202 results found
Mitchell H, Gwynne S, Ronchi E, et al., 2023, Integrating wildfire spread and evacuation times to design safe triggers: Application to two rural communities using PERIL model, Safety Science, Vol: 157, ISSN: 0925-7535
The hazards posed by a wildfire increase significantly when it approaches the wildland–urban interface. Evacuation of rural communities is frequently considered by local authorities and residents. In this context, evacuation triggers are locations that when reached by the wildfire indicate it is time to evacuate. Triggers are often arbitrarily defined via identifiable landmarks, do not include a safety factor, and do not account for fire spread or how long the evacuation takes. Ill-designed triggers may not safely inform decision making. It is necessary to create evacuation triggers that take into account both how a fire spreads towards the community, and how a community evacuates. This paper outlines a framework for developing triggers through the coupling of wildfire and evacuation models. We implement the previous theory of Cova et al. (2005) and others on triggers into a tool known as PERIL for generating trigger perimeters around a community, using the fire spread model FARSITE. A safety factor is included to address uncertainties in the wildfire or evacuation calculations. PERIL was applied to two real communities for the Swinley forest community (UK), and Roxborough Park community (USA). These communities were chosen because of previous work studying their actual evacuations. PERIL, which is available in open source, can be applied to inform safer strategies for to protect rural communities threatened by wildfires.
Hu Y, Rein G, 2022, Development of gas signatures of smouldering peat wildfire from emission factors, INTERNATIONAL JOURNAL OF WILDLAND FIRE, ISSN: 1049-8001
Santoso MA, Christensen EG, Amin HMF, et al., 2022, GAMBUT field experiment of peatland wildfires in Sumatra: from ignition to spread and suppression, INTERNATIONAL JOURNAL OF WILDLAND FIRE, Vol: 31, Pages: 949-966, ISSN: 1049-8001
Ang CD, Peiro J, Riess I, et al., 2022, Analysis of fire throttling in longitudinally ventilated tunnels with a one-dimensional model, Fire Technology, Vol: 58, Pages: 2925-2947, ISSN: 0015-2684
Fire throttling is the increase in flow resistance due to a large fire in a longitudinally ventilated tunnel. Although the fire throttling effect has been been known and studied for tunnels over the last 40 years, there is not yet a consistent one-dimensional (1D) model that can describe this behaviour or a framework suitable for practical application. We propose a semi-empirical model, based upon pipe flow engineering principles, to describe this effect by separating the resistance to flow, or pressure loses in three parts: upstream of the fire, locally at the fire, and downstream of the fire. The proposed 1D model called TE1D is derived from a simple steady one-dimensional momentum balance in which a semi-empirical mean temperature distribution is assumed across the tunnel. We verify the model by comparing the pressures losses it predicts with those calculated in CFD simulations based on OpenFOAM and Fire Dynamics Simulator. The comparison shows good agreement between the CFD codes for the range of fires sizes considered from 5 to 50 MW and good agreement between TE1D and the CFD results with the proposed 1D model for fire sizes below 30 MW. However, for values above there are large discrepancies between the results obtained by the TE1D and CFD. We posit as a potential explanation that these differences are due to flow and temperature stratification which is not accounted for in the 1D model. The model using pipe flow principles allows engineers to adopt this model for design, together with other pressure losses considered in tunnel ventilation.
He X, Hu Z, Restuccia F, et al., 2022, Experimental study of the effect of the state of charge on self-heating ignition of large ensembles of lithium-ion batteries in storage, Applied Thermal Engineering, Vol: 212, Pages: 1-11, ISSN: 1359-4311
Self-heating can cause the ignition of open-circuit Lithium-ion batteries. Current safety literature focuses on the self-heating chemistry of a single cell, ignoring the effects of heat transfer. However, a large ensemble of batteries has a non-uniform temperature distribution and therefore self-heating ignition is dominated by both heat transfer and chemistry. This type of ignition is of importance when batteries are stored for long periods of time and in large ensembles but has been rarely studied to date. This paper studies the effect of the state of charge (SOC) on the self-heating behavior of LiCoO2 prismatic cells. The SOC of 0% (of interest in the safety of waste facilities), 30% (transport), 50% (storage), 80% (aged battery) and 100% (fully-charged battery), and 1, 2 and 4 cells stacked together were studied using oven experiments. Results show that cells at all SOC can self-ignite. Flames were only observed for SOC larger than 80%. We compare two temperature criteria: the temperature of the middle cell using the critical increase rate of 10 ℃/min defined in standard SAE-J2464, and the ambient temperature around the ensemble when triggering ignition. Both temperature criteria decrease with increasing SOC showing that the hazard grows with energy density. The cell temperature criterion is independent of the number of cells, while the ambient temperature criterion decreases as the number of cells increases, which indicates the increased risk of self-heating ignition when cells are stacked together in ensembles. Thus, the ambient temperature criterion should be used to design safe storage rather than the standard cell temperature increase rate, which does not represent well the criticality of ignition. The effective kinetics and thermal properties at different SOCs are extracted based on the Frank-Kamenetskii theory and are used to upscale laboratory results to storage conditions. The results in this work can improve the safety of the storage and provide scient
Kotsovinos P, Christensen EG, Rackauskaite E, et al., 2022, Impact of ventilation on the fire dynamics of an open-plan compartment with exposed timber ceiling and columns: CodeRed #02, Fire and Materials: an international journal, ISSN: 0308-0501
The desire by developers and architects to build mass timber buildings using cross laminated timber (CLT) and glulam has significantly increased globally in the last decade due to its benefits with regards to sustainability as well as other architectural and commercial drivers. This paper presents novel experimental evidence from CodeRed #02, the second in a series of large scale fire experiments carried out inside a purpose-built, open-plan compartment to capture fire dynamics in large compartments with exposed timber. The experiment used a continuous wood crib (6 × 29 m) as a controlled movable fuel load. The aim of the CodeRed #02 experiment was to study the impact of reduced ventilation on fire dynamics by keeping all other parameters the same as CodeRed #01 (Kotsovinos et al., 2022), with the exception of ventilation area which was reduced by almost half. The reduction in ventilation was found to significantly impact the fire dynamics by slowing the fire spread and burning rate. The reduced ventilation led to an increased fire duration by 4 min 30 s, which corresponds to 20% longer duration compared to CodeRed #01. The reduced ventilation had a greater overall impact on the rate of flame spread across the CLT (−23%) than the crib (−8%) compared to CodeRed #01. While the maximum temperature and incident heat fluxes inside the compartment were approximately the same as in CodeRed #01, their evolution in time and space were significantly different. The external flames were higher than in CodeRed #01 (3–3.5 m compared to 2.5–3 m) and protruded further laterally (up to ~4–5 m compared to ~1 m) outside of the compartment from the large end openings. Unlike CodeRed #01, the external flaming from CodeRed #02 pulsated between visible flames and dark soot with significantly greater frequency. This was caused by the limited ventilation resulting in incomplete combustion in CodeRed #02. The peak heat release rate of CodeRed #02 w
He X, Zhao C, Hu Z, et al., 2022, Heat transfer effects on accelerating rate calorimetry of the thermal runaway of Lithium-ion batteries, Process Safety and Environmental Protection, Vol: 162, Pages: 684-693, ISSN: 0263-8762
The thermal runaway of Lithium-ion batteries (LIBs) is a fire hazard. The Accelerating Rate Calorimetry (ARC) device is commonly used to investigate thermal runaway parameters of LIBs by assuming adiabatic conditions. However, this assumption ignores internal heat transfer within the cell and external heat transfer at the cell surface. In this work, we conducted ARC experiments using prismatic LiCoO2 cells of 50 mm in side to study the effect of heat transfer limitations. Results show that the external temperature difference between this cell surface and ARC walls varies between 0 and 1.5 ℃ before thermal runaway and increases from 10 to 130 ℃ while thermal runaway occurs. Ignoring external heat transfer causes the heat of reaction of the cell to be underestimated by 12%. To study the internal heat transfer, two models are developed and show that heat transfer causes an internal temperature difference that causes an error of kinetics estimation, and the error grows with cell size. Ignoring heat transfer leads to errors on the thermal runaway parameters quantified by ARC, and these errors could propagate to battery safety design and predictions. This study contributes to designing better ARC experiments and a better understanding of battery safety.
Kotsovinos P, Rackauskaite E, Christensen E, et al., 2022, Fire dynamics inside a large and open-plan compartment with exposed timber ceiling and columns: CodeRed #01, Fire and Materials: an international journal, Pages: 1-27, ISSN: 0308-0501
There is an increasing global demand to build from timber as it is a sustainable and attractive material. One of the key challenges associated with timber buildings is their performance in a fire, in particular, for medium- and high-rise buildings and when timber is exposed. Research on this topic to date has been performed in compartments smaller than 84 m2 which does not capture the fire dynamics of large compartments. This paper presents the first in a series of experiments carried out inside a large, purpose-built, open-plan compartment with a floor area of 352 m2. The large-scale compartment had a fully exposed, unloaded, cross-laminated timber (CLT) ceiling and glued laminated timber (glulam) columns, made with adhesives that have been tested to not exhibit char fall-off in fire. At 352 m2 floor area, this is currently the largest compartment fire experiment carried out globally. The compartment characteristics and the arrangement of the wood crib mimicked the previous series of experiments in Poland in a non-combustible compartment by Rackauskaite et al. (2021). The experiment was instrumented with thermocouples measuring the gas temperature in the compartment, and above two of the openings, as well as the temperature within the timber members. Plate thermometers were also included to measure the heat flux to the ceiling and of the external flaming. Additionally, fixed and drone-mounted cameras captured the fire. A protected steel column was added to calculate the equivalent fire exposure when compared to a standard fire resistance furnace test. The experiment was allowed to burn out without fire-fighting intervention. Continuous measurements were taken for 48 h. The wood crib was ignited at one end of the compartment. Flames rapidly spread across the timber ceiling to the other end of the compartment with the rest of the wood crib being involved in the fire at 5 min 36 s from ignition. The total duration of the fire was 22
Wang Z, Liu N, Yuan H, et al., 2022, Smouldering and its transition to flaming combustion of polyurethane foam: An experimental study, FUEL, Vol: 309, ISSN: 0016-2361
Hu Z, He X, Restuccia F, et al., 2022, Benchmarking Between COMSOL and GPYRO in Predicting Self-Heating Ignition of Lithium-Ion Batteries, Fire Technology, ISSN: 0015-2684
Recent studies have shown that self-heating ignition is a possible cause of fires when Lithium-ion batteries (LIBs) are stacked in large numbers, for example, during storage. The understanding of this ignition type is limited, and most current studies are based on numerical modelling. The different modelling tools found in the literature differ in their assumptions, capabilities, and resources needed, and may provide significantly different predictions. This study presents a benchmarking between COMSOL Multiphysics, which is one of the most prevailing tools used in modelling thermal-electrochemical behaviour of LIBs, and Gpyro, which is widely used in modelling ignition of solid fuels. Four case studies are designed with increasing levels of complexity: (1) just chemical kinetics at the microscale, (2) just heat transfer at the mesoscale, (3) self-heating behaviour at the mesoscale for coupled chemical reactions and heat transfer of a single cell, and (4) four-cell ensemble for multiphysics at a larger scale. The results of scenarios #3 and #4 are also compared to experiments. The results show that although COMSOL and Gpyro have significant differences in their assumptions and resources needed, both tools can accurately predict the critical conditions for ignition for self-heating, which validates their use to study the safety of LIBs.
Jahn W, Urban JL, Rein G, 2022, Powerlines and Wildfires: Overview, Perspectives, and Climate Change: Could There Be More Electricity Blackouts in the Future?, IEEE POWER & ENERGY MAGAZINE, Vol: 20, Pages: 16-27, ISSN: 1540-7977
Zhang X, Hu L, Zhang X, et al., 2022, Two dimensional temperature distributions in a ceiling jet generated by a finite line-source fire: An experimental study, Proceedings of the Combustion Institute, ISSN: 1540-7489
The temperature distributions of ceiling jets are fundamental characteristics in enclosure fire dynamics. It is also the basics in the designs of fire safety devices in buildings, like detection, sprinkler, smoke control and standard fire protection. However, the only exists equation is for the radial ceiling jet temperature profile induced by a point source. There are no studies on line source despite the fact that the non-axisymmetric sources are the more common fires in buildings. This paper, for the first time, investigates the temperature profiles in ceiling jet induced by a finite line-source fire plume impinging upon an unconfined ceiling. Experiments are carried out with a buoyant jet fire and a pool fire. The temperature profile under the ceiling was measured along with flow condition visualized by a laser sheet. It is found that the temperature profile is two-dimensional and decays slower in the y-direction (perpendicular to line source longer side) than that in the x-direction (parallel to line source longer side). The characteristic length scales for characterizing the temperature profiles in the two directions are then proposed on the basis of the dimensions of the plume impinging zone. An equation is derived to describe the two-dimensional temperature profile based on the characteristic length scales. The present study provides basic data and a new equation for temperature profiles of ceiling jet induced by finite line-sources for building fire science.
Cui W, Hu Y, Rein G, 2022, Experimental study of the ignition conditions for self-sustained smouldering in peat, Proceedings of the Combustion Institute, ISSN: 1540-7489
Tackling peatland wildfires, the largest fires on Earth in terms of fuel consumption, is an emerging combustion topic in the context of climate change and environmental protection. The understanding of the basic mechanisms of ignition of peat to initiate self-sustained smouldering is essential in the development of mitigation technologies, but it is not well studied yet in the literature. In this research, laboratory experiments were conducted to improve the understanding of how peat conditions (moisture content and bulk density) and the ignition protocol influence the ignition probability. A new ignition protocol was developed by stopping the heat source when 10% mass of the sample is lost. This mass-based ignition protocol was found to be robust to initiate self-sustained smouldering in peat samples for a wide range of soil conditions. By using the new ignition protocol, experiments using peat samples of moisture content from 100% to 180% with a range of bulk densities were conducted to investigate how these properties together influence the critical ignition conditions. Results show that although the moisture content plays a major role in the ignition probability, bulk density is also important. Increasing peat density increases the mass of water in a unit volume. This increase of heat sink makes the ignition more difficult. These findings contribute to studying smouldering peat fires and improve the understanding of ignition.
Rein G, Huang X, 2021, Smouldering wildfires in peatlands, forests and the arctic: Challenges and perspectives, Current Opinion in Environmental Science & Health, Vol: 24, Pages: 1-10, ISSN: 2468-5844
Wildfires can be divided into two types, flaming or smouldering, depending on the dominant combustion processes. Both types are present in most wildfires, and despite being fundamentally different in chemical and physical terms, one transitions to the other. Traditionally, science has focused on flames, while smouldering is often misinterpreted. But smouldering wildfires are emerging as a global concern because they cause extensive air pollution, emit very large amounts of carbon, are difficult to detect and suppress, and could accelerate climate change. Central to the topic are smouldering peat fires that lead to the largest fires on Earth. Smouldering also dominates the residual burning after flames have died out and firebrand ignition. Finally, smouldering is an important part of Arctic wildfires, which are increasing in frequency. Here, we present a scientific overview of smouldering wildfires, the associated environmental and health issues, including climate change, and the challenges in prevention and mitigation.
The large-scale adoption of wood as a construction material for tall buildings could pave the way for sustainable construction. Its adoption, however, is hindered by a limited understanding of wood's behaviour in a fire. In particular, the effect of oxygen and heat flux on the burning (including pyrolysis) and ignition behaviour of wood is poorly understood. We addressed this gap by studying the effect of oxygen concentration and heat flux on the burning and ignition behaviour of particleboard experimentally and computationally. Particleboard was chosen as a proxy for all woody construction materials. We conducted over 60 experiments in an FPA on samples of particleboard spanning different oxygen concentrations (0–21%), heat fluxes (10–70 kW/m2), sample densities (600–800 kg/m2), and sample thicknesses (6–25 mm). Only the heat flux and oxygen concentration significantly affected the charring rate, time-to-flaming ignition, and burning mode (pyrolysis, smouldering, flaming). To explore this effect further, we used a multi-physics model of particleboard charring developed in Gpyro. Combining the computational and experimental results, we showed that particleboard undergoes only pyrolysis in oxygen concentrations below 4%, smouldering between 4 and 15%, and flaming above 15% at a heat flux of 30 kW/m2. These oxygen concentration thresholds were found to decrease as the heat flux increases. We also showed that smouldering and flaming increases the charring rate by 25 and 37%, respectively. This means that the rate of loss of a section of structural wood, quantified by the charring rate, in a fire due to smouldering is similar to that of flaming combustion. In addition, we noted the existence of a triple point for the ignition of wood at which a slight change in environmental conditions can lead to either smouldering, flaming, or only pyrolysis. In summary, this paper quantified for the first time the contributions of the three modes of burning to
Rackauskaite E, Bonner M, Restuccia F, et al., 2021, Fire Experiment Inside a Very Large and Open-Plan Compartment: x-ONE, FIRE TECHNOLOGY, Vol: 58, Pages: 905-939, ISSN: 0015-2684
Ford A, Harrison S, Kountouris I, et al., 2021, Modelling human-fire interactions: combining alternative perspectives and approaches, Frontiers in Environmental Science, Vol: 9, Pages: 1-23, ISSN: 2296-665X
Although it has long been recognised that human activities affect fire regimes, the interactions between humans and fire are complex, imperfectly understood, constantly evolving, and lacking any kind of integrative global framework. Many different approaches are used to study human-fire interactions, but in general they have arisen in different disciplinary contexts to address highly specific questions. Models of human-fire interactions range from conceptual local models to numerical global models. However, given that each type of model is highly selective about which aspects of human-fire interactions to include, the insights gained from these models are often limited and contradictory, which can make them a poor basis for developing fire-related policy and management practices. Here, we first review different approaches to modelling human-fire interactions and then discuss ways in which these different approaches could be synthesised to provide a more holistic approach to understanding human fire interactions. We argue that the theory underpinning many types of models was developed using only limited amounts of data and that, in an increasingly data-rich world, it is important to re-examine model assumptions in a more systematic way. All of the models are designed to have practical outcomes but are necessarily simplifications of reality and as a result of differences in focus, scale and complexity, frequently yield radically different assessments of what might happen. We argue that it should be possible to combine the strengths and benefits of different types of model through enchaining the different models, for example from global down to local scales or vice versa. There are also opportunities for explicit coupling of different kinds of model, for example including agent-based representation of human actions in a global fire model. Finally, we stress the need for co-production of models to ensure that the resulting products serve the widest possible community.
He X, Hu Z, Restuccia F, et al., 2021, Self-heating ignition of large ensembles of Lithium-ion batteries during storage with different states of charge and cathodes, Applied Thermal Engineering, Vol: 197, ISSN: 1359-4311
Self-heating is a possible cause of ignition of the open-circuit Lithium-ion battery (LIB) during storage. However, previous studies mainly focused on self-heating of a single cell, without considering the effect of heat transfer on large-size storage. In this study, a one-dimensional computational model, coded in the Gpyro, is used to study ensembles containing 1 cell to 5 million cells. Results show that ignition occurs at the central cell of the ensemble, while the outer surfaces remain at ambient temperature. As the length of ensembles increases from 0.01 m to 10 m, cell thermal runaway temperatures quantified using the critical temperature increase rate of 10 °C/min as defined in standard SAE-J2464 are insensitive to ensemble size, decreasing from 188 °C to 184 °C, but the critical ambient temperature triggering ignition decreases with size from 183 °C to 98 °C. This shows that the critical ambient temperature should be used to guide storage rather than the standard suggested critical temperature increase rate, which does not represent the criticality of ignition. The model predicts that higher state of charge (SOC) cells are easier to self-ignite. An ensemble containing 5 million 80% SOC cells can self-ignite at 40 °C. Self-heating ignition propensity of the Lithium Cobalt Oxide cathode LIB is larger, compared with Lithium Nickel Cobalt Manganese Oxide cathode. This study finds that the SAE-J2464 standard is not sufficiently robust to understand self-heating ignition during storage, and predicts the effect of the SOC and cathode chemistry on critical ambient temperature, contributing to the protection against LIB fires.
Hu Z, He X, Restuccia F, et al., 2021, Anisotropic and homogeneous model of heat transfer for self-heating ignition of large ensembles of lithium-ion batteries during storage, Applied Thermal Engineering, Vol: 197, ISSN: 1359-4311
Self-heating ignition is a fire hazard in warehouses when stacking large quantities of reactive materials for storage, including lithium-ion batteries. Due to the heavy costs and dangerous fire risks, the thermal behaviour of large-scale LIB ensembles is usually studied by numerical methods. The state-of-the-art self-heating models on LIBs are either too computationally expensive to be applied to the predictions of large LIB ensembles, or capable of large ensemble predictions but missing important heat transfer characteristics like insulation in packaging. Based on four-step kinetics from the literature (Solid electrolyte interphase decomposition, negative-electrolyte reaction, positive-electrolyte reaction, and electrolyte decomposition), we have developed a 3D anisotropic homogeneous (Ani-Hom) transient heat transfer model that can incorporate complex packaging and is numerically affordable for large ensemble predictions based on COMSOL Multiphysics. The effect of packaging insulation is considered by using weight-averaged thermophysical properties and directional thermal conductivities. Lithium Cobalt batteries (LCO) are used as a case study. This Ani-Hom model was verified by comparing a box-scale simulation against an isotropic heterogeneous (Iso-Het) model from the literature. Both the predictions of temperature evolution and the heat generation agreed to within 5%, while the computational time of the Ani-Hom model is one order of magnitude lower than the Iso-Het model. The Ani-Hom model is then applied to LIB ensembles in four possible storage sizes, ranging from a single cell to a rack with around 10 million cells, with different packing configurations and spacing between cells. The model predicts that the presence of packaging insulation promotes self-heating ignition. A rack of this LCO LIBs is predicted to self-ignite at an ambient temperature of 45℃, which indicates that LIBs in a warehouse are vulnerable to fire hazards in warm environments. The presenc
Yuan H, Restuccia F, Rein G, 2021, Spontaneous ignition of soils: a multi-step reaction scheme to simulate self-heating ignition of smouldering peat fires, International Journal of Wildland Fire, Vol: 30, Pages: 440-453, ISSN: 1049-8001
As organic porous soil, peat is prone to self-heating ignition, a type of spontaneous initiation of fire that can take place at ambient temperatures without an external source. Despite the urgency to tackle peat fires, the understanding of the self-heating ignition of peat is insufficient. In this study, a computational model that integrates the mechanisms of heat transfer, mass transfer and chemistry is incorporated with a three-step reaction scheme that includes drying, biological reaction and oxidative oxidation to simulate the self-heating ignition of smouldering peat. The model is first validated against 13 laboratory-scale experiments from literature. For critical ignition temperature (Tig), the model gives accurate predictions for all experiments with a maximum error of 5°C. The validated model is then upscaled to predict Tig for field-size peat soil layers and compared with the predictions using a one-step scheme. The three-step scheme is shown to give more reliable predictions of Tig than the one-step scheme. According to the simulation results, for a 1.5-m-deep peat layer, self-heating ignition can occur at an average ambient temperature above 40°C. This is the first time that a multi-step scheme is used to simulate the self-heating ignition of peat, aiming to help in the prevention and mitigation of these wildfires.
Liu Y, Sun P, Niu H, et al., 2021, Propensity to self-heating ignition of open-circuit pouch lithium-ion battery pile on a hot boundary, FIRE SAFETY JOURNAL, Vol: 120, ISSN: 0379-7112
Wahlqvist J, Ronchi E, Gwynne SMV, et al., 2021, The simulation of wildland-urban interface fire evacuation: The WUI-NITY platform, Safety Science, Vol: 136, Pages: 1-12, ISSN: 0925-7535
Wildfires are a significant safety risk to populations adjacent to wildland areas, known as the wildland-urban interface (WUI). This paper introduces a modelling platform called WUI-NITY. The platform is built on the Unity3D game engine and simulates and visualises human behaviour and wildfire spread during an evacuation of WUI communities. The purpose of this platform is to enhance the situational awareness of responders and residents during evacuation scenarios by providing information on the dynamic evolution of the emergency. WUI-NITY represents current and predicted conditions by coupling the three key modelling layers of wildfire evacuation, namely the fire, pedestrian, and traffic movement. This allows predictions of evacuation behaviour over time. The current version of WUI-NITY demonstrates the feasibility and advantages of coupling the modelling layers. Its wildfire modelling layer is based on FARSITE, the pedestrian layer implements a dedicated pedestrian response and movement model, and the traffic layer includes a traffic evacuation model based on the Lighthill-Whitham-Richards model. The platform also includes a sub-model called PERIL that designs the spatial location of trigger buffers. The main contribution of this work is in the development of a modular and model-agnostic (i.e., not linked to a specific model) platform with consistent levels of granularity (allowing a comparable modelling resolution in the representation of each layer) in all three modelling layers. WUI-NITY is a powerful tool to protect against wildfires; it can enable education and training of communities, forensic studies of past evacuations and dynamic vulnerability assessment of ongoing emergencies.
Hu Z, He X, Restuccia F, et al., 2021, Numerical study of scale effects on self-heating ignition of lithium-ion batteries stored in boxes, shelves and racks, Applied Thermal Engineering, Vol: 190, ISSN: 1359-4311
The fire safety of Lithium-ion batteries (LIBs) during their storage and transport is becoming of prime importance for the industry, with a number of such fires reported in recent years. It is crucial to understand the mechanisms and causes of these fires to provide insights for prevention. Previous studies mostly focused on small ensembles with a few cells and the chemistry involved. The possibility of ignition resulting from heat transfer within a large-size ensemble of LIBs had received little attention before. Focusing on the fire safety of large-scale stored LIBs, we discuss the risk and likelihood of self-heating ignition, which is a known cause of fires in other industries (e.g. chemical storage). Taking LiCoO2 type of battery as a base case and using its chemical kinetics reported in the literature, we build a transient heat transfer model with multi-step reactions to analyze the self-heating behaviour of ensembles of LIBs. Four typical storage sizes, from a single cell to racks containing around 2 million cells, are simulated using COMSOL Multiphysics. The results show that the critical ambient temperature for self-heating ignition is significantly lower for a large-scale LIB ensemble (e.g. 60 °C for the rack), indicating spontaneous side reactions are not negligible heat sources in large LIB ensembles and self-heating poses potential fire hazards in storage. Effects of size and heat transfer in LIB ignition should therefore not be ignored. This work provides insights into the fire safety of Li-ion batteries and additional means of protection during storage and transport.
Santoso MA, Cui W, Amin HMF, et al., 2021, Laboratory study on the suppression of smouldering peat wildfires: effects of flow rate and wetting agent, International Journal of Wildland Fire, Vol: 30, Pages: 378-390, ISSN: 1049-8001
The application of water, or water mixed with suppressants, to combat wildfires is one of the most common firefighting methods but is rarely studied for smouldering peat wildfire, which is the largest type of fire worldwide in term of fuel consumption. We performed experiments by spraying suppressant to the top of a burning peat sample inside a reactor. A plant-based wetting agent suppressant was mixed with water at three concentrations: 0% (pure water), 1% (low concentration), and 5% (high concentration), and delivered with varying flowrates. The results showed that suppression time decreased non-linearly with flow rate. The average suppression time for the low-concentration solution was 39% lower than with just water, while the high-concentration solution reduced suppression time by 26%. The volume of fluid that contributes to the suppression of peat in our experiments is fairly constant at 5.7 ± 2.1 L kg−1 peat despite changes in flow rate and suppressant concentration. This constant volume suggests that suppression time is the duration needed to flood the peat layer and that the suppressant acts thermally and not chemically. The results provide a better understanding of the suppression mechanism of peat fires and can improve firefighting and mitigation strategies.
Rackauskaite E, Kotsovinos P, Lange D, et al., 2021, Collapse initiation and mechanisms for a generic multi-storeySteel frame subjected to uniform and travelling fires, International Journal of High-Rise Buildings, Vol: 10, Pages: 265-283, ISSN: 2234-7224
To ensure that fire induced collapse of a building is prevented it is important to understand the sequence of events that can lead to this event. In thids paper, the initiation of collapse mechanisms of generic a multi-storey steel frame subjected to vertical and horizontal travelling fires are analysed computationally by tracking the formation of plastic hinges in the frame and generation of fire induced loads. Both uniform and travelling fires are considered. In total 58 different cases are analysed using finite element software LS-DYNA. For the frame examined with a simple and generic structural arrangement and higher applied fire protection to the columns, the results indicate that collapse mechanisms for singe floor and multiple floor fires can be each split into two main groups. For single floor fires (taking place in the upper floors of the frame (Group S1)), collapse is initiated by the pull-in of external columns when heated beams in end bays go into catenary action. For single floor fires occurring on the lower floors(Group S2), failure is initiated (i.e. ultimate strain of the material is exceeded) after the local beam collapse. Failure in both groups for single floor fires is governed by the generation of high loads due to restrained thermal expansion and the loss of material strength. For multiple floor fires with a low number of fire floors (1 to 3) - Group M1, failure is dominated by the loss of material strength and collapse is mainly initiated by the pull-in of external columns. For the cases with a larger number of fire floors (5 to 10) - Group M2, failure is dominated by thermal expansion and collapse is mainly initiated by swaying of the frame to the side of fire origin. The results show that for the investigated frame initiation of collapse mechanisms are affected by the fire type, the number of fire floors, and the location of the fire floor. The findings of this study could be of use to designers of buildings when developing fire protection st
Purnomo DMJ, Bonner M, Moafi S, et al., 2021, Using cellular automata to simulate field-scale flaming and smouldering wildfires in tropical peatlands, Proceedings of the Combustion Institute, Vol: 38, Pages: 5119-5127, ISSN: 1540-7489
Peat wildfires are the largest fires on Earth involving both flaming and smouldering combustion, with one leading to the other. A common ignition source of smouldering fires in tropical peatlands are intentional flaming fires used to clear surface vegetation. To capture the behaviour of these fires, it is necessary to consider the interaction between flaming vegetation and smouldering peat. However, doing so is infeasible with the state-of-the-art wildfire models, as they do not consider the transition from flaming to smouldering and are computationally too expensive at the field-scale hundreds of hectares. In this work, we overcome these limitations and model both flaming and smouldering at the field-scale using cellular automata: that is a discrete mathematical model that uses simple rules to capture complex behaviour while remaining computationally light. The model was calibrated against existing experiments in the literature and used to predict the effect of peat moisture content on the behaviour of peatland wildfires. The model shows how flaming creates smouldering hotspots and how these hotspots merge – flaming spreads rapidly, consuming surface vegetation, leaving behind hotspots of smouldering peat which consumes most of the peat. The model was then applied to study a real prescribed fire of 573 ha peatland in Borneo in 2015, observed by drone footage. The model captured the spread patterns of the fire and predicted that 2.9 ha of peatland burnt after 3 months with 70% peat moisture content (dry-based). This ioutcome could have been reduced to 0.02 ha if the peat moisture content had been above 100%. This work improves the fundamental understanding of how peat wildfires spread at the field scale which has received little attention until now.
Richter F, Rein G, Kotsovinos P, et al., 2021, Thermal response of timber slabs exposed to travelling fires and traditional design fires, Fire Technology, Vol: 57, Pages: 393-414, ISSN: 0015-2684
Engineered timber is an innovative and sustainable construction material, but its uptake has been hindered by concerns about its performance in fire. Current building regulations measure the fire performance of timber using fire resistance tests. In these tests, the charring rate is measured under a series of heat exposures (design fires) and from this the structural performance is deduced. Charring rates are currently only properly understood for the heat exposure of a standard fire, not for other exposures, which restricts the use of performance-based design. This paper studies the charring rates under a range of design fires. We used a multiscale charring model at the microscale (mg-samples), mesoscale (g-samples), and macroscale (kg-samples) for several wood species exposed to different heating regimes and boundary conditions. At the macroscale, the model blindly predicts in-depth temperatures and char depths during standard and parametric fires with an error between 5% and 22%. Comparing simulations of charring under travelling fires, parametric fires, and the standard fire revealed two findings. Firstly, their charring rates significantly differ, with maximum char depths of 42 mm (travelling), 46 mm (parametric), and 59 mm (standard fire), and one (standard fire) to four (travelling fire) charring stages (no charring, slow growth, fast growth, steady-state). Secondly, we observed zero-strength layers (depth between the 200 °C and 300 °C isotherm) of 7 to 12 mm from the exposed surface in travelling fires compared to 5 to 11 mm in parametric fires, and 7 mm in the standard fire. Both traditional design fires and travelling fires, therefore, need to be considered in structural calculations. These results help engineers to move towards performance-based design by allowing the calculation of charring rates for a wide range of design fires. In turn, this will help engineers to build more sustainable and safe structures with timber.
Christensen EG, Hu Y, Purnomo DMJ, et al., 2021, Influence of wind and slope on multidimensional smouldering peat fires, Proceedings of the Combustion Institute, Vol: 38, Pages: 5033-5041, ISSN: 1540-7489
Smouldering peat fires are the largest fires on Earth, destroying an important ecosystem, and releasing large quantities of smoke, which is responsible for health issues and carbon emissions. Here we study the influence of wind direction (forward, perpendicular, and opposed) and slope (uphill, side hill, and downhill) on multidimensional smouldering spread, using a shallow open reactor. These conditions are known to be controlling variables in spread dynamics of flaming wildfires; however, wind and slope are rarely studied for smouldering wildfires. We conducted 21 experiments and compared the data to an additional 15 experiments from the literature. Where airflow was concurrent with spread (forward wind and uphill), both wind and slope increased the horizontal and in-depth spread rates by up to 101% and 32%, respectively, from quiescent and flat conditions. When airflow was perpendicular to spread (perpendicular wind and side hill), horizontal spread rate was increased by wind (up to 21%), but was negligibly influenced by slope. Airflow opposite to the spread direction (opposed wind and downhill) resulted in a negligible change in horizontal spread with wind, but a decrease in horizontal spread of up to 40% due to slope. We also found that spread in any direction on a slope can be evaluated as a function of the angle of the spread relative to the horizontal plane, regardless of the slope of the terrain. Our findings provide new insight into important field conditions affecting smouldering wildfires and provide a better understanding of their spread.
Yuan H, Richter F, Rein G, 2021, A multi-step reaction scheme to simulate self-heating ignition of coal: Effects of oxygen adsorption and smouldering combustion, Proceedings of the Combustion Institute, Vol: 38, Pages: 4717-4725, ISSN: 1540-7489
Self-heating ignition has been a fire hazard in coal production, transportation, and storage for decades. Self-heating ignition of coal is driven by two exothermic processes which are chemically and thermodynamically different: adsorption of oxygen and heterogeneous combustion (smouldering). In classical self-heating theory and previous computational studies, a lumped one-step reaction was used. However, this scheme does not differentiate the aforementioned two processes. This study develops a computational model that incorporates a 4-step reaction scheme, encompassing both adsorption and smouldering, to simulate self-heating ignition. The kinetic parameters for a bituminous coal are first obtained through inverse-modelling of thermogravimetric experimental data from the literature. Based on the 4-step reaction scheme and kinetic parameters, we simulate two sets of hot plate experiments from the literature and predict the critical ignition temperature of different sample thicknesses. These predictions are compared with the predictions using a 1-step reaction scheme. Predictions based on both schemes show a good agreement with experiments when sample thickness(L) is less than 20 mm. However, the accuracy of the model with1-step scheme decreases as the sample thickness increases. The critical ignition temperatures predicted by the 1-step scheme become significantly higher than the 4-step scheme when L > 20 mm and at L = 127 mm the difference is over 12%. According to the simulation results of the 4-step scheme, at the large-scale scenarios, adsorption is the dominant reaction before ignition and the acceleration of smouldering occurs afterwards. As 1-step reaction scheme does not differentiate adsorption and smouldering, a 4-step scheme is more suitable for realistic and large scale scenarios.
Yang J, Rein G, Chen H, et al., 2020, Smoldering propensity in upholstered furniture: Effects of mock-up configuration and foam thickness, APPLIED THERMAL ENGINEERING, Vol: 181, ISSN: 1359-4311
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