Effect of Ignitor Position and Orientation on Vertical Cone Calorimeter Tests

A novel three bilayers nanocoating containing MoS2 nanosheets and C60 was constructed on the surface of flexible polyurethane (FPU) foam by a layer-by-layer assembly method. MoS2 nanosheets were prepared by ultrasonic-assistant exfoliation method in a mixed solvent of N-Methyl-2-pyrrolidinone (NMP) and aqueous hydrogen peroxide (30% H2O2). MoS2-C60/FPU foam was prepared by alternately submerging the FPU foam into C60/guargum and MoS2/sodium alginate suspensions. Scanning electron microscopy (SEM) characterization showed that MoS2 nanosheets and C60 nanoparticles were uniformly distributed on the surface of FPU foam matrix. Thermogravimetric analysis demonstrated that MoS2-C60/FPU foam exhibited better thermal stability than the control FPU foam. Cone calorimeter test results revealed that MoS2-C60/FPU foam with the incorporation of 5.24 wt% MoS2-C60 nanocoating had a remarkable reduction in peak heat release rate (pHRR, 47.5% reduction), total heat released (THR, 51.1% reduction) and total smoke production (TSP, 33.1% reduction) compared with those of the control FPU foam. Furthermore, the morphology and structure of char residue after cone calorimeter test were investigated by SEM and Raman spectroscopy. The possible flame-retardant mechanism of MoS2-C60/FPU foam was proposed, and this significant improvement in flame retardancy could be ascribed to the insulating barrier and adsorption effect of MoS2 nanosheets, free radicals-trapping ability of C60 in condensed phase, and the catalytic carbonization effect of the MoS2-C60 nanocoating. This work provides a new approach for producing high quality flame retardant polyurethane foam materials.

A series of full-scale cable tray fire tests have been done and the results have been expressed in terms of heat release (rate and amount), smoke release (rate and amount), mass loss and gas emissions, as well as the standard properties of flame spread and extent of charring. These tests were carried out in two different full-scale facilities. The same cables have also been tested in the cone rate of heat release calorimeter, (ASTM Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, E 1354), in a horizontal orientation, and the same prop-erties (except for gas emissions) are measured. Moreover, the combustible materials which make up many of the cables have also been tested in both the cone calorimeter and the Ohio State University (OSU) rate of heat release calorimeter (ASTM Method for Heat and Visible Smoke Release Rates for Materials and Products, E 906). The rate of heat release results of the cone calorimeter tests on cables were well correlated, linearly, with the results of the full-scale tests. This was particularly true when the cone was used at an incident flux of 20 kW/m2. A model has therefore been devised to predict full-scale cable tray results. The amount of smoke obscuration resulting from all full-scale cable tests was heavily dependent on the extent of burning of the cables. Those cables that did not burn extensively and released very little smoke. Similarly, those cables that did not burn extensively released low amounts of combustion gases, notably CO and HCl. As far as smoke release is concerned, total smoke released in the full-scale fires correlated very well with smoke factors measured in the small-scale cone calorimeter tests. The total smoke released in the small-scale tests, following complete sample combustion, was a much less reliable measure of full-scale smoke release than the smoke factor. The two small-scale rate of heat release instruments correlated well with each other, on all properties, except for time to sustained burning. Some fire properties of the cable jacket material alone, in the cone calorimeter at 20 kW/ m2, can be used to give a priori indication of likely cable full-scale fire performance in a certain scenario. The properties most appropriate for this purpose are the peak rate of heat release and the smoke factor. The OSU calorimeter was a somewhat less reliable small-scale predictor than the cone calorimeter, based on jacket material results only. Fire tests with the cone calorimeter can thus be used for preliminary fire hazard assessmentof electrical cables when installed in vertical cable trays.

This paper summarizes the second part of a study over a two year period carried out at the Laboratory for Fuel Technology and Heat Transfer of the University of Gent in cooperation with Dow Benelux N.V. The first part of the study, focusing on the effects of cone calorimeter test variables as well as polyurethane (PU) flexible foam variables on the foam combustion characteristics, has been published recently (1) . In the second part of the study, the relative contributions of foams and fabrics on important fire hazard parameters such as ignition performance, peak rate of heat, smoke and carbon monoxide release and time to peak rate of heat release, were measured with the cone calorimeter and the Nordtest NT 032 calorimeter and compared. The study was carried out on sixteen different composites of main commercial fabrics and PU flexible foams. The same trends were found with both test methods: post-ignition composite performance is mainly determined by the fabric whereas ignition is influenced by foam and fabric to about the same extent. However, it was not possible to draw precise quantitative correlations, and to predict large-scale Nordtest NT 032 performance on the basis of cone calorimetry results.

Flexible and rigid polyurethane foams can be formulated with a wide variety of mechanical, thermal, chemical and physical properties. Since they are lightweight and can be engineered for specific purposes, they are finding increasing application in the world around us—the construction, insulation, furniture and transportation industries. Yet, hydrocarbon based foams are very flammable, so fire safety and fire performance are key factors for many applications, as well as for their long term use in most sectors. As such, multi-faceted research is underway in many countries with focus on foam fire behaviour, application and scaling of fire test results and product safety of polyurethane foams and related products. The purpose of this special section of Fire Technology is to communicate to the broad fire protection community a selection of interesting research findings and possible future advances related to the fire science and engineering of polyurethane foams. Three papers, describing both experimental and numerical investigations, are included in the section. As well as presenting new research findings, the papers address the implications of the results to product design and regulation, as well as fire test standard development. Authors representing research organizations and universities in Canada, the United Kingdom and the United States have contributed to this special section. The three papers compiled here deal with flexible polyurethane foam, which is used extensively in upholstered furniture, mattresses and other consumer products. Pitts [1] describes the detailed burning behavior of polyurethane foam using data from cone calorimeter tests, and discusses key issues associated with using the cone calorimeter to measure heat release rates of the foam. Hadden et al. [2] then examine the effects of the size of cone calorimeter specimens on measurements of critical heat flux for smoldering and flaming ignition, as well as temperatures and flame spread rates during smoldering of the foam. Finally, Ezinwa et al. [3] discuss the ability of two fire safety engineering models to predict full-scale fire behavior of foam slabs using information from cone calorimeter tests of the foam specimens. While these three papers cover only a small cross-section of issues related to fire safety testing of polyurethane foams, it is hoped that they generate discussion and interest leading to continued development of fire safe products and the associated performance test standards.

Laponite-based inorganic-organic hybrid coating to reduce fire risk of flexible polyurethane foams

Cone calorimetry experiments of on flexible polyurethane foam and flexible polyurethane foam covered with a variety of fire-blocking barrier fabrics were used to characterize and rank the effectiveness of barrier fabrics with the ultimate goal being an ability to predict the effectiveness of barrier fabrics for reducing the flammability of residential upholstered furniture. The primary measure used to characterize the burning behavior was heat release rate. The effect of the underlying sample substrate was shown to have a large effect on the burning behavior of flexible polyurethane foam samples, and a thermally insulating substrate was used during composite experiments. At times, rapid heat release rate fluctuations were observed, and in such cases approximate corrections were applied to correct for finite cone calorimeter time response. Measurements using thermocouples placed within the flexible polyurethane foam provided insights on flexible polyurethane foam pyrolysis behavior, the collapse rate of flexible polyurethane foam, and the thermal protective properties of barrier materials. Heat release rate temporal profiles for flexible polyurethane foam showed two distinct burning stages with peak values which have been attributed to sequential burning of species (primarily) derived from the diamine ( PHRR1) and polyol components ( PHRR2) used to manufacture the flexible polyurethane foam. When a barrier fabric was added, many of the composites displayed a three-stage burning behavior which was attributed to an initial short, intense burning (termed flash burning) stage associated with the barrier fabric covering followed by the two flexible polyurethane foam stages. Seven out of 16 flexible polyurethane foam/barrier fabric composites exhibited flame extinction prior to fuel burn out. Five out of the seven composites reignited when the spark ignition source was reapplied. Reignition allowed barrier fabric effectiveness to be assessed even for cases with flame extinction. Barrier fabric performance was shown to be consistent with four properties that were previously identified as important barrier fabric properties: barrier fabric flammability, gas permeability, thermal protection, and physical integrity. In addition, the current experiments indicate the presence and effectiveness of gas-phase active flame retardants in the barrier fabric can also play an important role. A limited number of tests were conducted to de-couple the effects of flame-retardant chemicals and physical effects of barrier fabrics on flexible polyurethane foam burning behavior. These tests showed that while flame-retardant chemicals can be effective in quenching and extinguishing the flames, the presence of effective barrier fabric shells is also very important in lowering the heat release rate of burning flexible polyurethane foam. In general, the presence of a barrier fabric was shown to reduce the heat release rate peak values during both flexible polyurethane foam burning stages. The magnitude of the peak associated with second-stage flexible polyurethane foam burning was deemed the most appropriate for characterizing the thermal protection provided by a barrier fabric. Since the times for PHRR2 also varied between composites, a measurement referred to as the peak fire growth rate (PFIGRA) parameter was calculated by dividing the heat release rate by time since time to ignition and PFIGRA2 was also considered for characterizing the barrier fabrics. Three possible classification schemes, each consisting of three classes, were introduced based on composite flame extinction and reignition behavior, PHRR2 values, and PFIGRA2 values. Each scheme provided differentiation between barrier fabric effectiveness. While the schemes were able to assess whether the barrier fabrics were particularly effective or ineffective, there were variations among classes of barrier fabrics having intermediate levels of effectiveness. Further work will be required to assess which, if any, of the classification schemes are most appropriate for predicting barrier fabric performance in residential upholstered furniture.

A novel MoS2–DOPO hybrid has been successfully synthesized through the grafting of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of MoS2 nanosheets using allyl mercaptan as an intermediate. MoS2–DOPO was used as a flame retardant additive to prepare flame-retardant flexible polyurethane foam (FPUF). The influence of MoS2–DOPO on the mechanical, thermal stability, and flame retardancy properties of FPUF composites were systematically investigated. The incorporation of MoS2–DOPO could not deteriorate greatly the tensile strength and 50% compression set of FPUF composites, but effectively improves the char residue. The cone calorimeter and smoke density tests results revealed that the peak heat release rate, total heat release, and the maximum smoke density of the MoS2–DOPO/FPUF composite were reduced by 41.3, 27.7, and 40.5%, respectively, compared with those of pure FPUF. Furthermore, the char residue after cone calorimeter tests and pyrolysis gaseous products of the MoS2–DOPO/FPUF composite were analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and thermogravimetric analysis/infrared spectrometry. The results suggested that the MoS2–DOPO hybrid played a synergistic flame retardant effect of gas and condensed bi-phase action. In addition, a possible flame retardancy and smoke suppression mechanism of the MoS2–DOPO/FPUF composite were proposed. This study provides a facile and promising strategy for the fabrication of polymer materials with excellent flame retardancy and smoke suppression properties.

A fire blocking coating made from chitosan, titanate nanotubes and alginate was deposited on a flexible polyurethane (FPU) foam surface by a layer-by-layer assembly technique in an effort to reduce its flammability. First, titanate nanotubes were prepared by a hydrothermal method. And then the coating growth was carried out by alternately submerging FPU foams into chitosan solution, titanate nanotubes suspension and alginate solution. The mass gain of coating on the surface of FPU foams showed dependency on the concentration of titanate nanotubes suspension and the trilayers's number. Scanning electron microscopy indicated that titanate nanotubes were distributed well on the entire surface of FPU foam and showed a randomly oriented and entangled network structure. The cone calorimeter result indicated that the coated FPU foams showed reduction in the peak heat release rate (peak HRR), peak smoke production rate (peak SPR), total smoke release (TSR) and peak carbon monoxide (CO) production compared with those of the control FPU foam. Especially for the FPU foam with only 5.65 wt % mass gain, great reduction in peak HRR (70.2%), peak SPR (62.8%), TSR (40.9%) and peak CO production (63.5%) could be observed. Such a significant improvement in flame retardancy and the smoke suppression property for FPU foam could be attributed to the protective effect of titanate nanotubes network structure formed, including insulating barrier effect and adsorption effect.

A controlled-atmosphere cone calorimeter was used to investigate the burning of one epoxy/fiberglass and two brominated epoxy/fiberglass composites. The composites were tested in normal oxygen and oxygen-enriched environments (oxygen concentration up to 30 percent) at 25, 35, and 50 kw/m2 heat fluxes. Results indicate that the heat flux had a major effect on the ignitability of epoxy/fiberglass and brominated epoxy/fiberglass while the oxygen concentration had a minor effect. The ignitability of epoxy/fiberglass was similar to that of brominated epoxy/fiberglass except the critical heat flux for ignition. For epoxy/fiberglass, the peak mass loss rate, peak heat release rate, and total heat released increased with the increase of oxygen concentration and heat flux, and the average specific extinction area decreased with the increase of oxygen concentration and heat flux. For brominated epoxy/fiberglass, the peak heat release rate and total heat released increased with the increase of oxygen concentration. In comparison with epoxy/fiberglass, brominated epoxy/fiberglass self-extinguishes faster, and produces more carbon monoxide (CO) and less carbon dioxide (CO2) during burning. The upward flame spread rate and upward flame spread length of each composite obtained in separate experiments can be correlated with the peak heat release rate data obtained from the cone calorimeter tests. The controlled-atmosphere cone calorimeter was effective in differentiating the burning of epoxy/fiberglass and brominated epoxy/fiberglass and is an effective tool for selecting materials to be used in the oxygen-enriched environments.

To reduce the flammability of flexible polyurethane (FPU) foams, the graphene oxide (GO) nanosheet filled coatings were deposited on the surface of the FPU foam via layer-by-layer (LbL) assembly method. This consisted of the preparation of the GO using the modified Hummers’ method. The coated FPU foams were then prepared by alternatively submerging the foam into a chitosan solution (0.5 %), a GO suspension (0.1 %), and an alginate solution (0.3 %) until the desired number of trilayers was deposited on the surface of the FPU foam. Scanning electron microscopic images showed that GO-filled coating was evenly distributed on the surface of substrate. Thermogravimetric analysis of the coated FPU foams suggested that the high mass of char residue can be obtained. The cone calorimeter test results of the coated FPU foams showed a reduction in the peak heat release rate (PHRR), peak smoke production rate (SPR), total smoke release (TSR), and peak carbon monoxide (CO) production can be obtained in comparison to the control. In particular, the sample assembled with 10 trilayers had a 8.31 wt % coating mass, which lead to a significant reduction in the peak HRR (59.9 %), peak SPR (45.6 %), TSR (30.5 %), and peak CO production (54.0 %). Such a significant improvement in flame retardancy suggested that the GO nanosheet is a good candidate as a flame-retardant LbL coating to reduce the flammability of FPU foam.

Cone calorimeter tests were conducted on eight different elec tric cable samples at four different external heat flux levels between 20 and 50 kW/m2. Four of the cable samples were sheathed with PVC-based materi als and four with polyolefin-based materials. Some of the cone calorimeter test results were compared with those of the horizontally ventilated laboratory-scale gallery fire test and the oxygen index test which had been previously conducted on these samples. From the ignitability data in the cone calorimeter test, these cable samples were considered to be thermally thick materials. The ignition times of the cables sheathed with a PVC-based mate rial were shorter than those of the cables sheathed with a halogen-free poly olefin. In addition, the heat and smoke release properties of the cable samples also depended mostly on the type of the main base polymer of the sheath ma terial. The correlations between the flame propagation property in the duct fire test and the peak heat release rate in the cone calorimeter test were un clear. On the other hand, there appeared to be relatively good correlations be tween the minimum O2 and maximum CO2 concentrations in the exhaust gas in the duct fire test and the peak heat release rate in the cone calorimeter test. Moreover, a considerably good nonlinear correlation between the limiting oxygen index and the peak heat release rate in the cone calorimeter test on the cable samples, particularly at the relatively low external heat flux level of 20 kW/m2, was shown.

The flammability of halogen-containing and halogen-free flame-retarded high-density polyethylene (HDPE) composites was characterized by UL94, limiting oxygen index (LOI), and cone calorimeter tests. Correlations among the data obtained from UL94, LOI, and cone calorimeter tests were analyzed, while the influences of flame-retardant mechanism and burning condition on the correlations were also discussed. Analysis of UL94 rating shows that there is modest correlation between UL94 rating and LOI value in that it is able to differentiate between UL94 HB and V-2/V-0 rating, and no correlations for UL94 rating and cone calorimeter measurements are found due to the differences in flame-retardant mechanisms and burning conditions. The precise correlations are found between LOI value and some cone calorimeter measurements (peak heat release rate and mean heat release rate at 300 s). However, there are weak correlations between LOI value and some measurements (time to ignition, total heat release, mean heat release rate at 180 s, and fire growth rate index) and no correlations for other measurements (mean heat release rate at 60 s and mean heat release rate at 120 s) in cone calorimeter. Meanwhile, there are significantly different fitted equations and coefficients between LOI value and cone parameters for halogen-containing and halogen-free formulations due to the obvious differentiation in flame-retardant mechanisms. The comprehensive discussion of burning conditions could further explain why the correlations among the data obtained from the three fire tests have significant discrepancies and also help to understand why different flame-retardant effectiveness appears in the three fire tests. © Springer 2015. Selection and peer-review under responsibility of the Asia-Oceania Association for Fire Science and Technology.

Functionalizing Ti3C2Tx for enhancing fire resistance and reducing toxic gases of flexible polyurethane foam composites with reinforced mechanical properties

Two-scale tests, microscale and bench scale, are conducted to analyze the flammability of a flexible polyurethane foam. Microscale tests include simultaneous thermal analysis coupled to Fourier transform infrared spectroscopy, and microscale combustion calorimeter (MCC). Evolved gas components, heat release rate per unit mass, total heat release, derived heat release capacity, and minimum ignition temperature are obtained. Bench scale tests are performed on cone calorimeter. Peak heat release rate per unit area, effective heat of combustion, minimum incident heat flux for ignition, and total heat release per unit area of different incident heat fluxes are obtained. FO-category of the PU foam is estimated by multiple discriminant function analysis based on the results of cone calorimeter test. The relationship between the two-scale tests is analyzed. The minimum ignition temperatures derived from multi heating rate MCC tests are used to predict the time to ignition and compared with the results from cone calorimeter tests. This PU foam is evaluated as a high fire hazard polymer having low heat release capacity, low ignition temperature, and short ignition time.

The characteristics of litter combustion have a significant impact on the spread of surface fires in the central Yunnan Province, a high-risk forest fire zone. The burning behavior of individual and mixed-species litter samples from five dominant tree species (Pinus yunnanensis Franch., Keteleeria evelyniana Mast., Quercus variabilis Blume., Quercus aliena var. acutiserrata, and Alnus nepalensis D. Don.) was assessed in this study using cone calorimeter tests. Fern fronds and fine branches were included in additional tests to evaluate their effects on specific combustion parameters, such as Fire Performance Index (FPI), Flame Duration (FD), Time to Ignition (TTI), Mass Loss Rate (MLR), Residual Mass Fraction (RMF), Peak Heat Release Rate (PHRR), and Total Heat Release (THR). There were remarkable differences in the burning properties of the three types of litter (broadleaf, pine needles, and short pine needles). The THR and PHRR values of P. yunnanensis were the highest, whereas the PHRR of the other species varied very little. Short pine needle litter showed incomplete combustion and a long flame duration. When measured against pure pine needle litter, mixtures of P. yunnanensis and broadleaf litter showed lower PHRR. When set side by side to pure pine needle litter, P. yunnanensis and broadleaf litter showed lower PHRR. THR rose when fine branches were included, underlining the significance of fine woody fuels in fire behavior. The insertion of ferns increases the percentage of unburned biomass, prolongs TTI, and dramatically reduces PHRR.