In the coal mining industry, explosions or mine fires present the most hazardous safety threats for coal miners or mine rescue members. Hence, the determination of the mine atmosphere explosibility and its evolution are critical for the success of mine rescues or controlling the severity of a mine accident. However, although there are numbers of methods which can be used to identify the explosibility, none of them could well indicate the change to the explosion risk time evolution. The reason is that the underground sealed atmospheric compositions are so complicated and their dynamical changes are also affected by various influence factors. There is no one method that could well handle all such considerations. Therefore, accurately knowing the mine atmospheric status is still a complicated problem for mining engineers. Method of analyzing the explosion safety margin for an underground sealed atmosphere is urgently desired. This article is going to propose a series of theoretical explosion risk assessment models to fully analyze the evolution of explosion risk in an underground mine atmosphere. Models are based on characteristics of the Coward explosibility diagram with combining mathematical analyzing approaches to address following problems: (1) for an "not-explosive" atmosphere, judging the evolution of explosion risk and estimating the change-of-state time span from "not-explosive" to "explosive" and (2) for an "explosive" atmosphere, estimating the "critical" time span of moving out of explosive zone and stating the best risk mitigation strategy. Such research efforts could not only help mine operators understand the explosibility risk of a sealed mine atmosphere but also provide a useful tool to wisely control explosive atmosphere away from any dangers. In order to demonstrate research findings, case studies for derived models are shown and are also used to instruct readers how to apply them. The results provide useful information for effectively controlling an explosive underground sealed atmosphere.
European standards regulate the certification procedure for determining chimney class temperature and the distance at which to install chimneys from combustible materials. These standards prescribe the heat stress test and the thermal shock test. The high number of roof fires due to the presence of a chimney that have recently occurred in European countries seems to be due to a weak certification procedure. In this article, experimental tests and numerical simulations have been performed to highlight the major differences between real and test conditions to identify critical aspects of the current certification procedure. The influence of the position of the chimney in the test structure, the thermocouples’ positioning and the thermal shock test initial condition have been investigated. It has been shown that flammable materials’ temperatures measured in the certification procedure can be lower than those in real installations, and this is mainly due to the fact that exhaust gas temperature in the certification procedure of chimneys can be even 350°C lower than in real installations. Then, real installations represent a more severe condition.
Carbon fiber laminate composites have been utilized in the aerospace industry by replacing lightweight aluminum alloy components in the design of aircraft. By replacing low flammability aluminum components by carbon fiber laminates, the potential fuel load for aircraft fires may be increased significantly. A pyrolysis model has been developed for a Toray Co. carbon fiber laminate composite. Development of this model is intended to improve the understanding of the fire response and flammability characteristics of the composite, which complies with Boeing Material Specification 8–276. The work presented here details a methodology used to characterize the composite. The mean error between the predicted curves and the mean experimental mass loss rate curves collected in bench-scale gasification tests was calculated as approximately 17% on average for heat fluxes ranging from 40 to 80 kW m–2. During construction of the model, additional complicating phenomena were investigated. It was shown that the thermal conductivity in the plane of the composite was approximately 15 times larger than the in-depth thermal conductivity, the mass transport was inhibited due to the high density of the laminae in the composite, and oxidation did not appear to significantly affect pyrolysis at heat fluxes up to 60 kW m–2.
The usage of concepts in scientific communication is critical to our ability to inform the reader about work that has been performed. The significance and thus the quality of scientific discussion rely on the precise use of concepts. In this second part of a two-part paper, concerning the scientific basis of polymer fire retardancy, the proper use of concepts is addressed. Distinct concepts in flame retardancy are discussed, such as fire residue, the correlation of fire performance with char yield according to van Krevelen, catalysis, and wicking. Synergy is discussed in detail, as well as approaches to quantify it, due to its importance for flame retardant polymers. The preceding first paper (part 1) discussed the proper use of scientific terms, thermal analysis, and fire testing. Thus, together these two papers support the community by offering recommendations and addressing some of the most relevant points. They encourage to review scientific practice in the field of flame retardancy of polymers.
Approximately 80%–90% of all fire-related fatalities take place in residential occupancies. The risk groups are well known, but the effectiveness of different measures has been less investigated. In this article, fire investigations from 144 unintentional fatal residential fires have been systematically analyzed and technical measures that would have been effective in preventing each fatality have been identified. The result shows that, generally, a thermally activated suppression system (e.g. sprinkler) has the highest potential effectiveness (68%) followed by a detector-activated system in bedroom and living room (59%) or smoke alarm (37%). For smokers with home care, however, the potential effectiveness of a thermally activated suppression system and home smoke alarm was significantly lower (31% and 14%, respectively). This indicates that different measures are effective for different groups. In one-fifth of the cases, the victim could have evacuated but chose not to do so, primarily to attempt to extinguish the fire.
The advantage of utilizing modeling to study fire performance of textiles is the ability to conduct detailed studies of the effect of fabric characteristics on flame spread. First, two textile materials are chosen for modeling that exhibit two limit cases: complete flame spread (nylon 6,6/cotton fiber fabric) and self-extinguish (flame retardant rayon/nylon 6,6/para-aramid fiber fabric) in the standard vertical flame test (ASTM D6413). Parameter estimation for unknown model parameters is performed for these samples followed by a sensitivity analysis. Then a new sample is modeled—flame retardant cotton fiber fabric, flame retardant cotton. This modeling exercise shows that computational fluid dynamics modeling is capable of capturing the fire characteristics of different fabric samples in the vertical flame test only when the parameters are carefully estimated considering the modeling assumptions and approaches. Additionally, several areas for further investigation are proposed to improve simulation capability when conducting vertical flame test modeling with textile samples.
Two types of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-based halogen-free flame retardants, ODOPB (2-(6-oxid-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)-1,4-benzenediol) and DOPO-PhOH (1,10-bis(4-hydroxyphenyl)-methylene-bispheny-1-oxophosphine oxide), were synthesized and incorporated into polyisocyanurate–polyurethane foams to investigate their effects on the thermal stability and flammability of polyisocyanurate–polyurethane foams. The thermal properties of the foams were determined using thermogravimetric analysis. The results showed that when compared to the polyisocyanurate–polyurethane control sample, the onset degradation temperatures of the foams were the same and the residues improved upon the addition of ODOPB, while for the polyisocyanurate–polyurethane/DOPO-PhOH foams, the onset degradation temperature and the residues were both improved. Furthermore, the physical–mechanical properties, flame retardant behavior, and morphological properties of foams were studied using thermal conductivity tests, compressive strength tests, the limiting oxygen index, cone calorimeter, and scanning electron microscopy. It was confirmed that the polyisocyanurate–polyurethane/DOPO derivative foams had the best physical–mechanical properties and flame retardancy compared to the polyisocyanurate–polyurethane/dimethyl methylphosphonate foam with the same phosphorus content added. The introduction of ODOPB caused a deterioration of the compression strength. However, the compression strength did not change upon the addition of DOPO-PhOH. The limiting oxygen index value showed a linear relationship with the phosphorous content in the foams upon the addition of ODOPB or DOPO-PhOH. Moreover, upon the addition of 20 phr ODOPB, the peak heat release rate of the foam was 25% lower than the polyisocyanurate–polyurethane control sample, while the reduced rate of the polyisocyanurate–polyurethane/20 phr DOPO-PhOH sample was 35%. In addition, for both the polyisocyanurate–polyurethane/ODOPB and polyisocyanurate–polyurethane/DOPO-PhOH foams, a continuous covering formed on the surface of residues was observed, which would obstruct heat and combustible gases from being transferred to the unburned foams.
The key challenges of the wildfire firefighting were long-distanced and high-lifted fire events and limited water access in wildlands. This article proposed a new low-flow and high-lift firefighting approach for the application of wildfire near transmission lines. To solve the challenges, we developed a comprehensive firefighting equipment set which consisted of a high-effective suppressant agent with properties to prevent reignition and a mobile firefighting platform with long-distance and high-lift features. The liquid suppression agent improved the effectiveness of fire suppression while reducing the consumption of water significantly. As the hydraulic flow was decreased for a given volume of water, the hydraulic pressure was increased. In this way, the platform can produce a hydraulic pressure over 120 bar for an effective lift of 500 m. The results of field experiments demonstrated that the proposed approach is able to control wildfires over a long distance and high lift, which proved the effectiveness of the approach.
Previous experimental and numerical studies have demonstrated the unwanted promotion effect caused by potential halon replacements added to hydrocarbon–air mixtures. To explore this abnormal phenomenon, the chemical and physical contributions of the addition of C6F12O (Novec 1230) and C2HF5 (HFC-125) on the laminar flame speeds of the CH4–air mixtures are numerically investigated. Numerical simulations are conducted using the CHEMKIN-PRO software with newly developed fluorinated compounds’ mechanisms. Based on the interaction between the chemical effect and the physical effect, the equivalence ratio zone is divided into synergistic zone and antagonistic zone. Furthermore, the fuel-like characteristics of C6F12O and C2HF5 are also studied. In the lean CH4–air condition, the agents contribute to increasing the equivalence ratio, thus increasing the flame speeds chemically but cooling the mixture physically. When the actual equivalence ratio of the agent–CH4–air mixture is larger than 1.10 (for the C2HF5 addition) or 1.20 (for the C6F12O addition), the agents create an over-rich fuel mixture, thus decreasing the flame speed chemically. The contribution of the chemical effect is studied under different initial temperature and pressure conditions. The results indicate that increasing the temperature slightly lowers the chemical contribution, whereas increasing the pressure largely increases the chemical contribution. Additionally, a sensitivity analysis is conducted to interpret the large chemical component increase under high pressure conditions.
Fire-induced decomposition of composite materials used for aircraft structures involves complex and coupled multi-physics phenomena studied through conventional standard tests such as cone calorimeter, FAR25.856(b):2003 and ISO2685:1998(e), for instance. It is proposed to address this issue within controlled environment and accurate heat loading. Thermal response and damage evolution are investigated experimentally and numerically to analyse the anisotropic and heterogeneous behaviour of decomposing composite laminates subjected to laser heating and confined within the test chamber of the BLADE facility developed at ONERA. Accurate heat transfer measurements are correlated with numerical results from MoDeTheC solver and post-decomposition micrographic imaging in order to analyse the material thermo-chemical behaviour and identify the damage mechanisms.
Intumescent coatings are the present-day state-of-art techniques to protect steel structures and other structural materials from fire hazards. Thermal insulation properties of such protective materials are normally deduced from standard fire tests, however, with least reference to char integrity and strength. This work proposes a simple and resourceful in situ experimental protocol to evaluate char strength of intumescent coatings on steel panels during hydrocarbon time–temperature fire test (at about 1200°C). It is based on in-process monitoring the physical integrity, mechanical stability, and thermal insulation capacity of fully developed char under a stream of air (airjet) before steel plate reaches its critical temperature. A bench-scale furnace designed in our laboratory to reproduce hydrocarbon fire scenario (UL1709) was upgraded to simulate air turbulence to impact the char strength. Silicone- and epoxy-based coatings on steel panels were tested under these conditions. Silicone-based coatings are found to have several interesting advantages over the latter. Furthermore, this protocol was extended to investigate the compositional influence on char strength in a set of silicon-based coatings.
Rectangular pool fires are common in the liquid fuel storage and transportation industries, but the existing burning rate correlations are largely focused on circular pool fires. Through experimental means, this work measured the steady mass burning rates of both n-heptane and gasoline fires in large-scale rectangular pools with aspect ratios ranging from 0.5 to 4.0. The effects of pool width and aspect ratio on the mass burning rate were investigated. A modified model was developed to estimate the mass burning rate in a rectangular pool fire as a function of the pool width and the aspect ratio. Correlations for n-heptane and gasoline burning rates were proposed based on the experimental results. The comparisons between the presented correlations and the existed circular burning rate correlations were analyzed accordingly.
Knowledge of the course of an automobile fire is an important issue in automobile fire safety and can have a significant impact on fire safety measures in car parks and other structures with a high concentration of automobiles. In this article, computer simulations of fire in an automobile interior and its influence on an adjacent vehicle are investigated. The results of simulations are compared with the results of the measurements obtained during a full-scale fire experiment conducted in Povazsky Chlmec (Slovakia) in 2009. The comparison confirms the accuracy of the simulation. A parameter study related to some selected material properties, which shows that seat material properties are the most important for the fire development, is described. Due to high computational requirements, a parallel version of the calculation is studied, and the influence of parallelization on performance and accuracy is tested as well. As the glass breakage is one of the most important factors affecting the course of an automobile fire, a simple practical criterion to determine when window breakage will occur is proposed.
Along with the phase-out of CF3Br (Halon 1301), several agents have been proposed as halon replacements for use in suppressing fires in aircraft cargo bays. However, these potential drop-in replacements were found to have a promotion effect on the explosion of an aerosol can, which tested by the US Federal Aviation Administration. Motivated by this problem, we measured the laminar burning velocity of premixed methane/air flames with added one of these agents, C6F12O (Novec 1230), in the counterflow configuration, for fuel/air equivalence ratios of 0.63, 0.68, 0.74, and 0.82. C6F12O was added at levels up to 3.5% by volume fraction to each mixture. Numerical simulations were performed using the detailed kinetic mechanism. The predicted results were in good agreement with the experimental measurements. The burning velocity for the very lean flames ( = 0.63) was increased with C6F12O added at low concentrations due to the additional heat release from C6F12O reaction, whereas for higher equivalence ratios ( = 0.68–0.82), it always decreased with all added agent concentrations. The extinction stretch rates have also been measured using the counterflow technique to gain further insight into the promotion/inhibition behavior of C6F12O in ultra-lean ( < 0.63) flames. The results showed that C6F12O has larger promotion effect for the ultra-lean conditions. Sensitivity analyses showed that lean flames are more sensitive to the fluorinated reactions compared to the rich. In addition, direct images of hydrocarbon flame inhibition by fluorinated ketone were provided for the first time to help interpret the experiments.
Coal can maintain smoldering combustion for a long time in the gob (mined-out) area which is a serious threat to the safety mining of a coal mine. However, few literatures can be obtained to well understand the smoldering phenomena of coal. To obtain the coal smoldering characteristics, vertical forward and reverse smoldering tests under different air flow rate were performed, and the smoldering combustion process, speed, and temperature were analyzed. It is found that although the combustion process of forward and reverse smoldering is significantly different, their smoldering speeds are the same and both increase monotonically with air flow rate as the higher the air flow rate is, the greater the oxygen consumption rate can reach. Even when the air flow rate is 0.074 m/min in that the wind speed belongs to the suffocation zone of the gob, the coal can still undergo smoldering until complete combustion. This indicates that the smoldering fire cannot be effectively extinguished by only accelerating the stoping speed of the working face to create fire in the suffocation zone during the mining process. And for a sealed fire zone, it is also difficult for the smoldering fire to be completely extinguished as the fire zone cannot be absolutely sealed. Meanwhile, the risk of reverse smoldering is greater than forward smoldering due to its larger smoldering temperature.
Vegetal species emit biogenic volatile organic compounds at elevated temperatures. Because of their combustibility, biogenic volatile organic compounds can modify the wildland fires propagation dynamics, changing them from a moderate behavior to an explosive propagation. This phenomenon is known as an accelerating forest fire. The origin of such phenomena can be the accumulation of biogenic volatile organic compounds in concentrations close to their lower flammability limit in seasons where the plants are themselves very flammable. There is a lack of information on the biogenic volatile organic compounds emissions of vegetal species typically found in wildland fires at temperatures higher than ambient temperature. In this work, we used a flash pyrolysis device linked to a gas chromatograph/mass spectrometer to investigate experimentally the biogenic volatile organic compounds emissions of Thymus vulgaris, Lavandula stœchas, and Cistus albidus between 70°C and 180°C. High amounts of terpenoid compounds were found, except for C. albidus emissions, including thymol, l-fenchone, and 3-hexen-1-ol. The information provided in this work could help to improve the characterization of thermal degradation of vegetal fuels and to incorporate the biogenic volatile organic compounds combustion in physical forest fires models. They also show that under the right circumstances, biogenic volatile organic compounds from these vegetal species could contribute to the development of an accelerating forest fire.
In this work, the pyrolysis and piloted ignition behavior of thermally thick paulownia wood brick for different orientations has been experimentally investigated, by using the conical heater. Three typical orientations were adopted, that is, upward, downward, and vertical cases with the incident heat flux ranging from 12 to 39 kW/m2. A numerical approach was used to test the effect of heat convection and radiation blockage on pyrolysis. The ignition time was observed to be strongly dependent on orientation. In detail, the shortest ignition time turns to be for downward orientation, but longest ignition time for vertical orientation. Total mass loss at ignition is weakly dependent on orientation. Meanwhile, critical mass flux increases with external heat flux rising and varies somewhat with orientation.
This study developed a method of using pure helium to generate a cold buoyant plume as the surrogate of a fire smoke for the study of the smoke-filling process in an atrium. Aided by the numerical simulations, a series of experiments in a 1:26.5 scale model of the full-size atrium with the fires up to 1.6 MW from the literature were conducted to investigate the similarity between a helium smoke and a hot fire smoke. Helium concentrations, smoke layer heights, and smoke optical densities were compared well between the current experiment and the simulations. The experimental study thus verified the capability of a helium smoke test to reproduce the smoke-filling process of the corresponding hot smoke test in the atrium studied. This study also showed how to model a hot smoke test with a t-squared fire by the corresponding helium smoke test by pre-mixing helium and artificial smoke in a mixing box.
This article examines potential use of a new device called multi-directional heat flux and velocity probe for simultaneous measurement of heat flux and flame speed in a diffusion flame. The probe consists of a thin-wall spherical shell with internal insulation to mitigate internal convection. Both pressure and temperature distributions around the sphere are used to indicate local velocity and heat flux. The multi-directional heat flux and velocity probe appears to be a more promising device than the bidirectional velocity probe in the sense that the sphere is a regular geometry with minimum flow separation and should lead to more predictable behavior. However, an outcome of this study is that the device must be used in conjunction with a fire code computational fluid dynamics model because the boundary layer is not isothermal so that the conventional pressure coefficient for a sphere leads to erroneous results.
This article investigates flame height and axial temperature profile of a buoyant turbulent line-source jet fire plume. Previous correlations have been mainly for axi-symmetrical fire sources or linear pool-type (no initial momentum) fire sources. Experiments were carried out for this study using a 3 mm (width) x 95 mm (length) line-source nozzle with propane as the fuel. Flame heights and axial temperature profiles were measured for different heat release rates. It was found that the flame heights can be well correlated by flame Froude number with a 2/3 power function based on scaling analysis. A global non-dimensional four-regions correlation (continuous flame region, intermittent flame region, line-plume region, and axi-symmetric-plume region) is proposed to characterize the axial temperature profile of a line-source jet fire plume.
This study investigated the performance of three kinds of transition metal ions (Mn2+, Cu2+, and Zn2+) modified zeolite 4A particles in suppressing methane/air coflowing flames on cup burner. Ion-exchange method was employed to incorporate different amount of transition metal ions into parent zeolite 4A. Fire suppression effectiveness of zeolites containing varied molar percentage of metal ions was tested by cup-burner method. Results showed that transition metal ions modified zeolites outperformed the parent zeolite 4A with a ranking order of Mn2+ > Cu2+ > Zn2+. Performance of the zeolite particles was affected by the percentage of transition ions loaded, which dominated the number of active sites and Brunauer–Emmett–Teller surface area of the particles. Increasing molar percentage of metal ions loading increased the capacity to scavenge flame radicals, but decreased Brunauer–Emmett–Teller surface area of the particles. There existed an optimized molar percentage of transition metal ions loading where the best fire-suppressing effectiveness was exhibited.
Large-scale experiments of n-heptane and gasoline continuous spill fires were conducted in an open area to study the spread and burning behavior of continuous liquid fuel spill fires on water. The fuel was ignited immediately after being released from an oil tank. Flame features and radiation flux were investigated with different discharge rates. It was observed that the spill fire undergoes three phases including fire growth and fuel spread, steady burning, and the transition to extinction. Data indicate that the discharge rate largely governs the spill fire characteristics. The maximum value of pool fire size, flame height, fuel spread rate, time average burning rate, and thermal flux all increase with the discharge rate. The facilities and data presented in this work may provide a basis for the future modeling study and the prediction of the possible secondary disaster induced by liquid fuel spill fires.
The fire performance of curable silicone-based coatings containing expandable graphite, organoclay, and calcium carbonate is evaluated in cellulosic fire scenario (standard ISO834) using a lab-scale furnace test. It is shown that the use of organoclay and calcium carbonate allows achieving same insulative performance when compared with organic commercial intumescent coating. The mode of action of these silicone-based coatings is fully investigated using thermal analyses and spectroscopic analyses including X-ray photoelectron spectroscopy. It is shown that the high fire performance of intumescent silicone-based coatings is due to (1) interactions between calcium carbonate and silicone matrix increasing the thermal stability of the resin and (2) the formation of calcium silicate embedding the top of the char and permitting the formation of an additional protective ceramic layer.
In order to improve the fire resistance of a fluoroelastomer when used as an insulating material, a combination of a triazine-based polymeric charring-foaming agent and ammonium polyphosphate as a novel intumescent flame retardant system was employed. The additional effect of zinc borate and modifying resins (ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, epoxy resin and ketone-aldehyde resin) on its fire resistance and thermal decomposition behavior was studied. Upon exposure to a 1000°C flame, the use of zinc borate and ketone-aldehyde resin reduced the backside temperature of intumescent fluoroelastomer-coated steel specimens, indicating a beneficial effect. Thermogravimetric, muffle furnace pyrolysis, scanning electron microscope and X-ray photoelectron spectroscope results revealed that the ketone-aldehyde resin adjusted the thermal decomposition temperature of the fluoroelastomer to match with that of the intumescent flame retardant-zinc borate system; in this way, the char residue formed was not only increased in quantity but also showed improved integrity and thermal stability.
The purpose of this study is to investigate the effect of the surface modification of a layered silicate (magadiite) on the flammability of both polyurea and amine-cured epoxy resin. Based on the surface chemistry of magadiite, both quaternary alkyl ammonium and silane modifier can be employed for the organo-modification. Nanocomposites of both polymers were prepared via ultrasound-assisted in situ polymerization. Dispersion of magadiite was investigated through X-ray diffraction and high-resolution transmission electron microscopy. Thermal stability and flammability were evaluated by thermogravimetric analysis and cone calorimetry, respectively. The addition of small amount of magadiite resulted in significant improvements in flame resistance with not much change in thermal stability for both polymers. Ammonium-modified magadiite improves the flame resistance, whereas silane modification helps to increase time to ignition of both polymers.
This study deals with the process of smoke filling in a compartment and the exhaust of smoke through a doorway located in a side of the enclosure. This configuration is a typical scenario of smoke propagation during a fire event in a compartment. This study focuses on the vertical temperature stratification in the smoke layer and its consequences on buoyancy flow induced at the doorway. From two theoretical approaches, considering or not considering the vertical temperature stratification in the smoke layer, this study highlights how vertical temperature stratification may modify the doorway flow. The first approach is a well-mixed description considering constant temperature and thus no thermal stratification in the smoke layer. The second one describes the vertical density stratification with multilayer approach. The results show that the vertical stratification is the consequence of the process of air entrainment within the plume. The consideration of temperature stratification in the smoke layer changes the prediction of the flow through the doorway. A sensitivity analysis points out how two variables (the initial buoyancy flux and the dimension of the enclosure) modify this influence. The discussion improves the understanding of the stratification in an enclosure and gives new insight into the predictions of smoke propagation for fire safety applications.
Polymer composite sandwich core panels are of interest for lightweight construction and portable shelter use. In this article, material selection and construction design were considered for an application which required a high level of fire safety performance. Phenolic + fiberglass skin composites with balsa wood core sandwich panels were constructed and first screened for fire performance with the cone calorimeter (ASTM E1354) at different heat fluxes. From these data, fire testing in the room corner test (ISO 9705) was conducted. The results indicated that these composites could only pass the room corner test if an aluminum skin was used to provide some additional fire protection to the underlying composite. Furthermore, it was found that cone calorimeter testing at very high heat flux (100 kW/m2) was not always indicative of fire performance in the room corner test. How the aluminum skin was mechanically attached to the panel as well as underlying composite construction played an important role in the full-scale fire test results.
The accelerating forest fire phenomenon for two real accidents is studied. This phenomenon is investigated using the thermochemical hypothesis, based on the ignition of a biogenic volatile organic compounds cloud accumulated in canyons. By heating a Rosmarinus officinalis plant in a specific hermetic enclosure, a mixture of 14 biogenic volatile organic compounds is identified and their mass fractions determined as temperature functions. The theoretical flammability limits of those components are calculated by means of empirical correlations. Froude-scaling law is applied to laboratory emission results to find the concentrations of biogenic volatile organic compounds at field scale. The comparison of the flammability limits with the calculated concentrations at real scale using this changing-scale analysis shows that the emitted biogenic volatile organic compounds can lead to an accelerating forest fire.
Burning on flat plates was studied at various orientations with respect to gravity. Flat wicks of ceramic (Kaowool PM) board (10 cm wide and 1–10 cm long) were saturated with methanol or ethanol. Steady flames were obtained that ranged from boundary layer flames to plume-type burning. The onset of unsteady flow and transition to turbulence commenced at Grashof numbers of 106–107, increasing with decreasing angle (toward underside burning). The average burning rate per unit area was recorded along with the flame location. Experiments on polymethylmethacrylate were used for comparison with the liquid-wick results. The results roughly correlated with laminar pure convective theory, and improved results were indicated when the gravity term associated with the pressure gradient normal to the plate was included. Theoretical results by the integral method to reduce the partial differential equations to ordinary differential equations are presented.
Relationship between internal fire whirls generated in a vertical shaft model was studied. A vertical shaft model of height 145 cm was constructed. Four fuels including methanol, ethanol, propanol, and gasoline of different pool sizes were used. Ventilation was provided from a sidewall for onsetting internal fire whirl. In the experiments, the flame height and mass loss rate of fuel while burning the pool fires were observed to increase at the same time. A linear correlation between flame height and mass fuel burning rate can be found for different liquid fuels. A parameter α, which describes the burning rate, calorific value, and the pool size of liquid fuel, was used to develop the correlation between the burning rate and flame height. The flame height was found to be linearly correlated with α. However, the normalized average flame height was found to be roughly constant with different values of α.
The thermal stability and fire performance of polyurea with silylated α-zirconium phosphate and ammonium polyphosphate are studied. The addition of ammonium polyphosphate reduces the thermal stability of the composites with and without silylated α-zirconium phosphate. The peak heat release rate reduction is lower in microscale combustion calorimetry than in cone calorimetry, which suggests that some physical process, like the formation of a barrier, is the process by which fire retardancy is obtained. Based on cone calorimetry, the peak heat release rate reduction does not depend on the loading of the silylated zirconium phosphate, and the combination with ammonium polyphosphate is less effective than ammonium polyphosphate alone.
The effect of fuel depth on flame spread over aviation kerosene and the characteristics of the subsurface flow has been investigated using schlieren system and a high-speed camera. For flame spread over aviation kerosene, there are shallow pool and deep pool regimes separated by a fuel depth of 8 mm. For the shallow pool regime, the pulsation amplitude of the main flame and the precursor flame increases, but the pulsation frequency of the flames decreases with an increase in fuel depth. For the deep pool regime, fuel depth has no obvious effect on the flame pulsation and the ratio of the length to the depth of the subsurface flow. The theoretical model of the rate of the subsurface flow based on the surface tension effect agrees well with experimental values.
Reaction to fire of several intumescent Gaialene formulations (Gaialene is a polypropylene-grafted starch) was investigated by mass loss cone calorimeter. Formulations exhibiting promising results were optimized by a design of experiments using mass loss cone calorimeter, UL-94, and limiting oxygen index tests as response. It is shown that melamine-/ammonium polyphosphate–based formulations do not exhibit as good results as ammonium polyphosphate used alone. High performance is observed for 30 wt% ammonium polyphosphate: 60% reduction of the peak heat release rate, high limiting oxygen index (30 vol% O2), and UL-94 V0 ranking at 1.6 mm (V2 at 0.8 mm).
Light gauge steel frame wall systems are commonly used in industrial and commercial buildings, and there is a need for simple fire design rules to predict their load capacities and fire resistance ratings. During fire events, the light gauge steel frame wall studs are subjected to non-uniform temperature distributions that cause thermal bowing, neutral axis shift and magnification effects and thus resulting in a combined axial compression and bending action on the studs. In this research, a series of full-scale fire tests was conducted first to evaluate the performance of light gauge steel frame wall systems with eight different wall configurations under standard fire conditions. Finite element models of light gauge steel frame walls were then developed, analysed under transient and steady-state conditions and validated using full-scale fire tests. Using the results from fire tests and finite element analyses, a detailed investigation was undertaken into the prediction of axial compression strength and failure times of light gauge steel frame wall studs in standard fires using the available fire design rules based on Australian, American and European standards. The results from both fire tests and finite element analyses were used to investigate the ability of these fire design rules to include the complex effects of non-uniform temperature distributions and their accuracy in predicting the axial compression strength of wall studs and the failure times. Suitable modifications were then proposed to the fire design rules. This article presents the details of this investigation on the fire design rules of light gauge steel frame walls and the results.
Characterization of the heat transfer to a cask engulfed in pool fire is extremely important. Experiments are carried out on diesel pool fires of diameters 0.5, 0.7, and 1.0 m with stainless steel 304L thermal casks of different sizes. Net surface heat flux on the cask is estimated using one-dimensional inverse heat conduction problem code. Velocities of the pool fires are measured using bidirectional probe to estimate the convective heat transfer coefficient (h). The concept of adiabatic surface temperature, using plate thermometer, is applied to the pool fires and the thermal casks. By employing a mixed boundary condition (adiabatic surface temperature and h) in computational fluid dynamics package, transient temperature and heat flux of the cask are estimated. These predicted data are within 10% of the experimental results. This study demonstrates that the transient adiabatic surface temperature of the pool fire can be used to predict the behavior of the thermal cask engulfed in an open pool fire.
This article addresses the flame retardancy of polyurea using three different sulfonate salts, sodium diphenylamine-4-sulfonate, 3-(1-pyridinio)-1-propane sulfonate, and ammonium sulfamate, and their combination with some conventional flame retardants. Cone calorimetry and thermogravimetry are used for the evaluation of the flame retardancy and thermal stability. Among the sulfonate salts, ammonium sulfamate shows the best flame retardancy both alone and in combination. The conventional additives that have been used include ammonium polyphosphate, expandable graphite, aluminum diethylphosphinate, melamine polyphosphate, and a chloroalkylphosphonate, as binary and ternary mixtures at 15 wt.% total loading. The nonsulfur-containing binary system exhibits higher ignition time and better flame and smoke resistance than do the ternary mixtures.
Studies are reported using experiments and numerical simulation, quantifying ignition characteristics of wet wood exposed to radiation at different altitudes. Experiments were conducted separately at an altitude of 3650 m in Lhasa and an altitude of 30 m in Hefei. The comparative experiments indicate that ignition is more likely to occur in the low-pressure environment in Lhasa than in a normal atmospheric pressure environment. A numerical model has been established to simulate the pyrolysis of wet wood at different ambient pressures. In the model, moisture evaporation, the flowing of combustible gas, and pressure work are involved. The pressure effect on the kinetic reaction of pyrolysis is also analyzed and concluded to be insignificant for the pyrolysis process of a whole wood slab.
Flame spread experiments over poly(methyl methacrylate) slabs with different inclinations were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). It is shown that the flame spreads significantly slower in Lhasa than in Hefei. For steep slabs with inclination angles of 75° and 90°, the preheat length in Lhasa is longer than in Hefei, whereas for mild inclinations (30° and 45°), it is slightly shorter in Lhasa than in Hefei. The peak total heat flux received by the fuel surface is lower in Lhasa than in Hefei. The measured flame temperatures did not present significant difference. This is actually caused by the combined effects of combustion inhibition due to the low oxygen concentration and less soot formation caused by lower ambient pressure and oxygen concentration in the plateau region, which result in less heat loss by radiation. Based on the analysis, it is concluded that the slower spread behavior in Lhasa is mainly a result of the lower heat feedback level to the solid surface.
To investigate the fire behavior under low pressure, four configurations of cardboard box fires were comparatively tested in a sea-level city, Hefei, and a high-altitude city, Lhasa. During each test, mass burning rate, total heat release rate, multipoint flame temperature, and radiative heat flux were measured. From the experimental data, some specific fire behavior was observed that (1) the mass burning rate divided by fire base dimension can be correlated against the production of pressure-squared times length-cubed (P2L3) to the power of 0.31, (2) the heat of combustion is lower in Lhasa probably due to the incomplete solid pyrolysis limited by oxygen, (3) the dimensionless plume temperature is correlated against the dimensionless flame height with a pressure term to the power of –2.0, and (4) the relative flame temperature estimated from the radiative heat flux indicated that the overall flame temperature is higher in Lhasa.
Flash point, an important physical property of the flammable liquids, is one of the main indicators to evaluate the fire hazard. In this article, a series of field measurement at different altitudes were carried out by using a portable flash point–measuring apparatus. The six tested altitudes are 3650, 3950, 4250, 4500, and 4750 m in Tibet plateau and 58 m in Hefei, China. Both the theoretical analysis and the experiment results show that the reciprocal of flash point is in linear relationship with the altitude. This article also ranks the fire hazard class of the flammable liquids at different altitudes, based on the classification codes in China. The correlation of fire hazard with altitude is of practical use for the safety management of flammable liquids during production, storage, transport, and usage in high-altitude plateau and aviation environments.
The proposed method of forecasting a single-room fire growth based on inverse modelling relies upon the assimilation of temperature measurements at the doorway level from floor to soffit height. These measurements are processed in the context of a two-zone model to obtain transient profiles of neutral plane height, XN, and upper layer temperature, Tu. An additional correlation is used to deduce the smoke layer height, h, within the fire room. The obtained profiles of Tu, XN and h over a given period of time (the ‘assimilation window’) are used to estimate the fire growth factor, α, the time delay, t0, and the heat loss factor, c, with a two-zone inverse modelling procedure. Instantaneous displays of the future fire development are then delivered. Experimental data of four furniture fires in an ISO-room are analysed to illustrate the proposed forecasting methodology, which provides positive lead times between 20 and 235 s, depending on the fire growth rate.
This numerical study focuses on the fire phenomenology associated with the presence of a cylindrical object immersed, at one particular location and orientation, within a large aviation-fuel fire in a moving fluid medium. An extension of the eddy dissipation concept is incorporated, allowing to investigate the roles of the wind speed and its direction on the fire growth, heat flux distribution and smoke products, such as carbon monoxide and soot. The predicted flame shape compares well with the measurements. Moreover, the study has shed new light on the effect of the variation, which is erratic in nature, from the average wind direction on the heat flux distribution. The outcome of the study is interesting, and the interaction model between turbulence and combustion is indeed adequate. The prediction indicates that the interaction between the large object and fire environment combined with the influence of wind conditions affects the location of the continuous flame zone dramatically. The increase in the wind speed results in an alteration of the distribution of the incident heat fluxes to the surface of the engulfed cylinder for a case where the fire and object are of comparable size. The highest heat flux occurs on the windward side of the cylinder for the low and medium winds but on the leeward side of the cylinder for the high wind. The peak heat fluxes to the medium or high wind are almost equal in magnitude but about 50% beyond the ones to the low wind.
Heat transfer to compartment surfaces was measured in fully developed fire experiments. The experiments involved scaled compartments ranging from 1/8th to 3/8th with full-scale height of 2.54 m. Gas temperatures reached 1000°C, and total surface heat flux could reach 200 kW/m2, with convection accounting for 25% of the total. A combination of thermopile heat flux gage, metal plate sensor, and gas and wall thermocouples was used to separate the convective and radiative components. The convective heat transfer coefficients were resolved experimentally. Convective heat transfer coefficient was correlated against temperature rise within the compartment for both flaming and after extinction phases.
Gypsum is often used as passive fire protection. Indeed, its latent heat effect reduces heat transfer through the structure. To improve composition and physical properties of such material, it is necessary to model its behaviour. Heat and mass transfer have to be considered in the model. For a better understanding of phenomena occurring during a fire event, it is important to study the porosity. In this study, a porosity measurement protocol is developed. The porosity distribution along the thickness of large board sample subjected to standard fire (ISO 834) on one face is studied. In addition, scale effect is taken into account. Finally, the effect of temperature and microstructure are analysed.
A small steel box, whose size was 1.0 m x 1.0 m x1.0 m, was built for studying the flame characteristics of small pool fires. The pressure inside this box could be altered by a vacuum pump as a laboratory test rig. The fuels including gasoline and n-heptane were tested. The flame height and the flame pulsation frequency of the small-scale pool fires were experimentally determined. The results show that the flame height is proportional to the ambient pressure, and it will decrease with reducing ambient pressure. The flame pulsation frequency also decreased with reducing ambient pressure, and the laminar flame occurs when the ambient pressure is low enough. Some theory models were developed to explain this phenomenon in experiments.