Fire performance of closed‐cell charring insulation materials in plasterboard‐insulation assemblies

This paper presents an experimental study on the fire performance of two types of plastic charring insulation materials when covered by a plasterboard lining. The specific insulation materials correspond to rigid closed‐cell plastic foams, a type of polyisocyanurate (foam A) and a type of phenolic foam (foam B), whose thermal decomposition and flammability were characterised in previous studies. The assemblies were instrumented with thermocouples. The plasterboard facing was subjected to constant levels of irradiation of 15, 25, and 65 kW m^?2 using the heat‐transfer rate inducing system. These experiments serve as (1) an assessment of the fire behaviour of these materials studied at the assembly scale and (2) an identification of the fire hazards that these systems pose in building construction. The manifestation of the hazards occurred via initial pyrolysis reactions and release of volatiles followed by various complex behaviours including char oxidation (smouldering), cracking, and expansion of the foam. Gas‐phase conditions may support ignition of the volatiles, sustained burning, and ultimately spread of the flame through the unexposed insulation face. The results presented herein are used to validate the insulation “critical temperature” concept used for a performance‐based methodology focused on the selection of suitable thermal barriers for flammable insulation.     

Experimental investigation and modelling study of long stick wood gasification in a top lit updraft fixed bed gasifier

We present results of an experimental study on long stick wood gasification, in an attempt to reduce wood gathering for gasification. This paper presents the results from experiments and the analyses of gasification using sticks with length 68 cm and diameter 6 cm. The moisture content of the wood was 25%. This top lit updraft gasifier operates with 180 W of blower power air supply to produce 9–10 kW of thermal energy, an energy yield of 50/1. Results were obtained for various flow conditions with airflow rates ranging from 25 to 45 m³/h. For modelling, the flaming pyrolysis time for long stick wood in the gasifier is calculated to be 2.1 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 37 cm and 36 cm respectively. The turn down ratio for the gasification is around 2. The rate of feed was between 9 and 10 kg/h and the gasifier operated continuously for 5 h in two runs to study the gasifier reliability. The performance studies in specific gasification rate, equivalence ratio, turn down ratio, superficial velocity, airflow, and gas flow are analyzed. The temperature ranged from 1185 K in the combustion zone to 400 K in the drying zone. The gas and airflows can be converted to the Air/Fuel equivalence ratio, the most important aspect of gasifier operation. The equivalence ratio shows operation in a combustion mode (6.3) at start up; in a flaming pyrolysis mode (1.2) for the middle part of the run; and in the charcoal gasification mode (5.7) at the end of the run. Measurement of the equivalence ratio is a simple way of analyzing the behaviour of the gasifier. From the results of present investigation, it is revealed that the top lit updraft gasifier is more suitable for long stick wood as feed when compared to conventional updraft gasifier.     

Ignition and combustion of low‐density polyimide foam

The ignition, flaming and smoldering combustion of low‐density polyimide foam have been studied using a cone calorimeter. Low‐density polyimide foam exhibits a high ignition resistance. The minimum heat flux for the ignition of flaming combustion ranges from 48 to 54 kW/m². This minimum heat flux also indicates the heat flux for transition from smoldering to flaming combustion. The flaming combustion results show that the heat release rate of low‐density polyimide foam is very low even at a high incident heat flux of 75 kW/m². The smoldering combustion results show that the smoldering of low‐density polyimide foam becomes significant when the incident heat flux is greater than 30 kW/m². The smoldering combustion of low‐density polyimide foam cannot be self‐sustaining when the external heat source is removed. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

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.     

Influences of 4ZnO·B2O3·H2O whisker based intumescent flame retardant on the mechanical,flame retardant and smoke suppression properties of polypropylene composites

In this work, the influences of 4ZnO·B₂O₃·H₂O zinc borate (ZB) whisker based intumescent flame retardant (IFR) containing ammonium polyphosphate and dipentaerythritol on the mechanical, flame retardant and smoke suppression properties of polypropylene (PP) composites were characterized by the universal testing machine, UL-94, limiting oxygen index (LOI), and cone calorimeter tests, respectively. The results indicate that only 1 phr of ZB could effectively improve the LOI value and slow down the burning rate of PP composite. The peak heat release rate, average of HRR, total heat release, peak smoke production rate, and total smoke production values are all decreased from 413.8 kW/m², 166.3 kW/m², 82.3 MJ/m², 0.0995 m²/s, and 17.9 m² for PPc/20IFR composite to 267.8 kW/m², 128.3 kW/m², 66.8 MJ/m², 0.0478 m²/s, and 12.6 m² for PPc/20IFR/1ZB composite, respectively. The scanning electron microscopy images, energy dispersive spectrometry, and Raman spectra of char residue reveal that ZB is helpful to form a compact and graphitized intumescent char residue so that the heat diffusion and oxygen transmission are greatly hindered. The thermogravimetry analysis-fourier transform infrared spectroscopy (TGA-FTIR) results show that less combustible volatiles and more H₂O vapor are generated with the appearance of ZB. Hence, the combustion mechanism in gas phase is suppressed.     

Evaluating the heat resistance of thermal insulated sandwich composites subjected to a turbulent fire

The fire structural response of sandwich composite laminates incorporating bio‐derived constituents subjected to a turbulent flaming fire was investigated. Fire structural tests were conducted on thermal insulated sandwich composites incorporating a thin surface‐bonded non‐woven glass fibre tissue impregnated with char‐forming fire retardant, ammonium polyphosphate. The sandwich composite laminates were loaded in compression at 10%, 15% or 20% of the ultimate compressive strength while simultaneously subjected to turbulent flames imposing an incident heat flux of 35 kW/m². Generally, the failure time increased with the reduced applied compressive load. The thermal insulated sandwich composite laminates had considerably improved fire resistance in comparison to their unmodified counterparts. The unmodified composites failed 96 s earlier than the thermal insulated specimens when the compression load was 10% of the ultimate compressive strength. The presence of ammonium polyphosphate at the heat‐exposed surface promoted the formation of a consolidated char layer, which slowed down heat conduction into composite laminate substrate. The fire reaction parameters measured via the cone calorimeter provided insights into the thermal response hence fire structural survivability of sandwich composite laminates. Copyright © 2015 John Wiley & Sons, Ltd.     

Combustibility of cyanate ester resins

Flaming and non‐flaming combustion studies were conducted on a series of polycyanurates to examine the effect of chemical composition and physical properties on the fire behavior of these crosslinked, char forming, thermoset polymers. Heats of complete combustion of the polymer and fuel gases were determined by oxygen bomb calorimetry and pyrolysis‐combustion flow calorimetry, respectively. Fire calorimetry experiments were conducted to measure the total heat released, the rate of heat release and the smoke generation in flaming combustion. Fire response parameters derived from the data include the thermal inertia, heat of gasification, effective heat of combustion and combustion efficiency. Halogen‐containing polycyanurates exhibited extremely low heat release rate in flaming combustion compared with the hydrocarbon resins yet produced significantly less smoke and comparable levels of carbon monoxide and soot. Published in 2005 by John Wiley & Sons, Ltd.     

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.     

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.     

Thermal insulation and anti-vibration properties of MoSi2-based coating on mullite fiber insulation tiles

Thermal protection materials with excellent thermal insulation properties and high reliability are crucial for aerospace vehicle. Mullite fiber insulation tiles coated with MoSi₂-borosilicate glass (MFIT@MoSi₂) were prepared by a simple slurry method. Results shown that the surface temperature rapidly reached 1043.1 °C under the heat flux of 450 kW/m², while the cold-surface remained at room temperature. The adjusting effects of MoSi₂-based coating on the thermal response and transfer properties of MFIT were investigated systematically. Compared with MFIT, the surface and internal temperatures of MFIT@MoSi₂ were obviously suppressed, due to the existence of MoSi₂-based coating with high emissivity, which effectively enhanced the thermal radiation of the surfaces. Finally, the structural reliability under coupled environment of heating (q₀ = 450 kW/m²) and random vibration with high magnitude (20–2000 Hz, Grms = 20 g) was also investigated. Destructive cracking and peeling of the coating were not observed, due to the excellent bonding strength between the coating and the substrate. The results provided an important basis for the potential application of insulation tiles with mullite fibers in aerospace vehicles and the design of lightweight thermal protection systems.     

Effect of boron carbide nanoparticles on the fire reaction and fire resistance of carbon fiber/epoxy composites

In this work the thermal behavior of a carbon-fiber composite impregnated with nano sized boron carbide based nanocomposites was investigated. First of all, the good dispersion and distribution of the particles in the matrix confirmed the effectiveness of the mechanical mixing. The presence of the ceramic filler did not affect the viscosity and the workability of the blends or the mechanical properties of the composites. The thermal stability of the fiber-reinforced materials was investigated by thermo-gravimetrical analysis in air and nitrogen. Their fire reaction was studied at different heat fluxes (35 and 50 kW/m²) by cone calorimeter while the flame resistance was evaluated trough residual mechanical properties after the exposition of the specimens to a direct flame of a torch (heat flux of 500 kW/m²). The experimental data suggested that boron carbide allows maintaining a residual structural integrity of the material after burning because of the chemical reactions that occur in the filler at high temperatures; the presence of boron carbide reduces the peak of heat release rate especially at higher heat-fluxes and improves the thermal stability of the composite hindering and retarding the thermal oxidation of the carbon fibers.     

An experimental investigation into the gasification reactivity of chars prepared at high temperatures

The gasification activities of three kinds of Binxian chars with carbon dioxide were studied at 1000–1300 °C and under atmospheric pressure in self-made thermal balance. The specific surface area of coal or chars was determined with BET methods during gasification. The results showed that the reaction rate of two rapid pyrolysis chars increases at the beginning and decreases subsequently with increasing carbon conversion at relatively high temperatures. The heating rate of coal has a significant effect on the gasification process. The activation energy of slow pyrolysis char varies between 160 kJ/mol and 180 kJ/mol during gasification. The activation energy of the two rapid pyrolysis chars displays a linear trend when the carbon conversion is less than 40% and decreases slowly afterwards.     

Studies on intumescent flame retardant polypropylene composites based on biodegradable wheat straw

Wheat straw (WS) has numerous advantages compared with traditional bioadditives such as starch and lignin. So in this work, based on WS and silica microencapsulated ammonium polyphosphate, flame retardant polypropylene/wheat straw (WSP) composites were prepared by melted blend method. Flame retardant and thermal properties of WSP composites have been investigated. The results of cone calorimeter show that peaks of heat release rate and total heat release of the flame retardant WSP composite decrease substantially compared with those of pure polypropylene. The peak of heat release rate value of the flame retardant WSP composite decreases from 1290.5 to 247.9 kW/m², and the total heat release value decreases from 119.4 to 46.3 MJ/m². Meanwhile, thermal degradation and gas products of the flame retardant WSP composite were monitored by thermogravimetric analysis and thermogravimetric analysis‐infrared spectrometry. The result of thermal analysis shows that the flame retardant WSP composite has a high thermal stability and has a 30.0 wt% residual char at 600°C. From this work, we hope to provide a method to prepare flame retardant polymer composites with a biodegradable natural material‐WS.     

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.     

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.     

Multifunctional deoxybenzoin-based epoxies: Synthesis,mechanical properties,and thermal evaluation

We describe 2,4,4′,6-tetrahydroxydeoxybenzoin (THDB) as a multifunctional cross-linker in conjunction with bis-epoxydeoxybenzoin (BEDB), affording new resins that combine excellent physical and mechanical properties with low flammability. The char residue and heat release capacity values of the cross-linked epoxies were measured by thermogravimetric analysis (TGA) and pyrolysis combustion flow calorimetry (PCFC), respectively. Resins fabricated from THDB exhibited low total heat release (13 kJ/g) and high char yields (34%), as well as good mechanical properties, making them suitable candidates for consideration in high performance adhesive applications. The desirable heat release and char yield properties of these structures are realized without the presence of any conventional flame retardant, such as halogenated structures or inorganic fillers that are commonly utilized in commercial materials.     

Chemical aspects of combustion toxicology of fires

This report describes work currently being carried out at the Fire Research Station, Borehamwood to Study the role of the fire atmosphere in causing incapacitation, injury and death of building occupants in fires. The work includes a detailed study of polymer degradation mechanisms (particularly synthetic) and product formation under carefully controlled laboratory conditions and fires, together with pathological and bioassay (in vivo) work being carried out elsewhere under contract. Analytical studies are reported using gas chromatography and mass spectrometry to identify the complex products formed during the controlled pyrolysis and thermal oxidative decomposition of butadiene-styrene latex rubber foam, polyacrylonitrile and polypropylene under low (30–400°C), medium (400–650°C) and high (700–900°C) temperature conditions. Studies are reported of the products formed during smouldering and flaming fires in an experimental 0.4 m³ fire chamber in an attempt to reproduce conditions relevant to the early stages of fires. In this way, chromatographic fingerprinting of the smouldering products from BS latex rubber foam, and the flaming products of wood wool and polypropylene are given and where possible the major components identified. The relevance of this analytical work in predicting the types of products likely to be encountered during various stages of burning is discussed. General information on the pathological studies and bioassay work being carried out at the Department of Forensic Medicine, University of Glasgow and at the Huntingdon Research Centre respectively are given in order to integrate the overall research programmes and methods of approach being adopted to give an insight into the very difficult area of toxicity assessment.     

Flaming pyrolysis model of the fixed bed cross draft long-stick wood gasifier

The future industrial development of biomass energy depends on the application of renewable energy technology in an efficient manner. Of all the competing technologies under biomass, gasifiers are considered to be one of most viable applications. The use of biomass fuel, especially biomass wastes, for distributed power production can be economically viable in many parts of the world through gasification of biomass. Since biomass, is a clean and renewable fuel, gasification gives the opportunity to convert biomass into clean fuel gas or synthesis gas for industrial uses. The preparation of feedstock for a gasifier requires time, energy and labour and this has been a setback for gasifier technology development. The present work is focused on gasification of long-stick wood as a feed material for gasifiers. This application makes reduction not only in the cost but also on the power consumption of feed material preparation. A 50 m³/h capacity gasifier was fabricated in the cross draft mode. The cross draft mode makes it possible to produce low tar content in producer gas. This cross draft mode operates with 180 W of blower supply for air to produce 10 kW of thermal output. The initial bed heights of the long-stick wood and charcoal are 58 cm and 48 cm respectively. Results were obtained for various flow conditions with air flow rates ranging from 20 to 30 m³/h. For modelling, the flaming pyrolysis time for long-stick wood in the gasifier is calculated to be 1.6 min. The length of the flaming pyrolysis zone and char gasification zone is found to be 34 cm and 30 cm respectively. The rate of feed was between 9 and 10 kg/h. Continuous operation for 5 h was used for three runs to study the performance. In this study we measured the temperature and pressure in the different zones as a function of airflow. We measured the gas flow and efficiency of the gasifier in order to determine its commercial potential for process and power industries.     

Thermal effect on surrounding combustibles in minivan passenger car fires

In the fire safety design of parking lots and buildings, estimating the possibility of fire spreading to surrounding combustibles, such as neighboring buildings and cars, is essential. The ignition possibility to surrounding combustibles can be predicted from the heat flux from a burning car to the combustibles. In this study, we conducted 2 full‐scale car fire experiments using minivan passenger cars and measured the heat fluxes to their surroundings. The cars were ignited at the rear bumper with 80 g of alcohol gel fuel. The windows were closed. Heat flux gauges were placed around the car to measure the heat flux in various directions. Cedar boards were placed next to the gauges, and burn damage to the boards was observed. When the windows shattered in succession, combustion in the passenger compartment became larger. At a distance of 50 cm from the burning car, the heat flux was greater than 40 kW/m², and most of the cedar boards were completely burned. At a distance of 1 m, the heat flux was 10 to 20 kW/m², and some of the cedar boards were burned. We devised a method for modeling the shape and temperature of flames in the burning cars. Furthermore, we propose a method for calculating heat fluxes in the lateral direction of the burning minivan passenger car, and we compared the calculated and measured heat fluxes as a means of verifying the proposed method. The shape of flame in the burning car was approximated as a rectangular prism to calculate the heat flux. The calculation results were in good agreement with the experimental results. The proposed method is expected to be useful for fire safety engineering.