Experimental study on heat release rate measurement in tunnel fires

Knowledge about the heat release rate (HRR) is essential for studying tunnel fires. The standard method in ISO 9705 is widely applied to calculate the HRR of combustion by measuring the consumption of oxygen in a fire. However, the studies of HRR measurement in full‐scale tunnel fires are rare because of the complication and costs of large experiments. This paper presents a system based on the principle of oxygen consumption calorimetry for the measurement of HRR and total heat release (THR) of full‐scale fires in tunnels. A total of 22 fire experiments are performed in a large‐scale ventilated testing metro tunnel with dimension of 100.0 m × 5.5 m × 5.5 m to validate the reliability and effectiveness of this system. Firstly, four oil spray fire tests are conducted with nozzle flow of 106 L/h at (1 ± 0.1) MW HRR to calibrate the instrumentation. Then, 18 full‐scale fire tests using square diesel pools at five sizes (0.5, 1.0, 2.5, and 5.0 m²) and wood cribs as fire sources are carried out for the measurement of HRR and THR. Results provided by the comparison between the measured HRR and THR values of the fire tests and the theoretically calculated ones show that our system works effectively in the HRR measurement of full‐scale fires in tunnels.     

用锥形量热仪研究聚氨酯泡沫的阻燃性能

在50 kW/m2辐射功率下,利用锥形量热仪研究了氢氧化铝、卤系阻燃剂、氮系阻燃剂和磷系阻燃剂阻燃聚氨酯泡沫(PUF)的阻燃特性,获得了点燃时间、最大热释放速率、总热释放、比消光面积及质量损失速度等参数。结果表明,将热释放速率、燃烧总释放热和烟气释放量作为材料阻燃性能好坏的评价指标,阻燃剂聚磷酸铵（APP）和三聚氰胺磷酸盐（MP）是PUF的理想阻燃剂。     

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.     

Effect of curprous oxide in combination with molybdenum trioxide on smoke suppression in rigid poly(vinyl chloride)

Further investigation of the synergistic effect of smoke suppression between cuprous oxide and molybdenum trioxide in rigid poly(vinyl chloride) (PVC) was carried out by using a cone calorimeter (cone) at a high incident heat flux of 50 kW m^?2. Experimental data derived from the cone calorimeter indicated that binary mixtures of Cu₂O and MoO₃ clearly showed the synergistic effect in reducing smoke by decreasing total smoke production (TSP), average specific extinction area (av‐SEA), and smoke production rate (SPR). This result is in good agreement with that obtained from the NBS smoke chamber. However, the combustion process of rigid PVC could clearly be seen from the heat release rate (HRR), curve, SPR, and fire degradation obtained from the cone test, which could not be determined from the NBS smoke chamber. It was also found that the binary mixture showed the synergistic effect by increasing was also found that the binary mixture showed the synergistic effect by increasing char residue and reducing the fire degradation of the PVC backbone at a high incident heat flux of 50 kW.m^?2. All experimental data well supported the early cross‐linking mechanism of the PVC backbone mentioned in the literature and were consistent with the fire degradation behavior obtained from the cone calorimeter.     

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.     

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.     

Fire performance and post‐fire mechanical properties of polymer composites coated with hybrid carbon nanofiber paper

In this study, glass fiber reinforced polyester composites were coated with carbon nanofiber/clay/ammonium polyphosphate (CCA) paper and carbon nanofiber/exfoliated graphite nanoplatelets/ammonium polyphosphate (CXA) paper. The composites were exposed to a heat flux of 35 kW/m² during the cone calorimeter testing. The testing results showed a significant reduction in both heat release rates and mass loss rates. The peak heat release rate (PHRR) of CCA and CXA composite samples in the major decomposition period are 23 and 34% lower than the control sample, respectively. The time to reach the PHRR for the CCA and CXA composite samples are ～ 125% longer than the control sample. After the composite samples were exposed to heat for different time periods, their post‐fire mechanical properties were determined by three‐point bending testing. The three‐point bending testing results show that the composite samples coated with such hybrid papers exhibit more than 20% improvement in mechanical resistance at early stages of combustion. The mechanism of hybrid carbon nanofiber paper protecting the underlying laminated composites is discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Experimental study on fire properties of interior materials used in low‐floor light‐rail trains

In this work, cone calorimeter tests were conducted to investigate fire properties of interior materials (floor covering [FC], aluminum plate covered with paint [APCP], light diffuser [LD], and gel coat [GC]) used in low‐floor light‐rail trains. Ignition time (t_ig) of each material decreases with the increase of radiative heat flux. The decreasing order of the four samples by ignition time under the same radiative heat flux is LD > APCP > FC > GC. The heat release rate (HRR), peak value of HRR (PHRR), time from ignition to PHRR (t_p), fire growth rate index (FIGRA), and fire growth index (FGI) rise with the increasing radiative heat flux. For the FC, LD, and GC, single HRR peak is observed in the HRR history while three peaks are observed for APCP. For PHRR, LD > FC > APCP > GC, while for t_p, GC < FC < APCP < LD. Under most conditions, the FIGRA and FGI of the FC is the highest among the four materials. Results of this work are beneficial to evaluate fire hazard of low‐floor light‐rail train and determine the emphasis of fire prevention.     

利用锥形量热仪研究聚氨酯硬泡的燃烧性能

利用锥形量热仪对硬质聚氨酯泡沫(RP UF)的燃烧特性进行了研究.通过对RP UF燃烧过程中的热释放速率、热释放总量、烟生成速率和总产烟量等进行系统性测试,讨论了聚醚多元醇、聚酯多元醇以及异氰酸酯指数(R值)对RP UF热危险性和烟气危险性的影响.结果表明,聚酯多元醇替代聚醚多元醇制备的RP UF燃烧过程中的热释放速率...     

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.     

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.     

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.     

Heat release rates of modern residential furnishings during combustion in a room calorimeter

Results are presented from a number of fire experiments that were conducted in a room environment to study the fire characteristics of typical residential furnishings and assist in the design of a subsequent phase of a project involving fully furnished room fire experiments. The experiments were conducted in a 16‐m² test room (with dimensions 3.8 m wide × 4.2 m long × 2.4 m high), which had a 1.5 × 1.5‐m window opening. The furnishings tested included mattresses, bed clothes, bed assemblies, upholstered seating furniture, clothing arrangements, books, plastic audio/video media and storage cases, toys, shoes, and a computer workstation setup. The smoke (gaseous products of combustion) from the room was collected using a hood system in order to measure the heat release rate (HRR) and optical density of the smoke. The test room was instrumented with load cells, heat flux gauges, thermocouples and velocity probes in order to take the following measurements: mass loss, total heat flux on gauge‐installed flush with the internal surfaces (floor, walls, and ceiling), temperatures at numerous locations, and gas velocities in the window opening. Twin‐size mattresses produced peak HRRs of approximately 3800 kW, and the maximum room temperature was approximately 980°C. The HRRs of bed assemblies of various sizes and configurations ranged from 1800 kW for a twin‐size bed to 6250 kW for a bunk bed. The maximum temperature and heat flux recorded in the experiments were 1071°C and 221 kW/m², respectively. Upholstered chairs and sofas had HRRs ranging from 630 kW for an ottoman to 3360 kW for a two‐seat sofa. In tests with clothing, toys, shoes, books, a computer workstation, and CD/DVD media, the peak HRRs ranged from 440 kW for a bookcase to 2045 kW for toys. Furnishings containing a large proportion of rigid thermoplastic plastics, such as shoes and media cases, produced very dense smoke even at low HRRs. The effect of parameters such as bed clothes, mattress type, foundation type, bed assembly and chair size, material composition, and fuel package arrangement was evident in the results. Because the room dimensions and wall lining materials remained constant, temperatures were linearly proportional to the peak HRR (and exposure time) until the ventilation limit (approximately 4100 kW) was reached. Copyright © 2014 John Wiley & Sons, Ltd.     

淀粉改性PBS的燃烧性能研究

在35 kW/m2热辐射功率下,研究了淀粉含量对聚丁二酸丁二醇酯(PBS)燃烧性能的影响。结果表明:PBS/淀粉的总热释放量(THR)、热释放速率(HRR)和有效燃烧热(EHC)随着淀粉含量的增加先降低再升高。当PBS与淀粉的质量比为10:2时,PBS/淀粉的燃烧性能最好。比较了PBS、PBS/淀粉和PBS/木粉在同样条件下的燃烧情况,其HRR的大小为:PBS/木粉>PBS>PBS/淀粉,而生烟速率SPR的顺序为:PBS>PBS/木粉>PBS/淀粉。     

Applicability analysis of mathematical models for the combustion characteristics in the pool fire

A pool fire characterized by high temperature and heat radiation, is a common accident in chemical industry. The important combustion characteristic parameters are the heat radiation flux, the burning rate, the flame height, etc., but the most significant one is the heat radiation flux. The calculation model of the pool fire has an important role to assess the accident. There are three types of widely used pool fire models, the Shokri and Beyler model, the Mudan model, and the point source model. The models are used to calculate the combustion parameters of three different kinds of oils in tanks of different scales. The predictions of three models are compared with the simulation results. The analysis shows that the point source model has a large error for pool fires with the diameter greater than 10 m and the thermal radiation flux smaller than 5 kW/m², and the model is more applicable to heavy crude pool fires. The scope of application of the Mudan model is broader, and this model ensures higher accuracy if the thermal radiation flux is smaller than 5 kW/m². The Shokri and Beyler model is more suitable for the case where the pool fire diameter is greater than 40 m and the thermal radiation flux is above 5 kW/m², and the results for the light crude pool fire based on this model are more reasonable.     

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.     

Influence of char-forming lignin in combination with aluminium phosphinate on thermal stability and combustion properties of polyamide 11 blends

Polyamide 11 (PA) blends based on char-forming industrial lignin and aluminum phosphinate (AlP) were prepared to improve flame retardant (FR) properties using a green and eco-friendly approach. This study investigates the thermal degradation and combustion behavior of PA blends prepared by using AlP in combination with two different types of industrial lignins (i.e., kraft lignin (DL) and lignosulphonate lignin (LL). Thermogravimetric (TG) analysis showed that ternary blends containing LL and AlP developed higher char residue up to 10.7 wt% upon decomposition in inert atmospheres. The combination of lignin and AlP increases the thermal stability by shifting the initial decomposition temperature (T_5%) and temperature at maximum decomposition (T_max) to a higher temperature range, attributed to the stabilization of decomposition products. Furthermore, combustion behavior studied by cone calorimeter (forced combustion) and pyrolysis combustion flow calorimeter (PCFC) tests presented a significant reduction in the peak of heat release rate (PHRR) and total heat release (THR). It was found that LL and AlP-containing blends more effectively decreased fire parameters like PHRR and THR than that of DL and AlP-containing blends. The best interaction with reduced fire-retardant properties was obtained when 10 wt% loading of lignin (DL/LL) and AlP was used. The reduction in heat release parameters was mainly ascribed to the condensed phase mechanism by forming an efficient protective char layer, which acts as a barrier against heat and mass transfer between the condensed and the gas phases. Raman spectroscopy analysis also confirmed the formation of the protective graphitic layer in the condensed phase.     

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     

The synergistic performance of multiwalled carbon nanotubes and sepiolite nanoclays as flame retardants for unsaturated polyester

The synergistic effect on the thermal decomposition and heat release rate (HRR) in particular the peak heat release rate (PHRR) of unsaturated polyester (UP) resin blended with multiwalled carbon nanotubes (MWNTs) and sepiolite nanoclay was investigated using thermal gravimetric analysis (TGA), pyrolysis combustion flow calorimetery (PCFC) and the cone calorimetery. Initial microcalorimeter findings established a synergistic effect for ternary system comprising a 10:0.5 wt% mixture of sepiolite:MWNT, respectively, which resulted in a 40% reduction in heat release capacity (HRC). This result was also confirmed within the well‐established cone calorimeter by a 50% reduction in PHRR in contrast to unfilled UP. The mechanism behind this reduction is thought to be due to the bridging of the MWNTs between the sepiolite clay needles, creating a tight protective surface layer that reduces the MLR. TGA also confirmed the advantage of such a ternary system through a 36^°C shift in the onset decomposition temperature and an 11% increase in residual char. Copyright © 2010 John Wiley & Sons, Ltd.     

Red phosphorus–controlled decomposition for fire retardant PA 66

The thermal degradation and the combustion behavior of glass fiber–reinforced PA 66 materials containing red phosphorus were investigated. Thermogravimetry (TG), TG coupled with FTIR, and TG coupled with mass spectroscopy were used to investigate the thermal decomposition. The flame retardant red phosphorus was investigated with respect to the decomposition kinetics and the release of volatile products. The combustion behavior was characterized using a cone calorimeter. Fire risks and fire hazards were monitored versus external heat fluxes between 30 and 75 kW/m². Red phosphorus acts in the solid phase and its efficiency depends on the external heat flux. The use of red phosphorus results in an increased amount of residue and in a corresponding decrease in total heat release. The decrease of the mass loss rate peak results in a corresponding decrease of the peak heat release. With increasing external heat flux applied the first effect on the total heat release decreases linearly, whereas the second effect on the peak heat release expands linearly. The investigation provides insight into the mechanisms of how the fire retardant PA 66 is achieved by red phosphorus controlling the degradation kinetics. Taking into account that a decrease of the volatile products also leads to a decrease of heat production in the flame zone and that the char acts as heat transfer barrier, a reduced pyrolysis temperature is suggested as a further feedback effect. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2060–2071, 2002