Publications
219 results found
Hu Y, Rein G, 2022, Development of gas signatures of smouldering peat wildfire from emission factors, INTERNATIONAL JOURNAL OF WILDLAND FIRE, Vol: 31, Pages: 1014-1032, ISSN: 1049-8001
- Author Web Link
- Cite
- Citations: 3
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.
Richter F, Jervis FX, Huang X, et al., 2021, Effect of oxygen on the burning rate of wood, Combustion and Flame, Vol: 234, ISSN: 0010-2180
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
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.
Vigne G, Wegrzynski W, Cantizano A, et al., 2021, Experimental and computational study of smoke dynamics from multiple fire sources inside a large-volume building, BUILDING SIMULATION, Vol: 14, Pages: 1147-1161, ISSN: 1996-3599
- Author Web Link
- Cite
- Citations: 7
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.
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.
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
- Author Web Link
- Cite
- Citations: 14
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
Hu Z, He X, Rein G, et al., 2020, Numerical study of self-heating ignition of a box of lithium-ion batteries during storage, Fire Technology, Vol: 56, Pages: 2603-2621, ISSN: 0015-2684
Many thermal events have been reported during storage and transport of large numbers of Lithium-ion batteries (LIBs), raising industry concerns and research interests in its mechanisms. Apart from electrochemical failure, self-heating ignition, driven by poor heat transfer could also be a possible cause of fire in large-scale ensembles of LIBs. The classical theories and models of self-heating ignition assume a homogeneous lumped system, whereas LIBs storage involves complex geometry and heterogeneous material composition due to the packaging and insulation, which significantly changes the heat transfer within the system. These effects on the self-heating behaviour of LIBs have not been studied yet. In this study, the self-heating ignition behaviour of a box containing 100 LiCoO2 (LCO) type of cylindrical cells with different insulation is numerically modelled using COMSOL Multiphysics with a multi-step reaction scheme. The model predicts that the critical ambient temperature triggering self-ignition of the box is 125°C, which is 30°C lower than that for a single cell, and the time to thermal runaway is predicted to be 15 times longer. The effects of different insulating materials and packing configurations are also analysed. This work provides novel insights into the self-heating of large-scale LIBs.
He X, Restuccia F, Zhang Y, et al., 2020, Experimental study of self-heating ignition of lithium-ion batteries during storage: effect of the number of cells, Fire Technology, Vol: 56, Pages: 2649-2669, ISSN: 0015-2684
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.
Mitchell H, Rein G, 2020, Matlab Code for PERIL (Population Evacuation tRigger aLgorithm)
PERIL (Population Evacuation tRigger aLgorithm).This code computes trigger perimeters for wildfire evacuation of a rural community. It was based on the work of Cova et al 2005.Matlab code written by Harry Mitchell, supervised by Guillermo Rein, 2018-2020.Department of Mechanical Engineering at Imperial College London.Public version 1, Oct 2020, London.
Amin HMF, Hu Y, Rein G, 2020, Spatially resolved horizontal spread in smouldering peat combining infrared and visual diagnostics, Combustion and Flame, Vol: 220, Pages: 328-336, ISSN: 0010-2180
Smouldering wildfires in peatlands can last for weeks, resulting in the release of large amount of soil carbon and harmful emissions with detrimental effects on human health and the environment. Despite their importance, smouldering fires are poorly understood. An experimental study was carried out here to measure the spread rate of peat fire in detail, using infrared (IR) imaging. Peat samples with different moisture contents were prepared and burned in an open reactor of 20 × 20 cm2 cross section and 10 cm depth, under laboratory-controlled conditions. In total, twelve experiments were studied, each lasting for 8 h on average. Infrared and visual cameras were synchronised, and images were acquired at a frequency of 1/min, for the duration of the experiment. Profiles of smouldering spread on the free surface of peat were tracked using an image intensity threshold and then used to calculate the horizontal spread rate. Temporally and spatially resolved spread rates are presented and analysed. Increasing the moisture content of the peat resulted in a decrease in spread rate and the smouldering front became increasingly irregular. At high moisture contents, spread at the lower layers of peat is faster compared to top surfaces which leads to formation of overhang, and IR is able to measure the formation of the overhang and its collapse as a step increase in horizontal spread. The overhang becomes more prominent when moisture content is increased. The new tool allows the study of unprecedented details in the spread of peat fires and can be adopted in future experimental studies.
Vermesi I, Richter F, Chaos M, et al., 2020, Ignition and burning of fibreboard exposed to transient irradiation, Fire Technology, Vol: 57, Pages: 1095-1113, ISSN: 0015-2684
Natural materials like wood are increasingly used in the construction industry, making the understanding of their ignition and burning behaviour in fires crucial. The state of the art of wood flammability is based mostly on studies at constant heating. However, accidental fires are better represented by transient heating. Here, we study the piloted ignition and burning of medium density fibreboard (MDF) under transient irradiation. Experiments are conducted in a Fire Propagation Apparatus under parabolic heat flux pulses with peak irradiation ranging from 30 to 40 kW/m2 and time-to-peak irradiation from 160 to 480 s. The experimental results reveal that the critical conditions for ignition of fibreboard vary over wide ranges: mass flux between 4.9 to 7.4 g/m2-s, surface temperature between 276 to 298°C, and heat flux between 29 to 40 kW/m2. Flameout conditions are studied as well, with observations of when it leads either to extinction or to smouldering combustion. We explored the experiments further with a one-dimensional pyrolysis model in Gpyro and show that predictions are accurate. Assuming a non-uniform density profile (a realistic assumption) improves the predictions in comparison to a uniform density profile by increasing the mass loss rate by 12%, decreasing the temperatures by 45%, and increasing the ignition time by 20 s. These results further support previous findings that a single critical condition for igntion or flameout established under constant irradiation does not hold under transient irradiation which indicates that ignition and extinction theories need improvements.
Bravo Diaz L, He X, Hu Z, et al., 2020, Review—meta-review of fire safety of lithium-ion batteries: industry challenges and research contributions, Journal of The Electrochemical Society, Vol: 167, Pages: 1-14, ISSN: 0013-4651
The Lithium-ion battery (LIB) is an important technology for the present and future of energy storage, transport, and consumer electronics. However, many LIB types display a tendency to ignite or release gases. Although statistically rare, LIB fires pose hazards which are significantly different to other fire hazards in terms of initiation route, rate of spread, duration, toxicity, and suppression. For the first time, this paper collects and analyses the safety challenges faced by LIB industries across sectors, and compares them to the research contributions found in all the review papers in the field. The comparison identifies knowledge gaps and opportunities going forward. Industry and research efforts agree on the importance of understanding thermal runaway at the component and cell scales, and on the importance of developing prevention technologies. But much less research attention has been given to safety at the module and pack scales, or to other fire protection layers, such as compartmentation, detection or suppression. In order to close the gaps found and accelerate the arrival of new LIB safety solutions, we recommend closer collaborations between the battery and fire safety communities, which, supported by the major industries, could drive improvements, integration and harmonization of LIB safety across sectors.
Ang CD, Rein G, Peiro J, 2020, Unexpected oscillations in fire modelling inside a long tunnel, Fire Technology, Vol: 56, Pages: 1937-1941, ISSN: 0015-2684
Richter F, Rein G, 2020, A multiscale model of wood pyrolysis in fire to study the roles of chemistry and heat transfer at the mesoscale, Combustion and Flame, Vol: 216, Pages: 316-325, ISSN: 0010-2180
Pyrolysis is a key process in all stages of wood burning from ignition to extinction. Understanding each stage is crucial to tackle wildfires and assess the fire safety of timber buildings. A model of appropriate complexity of wood pyrolysis and oxidation is missing, which limits the understanding of fires fuelled by wood. Progress towards this aim has been slow in recent years, as the role of chemical kinetics is still debated. Three predominant theories hypothesis that chemistry is either infinitely fast (de Ris), a function of char depth (Atreya), or a function of heat flux (Suuberg). This paper proposes a novel multi-scale model of wood pyrolysis and oxidation for predicting the charring of timber. The chemical kinetics sub-model was previously validated at the microscale (mg-samples). We favourably compare the complete model against a large range of mesoscale experiments (g-samples) found in the literature of different moisture contents (0–30%), heat fluxes (0–60 kW/m2), oxygen concentrations (0–21%), grain directions (parallel/perpendicular), and combinations thereof. The model was then used to calculate the transient Damköhler number of wood at different depths and heat fluxes. This analysis showed that chemistry and heat transfer are both important at all heat fluxes and stages of burning relevant to fire, which unifies the three theories by Suuberg, Atreya, and de Ris. We argue that the model is of currently appropriate complexity to predict the charring of timber. These findings improve our understanding of wood pyrolysis and the modelling of timber burning across scales.
Hu Y, Cui W, Rein G, 2020, Haze emissions from smouldering peat: The roles of inorganic content and bulk density, Fire Safety Journal, Vol: 113, Pages: 1-9, ISSN: 0379-7112
Smouldering peat fires are reported across continents and their emissions result in regional haze crisis (large scale accumulation of smoke at low altitudes) and large carbon foot prints. Inorganic content (IC) and bulk density vary naturally in peatlands and are among the important parameters governing peat fires. However, their roles in fire emissions remain unknown. In this work, bench-scale burning of sphagnum peat conditioned to different values of IC and bulk densities were conducted in the laboratory environment. Mass loss rate, spread rate and transient emissions of 20 gas species and particles (PM10, PM2.5 and PM1) were simultaneously investigated. We found that peat with 50% moisture content can self-sustain smouldering propagation if IC is less than 40%, or its bulk density is lower than 287.5 kg m−3. Increasing IC or bulk density decreases peat mass loss rate and spread rate. High IC peat releases lower gas fluxes (especially for CH4 and NH3) throughout the experiment. In the ignition stage, increasing IC leads to an increase in particles with diameter between 1 and 2.5 μm; in the fire spread stage, IC has no influence on the particle fluxes. In contrast, increasing bulk density delays both gas and particle emission fluxes without altering the smoke composition significantly. The fundamental understanding of how soil properties affect peat wildfires facilitates the development of mitigation technologies against haze.
Christensen EG, Fernandez-Anez N, Rein G, 2020, Influence of soil conditions on the multidimensional spread of smouldering combustion in shallow layers, Combustion and Flame, Vol: 214, Pages: 361-370, ISSN: 0010-2180
Smouldering peatland fires are capable of burning vast amounts of organic soils, resulting in the release of greenhouse gases into the atmosphere, as well as a significant deterioration of air quality causing in major regional crises known as haze events. Fundamental understanding of smouldering fire spread is essential for the development of mitigating technologies. In this paper, we have systematically conducted 63 experiments studying the individual and combined influence of two key factors affecting multidimensional smouldering spread in organic soils: moisture content (MC) and inorganic content (IC). Both lateral and in-depth smouldering spread were investigated using a novel shallow reactor. This shallow depth allows a greater number of experiments to be performed in a short period of time compared to deeper samples. Lateral spread was found to decrease linearly with moisture content (R2 > 90%); while in-depth spread rate increased linearly up to 300% from moisture content of 0% to 140%. Increased inorganic content linearly decreased the lateral spread rate but had little influence on in-depth spread in drier samples. Interestingly, in wetter samples, in-depth spread was in fact sensitive to inorganic content. A novel approach combining lateral and in-depth spread rates as vector components, revealed that the global spread is independent of moisture content, with an average spread rate of 8.7 and 8.4 cm/h for 2.5 and 40% IC, with changes in direction according to moisture content; going in-depth for wet soils, and laterally for dry soils. Similarly, increasing the IC encouraged downward spread for wet samples. We also report observations of a bifurcation of lateral spread, where spread would locally extinguish where the in-depth spread was greater than the lateral spread. These findings provide previously unknown insight into the relationship between lateral and in-depth spread in smouldering fires, ultimately improving the fundamental understanding of such
Richter F, Rein G, 2020, Reduced chemical kinetics for microscale pyrolysis of softwood and hardwood, Bioresource Technology, Vol: 301, Pages: 1-7, ISSN: 0960-8524
This work studies the chemical kinetics of wood pyrolysis by comparing nine reduced reaction schemes against 22 microscale experiments of softwood and hardwood from the literature. The complexity of reaction schemes ranged from 1 to 12 reactions, with 2 to 7 species. Using multi-objective optimization for isothermal and non-isothermal conditions, the kinetic parameters for each reaction scheme were derived. It was found that the uncertainty of a prediction increases with the number of model parameters, but the accuracy does not always increase with the number of parameters. The appropriate reaction scheme for hardwood is three parallel reactions, as it presents the optimal balance between accuracy and uncertainty. For softwood, a higher complexity could be justified. This work shows the benefits of finding an appropriately complex kinetic scheme by building up complexity from simple schemes.
Yuan H, Restuccia F, Rein G, 2020, Computational study on self-heating ignition and smouldering spread of coal layers in flat and wedge hot plate configurations, Combustion and Flame, Vol: 214, Pages: 346-357, ISSN: 0010-2180
Porous fuels have the propensity to self-heat. Self-heating ignition has been a hazard and safety concern in fuel production, transportation, and storage for decades. During the process of self-heating ignition, a hot spot forms in the fuel layer and then spreads as a smouldering fire. The understanding of hot spot and smouldering spread is important for prevention, detection, and mitigation of fires. In this paper, we build a computational model that unifies the simulation of self-heating ignition and smouldering spread by adopting a two-step kinetic scheme obtained from literature. The model is validated against hot plate experiments of coal in both flat and wedge configurations. The comparison shows that the model predicts the minimum ignition temperature (Tig) and transient temperature profiles reasonably well. The simulation results demonstrate that the hot spot originates at the hot plate and then spreads towards the free surface due to oxygen consumption. In the wedge configuration, the simulations show that the height of maximum temperature point decreases with wedge angle, and that the influence of wedge angle can be explained by the heat transfer. This model brings together two combustion phenomena (self-heating ignition and smouldering) that were traditionally studied separately and analyses the transient behaviour of hot spot and smouldering spread in detail. It deepens our understanding of self-heating fire and can help mitigate the hazard.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.