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Showing papers in "Fire Technology in 2020"


Journal ArticleDOI
TL;DR: In this article, the authors focus on the latest fire-safety issues of EVs related to thermal runaway and fire in Li-ion batteries and provide a qualitative understanding of the fire risk and hazards associated with battery powered EVs.
Abstract: Over the last decade, the electric vehicle (EV) has significantly changed the car industry globally, driven by the fast development of Li-ion battery technology. However, the fire risk and hazard associated with this type of high-energy battery has become a major safety concern for EVs. This review focuses on the latest fire-safety issues of EVs related to thermal runaway and fire in Li-ion batteries. Thermal runaway or fire can occur as a result of extreme abuse conditions that may be the result of the faulty operation or traffic accidents. Failure of the battery may then be accompanied by the release of toxic gas, fire, jet flames, and explosion. This paper is devoted to reviewing the battery fire in battery EVs, hybrid EVs, and electric buses to provide a qualitative understanding of the fire risk and hazards associated with battery powered EVs. In addition, important battery fire characteristics involved in various EV fire scenarios, obtained through testing, are analysed. The tested peak heat release rate (PHHR in MW) varies with the energy capacity of LIBs ($$E_{B}$$ in Wh) crossing different scales as $$PHRR = 2E_{B}^{0.6}$$. For the full-scale EV fire test, limited data have revealed that the heat release and hazard of an EV fire are comparable to that of a fossil-fuelled vehicle fire. Once the onboard battery involved in fire, there is a greater difficulty in suppressing EV fires, because the burning battery pack inside is inaccessible to externally applied suppressant and can re-ignite without sufficient cooling. As a result, an excessive amount of suppression agent is needed to cool the battery, extinguish the fire, and prevent reignition. By addressing these concerns, this review aims to aid researchers and industries working with batteries, EVs and fire safety engineering, to encourage active research collaborations, and attract future research and development on improving the overall safety of future EVs. Only then will society achieve the same comfort level for EVs as they have for conventional vehicles.

303 citations


Journal ArticleDOI
TL;DR: This review is focused on video flame and smoke based fire detection algorithms for both indoor and outdoor environments and the latest trend in literature which focuses on the hybrid approach utilizing both handcraft feature, and deep learning approaches is discussed.
Abstract: This review is focused on video flame and smoke based fire detection algorithms for both indoor and outdoor environments. It analyzes and discusses them in a taxonomical manner for the last two decades. These are mainly based on handcraft features with or without classifiers and deep learning approaches. The separate treatment is provided for detecting flames and smoke. Their static and dynamic characteristics are elaborated for the handcraft feature approach. The blending of the obtained features from these characteristics is the focus of most of the research and these concepts are analyzed critically. A fusion of both visible and thermal images leading to multi-fusion and multimodal approaches have conversed. It is a step towards obtaining accurate detection results and how the handcraft feature approach tackles the problems of flame and smoke detection, as well as their weaknesses are discussed which are still not solved. Some of these weaknesses can be tackled by developing a technology based on artificial intelligence named deep-learning. Its taxonomical literature study with a focus on the flame and smoke detection is presented. The strengths and weaknesses of this approach are discussed with possible solutions. The latest trend in literature which focuses on the hybrid approach utilizing both handcraft feature, and deep learning approaches is discussed. This approach aims to minimize the weaknesses still present in the current systems.

100 citations


Journal ArticleDOI
TL;DR: In this article, the authors review the recent understandings of the fundamental combustion processes in wire fire over the last three decades and highlight the complex role of the metallic core in the ignition, flame spread, burning, and extinction of wire fire.
Abstract: Electrical wires and cables have been identified as a potential source of fire in residential buildings, nuclear power plants, aircraft, and spacecraft. This work reviews the recent understandings of the fundamental combustion processes in wire fire over the last three decades. Based on experimental studies using ideal laboratory wires, physical-based theories are proposed to describe the unique wire fire phenomena. The review emphasizes the complex role of the metallic core in the ignition, flame spread, burning, and extinction of wire fire. Moreover, the influence of wire configurations and environmental conditions, such as pressure, oxygen level, and gravity, on wire-fire behaviors are discussed in detail. Finally, the challenges and problems in both the fundamental research, using laboratory wires and numerical simulations, and the applied research, using commercial cables and empirical function approaches, are thoroughly discussed to guide future wire fire research and the design of fire-safe wire and cables.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of aerogel, liquid cooling plate, and their combination on the prevention mechanism of thermal runaway propagation were investigated on the battery modules of electric vehicles, and the characteristics of temperature, voltage, mass loss, and venting were compared and analyzed.
Abstract: Preventing thermal runaway propagation is critical to improve the fire safety of electric vehicles. Experiments are conducted on the designed battery modules to study the effects of aerogel, liquid cooling plate, and their combination on the prevention mechanism of thermal runaway propagation. The characteristics of temperature, voltage, mass loss, and venting during the thermal runaway propagation process are compared and analyzed. The results indicate that: (1) adding the insulation material of aerogel can postpone the thermal runaway propagation, but may not completely cut-off the propagation process; (2) there is no obvious delay of thermal runaway propagation by adding the liquid cooling plate only, the propagation speed may be accelerated instead; (3) the thermal runaway propagation can be prevented by using aerogel and liquid cooling plate together. The study reminds us that safety design of battery thermal management system should consider the comprehensive heat transfer pathways in order to effectively prevent thermal runaway propagation.

52 citations


Journal ArticleDOI
TL;DR: A review of the state of the art on regulations, codes, plans and recommendations on WUI fire prevention and management in Spain is presented in this paper, highlighting the shortcomings due to the current lack of building and urban planning standards and technical codes for WUI communities.
Abstract: Southern Europe is recurrently being hit by forest fires affecting wildland–urban interface (WUI) areas which, particularly in the last decade, have resulted in tremendous consequences. In the years to come, self-protection of communities will be a first priority over fire suppression, demanding better fire-resistant and resilient WUI scenarios through actions grounded on solid and sound regulations and legislation. As of today, the European Union as a whole, and the Member States in particular, are belatedly articulating new and appropriate regulations and implementing policies for the protection of WUI areas against forest fires. Spain is one of the EU Member States, holding 1.1 million ha of WUI areas (above 4% of the total forested land) and experiencing an average of 12,500 forest fires per year over the past decade. In this paper a review of the state of the art on regulations, codes, plans and recommendations on WUI fire prevention and management in Spain is presented. Shortcomings due to the current lack of building and urban planning standards and technical codes for WUI communities are highlighted. We underline some paramount needs to be covered by scientific research and fire engineering in particular topics. Some of them have received little attention in the literature related to European WUI fires while some others have been almost unexplored, such as planning of low-fuel fringes, design of road networks and accessibility, dimension of water supply networks, study of ignitability and combustibility of residential vegetation, role of construction methods and materials, and the wildland–industrial interface. Outcomes from research activities on such topics should lead to appropriately drive and inform the policy making processes on WUI fire prevention and management in Spain and, by extension, in other southern European countries under a similar situation.

38 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the number of cells on self-heating self-attention and self-fire was investigated with Sanyo prismatic LiCoO2 cells at 30% state of charge.
Abstract: Lithium-ion batteries (LIBs) are widely used as energy storage devices. However, a disadvantage of these batteries is their tendency to ignite and burn, thereby creating a fire hazard. Ignition of LIBs can be triggered by abuse conditions (mechanical, electrical or thermal abuse) or internal short circuit. In addition, ignition could also be triggered by self-heating when LIBs are stacked during storage or transport. However, the open circuit self-heating ignition has received little attention and seems to be misunderstood in the literature. This paper quantifies the self-heating behaviour of LIB by means of isothermal oven experiments. Stacks of 1, 2, 3 and 4 Sanyo prismatic LiCoO2 cells at 30% state of charge were studied. The surface and central temperatures, voltage, and time to ignition were measured. Results show that self-heating ignition of open circuit LIBs is possible and its behaviour has three stages: heating up, self-heating and thermal runaway. We find for the first time that, for this battery type, as the number of cells increases from 1 to 4, the critical ambient temperature decreases from 165.5°C to 153°C. A Frank-Kamenetskii analysis using the measured data confirms that ignition is caused by self-heating. Parameters extracted from Frank-Kamenetskii theory are then used to upscale the laboratory results, which shows large enough LIB ensembles could self-ignite at even ambient temperatures. This is the first experimental study of the effect of the number of cells on self-heating ignition of LIBs, contributing to the understanding of this new fire hazard.

33 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the plausibility of using FDS v6.7 and zonal models to predict certain fire parameters (i.e. ceiling temperatures, heat fluxes, etc.) for informal settlement dwellings (ISDs) and to study the likelihood of fire spread.
Abstract: While fire-related injuries and deaths decreased in the global north over the past few years, they have increased in the global south. With more than one billion people residing in informal settlements (sometimes known as slums, ghettos or shantytowns), it is necessary that greater effort be placed on addressing and developing means for improving fire safety in these areas. As a result of advances made in computer technologies, emerging performance-based regulations and an increase in building complexity in the global north, the use of computer models simulating enclosure fires have increased dramatically. In this work an experimental investigation is presented for (a) a full-scale corrugated steel sheeting clad informal dwelling experiment and (b) a full-scale timber clad informal dwelling experiment. The experimental results are then compared to numerical models consisting of both simple two-zone (OZone) and computational fluid dynamic models. Currently, there is negligible literature available on Fire Dynamic Simulator (FDS) modelling of informal settlement dwellings (sometimes known as shacks or shanties) fires. This paper evaluates the plausibility of using FDS v6.7 and zonal models to predict certain fire parameters (i.e. ceiling temperatures, heat fluxes, etc.) for Informal Settlement Dwellings (ISDs) and to study the plausibility of using FDS to estimate the probability of fire spread. In this paper an introduction to ISDs is given with details pertaining to construction materials and considerations needed for numerical modelling of informal dwellings (i.e. thin permeable boundaries or combustible boundaries). Models are based upon (a) a prescribed heat release rate per unit area in FDS using data obtained from a Fire Propagation Apparatus test, and (b) an empirical two-zone model using OZone. The FDS validation guide was used to quantify the model uncertainties in order to give a critical separation distance at which fire spread between dwellings will not occur. It was found that at 3 m spacing between ISDs there is a 6% chance (based on the model uncertainties) that fire spread can occur. This is an important finding that highlights the danger associated with these closely spaced dwellings and the hope is that it can guide local government and Non-Governmental Organizations in future decision making. Three meters spacing between dwellings, however, may not be possible due to the socio-cultural-political-economic issues associated with informal settlements. This is one of the first papers to demonstrate FDS models against full-scale ISD experiments.

28 citations


Journal ArticleDOI
TL;DR: A summary of data collected via an international online survey regarding the models and users’ experiences and needs is presented, highlighting that the three key factors used to select a pedestrian evacuation model are overall consistent with the results of the 2011 survey.
Abstract: Pedestrian evacuation models are often used to assess life safety in the performance-based design process within fire safety engineering. Within this paper, a summary of data collected via an international online survey regarding the models and users’ experiences and needs is presented. This survey consisted of 22 questions focusing on: the assessment of the pedestrian evacuation model user community; their stated importance of model features to select a model; usage/awareness of models; knowledge of model validation and verification; training; and usage of multiple models. As such, the survey allowed the collection of information useful for instructing future pedestrian evacuation model development. The survey represents an expanded version of a previous survey conducted by the authors in 2011. Results with the previous survey were compared to identify any changes in preference and usage by pedestrian evacuation model users. The survey was completed by 234 respondents from 41 countries. The respondents had a wide range of education and occupational backgrounds and use models for a variety of different purposes. The results identified a total of 72 pedestrian evacuation models currently in use and indicated the most known models. In addition, the most used models were identified, and the results highlighted that the three key factors used to select a pedestrian evacuation model are overall consistent with the results of the 2011 survey: verification and validation, documentation, and data output of the model.

27 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared the pyrolysis and burning behavior of six engineered wood products (EWPs): oriented strand board (OSB), plywood, particle board (PB), low density (LDF), medium-density (MDF), and high density (HDF) fiberboard.
Abstract: Engineered wood products (EWPs) are a group of materials having a very similar chemical composition but having different and non-uniform thermo-physical properties throughout their thickness. Such materials present a significant challenge from the pyrolysis modelling point of view. The main focus of the paper is to study and compare the differences between six EWPs—oriented strand board (OSB), plywood, particle board (PB), low-density (LDF), medium-density (MDF) and high-density (HDF) fibreboard—in terms of their pyrolysis and burning behaviour. Vertical density profiles (VDPs), thermal degradation behaviour, and burning behaviour were studied and compared. There is a considerable need for a consistent and systematic approach in estimating pyrolysis model complexity and model input parameters. A systematic method to determine the minimum level of the EWPs decomposition model complexity to reproduce the thermal degradation behaviour as measured using thermogravimetric analysis and using the set of parallel reactions was applied. EWPs were found to have similar thermal decomposition onset and range. Maximal decomposition rates were within 25%. OSB, PB, LDF and HDF decomposition can be modelled using three-step parallel reactions scheme, MDF using four parallel reactions. A set of parallel reactions cannot describe the thermal degradation behaviour of plywood. Cone calorimeter tests at heat flux levels of 20 kW/m2, 50 kW/m2 and $$80\, \hbox {kW}/\hbox {m}^{2}$$ revealed that influence of the different thermo-physical properties on time to ignition and time to peak heat release rate (HRR) is not significant except LDF and HDF due to their very different density. Peak HRR varies between EWPs, which is attributed primarily to charring and different thermo-physical properties of the EWPs char. EWPs gas phase combustion parameters for the fire models were derived.

26 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of fluorocarbon and hydrocarbon surfactants on fire extinction performance and fuel transport rate through a foam layer were measured for solutions containing a mixture of fluorosurfactants and hydrocarbons.
Abstract: Fluorosurfactants used in current firefighting foams must be replaced with environmentally-friendly surfactants; however, current fluorine-free surfactants have subpar fire performance. Understanding how a surfactant affects fire performance of a foam is essential for developing new fluorine-free replacement surfactants. Surfactants can affect foam’s ability to form a barrier between a fuel-pool surface and the fire, thereby suppressing the fuel feeding the fire and extinguishing it. Fire extinction performance, fuel transport through a foam layer, foam degradation by fuel, and foam spread rate were measured for solutions containing a mixture of fluorocarbon and hydrocarbon surfactants as well as the individual surfactants to understand the roles of different surfactants in a formulation. The measurements show that surfactants that reduce foam degradation and fuel transport rates through a foam covering a hot pool result in faster fire extinction. Small synergistic effects for the mixture of fluorocarbon surfactant (Cap) and a hydrocarbon surfactant (Gluc215) were found in foam degradation rate and fuel transport rate through a foam layer. The surfactant mixture had 30% longer foam lifetime and two times smaller fuel flux through a foam layer than the fluorosurfactant solution (Cap) and differed with the hydrocarbon surfactant solution (Gluc215) by more than a factor of ten. However, when a different hydrocarbon surfactant (TX100) was used in a mixture with the fluorocarbon surfactant, synergism was not observed. The small synergistic effects resulted in a small reduction in fire extinction times at high foam application rates (> 500 mL/min) at which foams can cover the pool surface quickly. At small foam application rates (< 500 mL/min), effects of foam spread rates become significant; the fluorocarbon surfactant (Cap) formed wetter foam that spread quicker and led to smaller fire extinction times than those for the surfactant mixture (Cap + Gluc215). Thus, the foam spread, foam degradation, and fuel transport rate measurements performed in the presence of a hot fuel but in the absence of a fire can explain the surfactant’s effects on fire extinction times for the six formulations. Traditionally, aqueous film formation was thought to be the key for fire suppression of AFFF rather than the foam dynamics described in this work. Additional properties such as static and dynamic surface tensions, foam bubble diameter distribution, bubble coarsening, liquid drainage from the foam, and expansion ratio were also measured in the absence of a fuel, but did not explain the trends in extinction performance among the surfactants.

24 citations


Journal ArticleDOI
TL;DR: In this paper, hazards have been identified and means for preventing and controlling lithium-ion battery fires, including preventive measures during workshop and salvage activities, and tests were also performed with fixed fire suppression systems applying suppressant inside traction batteries which showed to improve their safety.
Abstract: The demand for lithium-ion battery powered road vehicles continues to increase around the world. As more of these become operational across the globe, their involvement in traffic accidents and incidents is likely to rise. This can damage the lithium-ion battery and subsequently pose a threat to occupants and responders as well as those involved in vehicle recovery and salvage operations. The project this paper is based on aimed to alleviate such concerns. To provide a basis for fire safety systems to be applied to damaged EVs, hazards have been identified and means for preventing and controlling lithium-ion battery fires, including preventive measures during workshop and salvage activities were studied. Tests were also performed with fixed fire suppression systems applying suppressant inside traction batteries which showed to improve their safety.

Journal ArticleDOI
TL;DR: In this article, the authors present results and analysis of a full-scale fire spread experiment of a mock 20 dwelling test settlement with a 4 by 5 layout aimed at understanding settlement-scale wildfire spread behavior.
Abstract: Large-scale urban conflagrations in informal settlements are a frequent global event, however there is a lack of experimental research and knowledge within literature on how informal settlements fires spread to support local or national intervention strategies. This paper, therefore, presents results and analysis of a full-scale fire spread experiment of a mock 20 dwelling test settlement with a 4 by 5 layout aimed at understanding settlement-scale fire spread behaviour. A “fire line” scenario was created by simultaneously igniting four dwellings in a row, and then allowing the fire to propagate through the settlement to replicate fire disasters involving large numbers of homes. Results highlight the critical hazard posed by the close proximity of neighbouring dwellings (1–2 m), with wind playing a primary role in directing and driving the spread process. Even with a relatively mild wind speed of 15–25 km/h, the fire spread through the entire mock settlement within a mere 5 min. Following ignition of a given dwelling, flashover is reached very quickly, with the temperatures reaching more than 1000°C within 1 min, and downwind neighbour structures igniting less than a minute thereafter. The results suggest that multi-dwelling effects are not dominant in these types of fires, but may become meaningful at a larger scale when branding and topography play a role. Findings show that on a global scale fire behaviour is analogous to a wildfire with a continuous fire front moving through an area, although individual dwellings still do follow the distinct phases of enclosure fires, except that collapse occurs more rapidly than in formal structures. This experiment represents one of the larger urban fire tests conducted to date, and the largest informal settlement fire experiment.

Journal ArticleDOI
TL;DR: In this paper, the thermal-runaway propagation over 18650 cylindrical lithium-ion battery was tested in the linear-arranged module with a 3-mm gap, and three tab-connection methods were investigated.
Abstract: Thermal-runaway propagation in battery systems can escalate the battery fire hazard and pose a severe threat to global users. In this work, the thermal-runaway propagation over 18650 cylindrical lithium-ion battery was tested in the linear-arranged module with a 3-mm gap. State of charge (SOCs) from 30% to 100%, ambient temperatures from 20°C to 70°C, and three tab-connection methods were investigated. Results indicate that the battery thermal-runaway propagation speed was about 0.35 ± 0.15 #/min, which increased with SOC and ambient temperature. The critical surface temperature of thermal runaway ranged from 209°C to 245°C, which increased with ambient temperature while decreased with SOC. Compared to the open-circuit module, the flat tab connection could cause an external short circuit to accelerate the thermal-runaway propagation, and the non-flat tab connection was more likely to trigger an explosion. A heat transfer analysis was proposed to qualitatively explain the speed and limiting conditions of thermal-runaway propagation, as well as the influence of SOC, ambient temperature, and tab connection. This work reveals the thermal-runaway propagation characteristics under well-controlled environments, which could provide scientific guidelines to improve the safety of the battery module and reduce battery fire hazards.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a methodology for calculating the thermal response of a cable cross-section allowing for heat transfer by conduction through each strand contact surface and radiation across inter-strand cavities.
Abstract: Cable-supported structures such as bridges and stadia are critical for the surrounding community and the consequences arising from a major fire event can be substantial. Previous computational studies into the thermal response of cables often employed simplistic heat transfer models that assumed lump capacitance or cross-sectional homogeneity without proof of validity. This paper proposes a methodology for calculating the thermal response of a cable cross-section allowing for heat transfer by conduction through each strand contact surface and radiation across inter-strand cavities. The methodology has been validated against two experiments of cables subjected to radiant heating and an input sensitivity analysis has been undertaken for the heat transfer and material parameters. The approach is compared against simple heat transfer lumped methods for a parallel-strand cable where it is shown that these lumped models are not always conservative. The model is then coupled with a two-dimensional generalised plain strain model to study the likely effect of the cross-sectional temperature gradients on the mechanical response. The study considers three qualitatively different hydrocarbon jet fire scenarios, both with and without external insulation for fire protection. It is shown that the proposed methodology can reproduce realistic cross-sectional temperature distributions with up to 50% temperature difference at the cable external surface and can capture the phenomenon of load shedding in a gradually heated cable. It is also shown that assuming a lumped thermal mass neglects the possibility of moment-inducing temperature gradients which are not considered in the ambient design of cables that is driven by tensile capacities. The proposed model and its predictions contribute towards an improved understanding and a more informed structural design of cable-supported structures in fire.

Journal ArticleDOI
TL;DR: In this article, five silicone surfactants are chosen as key component to prepare fluorine-free firefighting foams and the aqueous solution properties of the fluorine free firefighting foam are studied in details, including surface tension, interfacial tension, spreading property, viscosity and foaming ability.
Abstract: The application of conventional aqueous film-forming foam (AFFF) has been severely restricted due to the serious environmental hazard caused by the key component, fluorocarbon surfactants. Environmental-friendly fluorine-free firefighting foams need to be developed urgently. In this study, five silicone surfactants are chosen as key component to prepare fluorine-free firefighting foams. The aqueous solution properties of the fluorine-free firefighting foams are studied in details, including surface tension, interfacial tension, spreading property, viscosity and foaming ability. Foam drainage and foam spread on heptane surface are analyzed. Fire extinguishing and burn-back performance of fluorine-free foams is evaluated based on a small-scale standard method. Particularly, fire extinguishing and burn-back performance of a commercial AFFF is also evaluated as a comparison. Results show that fluorine-free foams cannot form aqueous film on cyclohexane surface, no matter whether spreading coefficient is greater than zero or not. Fluorine-free foams exhibit much better foam stability but worse foam spread property than commercial AFFF. Not all the fluorine-free foams containing silicone surfactant performed as well as AFFF containing fluorocarbon surfactant. Only fluorine-free foam containing silicone surfactant of OFX-5211 shows better fire extinguishing and burn-back performance than AFFF. The higher efficiency of fluorine-free foam in fire extinguishing and burn-back should be attributed to the stronger foam stability.

Journal ArticleDOI
TL;DR: In this article, a series of penetration tests using the stainless steel nail on 18,650 lithium iron phosphate (LiFePO4) batteries under different conditions are investigated. And the accelerating rate calorimeter is applied to reveal the thermal runaway mechanism.
Abstract: The nail penetration experiment has become one of the commonly used methods to study the short circuit in lithium-ion battery safety. A series of penetration tests using the stainless steel nail on 18,650 lithium iron phosphate (LiFePO4) batteries under different conditions are conducted in this work. The effects of the states of charge (SOC), penetration positions, penetration depths, penetration speeds and nail diameters on thermal runaway (TR) are investigated. And the accelerating rate calorimeter is applied to reveal the thermal runaway mechanism. The experimental results show that the higher the SOC of the battery, the higher the possibility and risk of TR of the battery, and there seems to be a critical penetration depth where TR occurs. The battery exhibits higher average temperature at higher penetration speeds. Whether the battery get into TR is not related to the penetration speed. When the penetration location near the positive pole and negative pole,the risk of thermal runaway is much higher than the centre position of the battery. The larger the diameter of the nail, the lower the overall temperature of the battery. What’s more, the results of the penetration tests under the condition of parameter coupling shows that the average temperature of battery are greatly affected by the parameters of SOC, penetration position. The temperature of the LiFePO4 battery is within 200°C when the TR occurs induced by the penetration, which is mainly due to the incomplete exothermic reaction inside the battery.

Journal ArticleDOI
TL;DR: In this paper, a 1D finite difference model was proposed to predict the propagation of a thermal runaway hazard in cell arrays and modules, which is critical to understand fire hazards in energy storage systems.
Abstract: Characterizing propagation of a thermal runaway hazard in cell arrays and modules is critical to understanding fire hazards in energy storage systems. In this paper, the thermal runaway propagation of a pouch cell array has been examined by developing a 1D finite difference model. The results are compared with experimental data. First, the thermal runaway reactions found in the literature are reviewed. Using the insight of the literature review and premixed flame propagation theory, a global first order Arrhenius type reaction is characterized. While applying the multiple kinetic reactions, an “onset temperature” of the combustion reactions has been determined by performing an induction time analysis on ethylene. The propagation speeds are predicted with a 1D finite difference model by using both multi-reaction kinetics and one step reduced-order kinetics. These results are in a good agreement with experiments for both 10 Ah and 5 Ah cell arrays.

Journal ArticleDOI
TL;DR: In this paper, a thorough bibliometric and network analysis is conducted on the basis of peer-reviewed publications on tunnel fires, seeking to provide insights in this topic, and it is identified that the most prolific journal is Tunnelling and Underground Space Technology, with 121 papers, accounting for 23.3% of the total.
Abstract: The topic of tunnel fire attracted considerable attention in past two decades. The popularity of this topic is mainly attributed to the widespread construction of long-span tunnels and their incident fire safety issues, as well as the frequent occurrence of catastrophic tunnel fires. To date, a number of research papers have been published focusing on specific aspects of tunnel fires such as fire dynamics, smoke extraction, fire suppression system, personnel evacuation, fire risk evaluation, and some others with broader areas of focus. In this work, a thorough bibliometric and network analysis is conducted on the basis of peer-reviewed publications on tunnel fires, seeking to provide insights in this topic. A total of 519 research articles are obtained from the Web of Science Core Collection database. It is identified that the most prolific journal is Tunnelling and Underground Space Technology, with 121 papers, accounting for 23.3% of the total. England is the most influential region with the highest citations per document, while China is the most prolific country with nearly a half of the total, where the University of Science and Technology of China is the primary contributor. The visualization and cluster analysis of research topics indicate that the currently bursting topics mainly concentrate on the smoke thermodynamics and smoke extraction based on model-scale tests. The reference analysis and co-citation network also confirm the findings.

Journal ArticleDOI
TL;DR: In this article, a series of relevant literatures and proposed an instrument that can be used to analyse the thermal runaway behavior at different pressure levels, which can provide the guidelines for the air transportation of lithium-ion batteries.
Abstract: When lithium-ion batteries (LIBs) are located at high altitude and low pressure,the characteristics of thermal runaway (TR) and its propagation are different,such as time to TR, the toxicity of TR gases, TR propagation time, mass loss rate, etc. In this article, the author summarized a series of relevant literatures and proposed an instrument that can be used to analyse the TR behavior at different pressure. It is found that: with the decrease of ambient pressure, the TR trigger time becomes longer and the maximum surface temperature decrease. Moreover, the gas released by TR becomes more toxic as the environmental pressure decreases. Beside, the average propagation time between adjacent LIBs is not much difference when the environmental pressure decreases, and when the 18,650 battery module is distributed in a cylindrical shape, the thermal runaway propagation path is basically unchanged as the environmental pressure decreases. This work details TR and its propagation feature under different pressure, and can provide the guidelines for the Air transportation of LIBs.

Journal ArticleDOI
TL;DR: If situational awareness is incorporated in emergency evacuation procedure, it can improve the evacuation efficiency in a fire exposed high-rise building; wherein up to 24% reduction in evacuation time is achieved.
Abstract: Fire in buildings pose a significant threat to occupants, first responders as well as the structural system. Rapid spread of fire and smoke in buildings can hinder the process of evacuation resulting in loss of human life. Such situations call for a reliable egress system that provides safe evacuation of occupants in minimal time. Updating the occupants and first responders with much-needed situational awareness such as accessible stairwells and exits during the disaster can not only lead to efficient evacuation but also shorten the duration of evacuation in some scenarios. This paper examines occupant evacuation scenarios in fire exposed high-rise buildings. A parametric study is carried out on evacuation strategies in a 32-story typical office building during different fire exposure scenarios. The movement of occupants with and without situational awareness is simulated. The effect of critical parameters such as number of stories, width of the egress paths, location and number of exits on the evacuation process is evaluated. The time required for occupants to evacuate the building is estimated under normal conditions (to simulate fire evacuation drill) and under realistic fire exposure. Results from the study indicate that the two most significant factors that influence evacuation time are the location of stairway within the building and the floors at which fire starts. When fire starts at the lower levels of the building, the evacuation time is the highest. More importantly, if situational awareness is incorporated in emergency evacuation procedure, it can improve the evacuation efficiency in a fire exposed high-rise building; wherein up to 24% reduction in evacuation time is achieved.

Journal ArticleDOI
TL;DR: In this paper, Li et al. studied the thermal runaway characteristics of the lithium iron phosphate (LFP) battery used in energy storage station, and showed that stopping the overcharging process in time after the first battery safety vent is opened can effectively suppress the further development of thermal runaway, and maintain a safe state within 2h.
Abstract: In order to study the thermal runaway characteristics of the lithium iron phosphate (LFP) battery used in energy storage station, here we set up a real energy storage prefabrication cabin environment, where thermal runaway process of the LFP battery module was tested and explored under two different overcharge conditions (direct overcharge to thermal runaway and overcharge to safety vent open-standing–recharge to thermal runaway). In this experiment, surveillance cameras, infrared imagers, temperature detectors, and gas detectors were used to guarantee all-around online observation. The experimental results show that under the conditions of these experiments, stop the overcharging process in time after the first battery safety vent is opened can effectively suppress the further development of thermal runaway, and maintain a safe state within 2 h. It also indicates that the thermal runaway process of LFP battery module changes with heat accumulation which needs reaction time, if the heat accumulation could be stopped in time, the occurrence of thermal runaway accidents would be avoided. This provides effective theoretical guidance for safety warning and fire protection of electrochemical energy storage stations with LFP battery system.

Journal ArticleDOI
TL;DR: A learning-by-synthesis approach is contributed to facilitate the utilization of a machine learning paradigm to enhance situational awareness for fire fighting in buildings.
Abstract: Using the zone fire model CFAST as the simulation engine, time series data for building sensors, such as heat detectors, smoke detectors, and other targets at any arbitrary locations in multi-room compartments with different geometric configurations, can be obtained. An automated process for creating inputs files and summarizing model results, CData, is being developed as a companion to CFAST. An example case is presented to demonstrate the use of CData where synthetic data is generated for a wide range of fire scenarios. Three machine learning algorithms: support vector machine (SVM), decision tree (DT), and random forest (RF), are used to develop classification models that can predict the location of a fire based on temperature data within a compartment. Results show that DT and RF have excellent performance on the prediction of fire location and achieve model accuracy in between 93% and 96%. For SVM, model performance is sensitive to the size of training data. Additional study shows that results obtained from DT and RT can be used to examine the importance of each input feature. This paper contributes a learning-by-synthesis approach to facilitate the utilization of a machine learning paradigm to enhance situational awareness for fire fighting in buildings.

Journal ArticleDOI
TL;DR: In this article, a full-scale thermal runaway test of the real lithium-ion battery pack is conducted in order to evaluate the fire hazards of the electric vehicle, and the experimental process can be divided into three stages according to the combustion behavior: (1) thermal runaway of the triggered module was induced and shows transient jet flame; (2) the thermal runaway propagated between cells and further resulted in the constant repetition of ignition and reignition behavior; (3) the fire extinguish stage, in which the flame was suppressed and released a considerable amount of smoke.
Abstract: The fire accidents caused by the thermal runaway of lithium-ion battery has extremely impeded the development of electric vehicles. With the purpose of evaluating the fire hazards of the electric vehicle, a full-scale thermal runaway test of the real lithium-ion battery pack is conducted in this work. The experimental process can be divided into three stages according to the combustion behavior. (1) Thermal runaway of the triggered module was induced and shows transient jet flame; (2) thermal runaway propagated between cells and further resulted in the constant repetition of ignition and re-ignition behavior; (3) the fire extinguish stage, in which the flame was suppressed and released a considerable amount of smoke. It is worth mentioning that it takes 22 s to evolve the triggered thermal runaway event to the worst case that the flame can spread throughout the whole cargo compartment. However, the water cannot directly act on the cells due to the shielding of the pack’s cover in the fire extinguish stage, which greatly limits its cooling effect. The potential flame spread over electric vehicle is observed in this work, which can provide useful guidelines for the safety design of lithium-ion battery system.

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TL;DR: In this paper, the influence of the proportion of each component in the extinguishant formula on the coating effect was analyzed, and the extinguishing effect of the optimized four dry extinguishing agents was tested by a portable spray device.
Abstract: Environmental-friendly and highly efficient combustion suppression performance is the requirement for extinguishant. Dry water extinguishant integrates the advantages and characteristics of both dry powder and water mist extinguishant, so it has better fire extinguishing efficiency. Moreover, dry water extinguishant has less residue, no fugitive settling, non-toxic and harmless advantages after fire extinguishing. This work focus on producing dry water extinguishant powder by high-speed shearing. Then, the influence of the proportion of each component in the extinguishant formula on the coating effect was analyzed. The extinguishing effect of the optimized four dry extinguishing agents was tested by a portable spray device. Experiment results show that optimized four extinguishing agents are effective in extinguishing n-heptane fire and anhydrous ethanol fire. Among them, ammonium dihydrogen phosphate dry water extinguishant has the highest extinguishing efficiency to n-heptane fire, and potassium oxalate dry water extinguishant has the highest extinguishing efficiency to anhydrous ethanol fire.

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TL;DR: In this article, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center's Zero Gravity Research Facility (the 5.18 ǫ s drop tower).
Abstract: There are no existing experimental studies of flame spread rate trends for ultra-thin solid samples. Previous theory has predicted that for concurrent flame in kinetic regime, the flame spread rate decreases as the sample thickness decreases and there is a critical thickness below which burning is not possible. To test this hypothesis, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center’s Zero Gravity Research Facility (the 5.18 s drop tower). The tested samples are cellulose-based materials of various area densities, ranging from 0.2 mg/cm2 to 13 mg/cm2, as low as one order of magnitude less than those ever tested before. Each sample is 30 cm long by 5 cm wide and is burned in a low-speed concurrent air flow (5 to 30 cm/s). The results show that the concurrent flame spread rate is proportional to the flow velocity relative to the flame and is inversely proportional to the sample area density. A theoretical formulation, provided in this work, suggests that the flame length has a linear relationship with the relative flow speed and has no direct dependency on the sample area density. The experimental data supports this conclusion. From the images recorded in the experiments, a unique flame base tubular structure directed upstream away from the burnout zone is observed for thin samples. This structure is suspected to be due to flame stretching and localized blowoff caused by the oxidative pyrolysis Stefan flows at the sample burnout. This can be an indication that the chemical time becomes comparable to the flow time of the Stefan flow and the tested samples are approaching the kinetically-limited thickness. For the thinnest tested sample (0.2 mg/cm2), flames with concurrent and opposed dual natures are observed when the air flow rate is low (< 20 cm/s). At the lowest tested flow rate (5 cm/s), the flame spread rate exceeds the air flow rate and the flame transits to an opposed flame in the concurrent flow. The dual nature and flame transition are presented and discussed. This study provides detailed examination through high-resolution images of the transition between the concurrent to opposed flame spread modes.

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TL;DR: Li et al. as mentioned in this paper used non-destructive computed tomography (CT) to analyze cylindrical Li-ion battery samples that underwent thermal runaway and exploded, and demonstrated the ability of CT for post-mortem incident analysis and the limitations of current vent design.
Abstract: Battery explosion incidents hinder the development and application of Li-ion batteries. This paper describes the use of nondestructive computed tomography (CT) to analyze cylindrical Li-ion battery samples that underwent thermal runaway and exploded. Unlike destructive analysis methods, which can lead to a loss of battery structural information, CT scan allows direct observation of a battery’s internal structure without disassembly. In this study, two case studies of 20700 and 18650 batteries show that sidewall and bottom case rupture was caused by blockage of the battery vent region, which prevented the release of the generated gas. This work demonstrates the ability of CT for post-mortem incident analysis and the limitations of current vent design, and also gives insight to a safety issue with some cylindrical batteries.

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TL;DR: An infrared image-based feedback control system for intelligent fire monitor to realize automatic aiming of the fire site and continuous fire tracking in the process of fire extinguishing through adjusting of the yaw angle of theFire monitor.
Abstract: An infrared image-based feedback control system for intelligent fire monitor was proposed in this paper, whose aims are to realize automatic aiming of the fire site and continuous fire tracking in the process of fire extinguishing through adjusting of the yaw angle of the fire monitor. Firstly, infrared camera was used to capture images of the fire site, and under high temperatures, the fire would be easily observed. An improved adaptive image threshold segmentation scheme was developed for image background segmentation and fire acquisition. The fire region in the captured image was considered as region of interest (ROI) and the geometric center of which was calculated. Due to the special advantageous structural design of the proposed system, the geometric center of ROI representing the actual fire was considered as the direction which the fire monitor should aim at. Furthermore, a fuzzy control scheme simulating the operating mode of firefighters was proposed, and the ROI center position deviation and deviation rate were considered as inputs of the control system. Experimental results show that, after the fire was detected by the system, the fire monitor could be yawed to the direction of the fire within 2000 ms, and the deviation of image position is less than 1.6 pixels. Similarly, the proposed system could be well adapted to the changing position of the fire caused by combustion. And after no more than image iteration of three frames, the controller realizes aiming of the fire by the fire monitor, and the final deviation is less than 0.1 pixels. In general, the proposed infrared image feedback control system for fire horizontal position aiming of intelligent fire monitor has great potential for intelligent fire extinguishing by fire-fighting robots.

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TL;DR: In this paper, a flame is established over a solid cylindrical polyethylene coated metallic wire and spreads at a steady rate, in low velocity flow conditions allowed by the absence of buoyancy.
Abstract: The objective of this work is to quantify for the first time soot-related radiative heat transfer in opposed flow flame spread in microgravity. This article presents experimental results obtained in parabolic flight facilities. A flame is established over a solid cylindrical polyethylene coated metallic wire and spreads at a steady rate, in low velocity flow conditions allowed by the absence of buoyancy. Implementing the Broadband Modulated Absorption/Emission technique, the two-dimensional fields of soot volume fraction and temperature are obtained for the first time in flame spread configuration over an insulated wire in microgravity. The consistency of the results is assessed by comparing results from independent experimental runs. From these fields, radiative losses attributed to soot in the flame are computed at each location. This map of radiative losses together with the profile of the wire surface are then used as inputs to a novel experimental approach that enables the assessment of soot radiative heat feedback to the wire. Results are extracted from a specific case of a flame propagating over a polyethylene coated Nickel–Chrome wire at nominal pressure. The oxidizer, composed of 19% oxygen and 81% nitrogen in volume is blown at opposed flow parallel to the wire at a velocity of $$200\,\hbox {mm}\cdot\hbox{s}^{-1}$$. This new approach provides the first detailed quantitative measurements which are required to check the relevance of heat transfer models under development, therefore to better understand the mechanisms driving flame spread in microgravity.

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TL;DR: In this paper, an experimental platform for lithium ion battery fire and explosion is designed and built, and the effects of different arrangements, including vertical 2 × 2 and vertical 4µ×µ1, and initial pressure (96kPa and 61kPa) on Li ion battery thermal runaway are studied.
Abstract: In order to investigate the thermal runaway mechanism of 18650 lithium ion batteries and the related hazards, an experimental platform for lithium ion battery fire and explosion is designed and built. The effects of different arrangements, including vertical 2 × 2 and vertical 4 × 1, and initial pressure (96 kPa and 61 kPa) on lithium ion battery thermal runaway are studied in this paper. Compared with the results of thermal runaway characteristics with two arrangements, a higher explosion pressure, a larger mass loss, more O2 consumption and more CO and CO2 production are observed of vertical 2 × 2 batteries due to the larger contact area between batteries. The explosion pressure of vertical 4 × 1 batteries decreases gradually with thermal runaway propagation. For vertical 2 × 2 batteries, the explosion pressure of battery C, D is about twice as large as battery A. The intensity of chemical reaction is more violent under 96 kPa which cause a lower onset temperature and a shorter onset time than that under 61 kPa. The thermal runaway propagation hazard can be reduced by decreasing the contact area between batteries. The results could provide useful guidance for the safety of lithium ion battery transportation in civil aviation.

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TL;DR: In this article, a 20 cm-wide air curtain spanning entire lateral section was installed underneath the tunnel ceiling to stop the propagation of smoke produced by 1MW fire and 2MW fire respectively.
Abstract: Air curtain is an effective means to stop the propagation of smoke in buildings to provide smoke-free area for safe egress of occupants in case of fires. To understand its effectiveness of smoke confinement in tunnel fires, full-scale tests were conducted in a tunnel of 140 m long and with varying heights of 5.0 m to 5.9 m and varying widths of 5.8 m to 10.8 m. A 20 cm-wide air curtain spanning entire lateral section was installed underneath the tunnel ceiling. The experiment showed that air curtain at exit velocities of 12 m/s and 16 m/s can stop the propagation of smoke produced by 1 MW fire and 2 MW fire respectively. Numerical simulation using ANSYS FLUENT was then conducted and the numerical results were basically consistent with those of experiment. To explore how the design parameters of air curtain, i.e., the width, the exit velocity and its angle, affect its effectiveness of smoke confinement at varying heat release rates, a number of numerical simulations were further conducted. The relationship of design parameters of air curtain with heat release rates was proposed and it can be used in the design of air curtain in tunnel fires.