Effects of variations in incident heat flux when using cone calorimeter test data for prediction of full‐scale heat release rates of polyurethane foam

The development of methods to predict full‐scale fire behaviour using small‐scale test data is of great interest to the fire community. This study evaluated the ability of one model, originally developed during the European Combustion Behaviour of Upholstered Furniture (CBUF) project, to predict heat release rates. Polyurethane foam specimens were tested in the furniture calorimeter using both centre and edge ignition locations. Input data were obtained using cone calorimeter tests and infrared video‐based flame area measurements. Two particular issues were investigated: how variations in incident heat flux in cone calorimeter tests impact heat release rate predictions, and the ability of the model to predict results for different foam thicknesses. Heat release rate predictions showed good agreement with experimental results, particularly during the growth phase of the fire. The model was more successful in predicting results for edge ignition tests than for centre ignition tests and in predicting results for thinner foams. Results indicated that because of sensitivity of the burning behaviour to foam specimen geometry and ignition location, a single incident heat flux could not be specified for generating input for the CBUF model. Potential methods to determine appropriate cone calorimeter input for various geometries and ignition locations are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Flame retardant performance of various UL94 classified materials exposed to external ignition sources

The flammability of eight halogen‐free styrene resins and one halogen‐containing styrene resin was characterized by UL 94 VB, LOI and cone calorimeter tests. Their burning behaviour was also measured when exposed to three external ignition sources (methenamine tablet, candle, paper ball). Five resins were used for 19″ monitor housings and the others for 25″ TV. The LOI values of UL 94 V‐2, V‐1 and V‐0 rated resins were higher than that of HB. The heat release rate decreased as the UL 94 ratings increased from HB to V‐0. When these resins were exposed to three external ignition sources, UL 94 V‐1 and V‐0 rated resins showed a self‐extinguishing property after removal of the fire and did not cause fire growth in either 19″ monitor or the 25″ TV housings in all cases. However, UL 94 V‐2 and HB rated resins were easily ignited and spread fire by dripping burning trickles. The burning rate of V‐2 resin was slower than that of HB. Copyright © 2004 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.     

Fire performance studies on glass-reinforced plastic laminates

Polyester, epoxy and phenolic glass-reinforced laminates were compared in terms of their fire properties in the cone calorimeter. The presence of a gel coat on the polyester and epoxy products had some effect, mainly in the FR grades. The FR polyester with a brominated flame retardant showed a marked decrease in rate of heat release and in rate of smoke production. Aluminium hydroxide (commonly called alumina trihydrate of ATH) caused a significant delay in ignition time for the epoxy product and some reduction in rate of heat release but rate of smoke release was still relatively high. Phenolic laminates showed a long ignition time and relatively low rate of heat release (RHR). The peak RHR was further reduced by the presence of aluminium hydroxide and by changing the type of glass reinforcement. The influence of thickness was explored for a series of phenolic laminates in both cone calorimeter and the International Maritime Organization (IMO) surface flammability test. Ignition delay time was significantly affected and the cone calorimeter results showed that the shape of the RHR curve was also changed as the thickness increased. However, the heat release measurements in the IMO test were not sensitive enough to pick up the differences in this property. The type of substrate under the laminate significantly altered the burning rate but this may have been because they were not glued or mechanically fixed.     

Development of fire‐retarded materials—Interpretation of cone calorimeter data

There is little consensus within the fire science community on interpretation of cone calorimeter data, but there is a significant need to screen new flammability modified materials using the cone calorimeter. This article is the result of several discussions aiming to provide guidance in the use and interpretation of cone calorimetry for those directly involved with such measurements. This guidance is essentially empirical, and is not intended to replace the comprehensive scientific studies that already exist. The guidance discusses the fire scenario with respect to applied heat flux, length scale, temperature, ventilation, anaerobic pyrolysis and set‐up represented by the cone calorimeter. The fire properties measured in the cone calorimeter are discussed, including heat release rate and its peak, the mass loss and char yield, effective heat of combustion and combustion efficiency, time to ignition and CO and smoke production together with deduced quantities such as FIGRA and MARHE. Special comments are made on the use of the cone calorimeter relating to sample thickness, textiles, foams and intumescent materials, and the distance of the cone heater from the sample surface. Finally, the relationship between cone calorimetry data and other tests is discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental investigation and numerical modelling of the fire performance for epoxy resin carbon fibre composites of variable thicknesses

This paper applies a unique integrated approach to determine the flammability properties of a composite material (epoxy with carbon fibre) and compares its fire behaviour at two different thicknesses (2.1 and 4.2 mm) by performing small scale (thermo‐gravimetric analysis (TGA)/Fourier transform infrared radiation) and meso‐scale tests (cone calorimeter). For small‐scale tests, experiments were conducted in nitrogen using TGA coupled to gas analysis by Fourier transform infrared radiation. These results allow the determination of thermal stability, main degradation temperature and main gaseous emissions released during the thermal degradation. For meso‐scale tests, experiments were carried out using a cone calorimeter with sample dimensions of 100 × 100 mm at five heat fluxes (30, 40, 50, 60 and 70 kW/m²). The results show that the ignition time increases with an increase in the thickness of the material. Relative hazard classification of the fire performance of the current composites has also been compared with other materials using parameters obtained elsewhere. In addition, the effective ignition, thermal and pyrolysis properties obtained from the ignition and mass loss rate experiments for the 4.2‐mm thick samples were used in a numerical model for pyrolysis to predict well ignition times, back‐surface temperatures and mass pyrolysis rates for all heat fluxes as well as for the 2.1‐mm thick samples. Note that the ignition temperature obtained in the cone agrees with the main degradation temperature in the TGA. The flammability properties deduced here can be used to predict the heat release rate for real fire situations using CFD modelling. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling of heat release rate in upholstered furniture fire

Many fatal residential fires started from burning upholstered furniture, and so upholstered furniture fire has been studied rather extensively in developed countries. As many upholstered furniture were made in China, the hidden fire risk should be studied more. In this paper, full‐scale experiments on the burning of upholstered furniture manufactured in China were conducted and analyzed. The oxygen consumption method was used to measure the heat release rate in a room calorimeter. An ignition source of a 20‐kW gasoline pool fire of 0.2‐m diameter was used to test square foam cushions and 4‐seater sofas. A model of heat release rate predicting upholstered furniture fire in a room was developed on the basis of earlier Swedish works. Results were then used to justify the application of the Combustion Behaviour of Upholstered Furniture model to predict the heat release rate of furniture manufactured in China. The numerical values of key parameters in the model were determined. It is proposed to build up a database that can be used to model heat release rates upon burning furniture. Detailed procedures are illustrated in this paper.     

The Accumulation of Flammable Gases in Cone Calorimeter Tests is Responsible for Flash Ignition of Wool and Cotton Samples

In this paper a possible explanation is presented for the differences found between the fire behaviour of materials in small-scale cone calorimeter tests and the large-scale furniture calorimeter. The results obtained with cone calorimeter/FTIR equipment at 35 kW m⁻² will show that the early flash ignitions of typical materials like cotton and wool are due to the liberation of flammable gases during the pyrolysis phase and the typical ignition situation on the cone calorimeter, that is, the presence of a sparking igniter above the sample. This fast flash ignition and the early heat release behaviour on the cone calorimeter may be in contradiction to the early fire growth in other fire tests where the ignition conditions are clearly different from pyrolysis circumstances, that is, ignition via a burning newspaper, match, gas flame, etc.     

Thermal properties of polyethylene flame retarded with expandable graphite and intumescent fire retardant additives

Low‐density polyethylene was flame retarded by combinations of expandable graphite with either ethylenediamine phosphate or 3,5‐diaminobenzoic acid phosphate. Cone calorimeter, laser pyrolysis, and open flame exposure tests (supported by video and infrared camera data capture and analysis) were conducted to assess ignition and burn behavior. Cone calorimeter results indicated substantial reductions in the peak heat release rates for all flame‐retarded samples but with reduced ignition times and increased flame out times. Smoke generation was suppressed in the presence of expandable graphite. Infrared and video data from open flame fire tests indicated cohesive bonding of expanded strings and thermal shielding properties in all binary systems. All binary systems delivered fire retardation exceeding any of the single fire retardant compounds. They were also able to withstand higher temperatures before ignition, burn through, or sag occurred. All ethylenediamine phosphate‐containing binary systems prevented sample burn through, maintaining structural integrity of samples until eventual melting of the polymer media occurred. Thermogravimetric analysis laser pyrolysis results confirmed the good thermal shielding imparted by the intumescent additives. Copyright © 2016 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.     

Heat release rate and computer fire modelling vs real‐scale fire tests in passenger trains

The materials and products used in passenger trains may not be the first ignited element, but during the fire development, these materials, especially ceiling linings and wall coverings, contribute significantly to the fire growth. The fire safety requirements in passenger trains consist mainly of bench‐scale tests, with particular focus on the sample geometry, position and fire exposition. When this information is extrapolated to real end use conditions limitations appear. In this paper, a discussion of the use of fire dynamics simulator model and heat release rate experiments in cone calorimeter (bench‐scale test) is presented in order to represent the fire development in a passenger train compartment. For the study, two fire scenarios were selected: (1) the single burning item SBI test (modified) and (2) a passenger train compartment. Initially, the limitations of the assumptions and hypothesis made when producing the model were analyzed and the research team carried out a sensitivity study of the model results considering different grid sizes. In order to validate the model, both bench‐ and full‐scale fire tests were considered based on the results provided by the European research program FIRESTARR. The limitations and uncertainties in the results demonstrate the importance of two basic factors: the incident heat flux in the cone calorimeter tests and the prescribed ignition temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Heat release kinetics

The role of solid‐state thermal degradation kinetics in steady‐flaming combustion is examined. Expressions for the burning surface temperature, pyrolysis zone depth and fractional mass loss rate are derived from heat transport limited, nonisothermal pyrolysis kinetics. The predicted magnitude of these fire response parameters and their variation with incident heat flux are in qualitative agreement with experimental data from the literature. A material flammability parameter emerges from the analysis that has the units (J/g‐K) and significance of a heat release capacity. Published in 2000 by John Wiley & Sons Ltd.     

Flammability studies of thermally resistant polymers using cone calorimetry

The effectiveness of a set of thermally resistant polymers was evaluated for aircraft applications using the cone calorimeter (ASTM E1354/ISO 5660) under heat fluxes simulating real scale fires. This study included eight developmental and commercial thermally resistant polymers available in the literature and/or marketplace. The polymers included were aromatic polyester, polyetherimide, fluorine‐containing polyetherketone, phosphorus and fluorine‐containing co‐polyetherketone, fluorine and phosphorus‐containing polyether, fluorine‐containing polyester, poly(dimethylsiloxane)etherimide and polysulfone. The effects of fluorine, phosphorus, silicon and sulfone group in polymers were examined. This evaluation was based on time to ignition, peak, average and total heat release rates obtained at an external heat flux of 50 kW/m². Other parameters such as effective heat of combustion, mass loss and rate of smoke and toxic gas evolution were collected during the cone calorimeter test. Copyright © 2000 John Wiley & Sons Ltd.     

Enhancement of fire retardancy properties of glass fibre–reinforced polyesters composites

This paper presents the results of an experimental investigation on the fire retardancy properties of glass fibre–reinforced polyester (GFRP) composites with bisphenol‐A vinylester and isophthalic polyester as matrices and low electrical conductivity E‐glass fibres as reinforcement. The fire protection systems tested were alumina trihydrate (ATH), decabromodiphenyl ether (DBDE), and antimony trioxide (Sb₂O₃). A mass loss cone calorimeter was used to obtain the properties of heat release rate (HRR), peak HRR, total heat released, total mass loss, time to ignition, and time of combustion. Moreover, limiting oxygen index (LOI), UL‐94, and glow‐wire tests were also performed. The fire tests were carried out in order to investigate if the combination of ATH and DBDE could have “additive,” “antagonistic,” or “synergistic” effects on the flame retardant properties of the GFRP studied in this work. In addition, the influence of the ATH content variation on flame retardant properties was also evaluated. The results indicate that the sole addition of ATH at 47.7 phr could lead to the complete inhibition of the composites ignition, while the materials containing DBDE exhibit ignition and flame propagation in the cone calorimeter test.     

Fire and flame retardants for PVC

The flammability performance of PVC plays a significant role in its selection for many applications. Its relatively high chlorine content (56.8%) makes it more resistant to ignition and burning than most organic polymers. In the case of flexible PVC, the plasticizers that contribute flexibility in most instances detract from its resistance to fire. To meet specifications such as oxygen index, heat release, smoke evolution, or extent of burning in cable tests, flame‐retardant (FR) and smoke‐suppressant (SS) additives are often incorporated. Synergistic combinations of FR and SS additives help PVC formulations meet many stringent FR specifications cost effectively.     

Heat release and classification of fire retardant wood products

A comparison is presented of cone calorimeter heat release data between fire retardant treated and untreated wood products. The test results show significant differences between these two groups. The parameters included in the comparison are time to ignition, rate of heat release (peak and average values) and total heat release. The wood-based products were also tested in different small-scale national standard fire tests and in the full-scale room fire test. Fire retardant wood products achieve an improved classification both in present national systems and in possible new systems based on the cone calorimeter and the room fire test.     

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.     

Flammability of GRP for use in ship superstructures

The burning characteristics of glass-reinforced panels with an isophthalic polyester resin, the same resin with an inorganic flame retardant, two differing vinylester resins or a resole phenolic as the matrix were tested at a range of incident heat flux values using a cone calorimeter. The phenolic composite was superior at all levels showing a longer ignition time, reduced heat output, less contribution to a low-level sustained fire (25 kWm^?2) and lower smoke yield.     

A sample holder for determining material properties

The determination of material properties, such as thermal conductivity, for use in fire models requires precise knowledge of all heat losses. For example, the ignition and subsequent burning of solid samples is sensitive to heat losses from the rear surface of the tested sample. The heat loss depends on the sample holder and its environment. Theoretical predictions of ignition and pyrolysis in standard flammability apparatuses show that the construction of the sample holder has a surprisingly large effect on measured properties especially for thermally thin samples. This makes flammability measurements and inferred thermal properties apparatus dependent. For example, ignition measurements of 6.4 mm (1/4″) plywood samples show a 40% reduction in the critical heat flux for ignition. The back and sides of the sample were sealed by wrapping it with aluminium foil tape. Heat losses from the sample were minimized by placing it on a sample holder having four layers of 3.2 mm (1/8″) thick insulating ceramic paper surrounded by an outer layer of aluminium tape. A detailed mathematical model is developed to fully characterize the thermal response of a sample to a prescribed heat flux in a standard flammability apparatus. The model is used to estimate the residual heat losses not eliminated by the sample holder. Model predictions accurately track the temperature response of blackened brass plates of different thicknesses exposed to several different incident heat fluxes. Brass, of course, has well known thermophysical properties; so, it also provides an excellent means for in situ calibration of the incident heat fluxes. Copyright © 2000 John Wiley & Sons, Ltd.