175 results found
Rein G, Huang X, 2021, Smouldering Wildfires in Peatlands, Forests and the Arctic: Challenges and Perspectives, Current Opinion in Environmental Science & Health, Pages: 100296-100296, ISSN: 2468-5844
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.
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
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
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.
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.
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.
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.
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.
Purnomo DMJ, Bonner M, Moafi S, et al., 2020, Using cellular automata to simulate field-scale flaming and smouldering wildfires in tropical peatlands, Proceedings of the Combustion Institute, ISSN: 1540-7489
Vigne G, Wegrzynski W, Cantizano A, et al., 2020, 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
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.
Heidari M, Kotsovinos P, Rein G, 2020, Flame extension and the near field under the ceiling for travelling fires inside large compartments, Fire and Materials: an international journal, Vol: 44, Pages: 423-436, ISSN: 0308-0501
Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load‐bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open‐plan generic office compartment with a floor area of 960 m2 and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m2 for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m2 for the Hasemi and Lattimer models, compared with 215 to 228 kW/m2 for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than T
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.
Zanoni MAB, Rein G, Yermán L, et al., 2020, Thermal and oxidative decomposition of bitumen at the Microscale: Kinetic inverse modelling, Fuel, Vol: 264, Pages: 1-11, ISSN: 0016-2361
Understanding the thermal decomposition of fuels and estimating their kinetic parameters are essential for simulating chemical reactions in numerical models. In this work, 2-step, 3-step, 4-step, and 5-step kinetic mechanisms for bitumen combustion were developed. The kinetic parameters were optimized via inverse modelling (genetic algorithm) by coupling thermogravimetry (TG) and differential thermogravimetry (DTG), conducted at 5, 10, 20, and 40 °C min−1 under nitrogen and air atmospheres. A 3-step mechanism that includes competing pyrolysis and oxidation reactions was identified as the simplest mechanism able to appropriately simulate all TG experiments, thus avoiding the need for more complex mechanisms. A unique set of kinetic parameters was found by averaging all the parameters optimized at different heating rates and atmospheres, resulting in an average error of 6% when compared with experimental data. This is the first time that averaged optimized parameters were employed, providing similar results as optimizing against all experiments at once. Differential scanning calorimetry experiments were used to calculate the heat of pyrolysis and oxidation, and showed that char oxidation provided the highest energy release, whereas bitumen and asphaltene oxidation represented a 30–110 times lower heat of reaction. This is the first time that thermogravimetry and differential scanning calorimetry experiments were used to optimize kinetic parameters for bitumen combustion.
Kotsovinos P, Atalioti A, Rein G, et al., 2020, Analysis of the thermomechanical response of structural cables subject to fire, Fire Technology, Vol: 56, Pages: 515-543, ISSN: 0015-2684
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.
Purnomo D, Richter F, Bonner M, et al., 2020, Role of optimisation method on kinetic inverse modelling of biomass pyrolysis at the microscale, Fuel: the science and technology of fuel and energy, Vol: 262, ISSN: 0016-2361
Biomass pyrolysis is important to biofuel production and fire safety. Inverse modelling is an increasingly used technique to find values for the kinetic parameters that control pyrolysis. The quality of kinetic inverse modelling depends on, in order of importance, the quality of the experimental data, the kinetic model, and the optimisation method used. Unlike the two former components, the optimisation method chosen, i.e. the combination of algorithm and objective function, is rarely discussed in the literature. This work compares the accuracy and efficiency of five commonly used advanced algorithms (Genetic Algorithm, AMALGAM, Shuffled Complex Evolution, Cuckoo Search, and Multi-Start Nonlinear Program) and a simple algorithm (a Random Search) to find the kinetic parameters for cellulose and wood pyrolysis at the microscale. These algorithms are combined with seven objective functions comprising concentrated and dispersed functions. The results show that for cellulose (simple chemistry) the use of an advanced optimisation algorithm is unnecessary, since a simple algorithm achieves similarly high accuracy with higher efficiency. However, for wood (complex chemistry) a combination of an advanced algorithm and a concentrated function greatly improve accuracy. Among the 25 possible combinations we investigated, Shuffled Complex Evolution with mean square error objective function performed best with 0.91% error in mass loss rate and 0.88 × 1013 CPU time. These findings can guide the selection of the best optimisation method to use in inverse modelling of kinetic parameters and ensuring both accuracy and efficiency.
Bonner M, Wegrzynski W, Papis BK, et al., 2020, KRESNIK: A top-down, statistical approach to understand the fire performance of building facades using standard test data, Building and Environment, Vol: 169, ISSN: 0360-1323
The facade is one of the most complex parts of a building, performing multiple objectives of value to the occupants. The frequency of facade fires in tall buildings is increasing, therefore it is crucial to understand the behaviour of such facades in a fire, but there is currently no theory, model, or series of experiments that allows this understanding. This paper takes a top-down, data driven approach to understanding facade behaviour by analysing a unique database, named KRESNIK, containing 252 commercial facade fire tests, the first time such data has been analysed. We found that the outputs from these tests were correlated, which could be used to gain more information of facade performance than simply pass or fail; and that the different layers of a facade can have a significant effect, particularly the addition of a cavity. Rainscreen facades performed the worst (45% failed), whereas none of the ETICS or sandwich panels in KRESNIK failed. We also found that the choice of cladding material of these rainscreens is the most important factor in driving their fire performance, but that neither its total fuel nor its conductive resistance can predict fire performance. Finally, we found that repeated tests of identical facades could have major variations in the outputs, but that whether the facade ignited or not tended to remain consistent across repeats. These results help to identify critical factors in facade flammability, better informing engineering decisions, and contributing to the design of safe tall buildings.
The International Association of Fire Safety Science (IAFSS) is comprised of members from some 40 countries. This paper presents the Association's thinking, developed by the Management Committee, concerning pressing research needs for the coming 10 years presented as the IAFSS Agenda 2030 for a Fire Safe World. The research needs are couched in terms of two broad Societal Grand Challenges: (1) climate change, resiliency and sustainability and (2) population growth, urbanization and globalization. The two Societal Grand Challenges include significant fire safety components, that lead both individually and collectively to the need for a number of fire safety and engineering research activities and actions. The IAFSS has identified a list of areas of research and actions in response to these challenges. The list is not exhaustive, and actions within actions could be defined, but this paper does not attempt to cover all future needs.
Jeanneret C, Gales J, Kotsovinos P, et al., 2019, Acceptance Criteria for Unbonded Post-Tensioned Concrete Exposed to Travelling and Traditional Design Fires, Fire Technology, ISSN: 0015-2684
Restuccia F, Fernandez-Anez N, Rein G, 2019, Experimental measurement of particle size effects on the self-heating ignition of biomass piles: Homogeneous samples of dust and pellets, Fuel, Vol: 256, ISSN: 0016-2361
Biomass can become an important fuel source for future power generation worldwide. However biomass piles are prone to self-heating and can lead to fire. When storing and transporting biomass, it is usually in the form of pellets which vary in diameter but are on average in the order of 7 mm. However, pellets tend to break up into smaller particles and into dust down to the µm size. For self-heating, size of particles is known to matter but the topic is poorly studied for biomass piles. This work presents an experimental study on the self-heating ignition behaviour of different particle sizes of wheat biomass. We study for the first time homogeneous samples from the dust scale to pellet diameter size, ranging from diameters of 300 µm to 6.5 mm. Experiments are done in an isothermal oven to find minimum ignition temperatures as a function of sample volume. The results are analysed using Frank-Kamenetskii theory. For the homogeneous biomass samples studied, we show that particle diameter variation does not bring a large change in self-heating ignition behaviour. The present work can be used to help quantify size effects on biomass ignition and help address the safety problems of biomass fires.
Hu Y, Christensen EG, Amin HMF, et al., 2019, Experimental study of moisture content effects on the transient gas and particle emissions from peat fires, Combustion and Flame, Vol: 209, Pages: 408-417, ISSN: 0010-2180
Peat fires are a global-scale source of carbon emissions and a leading cause of regional air quality deterioration, especially in Southeast Asia. The ignition and spread of peat fires are strongly affected by moisture, which acts as an energy sink. However, moisture effects on peat fire emissions are poorly understood in the literature. Here we present the first experimental work to investigate transient gas and particle emissions for a wide range of peat moisture contents (MCs). We include drying, ignition, smouldering spread, and even flaming stages. Peat samples conditioned to different MCs were burnt in the laboratory where a suite of diagnostics simultaneously measured mass loss rate, temperature profiles, real-time concentration of 20 gas species, and size-fractioned particle mass. It was found that MC affects emissions, in addition to peat burning dynamics. An increase in MC below a smouldering threshold of 160% in dry basis leads to a decrease in NH3 and greenhouse gas emissions, including CO2 and CH4. The burning of wet peat emits more coarse particles (between 1 and 10 µm) than dry peat, especially during the ignition stage. In contrast, flaming stage emits mostly soot particles less than 1 µm, and releases 100% more fully oxidised gas species including CO2, NO2 and SO2 than smouldering. The examination of the resulting modified combustion efficiency (MCE) reveals that it fails to recongnise smouldering combustion with sufficient accuracy, especially for wet peat with MC > 120%. MCE confuses drying and flaming, and has significant variations during the ignition stage. As a result, MCE is not valid as a universal fire mode indicator used in the field. This work fills the knowledge gap between moisture and emissions, and provides a better understanding which can help mitigate peat fires.
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