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For more than a century, smoke explosions have been documented in the fire research literature. Yet even with this long history, smoke explosions have received very little attention in the fire research community. The few review articles on unexplained explosions (overpressure events) have adopted the conventional names of smoke explosions, backdraft, smoke gas explosions or rapid fire progression. Anecdotal evidence from firefighters have shown a number of overpressure events that cannot be explained as a gas leak or flammable liquids ignition. In this study, experiments were conducted in a plywood lined compartment with a timber crib as a sustained fire source and the ignition source. The compartment had a single vent that was open for the entire time. After an extended period of burning, the flames detached from the crib, traveled around the compartment, and finally self-extinguished. Sometime after the flames self-extinguished, the compartment erupted in flames culminating in a large horizontal flame projecting more than 2 m from the vent opening. In this study, a consistent cycle that leads to an overpressure event has been identified. A total of 29 overpressure events were created in 13 experiments with many experiments experiencing multiple overpressure events. Gas species, compartment temperatures, vent velocities, and compartment pressure were all recorded during the experiments. Conditions in the compartment immediately prior to the overpressure event are reported. Having demonstrated that an overpressure event within a combustible compartment can be reproduced, future research is recommended to better quantify the conditions leading to an overpressure event. [ABSTRACT FROM AUTHOR]

Self-compassion involves treating oneself with the same kindness, understanding, and forgiveness that one would typically offer a friend in times of suffering or adversity. While self-compassion has shown consistent benefits in research and therapy, including psychological and physical health benefits, some individuals practicing it may initially encounter adverse reactions known as "backdraft." Backdraft has been theorized to be an inevitable part of healing and recovery from past hurts and trauma. However, empirical studies specifically examining backdraft experiences in the context of self-compassion are lacking. This commentary argues that integrating broader literature outside of self-compassion is crucial for advancing our understanding of the causes of backdraft and identifying practices to alleviate it. Specifically, ideas drawn from traditional Buddhist practices and phenomena conceptually similar to backdraft, such as fear of self-compassion from compassion-focused therapy and adverse effects of meditation practices used in mindfulness-based interventions, should be considered. This commentary concludes that there is an urgent need to establish a clear definition of backdraft. This may promote empirical investigations of the backdraft experiences arising from self-compassion interventions. Only through empirical research can we better understand this backdraft phenomenon, with the ultimate goal of reducing short- and long-term harm and improving the efficacy of self-compassion programs. [ABSTRACT FROM AUTHOR]

The backdraft dynamics are numerically investigated using a proposed combustion model that attempts to accurately simulate the multi-combustion regime with a fast flame propagation in the inhomogeneous thermal condition. This scenario is often found in the limited-ventilation fires. The modeling strategy includes the flame-front tracking by the level-set function and the solution of non-adiabatic flamelet and a stratification parameter. In a comparison to the previous works, the present approach shows a better agreement with experiments. The results also underline the important effect of gravity current that promotes the rapid flame evolution in the case with less-dense initial mixture. Four different phases are identified based on the transient characteristics of backdraft, and they are (a) initial ignition, (b) free propagation, (c) limited-front propagation and (d) accumulation & flame-ejection. The dominant driving forces of buoyancy convection and turbulence effect on burning velocity are revealed. The backdraft process is found to encompass the initial premixed flame propagation and the diffusion burning outside the chamber following the formation of fireball. This work gains the valuable insights on the backdraft dynamics and provides useful information to design effective protection measures.

Backdraft is a special phenomenon in fire research because of its explosive consequence and the occurrence of uncertainty. The delay time of occurrence has been of interest in recent years as this influences the safety and efficiency of firefighting. This paper investigated the location of the opening and whether it affects the delay time of the backdraft. Results show that the location of the opening dramatically dominates the delay time. The hot/cold air mixing path and instantaneous localized fire ignitions determine the delay time. A 'curtain-like' effect for the backdraft time delay was observed. The lower opening demonstrates about 50–70 % delay time compared to the upper and middle locations. In the presence of identical fire conditions and door closure control, the extended flammable gas dilution resulting from the upper opening does not significantly impact the onset of backdraft. Hence, the effective volume above the ignition location determines the delay time of the backdraft. Furthermore, the choice of chamber material is a crucial factor influencing the likelihood of backdraft occurrence. Utilizing a material with enhanced cooling capacity reduces the probability of backdraft. This provides insight into the firefighting and intervention tactics when ventilation-restricted compartment fire occurs. [ABSTRACT FROM AUTHOR]

Backdraft is an explosive fire phenomenon which typically occurs during fire-fighting activities, occasionally leading to fire-fighter fatalities. Real backdraft incidents involve complex fuel gas mixtures consisting of the products of underventilated burning and pyrolysis following burnout. However, most experimental research into backdraft has used methane gas or flammable liquids as fuel. Some aspects of real backdraft behavior may have been overlooked as a consequence of this simplicity. A reduced scale series of compartment fire tests have been carried out to investigate the critical factors governing the onset of backdraft, using polypropylene and high density polyethylene samples as fuel. It is established that there are critical temperatures for auto-ignition of the pyrolysis gases leading to backdraft which vary with fuel properties. For polypropylene the highest temperature in the compartment must be above 350°C for auto-ignition of the fuel gases, while mixtures in the presence of a pilot source can be ignited down to about 320°C. Backdraft cannot occur when the compartment temperature is below 320°C. For polyethylene, the corresponding temperature for auto-ignition is 320°C. In parallel with these tests, a series of pyrolysis investigations have been carried out using the fire propagation apparatus, with FTIR gas analysis. The observed critical temperatures for backdraft correlate well with the evolved pyrolysis gases. Analysis shows that higher temperatures are required for backdraft when the CO/CO2 ratio is small, and that below the auto-ignition temperature, backdraft can only occur above a CO/CO2 ratio of about 35%. It is concluded that the crucial factors determining whether backdraft occurs or not are the maximum temperature and the CO/CO2 ratio in the compartment, prior to opening the door. [ABSTRACT FROM AUTHOR]

Smoke production, flashover and backdraft are the three main thermal phenomena that occur during fires. Produced by any fire, smoke is responsible for 90% of fire-related deaths. Flashover and backdrafts, on the other hand, occur in confined fires. Very difficult to predict, they account for many firefighter casualties. A few simple rules regarding construction and prevention in the home could limit the number and seriousness of fires. [ABSTRACT FROM AUTHOR]

Large eddy simulation (LES) was performed to investigate backdraft in reduced-scale compartments using the fire dynamics simulator. Mixing-controlled fast chemistry combustion model was adopted in the LES predictions of the backdraft phenomenon. The effect of the opening geometry of the compartment on the critical fuel percentage required for backdraft occurrence was numerically investigated by considering compartments with a door or a slot opening. The LES with the mixing-controlled fast chemistry combustion model provided reasonable results for the gravity current and backdraft development process in the reduced-scale compartments. The predicted results of the critical fuel percentage for backdraft occurrence were in good agreement with those obtained by previous experiments on door and slot opening geometries. The LES also predicted the trend in peak pressure with increasing fuel concentration inside the compartment reasonably well. The oxygen concentration of the entrained airflow inside the compartment affected the peak pressure during backdraft development. The peak pressures for the compartment with a slot opening were higher than those for a compartment with a door opening at the same fuel concentration. The difference in the peak pressures between the two compartment geometries was attributed to the difference in the entrained oxygen concentration caused by different ignition times. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical experiments on fire development and the backdraft phenomenon. The numerical model of fire development built with the use of Ansys Fluent was then validated based on literature data taken from real fire experiments. Some theoretical foundations of airflow and combustion modelling were added. Some features of the numerical model, which allowed for its high accuracy to be achieved, were widely discussed. Since large buoyancy forces were involved, to reproduce the decrease of the atmospheric pressure with height, a variable static pressure was applied using UDF (user-defined function).The results showed good accordance taking into account both the temperature profiles and the distribution of the airflow velocity. Once the model was validated, the research was extended to examine the backdraft phenomenon. The results revealed characteristic phases of the phenomenon and the occurrence of the gravity current as well, which were reported by empirical experiments.

This study investigates the burning history of medium-density fibre (MDF) cribs in an underventilated enclosure with two vertical openings in the front wall. Such compartment fires have been explored before by other researchers and demonstrated the conditions that would lead to smoke explosions (Sutherland, 1999; Chen, 2012) [1,2]. A total of 19 experiments were completed, 5 of which led to smoke explosions. A gas conditioning system is utilised for the experiments which included a hydrocarbon analyser and an enhanced Phi-meter. Heat release rate, mass loss rate, temperatures, pressures, and O 2 , CO 2 and CO gas concentrations within the compartment are measured for each experiment. Compartment fires with MDF crib fuel in underventilated conditions can lead to smoke explosions for both porosity-controlled and surface-controlled cribs. The smoke explosion is found to be occurring when the changes of pyrolysate gases and oxygen concentrations in the compartment form a flammable mixture. The equivalence ratio of the compartment was found between 1.5 and 2.0 before the occurrence of smoke explosions. Transformation of flaming combustion to smouldering was generally observed as a precursor for the accumulation of unburned fuel and the occurrence of smoke explosion. • Difference between smoke explosion and backdraft is reviewed. • The occurrence of smoke explosions is explained by experimental work. • Transition to smouldering was generally observed as a precursor of smoke explosion. [ABSTRACT FROM AUTHOR]

This work is aimed the evolution of the behaviour of a strongly contained wall fire in an enclosure during the postflashover period. It has characterised the fire intensity decay up to extinction of a wall fire by lack of oxygen and the effects of a sudden door opening on the formation of an air gravity wave capable to bring the backdraft phenomenon. To better understand these two sequential fire scenarios, the study was divided into two complementary parts performed in the same laboratory scale experimental setup. The first part consists to stabilise a steady wall fire at the rear of the compartment and to follow its evolution when a door closes the aperture leaving only a thin slot opened to limit the air entering. It has been observed the formation of a ghosting flame moving through the compartment before dying at the aperture. By supposing the continuation of the fuel solid pyrolysis after flame extinction due to the radiation of the hot environment, fuel vapours continue to fill the compartment. The second part will study the effects of a reopening of the door. It has been observed and characterised the formation and the propagation of a gravity wave through the enclosure. This is representative of the development of the first stage of the backdraft. Tests are performed to measure the aerodynamic properties of the flow behaviour.

Backdraft dynamics and effects of initial fuel mass fraction on backdraft behavior were studied computationally using fire dynamics simulator with a Model-free simulation (MFS). The effects of one- and three-step reaction mechanisms on backdraft development and temporal pressure variation were examined. Thermal radiation effects were studied by considering the gray-gas-radiation (GRAY) and adiabatic model (ADIA). The gravity current and backdraft development were reasonably reproduced by the MFS. The temporal pressure rise inside the compartment showed a similar trend to previous experiments. ADIA did not predict the local ignition near the bottom wall, while GRAY did predict. The critical fuel mass fraction (Yf) for backdraft occurrence was determined from the two-peak characteristic in the pressure, and the predicted Yf was reasonable, compared with the experiments. Complex mixed combustion modes were found locally during backdraft development. MFS with finite chemistry was found to be a potentially good computational tool for backdraft dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Safety & Fire Technology / Bezpieczeństwo i Technika Pożarnicza is the property of Centrum Naukowo-Badawcze Ochrony Przeciwpozarowej and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A letter to the editor is presented in response to the article “Theoretical Flammability Diagram for Analyzing Mine Gas" by Tingguang Ma and Michael D. Larrañaga published in the August 08, 2013 issue.

The backdraft development process in a reduced-scale compartment of 1.2 m × 0.6 m × 0.6 m was visualized computationally. A three-dimensional (3-D) model-free simulation was performed using the fire dynamics simulator (FDS) developed by the National Institute of Standards and Technology (NIST) along with a global finite chemistry combustion model. Backdraft development, involving the gravity current of inflowing air, flame ignition, and flame propagation, was reasonably visualized with FDS. Additionally, the explosive fireball behavior passing through an opened window was well-simulated with the finite chemistry combustion model. The model-free simulation created using the FDS program and global finite chemistry combustion model can be used as an effective tool for visualization of backdraft phenomena. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Compartment fires are commonly discussed in the classical sense with the compartment fire growth history starting with the incipient phase leading into the growth phase that transition through flashover into the fully developed phase and ends in the decay phase. However, when a fire starts in a closed compartment where only ventilation is the leakage available, the fire can start to smolder and produce large quantities of CO and unburned hydrocarbons. These products of incomplete combustion accumulate in the compartment and create an extremely hazardous condition. If the conditions are right and a large vent becomes available, such as a fire fighter opening a door, a rapidly developing flame front spreads through the enclosure burning the available fuel that has mixed with the incoming air, culminating in a large fireball outside the opening. This catastrophic event is known to fire fighters as a backdraft and by definition requires a sudden change it the ventilation. Anecdotal evidence supports a different phenomenon in which a closed compartment suddenly erupts in flames breaking glass and even causing structural damage without a vent ever being open. This phenomenon is referred to here as a smoke explosion. Recent work has focused on improving our understanding of these poorly understood events and the conditions that precede them. A series of small scale experiments have been conducted burning a timber crib inside an enclosure with tightly controlled ventilation. Under certain fire conditions, the compartment will suddenly erupt, ejecting smoke and flames from the small openings in the compartment. This paper describes the experimental results from the smoke explosion research and compares the smoke explosion to the more familiar phenomena known as backdraft. [Copyright &y& Elsevier]

Copyright of Safety & Fire Technology / Bezpieczeństwo i Technika Pożarnicza is the property of Centrum Naukowo-Badawcze Ochrony Przeciwpozarowej and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The backdraft experiments involved three full-scale room fire tests that used solid furnishing, loveseats. From experimental data, a backdraft caused two temperature peaks. The first one was below 600°C. Then, an abrupt opening of the front door led to a supply of a large amount of fresh air, followed by an indication of sudden temperature rise. The second peak temperature was over 600°C. Meanwhile, the deflagration resulted in the gases heating and expanding within the fire space, thus forcing unburned gases out of the vent ahead of the flame front. Comparing both cases with natural gas and solid loveseat as the fuel in backdraft, the former can achieve pre-mixture state and readily create an instant explosion wave phenomenon; however, this wave disappeared immediately. On the other hand, the solid loveseat used as the fuel in this study produced backdraft within 30-50 s after opening of the door. After the occurrence of backdraft, fire maintained a period of fully developed stage, which was consistent with the conditions in actual fires. [ABSTRACT FROM AUTHOR]

With the advances in building materials and practices through the building expansions of the 1980's and 90's, along with the inherent benefits of these improvements, some unwanted side effects have resulted as well. Indoor Air Quality (IAQ) issues ranging from mold and dust accumulations have become both a nuisance as well as, in some instances health issues to many homeowners who own houses with these inherent problems. One such chronic building issue is the result of the failure to recognize the house - heating (or combustion) appliance as a "System". This problem is known as "Depressurization Induced Combustion Re-Entry". Depressurization Induced Combustion Re-entry is the re-introduction of combustion emissions back into a structure as a result of negative air pressures developed by the structure as well as the location of the point of discharge of the emissions from the combustion appliance. Combustion appliances can be anything from a boiler, furnace or fireplace and this problem occurs regardless of the type of combustion fuel being consumed in the structure. This paper will address the root causes of Depressurization Combustion Re-Entry using excerpts of cases investigated and assisted in litigation The paper will also address house and system modifications that can be performed to reduce or eliminate the effects of Depressurization Induced Combustion Re-Entry. [ABSTRACT FROM AUTHOR]

This work is aimed the evolution of the behaviour of a strongly contained wall fire in an enclosure during the postflashover period. It has characterised the fire intensity decay up to extinction of a wall fire by lack of oxygen and the effects of a sudden door opening on the formation of an air gravity wave capable to bring the backdraft phenomenon. To better understand these two sequential fire scenarios, the study was divided into two complementary parts performed in the same laboratory scale experimental setup. The first part consists to stabilise a steady wall fire at the rear of the compartment and to follow its evolution when a door closes the aperture leaving only a thin slot opened to limit the air entering. It has been observed the formation of a ghosting flame moving through the compartment before dying at the aperture. By supposing the continuation of the fuel solid pyrolysis after flame extinction due to the radiation of the hot environment, fuel vapours continue to fill the compartment. The second part will study the effects of a reopening of the door. It has been observed and characterised the formation and the propagation of a gravity wave through the enclosure. This is representative of the development of the first stage of the backdraft. Tests are performed to measure the aerodynamic properties of the flow behaviour. [ABSTRACT FROM AUTHOR]

This paper is an attempt to integrate theoretical Computational Fluid Dynamics (CFD) calculations with practical fire-fighting tactics commonly used when arriving at the scene of an underventilated fire. The paper shows that CFD has a great potential in improving understanding and creating better effectiveness in the estimation of fire-fighting tactics. If burning has occurred in a lack of oxygen for a long time, excessive pyrolysis products may have accumulated in the fire compartment. If air is suddenly introduced in the compartment a backdraft may occur. The CFD code used for the simulations is fire dynamics simulator (FDS). In this paper, we focus on the conditions that can lead to backdraft, and not the deflagration or rapid combustion in itself. Therefore, the simulations focus on the gravity current and the mixing process between cold fresh air and hot smoke gases by considering a uniform temperature inside the building as initial condition. The different tactics studied include natural ventilation, positive pressure ventilation (PPV) and dilution by water mist. Their effectiveness is observed comparing them with a reference scenario, where no action is taken. The main objective of natural ventilation is to find the fire source, and the venting is more effective with several openings. Tactics involving PPV are very effective in evacuating the unburnt gases, but increases the mixing, and consequently the probability of backdraft during the early stage of operation. On the other hand, the addition of water mist can reduce the danger of backdraft by reducing the concentration of unreacted combustible gases below the critical fuel volume fraction (CFVF), where ignition cannot occur. If the dilution level is insufficient the danger of backdraft is increased, mainly because the process of gases evacuation is longer due to cooling, which reduces the density difference between hot and cold gases. During a fire-fighting operation, the choice of tactic depends mainly on whether there are people left in the building or not, but also on the fire-fighters’ knowledge of the building’s geometry and the fire conditions. If the situation shows signs of strongly underventilated conditions, the danger of backdraft has to be considered and the most appropriate mitigation tactics must be applied. [ABSTRACT FROM AUTHOR]

The phenomenon of backdraft is closely linked to the formation of a flammable region due to the mixing process between the unburned gases accumulated in the compartment and the fresh air entering the compartment through a recently created opening. The flow of incoming fresh air is called the gravity current. Gravity current prior to backdraft has already been studied, Fleischmann (, Backdraft phenomena, NIST-GCR-94-646. University of California, Berkeley) and Fleischmann (, Numerical and experimental gravity currents related to backdrafts, Fire Safety Journal); Weng et al. (, Exp Fluids 33:398–404), but all simulations and experiments found in the current literature are systematically based on a perfectly regular volume, usually parallelipedic in shape, without any piece of furniture or equipment in the compartment. Yet, various obstacles are normally found in real compartments and the question is whether they affect the gravity current velocity and the level of mixing between fresh and vitiated gases. In the work reported here, gravity current prior to backdraft in compartment with obstacles is investigated by means of three-dimensional CFD numerical simulations. These simulations use as a reference case the backdraft experiment test carried out by Gojkovic (, Initial Backdraft. Department of Fire Safety Engineering, Lunds Tekniska Högskola Universitet, Report 3121). The Froude number, the transit time and the ignition time are obtained from the computations and compared to the tests in order to validate the model. [ABSTRACT FROM AUTHOR]

A sub-grid scale model for partially premixed combustion has been implemented into an existing LES code and applied to simulate turbulent deflagration in backdraft and its mitigation by watermist in a scaled-compartment with different vent geometries. The model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion, while the flame index concept was used to separate the two different combustion regimes. Simulations were conducted for the reduced scale tests of Weng and Fan (2002). Reasonable agreements have been obtained for species concentrations, total mass outflow and inflow rates, maximum pressure, and likelihood of the occurrence of the fireball outside the container. The numerical study has highlighted the mitigation effect of watermist by reducing the laminar burning velocity of the mixture and the influence of the end opening geometries on the occurrence of backdraft. [ABSTRACT FROM AUTHOR]

Abstract: A sub-grid scale model for partially premixed combustion has been adapted and applied to simulate the backdraft phenomena. A fast deflagration or backdraft is produced when into a hot, fuel-rich compartment an inflow of fresh air is suddenly allowed through an opening. It is essentially a violent combustion process involving both premixed and non-premixed regimes. The present model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion. The ‘flame index’ concept was used to separate the two different combustion regimes. This index describes the structure of the flame based on fuel and oxygen gradients. Due to the lack of detailed experimental measurements, the results were largely analysed qualitatively. The predictions have provided valuable insight into the backdraft phenomenon suggesting that the development of backdraft can be divided into five phases, i.e. initial condition, free “spherical propagation, “plane” front propagation, stretching of the flame front through the opening and fireball outside the container. Quantitatively, the experimentally measured and predicted lapse of time between the maximum over- and under-pressure at the opening of the container is found to be in reasonably good agreement. [Copyright &y& Elsevier]

The article describes full-scale backdraft experiments in a shipping container using methane as a fuel. Numerical modelling has followed the experimental setup. The numerical simulations show the initial gravity current, the ignition, the spreading of flame in the enclosure, the external fireball, and the subsequent decay. The Detached Eddy Simulation (DES) approach has been used to model turbulence. In order to describe the combustion process of the mixture from the local ignition to progressive deflagration, three separate combustion models have been implemented for laminar, low- and high-intensity turbulence flow regimes. The calculated ignition time is slightly shorter than the average ignition time observed in the experiments. The fire front progresses through the combustible mixture, generating a cloud of hot gases that are accelerated from the container into the external environment. The velocity increases up to 20 m/s. When the fire front reaches the door, combustion continues outside the enclosure as the fuel has been pushed through the door. The comparison between the calculated time history of relative pressure and the pressure sensor record shows that the numerical simulations slightly overpredict the flame front speed, with a stronger pressure pulse and higher temperatures than the observations. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports preliminary computational fluid dynamics (CFD) simulations of backdraft observed in an experimental rig at Lund University. The analysis was performed with the CFX software using the Detached Eddy Simulation (DES) turbulence model, a hybrid of Large Eddy Simulation (LES) and RANS, in combination with the EDM combustion model. The DES model uses a RANS formulation in wall proximity to avoid computationally expensive grid resolution that is necessary for realistic LES predictions in wall layers. The preliminary results are qualitatively promising. The simulations began at the instant at which the door opens. A stream of fresh and cold air enters the enclosure as a gravity current. In the rig, ignition was triggered by flammable conditions existing at a wire, which was constantly heated. In the CFD model the ignition time is computed automatically when flammability conditions are reached inside the enclosure, at the wire, as part of the analysis. Subsequently, the fire front is formed. The deflagration expels fuel-rich mixture into environment, and the combustion continues outside the enclosure as a typical ‘secondary’ event. Considering that backdraft is a very complex phenomenon, the outcome is considered by the authors to be encouraging. [Copyright &y& Elsevier]

A dynamical model of temperature of hot smoke layer is quantitatively established based on the whole backdraft procedure induced by liquid fuel. The whole procedure consists of the preburn fire (the first period), the secondary fuel injection (the second period) and backdraft development (the third period). The model considers enthalpy loss of liquid fuel volatilization and hot smoke layer mass gain. In this paper, simulative results of the model are well compared with experimental results, and simulative results of the model are analyzed. Furthermore, combustion efficiency under limited ventilation and practical combustion reaction rate are worth investigating. [ABSTRACT FROM AUTHOR]

Abstract: Flame spread after air is suddenly introduced to a vitiated compartment in backdraft is between non-premixed and premixed flame spread under a ventilation-controlled condition. And it is necessary, but difficult to numerically simulate it. In this paper, an attempt of backdraft simulation is introduced. Numerical models including a subgrid scale laminar flamelet model and a partially premixed model are imbedded in FDS3.0 source code for backdraft simulation. Some significant fire characteristics reported in previous backdraft experiments can be seen in the numerical results. It is also indicated that these combined models can be used to predict the partially premixed combustion and fire phenomena under ventilation-controlled conditions. [Copyright &y& Elsevier]

The backdraft phenomenon in room fires is a typical example of nonlinear behavior. In this paper, a simplified mathematical model of the backdraft phenomenon is established based on energy balance equation and the dimensionless model equations are presented using concepts of nonlinear dynamical system theory, the nonlinear dynamical mechanism is analyzed, and the relationship between system control variables and fire conditions is studied. [Copyright &y& Elsevier]