An experimental setup for observation of smoldering‐to‐flaming transition on flexible foam/fabric assemblies

Fires that involve upholstered furniture frequently begin as a smoldering combustion and, with time, transition to a flaming combustion, which sharply increases the level of hazard. Therefore, understanding how the compositions of the primary flammable components of the furniture, ie, flexible foam and upholstery fabric, affect this transition is important for fire safety considerations. In the current study, an experiment was designed to observe this transition using a sample consisting of 30 × 15 × 6 cm³ rectangular foam block covered with 30 × 15 cm² piece of fabric. For a representative system of 1.8 lb/ft³ (29 kg/m³) flexible polyurethane foam and 11 oz (0.37 kg/m²) cotton fabric, 0.69 transition probability was measured. This probability decreased by a factor of 4 when a small amount of phosphorus‐based flame retardant, Fyrol® HF‐9, was added to the foam. The transition to flaming was speculated to be associated with the formation of adjacent pyrolysis and smoldering regions within the foam. The pyrolysis region, dominated by anaerobic decomposition, provided gaseous fuel, the ignition of which resulted in the transition. The smoldering region, dominated by oxidation reactions at the solid‐gas interface, generated the heat necessary to maintain the pyrolysis process and ignite the gaseous fuel.     

The piloted transition to flaming in smoldering fire retarded and non‐fire retarded polyurethane foam

The piloted transition from smoldering to flaming, though a significant fire safety concern, has not been previously extensively studied. Experimental results are presented on the piloted transition from smoldering to flaming in non‐fire retarded (NFR) polyurethane foam and the fire retarded polyurethane foam Pyrell^®. The samples are small blocks, vertically placed in the wall of an upward wind tunnel. The free surface is exposed to an oxidizer flow and a radiant heat flux. The smolder product gases pass upwards through a pilot. The experiments on NFR foam show that the smolder velocity and peak smolder temperature, which increase with the oxygen concentration and heat flux, are strongly correlated to the transition to flaming event, in that there are minimum values of these parameters for transition to occur. The existence of a minimum smolder velocity for ignition supports the concept of a gaseous mixture reaching a lean flammability limit as the criterion for the transition to flaming. To compensate for the solid‐ and gas‐phase effects of the fire retardants on the piloted transition in Pyrell, it was necessary to increase the oxygen concentration and the power supplied to the smolder igniter and the pilot. The piloted transition is observed in oxygen concentrations above 17% in NFR foam and above 23% in Pyrell. The results show that although Pyrell is less flammable than NFR foam, it is still susceptible to smoldering and the piloted transition to flaming in oxygen‐enriched environments, which is of interest for special applications such as future space missions. Copyright © 2008 John Wiley & Sons, Ltd.     

Fire properties of surrogate refuse‐derived fuels

This paper investigates the fundamental fire properties of surrogate refuse‐derived fuels (RDF), a class of multicomponent materials characterized by high void fraction, with particles of polydisperse sizes and significant internal porosity. A surrogate RDF was developed to improve the reproducibility of experimental measurements. This surrogate RDF reflects typical municipal solid waste collected in the city of Newcastle, in the state of New South Wales in Australia. The material consists of shredded newspaper, wood, grass and plastic bags, with small amounts of sugar and bread. About 95% of the material passes through 50 mm square screens, as required by ASTM E828 standard for RDF‐3 specification. The experiments presented in this paper were performed with the components of the RDF dried in a forced‐air oven at 103° C, except for grass which was dried under nitrogen. The material was found to be very hygroscopic, requiring special care in handling. The experiments performed in the cone calorimeter were designed to measure the heat release rate, total heat release, time to ignition, time to extinction, effective heat of combustion and formation of CO during the combustion process, as a function of sample thickness, sample density and the magnitude of the imposed radiative heat flux. The thermophysical properties of the surrogate material were either measured (solid density, void space, particle density, particle porosity) or extracted from the published data (heat capacity). The present surrogate RDF material was found to ignite easily, within a few seconds of the imposition of the incident heat flux of 40 kW m^?2, and then to reach rapidly the peak heat release rate of 110–165 kW m^?2. The deduced values of the critical heat flux, pyrolysis temperature and effective thermal conductivity are 9–10 (±2) kW m^?2, 280–310 (±30)° C, and 0.4–0.7 (±0.3) W m^?1 K^?1, respectively, depending on the material density. The effective heat of combustion of the RDF was estimated as 15.3 MJ kg^?1. The material produced 1 kg of CO per 18 kg of dried RDF, mostly during smouldering phase after the extinguishment of the flaming combustion. These results indicate that dried RDF pose significant fire risks, requiring that fire safety systems be implemented in facilities handling RDF. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental study on the radiative ignition of silicones

Silicones comprise a wide variety of materials such as fluids, elastomers, resins, and foams. This paper reports the ignitability of some typical silicones under various external radiant heat fluxes. The ignitability of silicones was studied using a cone calorimeter under radiant heat flux levels of 0.5–60 kW m⁻². The time to ignition of the silicones was found to be proportional to a power of the incident heat flux that varies from −1.33 to −2.84. For silicone fluids, viscosity (or molecular size) is the key variable in controlling the ignitability. For silicone elastomers, the fillers play an important role in controlling the ignitability, especially at incident heat fluxes lower than 35 kW m⁻². The ignitability of silicone resins depends on the chemical structure of the resins: the pure trifunctional resin has the lowest ignitability. The ignitability of the silicone foams having the same density depends on the foam thickness, especially at incident heat fluxes lower than 30 kW m⁻². © 1998 John Wiley & Sons, Ltd.     

Ignition studies of cerium nitrate treated towels

This study evaluated the ignitability of cotton towel material saturated with an oxidizer solution of 0.5 N cerium nitrate in 2 N nitric acid. Four types of ignition testing were performed in this work: self‐heating oven tests, hot object ignition tests, radiative smoldering ignition tests, and piloted flaming ignition/burning rate tests. Results indicate that cerium nitrate significantly enhances the ignitability of the towels. Self‐heating properties of cerium nitrate treated towels were measured using the standard constant temperature oven method described by Bowes. Based upon these self‐heating properties, self‐heating is not a hazard for storage scenarios other than bulk storage (depths of several meters) of cerium nitrate treated towels at room temperature. Surface ignition of hot objects was observed for object temperatures as low as 250°C placed upon room temperature cerium nitrate treated towels. Ignition for hot objects buried within a pile of towels occurred for object temperatures as low as 230°C. Radiant heating tests of cerium nitrate treated towels showed initiation of smolder at heat fluxes as low as 3 kW/m² at surface temperatures as low as 175°C. This compares with ordinary cellulosic materials that require 7–8 kW/m² heat fluxes and temperatures of 250°C. All four scenarios demonstrate enhanced ignitability and burning rates of cerium nitrate treated towels. Copyright © 2005 John Wiley & Sons, Ltd.     

Flame spread measurements on wood products using the ASTM E 1321 LIFT apparatus and a reduced scale adaptation of the cone calorimeter

Flame spread experiments were conducted in an ASTM E 1321 lateral ignition and flame transport (LIFT) apparatus and a reduced scale ignition and flame spread test (RIFT) adaptation of the cone calorimeter. Wood‐based products were tested and a flame spread model was applied to the results to obtain the flame spread parameter and the minimum heat flux required for flame spread. The materials used were plywood, medium density fibreboard, hardboard, two‐particle board products, Melamine (Melteca) covered products with two types of wood substrate along with New Zealand grown Rimu, Beech, Macrocarpa and Radiata Pine. The RIFT gave comparable results to the LIFT for several of the materials investigated. There appeared to be an effective limit on suitable materials that can be successfully tested in the RIFT to those that have a minimum flux for flame spread of less than 7kW/m². This limitation was due to the rapid decay of the heat flux profile along the sample and the lower resolution dictated by the smaller size of the RIFT apparatus. It was found that the limit on the minimum heat flux for flame spread was approximately equivalent to a minimum ignition flux of 18kW/m². Copyright © 2009 John Wiley & Sons, Ltd.     

Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions

The first part of this study focuses on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) moulded foams. A decrease in heat flux (down to 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 25 mm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW m^?2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large differences in combustion performance in small-scale flammability tests performed almost identically in the cone calorimeter. In the second part of this study the effects of foam variables, such as foam type, density and melamine content, are defined. These effects were clearly pronounced at radiant flux levels of 15–25 kWm^?2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion in HR-slabstock and all MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.     

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.     

Combustion properties of Brazilian natural wood species

This paper investigates the combustion characteristics of 12 wood species natural to Brazil. A mass loss cone calorimeter was used to obtain the properties associated with (i) heat release rate (HRR), peak HRR, and total heat released; (ii) total mass loss and mass loss rate; (iii) average effective heat of combustion; and (iv) time to ignition, time of pyrolysis and temperature of ignition. The samples used in this work were as follows: (i) prepared in accordance to ISO 5660‐1:2002; (ii) oven dried; (iii) irradiated with a constant heat flux of 50 kW/m²; and (iv) exhibit wood fiber orientation in a plane orthogonal to the flux incidence. Finally, the paper explores the possibility of linking the obtained combustion properties with the density and classes of selected wood species. Copyright © 2014 John Wiley & Sons, Ltd.     

Studying smoldering to flaming transition in polyurethane furniture subassemblies: Effects of fabrics,flame retardants,and material type

The transition from smoldering to flaming was studied on fabric, batting, and foam assemblies via an electric spot ignition source of similar intensity to a cigarette. The materials studied included four different fabrics (cotton, polyester, cotton/polyester blend, flame retardant cotton/polyester blend), two types of batting (cotton, polyester), and three types of polyurethane foam (nonflame retardant, flame retardant by FMVSS 302 testing, flame retardant by BS5852 testing). The results from testing found that materials highly prone to smoldering could propagate smoldering into foams and lead to ignition, whereas materials that tended to melt back from the ignition source did not. Flame retardant fabrics or foam can and do prevent the transition from smoldering to flaming provided sufficient levels of flame retardants are incorporated in the upholstery fabric or foam. The transition from smoldering to flaming of cotton fabric/nonflame retardant foam assembly was also studied using temperature measurements and evolved gas analysis. It was determined that the transition takes place when the oxygen consumption by accelerating smoldering front exceeds the oxygen supply. At this point, the solid fuel gasification becomes driven by thermal decomposition rather than by surface oxidation which leads to high enough concentrations of fuel for flaming combustion to occur.     

Effects of retainer frame,irradiance level and specimen thickness on cone calorimeter test results

The effects of retainer frame use, irradiance level and specimen thickness were studied as the second phase work of a round robin project on the cone calorimeter. The project was conducted in support of various U.S. building code groups, developing a system to determine the degrees of combustibility of building materials. The results of the second phase and a comparison with the corresponding round robin results conducted at 75 kW/m² according to the Board for the Coordination of the Model Codes (BCMC) protocol, are presented here. For most of the materials, no significant differences in parameters measured in the cone calorimeter were found when the retainer frame was not used, versus when the retainer frame was used. The irradiance of 50 kW/m² compared with 75 kW/m² produced significantly longer ignition times (with one exception) and lower heat‐release‐related variables as expected. The exception was gypsum board, for which heat release related values were usually higher at 50 kW/m² than at 75 kW/m². The specimen thickness effect could not be studied adequately due to the small number of tests conducted. A significant thickness effect was shown for the heat‐release‐related variables but not for time to ignition. The effect, however, was opposite for polyurethane foam in comparison with cellulosic materials. Copyright © 2004 John Wiley & Sons, Ltd.     

Flammability behavior of fiber–fiber hybrid fabrics and composites

The effect of heat flux levels on burning behavior and heat transmission properties of hybrid fabrics and composites has been investigated using cone calorimeter and heat transmission techniques. The hybrid fabric structures woven out of E‐glass (warp) and polyether ether ketone (PEEK) (weft) and E‐glass (warp) and polyester (weft) have been studied at high heat flux levels keeping in view the flame retardant requirements of structural composites. The performance of the glass–PEEK fabric even at high heat flux levels of 75 kW/m² was comparable with the performance of glass–polyester fabric evaluated at 50 kW/m². The results further demonstrate that glass–PEEK hybrid fabrics exhibit low peak heat release rate, low heat release rate, low heat of combustion, suggesting an excellent combination of materials and fall under the low‐risk category and are comparable with the performance of carbon fiber‐epoxy‐based systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of fire‐damaged glass‐reinforced phenolic composites

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

An examination of piloted ignition characteristics of cellulosic materials using the ISO ignitability test

The ISO Ignitability Test apparatus is used to determine the times to ignition for cellulosic materials under an incident radiative flux within the range 1--5 kW/m². A linear relationship is determined between time to ignition and incident flux, and a means of using these results to classify building materials is proposed, based upon an empirical flux-time product.     

Further variations of smoke density with heat flux

The heat flux in the NBS smoke chamber has been varied from 1.0 to 5.0 W cm^?2 in 0.5 W cm^?2 steps for some fifteen natural and synthetic materials. These experiments confirm the results given in previous papers for a smaller heat flux range, namely that smoke density varies ove4r the temperature/heat flux range. The extended range studied ensured that a much higher proportion of the materials reached a heat flux at which ignition occurred. As before at this and higher heat fluxes, the experiments were repeated in the flaming mode to ensure better reproducibility. With a few exceptions the general shape of the specific optical density/heat flux plot was similar, with a steep rise to a peak and then a corresponding drop to a low value at high fluxes. At 5 W cm^?2the drop had not been reached in some cases, but it is assumed to occur later by inference from earlier work on a smaller-scale apparatus at high temperatures. Complex materials can give unusual plots during the transition from pyrolysis to combustion. This is true of certain polymers containing fire retardant when the pyrolysis of the additive can have a separate effect.     

Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen‐free flame retardant polyolefin compounds

Seven halogen‐free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m² during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no‐burn) results. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental study of peat ignition upon exposure to radiant energy

Peat ignition upon exposure to radiant energy was studied experimentally for various kinds typical of bogs of Tomsk Region (Russia) and bogs near the city of Edinburgh (UK). The exposure time and energy density required for ignition of various kinds of peat; the characteristic burning surface temperature; and the range of radiant flux in which the combustion mode changed from flaming to smoldering were determined.     

Fire performance of charring closed‐cell polymeric insulation materials: Polyisocyanurate and phenolic foam

Results are presented from 2 series of ad hoc experimental programmes using the cone calorimeter to investigate the burning behaviour of charring closed‐cell polymeric insulation materials, specifically polyisocyanurate (PIR) and phenolic (PF) foams. These insulation materials are widely used in the construction industry due to their relatively low thermal conductivity. However, they are combustible in nature; therefore, their fire performance needs to be carefully studied, and characterisation of their thermal degradation and burning behaviour is required in support of performance‐based approaches for fire safety design. The first series of experiments was used to examine the flaming and smouldering of the char from PIR and PF. The peak heat release rate per unit area was within the range of 120 to 170 kW/m² for PIR and 80 to 140 kW/m² for PF. The effective heat of combustion during flaming was within the range of 13 to 16 kJ/g for PIR and around 16 kJ/g for PF, while the CO/CO₂ ratio was within 0.05 to 0.10 for PIR and 0.025 to 0.05 for PF. The second experimental programme served to map the thermal degradation processes of pyrolysis and oxidation in relation to temperature measurements within the solid phase under constant levels of nominal irradiation. Both programmes showed that surface regression due to smouldering was more significant for PF than PIR under the same heat exposure conditions, essentially because of the different degree of overlap in pyrolysis and oxidation reactions. The smouldering of the char was found to self‐extinguish after removal of the external heat source.     

Combustion behavior characterization of major crops through cone calorimeter

Induced by extremely inflammable characteristic, fire accidents worldwide of crops frequently occur and give rise to loss of life and personal injury. Given this problem, combustion behavior characterization of four major crops was investigated by cone calorimeter. Results confirmed the less quantity of crops needed longer time to be ignited. Meanwhile, the linear relation between the inverse square of time to ignition and heat flux of crops was found. For heat release rate (HRR), it was demonstrated that more quantity of crops prolonged the heat release process. For instance, with heat flux of 50 kW/m², HRR values of 100 and 50 g soybean at 400 seconds were 212 and 40 kW/m². Besides, peak values of HRR (PHRR) were close with different mass, especially for corn. Interestingly, compared to less quantity, more quantity crops were harder to be ignited at same heat flux. In addition to soybean, PHRR and total heat release (THR) of crops was gradually increased with the increasing heat flux. Meanwhile, THR values of 100 g crops were lower than double THR of 50 g crops. The investigation of combustion behavior characteristic could guide the safety storage of crops, thus avoiding the occurrence of crops fire hazards.     

The thermal characteristics of different intumescent coatings

Intumescent coatings are among the most efficient ways of fire retarding flammable materials. The coatings swell under the influence of heat and form a thick porous charred layer. The latter perfectly insulates the substrate against an excessive increase of temperature and oxygen access. In order to make intumescent coatings effective, proper selection of the essential components, i.e. carbonizing, foam‐producing and dehydrating materials, is necessary. The choice of components for an intumescent fire retardant composition has an essential effect on the rate of charred mass formation and its structure. The influence of different modifiers added to amino resins during the process of condensation on fire retardant and heat‐insulating efficiency of intumescent coatings for wood is presented. The fireproofing efficiency was studied by determining the heat release rate, the effective heat of combustion, the mass loss rate and the specific extinction area during the combustion of samples was investigated. The most efficient coating, both from the point of view of fire retardancy and heat insulating properties, was found to be that based on amino resin prepared from urea, dicyandiamide and monoammonium phosphate and dextrin. The exposing of wood coated with urea‐dicyandiamide‐phosphate‐formaldehyde resin supplemented by dextrin to a heat flux of 35 kW/m² for 30 min did not result in ignition and no increase occured in heat release, mass loss rates or in effective heat of combustion. Copyright © 1999 John Wiley & Sons, Ltd.