Test Protocol. For the acceptance of polymeric materials, two criteria are used: (a) Fire Propagation Index (FPI) ⩽6 (ms^−1/2)/(kWm⁻¹)^2/3 and (b) Smoke Development Index (SDI) ⩽0.4 (gg⁻¹) (ms^−1/2)/(kWm⁻¹)^2/3. Materials are tested in the ASTM E 2058 Fire Propagation Apparatus (previously identified as the Factory Mutual Research Flammability Apparatus). The Fire Propagation Index (FPI) is formulated from: (a) the Thermal Response Parameter (TRP), which relates the time‐to‐ignition to the net heat flux to the sample surface, and (b) the chemical heat release rate measured during the upward fire propagation in air having a 40% oxygen concentration to simulate flame heat transfer at large scale. The SDI is related to the smoke release rate and is obtained by multiplying the FPI value by the smoke yield. The smoke yield is defined as the ratio of the total mass of smoke released per unit mass of the vapours of the polymeric material burned. Small and large‐scale fire test data have been included in the paper in support of the 4910 Test Protocol criteria. Highly halogenated and high temperature specialty polymeric materials and highly modified ordinary thermoplastics are found to satisfy the criteria. Copyright © 2001 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.     

Sensitivity of the Room/Corner test to variations in the test system and product properties

The effects of variations in the ISO 9705 Room/Corner Test equipment and product properties are discussed. Previous experimental results are reviewed and some new results from the EUREFIC fire research programme are reported. The effects considered include the room dimensions, the burner size, the heat output of the burner and the stand-off distance of the burner. The error in the measured peak rate of heat release caused by the finite response time of the oxygen consumption calorimeter due to mixing of the exhaust gases is analyzed in detail. The effect of material properties determined with the cone calorimeter are evaluated by employing models simulating the Room/Corner Test.     

Modelling the heat release rate of aircraft cabin panels in the cone and OSU calorimeters

A computer model was developed to calculate the heat release rate of aircraft cabin panels in the OSU calorimeter based on their thermophysical, thermochemical and geometrical properties. It calculates the temperature profile through the panel as a function of time and uses the measured kinetic constants of the individual materials to deduce the mass loss rate. The mass loss rate is multiplied by the heat of combustion of the volatiles to obtain the heat release rate which would be measured in the Cone calorimeter. This heat release rate is used in an energy balance at the surface of the specimen to calculate the rise in enthalpy of the flue gases in the OSU calorimeter and thus the specimen's heat release rate in that apparatus. The calculated heat release rates are in reasonable agreement with measurements in the Cone and OSU calorimeters.     

Molar group contributions to polymer flammability

The specific heat‐release rate is the molecular‐level fire response of a burning polymer. The Federal Aviation Administration obtains the specific heat‐release rate of milligram samples by analyzing the oxygen consumed by the complete combustion of the pyrolysis gases during a linear heating program. Dividing the specific heat‐release rate (W/g) by the rate of the temperature rise (K/s) of a sample during a test gives a material fire parameter with the units (J/g K) and significance of the heat (release) capacity. The heat‐release capacity appears to be a true material property that is rooted in the chemical structure of the polymer and is calculable from additive molar group contributions. Hundreds of polymers of known chemical compositions have been tested to date, providing over 40 different empirical molar group contributions to the heat‐release capacity. Measured and calculated heat‐release capacities for over 80 polymers agree to within ±15%, suggesting a new capability for predicting flammability from the polymer chemical structure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 548–563, 2003     

Evaluation of thermal fire hazard of 10 polymeric building materials and proposing a classification method based on cone calorimeter results

The use of polymeric building materials has been grown in many countries of Middle East in recent years. However, there are only a few fire testing laboratories in this region. Therefore, development of a method for controlling the reaction to fire of materials with bench scale tests is necessary. Providing a framework for classification of thermal fire hazard of materials based on bench scale heat release rate results was attempted. The fire behavior of 10 polymeric building materials was tested with cone calorimeter. The relationship between reaction to fire variables and physical properties of tested samples was examined. The thermal fire hazards of materials were assessed using methods presented by different researchers and with Conetools software. The results revealed that time to ignition, peak rate of heat release, and total heat release are essential variables for determining the fire hazard of materials. A classification method is proposed, which can be used in building codes in countries where the full‐scale test facilities are not available. The method also can be used for quality control purpose and evaluation of fire behavior of materials in bench scale by manufacturers. An example of potential requirements for interior finishes for some occupancy types is also presented. Copyright © 2013 John Wiley & Sons, Ltd.     

Controlled-atmosphere cone calorimeter studies of silicones

A controlled-atmosphere cone calorimeter was used to investigate the burning of a silicone fluid and two silicone elastomers. The silicone materials were tested at 50 kW/m² incident heat flux in environments containing 15–30% oxygen. The test results were compared with a high molecular weight hydrocarbon fluid and an ethylene propylene rubber in terms of time to ignition, peak heat release rate and total heat released, carbon monoxide yield and carbon monoxide production rate, and smoke production and smoke production rate. The data from this study show that when materials burn in oxygen-enriched, normal, and vitiated atmospheres, silicone-based materials have a comparatively low peak heat release rate, total heat released, average CO production rate, and average smoke production rate as compared with organic-based materials. The smoke production and smoke production rate of silicone elastomers can be significantly reduced by adding appropriate smoke suppressants and additives. © 1997 John Wiley & Sons, Ltd.     

Standardization of high-temperature specific heat capacity test parameters of fire-resistant gypsum board

The specific heat capacity at the high temperature of fire-resistant gypsum boards plays a vital role in the simulation accuracy of the thermal response for cold-formed steel (CFS) composite structures. However, there are not given comprehensive and accurate values in the existing standard for test parameters (including heating rate, sample quality, and sample size) used in the test of the specific heat capacity of gypsum boards. This situation leads to large differences in test results. This paper aimed to provide standardized test parameters for obtaining accurate specific heat capacity curves of gypsum boards. First, the effect of test parameters was quantified by 10 groups of specific heat capacity tests of gypsum boards through the uniform design; Then, the standardized values of test parameters were proposed combined with sample composition analysis and finite element numerical analysis: the heating rate was 12°C/min, the sample mass was 18 mg, the sample particle size was 45 to 48 μm; Finally, the standardized test parameters were verified by comparing with the test results of cold-formed steel composite floors in the literature. The results show that the specific heat capacity curve of gypsum boards measured by the standardized test parameters proposed to this paper has good accuracy for simulating the time-temperature curve of cold-formed steel composite floors. It is conducive to accurately assess the fire resistance of cold-formed steel composite floors. The test parameter standardization method can also be extended to other building materials. As a result, the specific heat capacity test can follow a basic standard.     

An investigation into the effects of gravity level on rate of heat release and time to ignition

Two experiments were performed on board an aircraft flying repeated parabolic trajectories to generate free-fal conditions. The first experiment investigates the way in which rate of heat release (RHR) varies with gravity for a candle flame under an imposed low-speed flow. In line with previous studies of flame spread rate it has been shown that rate of heat release drops significantly in imcrogravity. The heat loss due to radiation decreases by a larger proportion than that due to non-radiative processes indicating a lower flame temperature. The RHR from a microgravity flame is flow rate dependent, increasing for increased flow rate at air speeds under 0.03 ms^?1. For the geometry used in this experiment hypergravity caused only a small increase in RHR. The second experiment studied the ignitability of thermoplastics under an imposed radiant heat flux. The ignition test apparatus consists of a conical spiral heating element positioned horizontally above the sample, a continuous spark ignition source and a removable heat shield. Experiments were conducted in a sealed pressure chamber on samples of either PMMA or POM, 1.5 mm thick, with a ceramic backing. There is some indication that gravity influences the time to ignition for some materials.     

The calculation of the heat release rate by oxygen consumption in a controlled‐atmosphere cone calorimeter

The standard cone calorimeter according to ASTM E 1354 and ISO 5660 enables reaction‐to‐fire tests to be performed in ambient atmospheric conditions. A controlled‐atmosphere chamber modifies the standard apparatus in a way that allows tests to be performed in nonambient conditions as well. The enclosed chamber is placed underneath the standard exhaust hood and does not have a closed connection to the hood. With this open arrangement, the exhaust gases are diluted by excess air drawn in from the laboratory surroundings. Heat‐induced changes in the consequential dilution ratio affect the calculation of fire quantities and, when neglected, lead to deviations of up to 30% in heat release rate. The paper introduces a test protocol and equations to calculate the heat release rate taking dilution effects into account. A mathematical correction is shown that compensates for the dilution effects while avoiding extensive mechanical changes in the equipment. Copyright © 2013 John Wiley & Sons, Ltd.     

Flammability testing of pure and flame retardant-treated cotton fabrics

A Controlled-atomosphere cone calorimeter was used to investigate the burning of pure and flame retardant-treated cotton fabrics. The condensed-phase flame retardants used were Morguard (containing ammonium dihydrogen phosphate and diammonium hydrogen phoisphate) and Nochar (containing ammonium sulfate and a sodium salt). The fabrics were tested at 25 kW m^?2 incident heat flux in environments containing 15–30% oxygen. The flame retardants increased the time to ignition, residue yield, and CO and CO₂ yields. The flame retardants decreased the peak and average mass loss rates, the peak and average heat release rates, the effective heat of combustion at peak heat release rate, and the propensity to flashover. The effect of oxygen concentration on the burning of pure and flame retardant-treated cotton fabrics has also been investigated. The flame retardants had better performance when the treated fabrics burned in the lower oxyge concentrations. The result of this study indicate that the controlled-atmosphere cone calorimeter is a good tool for studying the effect of flame retardant and oxygen concentration on the burning of materials.     

Investigation of polymeric materials using the cone calorimeter

The use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO₂, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.     

Rate of heat release measurements with the Swedish box test

The Swedisn box apparatus was modified to include an oxygen analysis of the exhaust gases to be compared with the conventional exhaust gas temperature measurement. A slow-burning material shows good correlation between the temperature measurement and the rate of heat release. A fast-burning material, however, consumes all the available oxygen, and the temperature measurement becomes a measure of only the thermal properties of the material.     

Intercalated kaolinite with ammonium dihydrogen phosphate as an effective flame retardant to enhance the flame retardance and smoke suppression of epoxy resins

To improve the compatibility and flame retardance of kaolinite (Kaol) in polymeric materials, ammonium dihydrogen phosphate (ADP) was intercalated into kaolinite to obtain a novel intercalated kaolinite (K-ADP) for enhancing thermal stability, flame retardance, smoke suppression, and mechanical performance of epoxy resins (EPs). The results show that the presence of K-ADP exerts a more positive effect on reducing the heat release and smoke generation of EPs than the same addition of Kaol. Condensed phase analysis shows that EP/K-ADP composite generates more aromatic cross-links in the condensed phase to reinforce the compactness and intumescence of char compared to EP/Kaol composite. Especially, 5 wt% K-ADP confers a 43.7% reduction in peak heat release rate value and a 36.3% reduction in peak smoke production rate value to EP. Toxic gases analysis shows that K-ADP conduces to inhibiting the release of combustible gases including isocyanates and aromatic volatiles, and generating incombustible gases including ammonia and carbon dioxide to reduce the intensity of EP combustion. The mechanical test shows that K-ADP imparts less adverse impact on mechanical behavior to EP composites than Kaol due to the good dispersion and compatibility between K-ADP with EP matrix.     

Critical considerations on the use of a bi‐directional probe in heat release measurements

In various medium to large scale fire test equipment, such as the ISO room corner (RC) test and more recently the single burning item (SBI) test, the mass flow measurement of the combustion gases plays a key role in the determination of the heat release rate and smoke production rate. To date a bi‐directional low‐velocity pressure probe has been used to calculate this flow based on a differential pressure measurement on the axis of the exhaust duct. The objectives of this paper were to evaluate this bi‐directional probe—and the modified SBI version—when used for measuring flows in exhaust ducts. Recommendations are given on the future use of pressure probes measuring exhaust gas mass flows. Copyright © 2005 John Wiley & Sons, Ltd.     

Extension and evaluation of the integral model for transient pyrolysis of charring materials

In most numerical simulations of fire growth and fire spread, pyrolysis models are required to calculate the reaction of the solid material to an incident heat flux. Important results of the pyrolysis model are the mass release rate of combustible pyrolysis gases and the surface temperature. In this paper an integral model is evaluated for the prediction of pyrolysis of charring materials. An existing integral model is extended with a finite and semi‐infinite cooling state. In this state both char and virgin material are present but the pyrolysis reactions have been interrupted due to insufficient heat supply. The results show that such a cooling state can occur in flame spread calculations. Simulations with the integral model are further compared with the results of a moving grid model, which has the same physical basis. Unlike the integral model, the moving grid model does not require any assumption for the temperature profile in the solid. The influence of the quadratic assumed temperature profile in the integral model on the accuracy of the predictions of the mass release rate of pyrolysis gases is evaluated for several cases. It is shown that the integral model has problems with sudden variations of the external heat flux. Copyright © 2005 John Wiley & Sons, Ltd.     

On non‐combustibility of commercial building materials

Non‐combustibility is discussed on the basis of experimental data for 66 commercial building materials obtained from two standard test methods: EN ISO 1716 oxygen bomb calorimeter and EN ISO 1182 cylindrical furnace. The sample materials are divided into five categories: concrete and ceramics, thermal/acoustic insulation materials, wall or ceiling boards, mortars and adhesives and thin coatings. To better distinguish between non‐combustible and combustible materials, an effective modified heat of combustion is defined and calculated for all materials tested in both methods. The materials studied exhibited very different mass loss values and a low tendency to auto‐ignite in the cylindrical furnace. Revised criteria for class A1 are proposed for better accuracy of reaction‐to‐fire assessment. It is proposed to use the oxygen bomb calorimeter with only one limit for the heat of combustion, that is, a value of 5 MJ/kg for all materials. The proposed approach is a very efficient tool for fast and inexpensive screening for non‐combustibility of building products and is expected to be a more precise method to distinguish between non‐combustible and combustible materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Cable tray fire tests in a confined and mechanically ventilated facility

Cable fires are one of the main fire hazards in nuclear power plants. As part of the cable fire spreading (CFS) campaign of the OECD PRISME‐2 programme, 3 real‐scale cable tray fire tests were performed in open atmosphere (1 CFS support test, named CFSS‐2) and in a confined and mechanically ventilated facility (2 CFS tests, named CFS‐3 and CFS‐4). This study aims at investigating the effects of confined and ventilated conditions on cable tray fires that used a halogen‐free flame retardant cable‐type. The CFS‐3 and CFS‐4 tests involved 2 ventilation renewal rates of 4 and 15 h^?1, respectively. The confined conditions lead to decrease the fire growth rate and the peaks of mass loss rate and heat release rate, compared with open atmosphere. The reductions are larger for the lower ventilation renewal rate. Furthermore, it is shown that the CFS‐4 test may be classified as a well‐ventilated fire and the CFS‐3 test as an under‐ventilated fire. For this last one, its fire characteristics and its consequences in the fire room highlight an oscillatory behaviour, with the same low frequency, for about 30 minutes. These oscillations arise from successive combustions of unburnt gases.     

Novel phosphorus‐based flame retardants containing 4‐tert‐butylcalix[4]arene: Preparation and application for the fire safety of epoxy resins

A novel flame retardant (FR) containing phosphorus and 4‐tert‐butylcalix[4]arene was synthesized and characterized. The FR combined with ammonium polyphosphate (APP) was then incorporated into epoxy resins (EPs) at different ratios. The flame retardancy, thermal stability, and smoke‐releasing properties were investigated. The limiting oxygen index was as high as 30.8% when the mass fraction ratio of the FR to APP was 1:2. The improved FR effect have been due to the combined FR effects between the FR and APP. The char residue content at 800 °C under a nitrogen atmosphere increased notably from 8.22% to 17.6% when the FR APP was incorporated into EP; this indicated an improvement in the thermooxidation resistance. From the cone test, we found that both the total heat‐release and peak heat‐release rate of the FR resins were reduced. Compared to the resins containing no FRs, the smoke‐production rate and total smoke‐production results indicate that the FR resins also exhibited good smoke‐suppression properties. Generally, the stable char layer of the FR APP–EP not only effectively prevented the release of combustion gases but also hindered the propagation of oxygen and heat into the interior substrate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45105.