Publications
219 results found
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
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.
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.
Yuan H, Huang X, Rein G, 2020, Gpyro workbook on pyrolysis & smouldering problems, Publisher: Zenodo
Gpyro is a powerful open-source simulation tool for computational study of pyrolysis and smouldering.Due to the large number of input parameters and high degree of flexibility in specifying them, some beginning learners may still have difficulty in using this tool well, especially when applying it to investigate a specific case.We therefore produce this document, aiming to further help Gpyro users. We adapt published researches to several typical solid pyrolysis/smouldering problems and demonstrate how to use Gpyro to solve these problems. In the solutions, the key setting steps and validated simulation results are shown along with some input files attached as reference. We hope this document can serve as a complementary document to the official user-supporting files (ie. technical reference and user’s guidance) and provide more details for the implementation of Gpyro. Since it is a complementary rather than an overall user’s guidance, before reading this document, users should first read through technical reference and user’s guidance to get familiar with the basics on concepts, physical models, and implementation of Gpyro.
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.
McNamee M, Meacham B, van Hees P, et al., 2019, IAFSS agenda 2030 for a fire safe world, Fire Safety Journal, Vol: 110, Pages: 1-7, ISSN: 0379-7112
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.
Ronchi E, Gwynne SMV, Rein G, et al., 2019, An open multi-physics framework for modelling wildland-urban interface fire evacuations, Safety Science, Vol: 118, Pages: 868-880, ISSN: 0925-7535
Fire evacuations at wildland-urban interfaces (WUI) pose a serious challenge to the emergency services, and are a global issue affecting thousands of communities around the world. This paper presents a multi-physics framework for the simulation of evacuation in WUI wildfire incidents, including three main modelling layers: wildfire, pedestrians, and traffic. Currently, these layers have been mostly modelled in isolation and there is no comprehensive model which accounts for their integration. The key features needed for system integration are identified, namely: consistent level of refinement of each layer (i.e. spatial and temporal scales) and their application (e.g. evacuation planning or emergency response), and complete data exchange. Timelines of WUI fire events are analysed using an approach similar to building fire engineering (available vs. required safe egress times for WUI fires, i.e. WASET/WRSET). The proposed framework allows for a paradigm shift from current wildfire risk assessment and mapping tools towards dynamic fire vulnerability mapping. This is the assessment of spatial and temporal vulnerabilities based on the wildfire threat evolution along with variables related to the infrastructure, population and network characteristics. This framework allows for the integration of the three main modelling layers affecting WUI fire evacuation and aims at improving the safety of WUI communities by minimising the consequences of wildfire evacuations.
Santoso MA, Christensen EG, Yang J, et al., 2019, Review of the transition From smouldering to flaming combustion in wildfires, Frontiers in Mechanical Engineering, Vol: 5, ISSN: 2297-3079
Wildfires are uncontrolled combustion events occurring in the natural environment (forest, grassland, or peatland). The frequency and size of these fires are expected to increase globally due to changes in climate, land use, and population movements, posing a significant threat to people, property, resources, and the environment. Wildfires can be broadly divided into two types: smouldering (heterogeneous combustion) and flaming (homogeneous combustion). Both are important in wildfires, and despite being fundamentally different, one can lead to the other. The smouldering-to-flaming (StF) transition is a quick initiation of homogeneous gas-phase ignition preceded by smouldering combustion, and is considered a threat because the following sudden increase in spread rate, power, and hazard. StF transition needs sufficient oxygen supply, heat generation, and pyrolysis gases. The unpredictable nature of the StF transition, both temporally and spatially, poses a challenge in wildfire prevention and mitigation. For example, a flaming fire may rekindle through the StF transition of an undetected smouldering fire or glowing embers. The current understanding of the mechanisms leading to the transition is poor and mostly limited to experiments with samples smaller than 1.2 m. Broadly, the literature has identified the two variables that govern this transition, i.e., oxygen supply and heat flux. Wind has competing effects by increasing the oxygen supply, but simultaneously increasing cooling. The permeability of a fuel and its ability to remain consolidated during burning has also been found to influence the transition. Permeability controls oxygen penetration into the fuel, and consolidation allows the formation of internal pores where StF can take place. Considering the high complexity of the StF transition problem, more studies are needed on different types of fuel, especially on wildland fuels because most studied materials are synthetic polymers. This paper synthesises the r
Zhu J, Jahn W, Rein G, 2019, Computer simulation of sunlight concentration due to façade shape: application to the 2013 Death Ray at Fenchurch Street, London, Journal of Building Performance Simulation, Vol: 12, Pages: 378-387, ISSN: 1940-1507
Reflected sunlight from the Walkie-Talkie building in 20 Fenchurch Street, London, was reported to have caused the melting of plastic components of a car parked at street level in late August of 2013. The incident was explained by the concave-shaped south façade of the building, which converges solar radiation into a hotspot. In this study, we test the sunlight concentation hypothesis with a lighting simulation. A geometry model with material properties was created, and different weather situations were modelled. The results are illustrated in irradiance maps indicating time, position and peak heat fluxes. The highest simulated flux on the day of the incident was 3320 Wm−2 (10 to 15 fold increase compared to direct solar radiation). Additionally, the specific time and day for maximum heat fluxes between June and December were determined . For the worst scenario, which was avoided becuase the sky was partially cover with clouds that day and the hotspot did not fall on street level, the simulations showed that the peak heat flux would have reached well over 4000 Wm−2.
Heidari M, Robert F, Lange D, et al., 2019, Probabilistic study of the resistance of a simply-supported reinforced concrete slab according to Eurocode parametric fire, Fire Technology, Vol: 55, Pages: 1377-1404, ISSN: 0015-2684
We present the application of a simple probabilistic methodology to determine the reliability of a structural element exposed to fire when designed following Eurocode 1-1-2 (EC1). Eurocodes are being used extensively within the European Union in the design of many buildings and structures. Here, the methodology is applied to a simply-supported, reinforced concrete slab 180 mm thick, with a standard load bearing fire resistance of 90 min. The slab is subjected to a fire in an office compartment of 420 m 2 floor area and 4 m height. Temperature time curves are produced using the EC1 parametric fire curve, which assumes uniform temperature and a uniform burning condition for the fire. Heat transfer calculations identify the plausible worst case scenarios in terms of maximum rebar temperature. We found that a ventilation-controlled fire with opening factor 0.02 m 1/2 results in a maximum rebar temperature of 448°C after 102 min of fire exposure. Sensitivity analyses to the main parameters in the EC1 fire curves and in the EC1 heat transfer calculations are performed using a one-at-a-time (OAT) method. The failure probability is then calculated for a series of input parameters using the Monte Carlo method. The results show that this slab has a 0.3% probability of failure when the compartment is designed with all layers of safety in place (detection and sprinkler systems, safe access route, and fire fighting devices are available). Unavailability of sprinkler systems results in a 1% probability of failure. When both sprinkler system and detection are not available in the building, the probability of failure is 8%. This novel study conducts for the first time a probabilistic calculation using the EC1 parametric curve, helping engineers to identify the most critical design fires and the probabilistic resistance assumed in EC1.
Roenner N, Yuan H, Kraemer RH, et al., 2019, Computational study of how inert additives affect the flammability of a polymer, Fire Safety Journal, Vol: 106, Pages: 189-196, ISSN: 0379-7112
All polymers are flammable to some degree. For safety, polymer flammability is most commonly reduced through flame retardants that are designed to primarily act chemically as opposed to physically. Here, we investigate computationally using the code Gpyro how inert additives such as hollow glass spheres (HGS) and boron nitride platelets (BNP) alter the flammability properties of glass fibre reinforced polybutylene terephthalate (PBT-GF), in a cone heater and UL94 setup. The Gpyro model is first validated against experiments and another code, both from the literature, for pure PBT-GF. According to the predictions, HGS leads to higher surface temperatures but lower temperatures in-depth, whereas adding BNP yields the opposite effect. Modelling numerically the cone heater setup shows that at 50% HGS loading, the time to ignition is reduced to a quarter while the semi-steady state mass loss rate is reduced to a third; at 50% BNP loading, the time to ignition is doubled while the peak mass loss rate is approximately doubled. In the UL94 setup, where the sample is smaller than cone heater, the effects are similar although less pronounced. A sensitivity study of the thermophysical properties shows that time to ignition is primarily controlled by emissivity, density and specific heat capacity, while peak mass loss rate is controlled by thermal conductivity and specific heat capacity. This work shows how heat transfer within a thermoplastic polymer can be utilised to improve its flammability characteristics through inert additives as well as the limitations of this retardancy approach.
Vigne G, Gutierrez-Montes C, Cantizano A, et al., 2019, Review and validation of the current smoke plume entrainment models for large-volume buildings, Fire Technology, Vol: 55, Pages: 789-816, ISSN: 0015-2684
The design of smoke management systems in large-volume enclosures is of utter importance for life safety, property protection, and business continuity in case of fire. Despite the recent international trend in smoke control design towards the use of advanced fire models, simple plume entrainment correlations are the basis of the discipline and are still a common practice since they are often incorporated in technical documents for the design of smoke control systems. Different plume entrainment correlations have been developed over the years and are cited in different national codes and design guides. These correlations have been widely investigated for fires in small enclosures, but their applicability and accuracy in large enclosures is not clear. The present work studies the suitability and applicability of these approaches to properly predict the fire induced conditions within large volumes. The results obtained from the plume entrainment correlations have been compared with full scale experimental data in an 8.000 m3 enclosure. Based on the results obtained by this analysis performed in a large-volume enclosure, the current methods available of modelling fire and determining the smoke produced by the fire might not be suitable. It was observed that for the steady state, the McCaffrey correlation gave results closest to the experiments, and for the transient evolution of the smoke layer, the Zukoski correlation. On the contrary, the popular Thomas method underpredicted smoke production and entrainment, giving the highest smoke layer interface heights and leading to estimations that are not conservative (with errors between 36.5% and 101%). The authors analyze the reasons for the discrepancies and give some practical recommendations for the design of smoke control in large volume buildings, such as that the use of such models to predict the smoke production of a given fire shall be only a first approximation and not a design tool, especially when using those
Richter F, Rein G, 2019, Heterogeneous kinetics of timber charring at the microscale, Journal of Analytical and Applied Pyrolysis, Vol: 138, Pages: 1-9, ISSN: 0165-2370
Timber is becoming a popular construction material even for high-rise buildings despite its poorly understood fire behaviour. In a fire, timber—a natural polymer—degrades in the thermochemical process of charring, causing it to lose structural strength. In spite of significant research on the physics of charring, the chemical kinetics—reactions and kinetic parameters for pyrolysis and oxidation—remains a scientific challenge to model accurately. Current kinetic models are either computationally too expensive or neglect key chemical pathways. Here we derive a new appropriate kinetic model for fire science at the microscale using a novel methodology. First, we built a kinetic model for each component of timber (cellulose, hemicellulose, and lignin) from literature studies and experiments of the components. Then, we combined these three models into one kinetic model (8 reactions, 8 chemical species) for timber. This approach accounts for chemical differences among timber species. However, the timber model is only able to reproduce the trend in the experiments when literature parameters are used. Using multi-objective inverse modelling, we extract a new set of optimised kinetic parameters from 16 high-quality experiments from the literature. The novel optimised kinetic model is able to reproduce these 16 and a further 64 (blind predictions) experiments nearly within the experimental uncertainty, spanning different heating rates (1–60 K/min), oxygen concentrations (0–60 %), and even isothermal experiments (220–300 °C). Furthermore, the model outperforms current kinetic models for fire science in accuracy across a wide range of conditions without an increase in complexity. Incorporated into a model of heat and mass transfer, this new and optmised kinetic model could improve the understanding of timber burning and has the potenial to lead to safer designs of timber buildings.
Fernandez-Anez N, Christensen K, Frette V, et al., 2019, Simulation of fingering behavior in smoldering combustion using a cellular automaton, Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 99, ISSN: 1539-3755
Smoldering is the slow, low-temperature, flameless burning of porous fuels and the most persistent type of combustion phenomena. It is a complex physical process that is not yet completely understood, but it is known that it is driven by heat transfer, mass transfer, and fuel chemistry. A specific case of high interest and complexity is fingering behavior. Fingering is an instability that occurs when a thin fuel layer burns against an oxygen current. These instabilities appear when conduction rather than convection is the dominant mode of heat transfer to the fuel ahead and the availability of oxygen is limited during the combustion of a thin fuel, such as paper. The pattern of the fingers can be characterized through the distance between them and their width, and can be classified into three different regimes: isolated fingers, tip-splitting fingers, or no fingers forming and a smooth continuous front. In this paper, a multilayer cellular automaton based on three governing principles (heat, oxygen, and fuel) is shown to reproduce all the regimes and the details of finger structures observed in previous experiments. It is shown how when oxygen is not limited, a smooth smoldering front is formed. If the oxygen speed decreases beyond a critical value, fingers appear first as tip-splitting fingers and later as isolated fingers, increasing the distance between them and decreasing their thickness. The oxygen consumed during oxidation influences these critical values with a positive correlation. This cellular automaton provides an alternative approach to simulate smoldering combustion in large systems over long times. That the model is able to reproduce the complex pattern formation seen in a fingering experiment validates the model. In the future, we could apply the model in various other geometries to make predictions on the outcome of smoldering combustion processes.
Rackauskaite E, Kotsovinos P, Jeffers A, et al., 2019, Computational analysis of thermal and structural failure criteria of a multi-storey steel frame exposed to fire, Engineering Structures, Vol: 180, Pages: 524-543, ISSN: 0141-0296
Structural fire design, until recently, has only assumed uniform fires inside the compartment, and the assessment of structural failure has been often based on a critical temperature criterion. While this criterion, to some extent, may be able to indicate the temperature at which the structural element is near to failure, it is based on standard fire tests and, therefore, its validity is limited to individual members exposed to uniform temperatures. It is unclear how representative a critical temperature criterion is of structural failure in the case of multi-story structures, particularly in the case of non-uniform fires such as travelling fires. Therefore, the aim of this study is to assess the validity of the critical temperature criterion for structures exposed to non-uniform fires and compare it to uniform fires. A generic 10-storey steel framed building is modelled using the finite element software LS-DYNA. In total, 117 different scenarios are investigated to cover a wide range of conditions of interest for design of modern steel buildings, varying the fire exposure (travelling fires, Eurocode parametric fires, ISO-834 standard fire, and SFPE standard), floor where the fire is burning, beam section size, and applied fire protection to the beams. For the different fire exposures considered, the analysis predicts structural failure at different times, in different locations and floors, and different failure mechanisms. Moreover, it is shown that there is no single worst case fire scenario: different fires can lead to failure in different structural ways. The comparison of the various structural and thermal failure criteria (ultimate strain, utilization, mid-span deflection, and critical temperature) show that there is no consistency between them, revealing a far more complex problem than reported in the literature. Lastly, this work has illustrated that the critical temperature criterion does not predict accurately the structural failure in time, space or failu
Yuan H, Restuccia F, Richter F, et al., 2019, A computational model to simulate self-heating ignition across scales, configurations, and coal origins, Fuel, Vol: 236, Pages: 1100-1109, ISSN: 0016-2361
Self-heating of fuel layers can trigger ignition when the temperature of the surroundings is sufficiently high. Self-heating ignition has been a hazard and safety concern in raw materials production, transportation, and storage facilities for centuries. Hot plate and oven-basket experiments are the two most used lab-scale experiments to assess the hazard of self-heating ignition. While extensive experiments have been done to study this phenomenon, modelling of the experiments is substantially lagging behind. A computational model that can accurately simulate self-heating ignition under the two experimental configurations has not been developed yet. In this study, we build such a model by coupling heat transfer, mass transfer, and chemistry using the open-source code Gpyro. Due to the accessibility of large amount of experimental data, coal is chosen as the material for model validation. A literature review of the kinetic parameters for coal samples from different origins reveals that there is a compensation effect between the activation energy and exponential factor. Combining the compensation effect with our model, we simulate 6 different experimental studies covering the two experimental configurations, a wide range of sample sizes (heights ranging from 5 mm to 126 mm), and various coal origins (6 countries). The model accurately predicts critical ignition temperature (Tig) for all 24 experiments with an error below 7 °C. This computational model unifies for the first time the two most used self-heating ignition experiments and provides theoretical insights to understand self-ignition for different fuels under different conditions.
Restuccia F, Masek O, Hadden R, et al., 2019, Quantifying self-heating ignition of biochar as a function of feedstock and the pyrolysis reactor temperature, Fuel, Vol: 236, Pages: 201-213, ISSN: 0016-2361
Biochar is produced from biomass through pyrolysis in a reactor under controlled conditions. Different feedstock and reactor temperatures produce materials with different physical and chemical properties. Because biomass, biochar and torrefied biomass are reactive porous media and can undergo self-heating, there is a fire hazard associated to their production, transport, and storage. This hazard needs to be tackled in biomass industries like power generation, where self-heating of biomass can cause significant problems, like the 2012 fire at Tilbury Power Plant (UK). Using basket experiments inside a thermostatically controlled laboratory oven, augmented with thermogravimetry and conductivity measurements, we experimentally study the ignition conditions of pellets and biochar made of softwood, wheat and rice husk. For softwood, we also study biochar produced at different reactor temperatures ranging from 350 to 800 °C. In total, 173 experiments were conducted with 1036 h of oven run time. By investigating the self-heating behaviour of these samples via the Frank-Kamenetskii theory, we quantify and upscale for the first time the reactivity of biochar as a function of feedstock and also of the reactor temperature. The results show that in order from higher to lower tendency to self-heating, the rank is softwood, wheat and rice husk. The reactivity of the softwood is not a monotonic function of pyrolysis reactor temperature but that biochar is most prone to self-heating when produced at 450 °C. Reactivity decreases at higher reactor temperatures, and at 600 °C the biochar is less reactive than the original feedstock. This work improves the fundamental understanding of the fire hazard posed by biomass self-heating, providing insights necessary for successful and safer biomass industries.
Huang X, Rein G, 2019, Upward-and-downward spread of smoldering peat fire, Proceedings of the Combustion Institute, Vol: 37, Pages: 4025-4033, ISSN: 1540-7489
Smoldering is the dominant combustion process in peat fire, releasing a large amount of carbon and smoke into the atmosphere. The spread of smoldering in peatland is a multi-dimensional process, which is slow, low-temperature, persistent, and difficult to detect. In this work, we investigate the upward spread of peat fire from the underground to the surface after forced ignition which is a relevant configuration but rarely studied. In the experiment, ignition is not possible if the igniter is deeper than 15 cm below the free surface, regardless of moisture content or density. Once ignited, the 1st-stage upward fire spread is initiated towards the free surface (opposed smoldering) with a peak temperature of 300 °C, leaving behind a char structure that does not collapse. Then, a 2nd-stage downward spread (forward smoldering) is activated with a peak temperature of 600 °C and regression of free surface. The upward spread is faster than the downward spread. The rates of both upward and downward spread decrease as the peat density or depth is increased. These experimental observations are successfully captured by a 1D computational model of heat and mass transfer with 5-step kinetics. Modelling results further suggest that (1) the oxygen diffusion controls the entire upward-to-downward spread of peat fire, (2) the oxidation of peat sustains the 1st-stage upward spread, and (3) the oxidation of char sustains the 2nd-stage downward spread. This is the first study investigating the upward spread of peat fire, which helps understand the persistence of peat fire and guide the fire prevention and suppression strategies.
Roenner N, Rein G, 2019, Convective ignition of polymers: New apparatus and application to a thermoplastic polymer, Proceedings of the Combustion Institute, Vol: 37, Pages: 4193-4200, ISSN: 0082-0784
A new convective ignition apparatus for polymers has been developed with measured flow and temperature fields. Polymer degradation and ignition is typically studied in fire science under radiative heating or direct contact with a pilot flame but this new apparatus allows for research to be conducted in a convective setting providing a missing piece of knowledge on flammability. Convective heating is a main mode of heat transfer in many real fires such as in the built or natural environment, like building fires or wildfires. The apparatus exposes one side of a sample to air between lab ambient and 735 °C at 0.7 to 5 m/s whilst measuring the sample 2D back side temperature via calibrated infrared. The 2D temperature and flow fields, convective heat transfer, and irradiation were studied under various operating conditions of temperature and flow. Polybutylene terephthalate (PBT) samples with glass fibre were ignited using a 735 °C hot stream. Samples of 2 mm thickness ignited after 30 s with a standard deviation lower than 1 s. The experimental work was augmented with numerical modelling of heat and mass transfer with pyrolysis chemistry in Gpyro, allowing for insight into the temperatures across the sample. Combining experimental with numerical work shows that ignition was observed at a surface temperature of 320 °C. Using this rig, ignition can be studied under a range of temperature and flow conditions filling the gaps of the literature which relies primarily on irradiated samples in natural convection conditions.
Hu Y, Christensen E, Restuccia F, et al., 2019, Transient gas and particle emissions from smouldering combustion of peat, Proceedings of the Combustion Institute, Vol: 37, Pages: 4035-4042, ISSN: 1540-7489
Smouldering combustion of peat drives the largest fires on Earth, and their emissions play an important role in global carbon balance and regional air quality. Here we report a series of controlled laboratory experiments of peat fires. Peat samples of 100% moisture content in dry basis were burnt in an open-top reactor with dimensions of 20 × 20 × 10 cm. The diagnostics are a unique set of simultaneous measurements consisting of real-time mass loss, up to 20 different gas species concentration, size-fractioned particle mass (PM10, PM2.5and PM1), temperature profile, and visual and infrared imaging. This comprehensive framework of measurements reveals that the evolution of the emissions varies in time with four observed stages (ignition, growth, steady and burn out) which are characterised by different combustion dynamics. Mass flux measurements show that CO2, CO, CH4and NH3are the four most predominant gas species emitted in the steady stage. Incorporating the mass loss rate, the transient emission factors (EFm) of both gas and particle species are calculated and reported here for the first time. Averaging the steady stage, the EFm of PM2.5reached 23.12 g kg-1, which accounts for 87.2% of the total particle mass, and PM1EFmwas reported to be 15.04 g kg-1. The EFm of alkane species (CH4, C2H6, C3H8, C4H10) were found to peak within the ignition stage, whereas the EFmof CO2, CO and NH3kept increasing during the steady stage. Because of these measurements, for the first time we were able to validate the EF calculated by assuming averaged values and a carbon balance, which is the preferred method used in remote sensing and atmospheric sciences. This work contributes to a better understanding of peat fire emissions and could help develop strategies tackling regional haze.
Richter F, Atreya A, Kotsovinos P, et al., 2019, The effect of chemical composition on the charring of wood across scales, Proceedings of the Combustion Institute, Vol: 37, Pages: 4053-4061, ISSN: 1540-7489
Structural softwood (timber) recently gained attention by architects and engineers as a construction material for high-rise buildings. Regulations restrict the height of these buildings due to safety concerns as their fire behaviour is poorly understood. The fire behaviour and loss of loadbearing capacity of timber is controlled by charring, whose chemical kinetics has rarely been studied. Current models of charring assume, without proof, the same reaction scheme and kinetic parameters apply to all wood species, which potentially introduces a large uncertainty. Here, the hypothesis is tested that the kinetics of different wood species insignificantly affects their charring behaviour. The kinetics is modelled by a microscale kinetic model—including pyrolysis and char oxidation reactions—which assumes that the three main components (cellulose, hemicellulose, and lignin) of wood degrade independently. Variation in the kinetics between different wood species is captured by their different chemical compositions within a wood group (softwood or hardwood). Hardwood is included for comparison. A database of over 600 compositions was compiled from literature, and studied across scales using a microscale (mg-samples) and mesoscale (kg-samples) model. All reactions, kinetic parameters, and physical properties were selected from literature. Both models were validated using blind predictions of high-fidelity experiments from literature. Variation in kinetics were found to have a small effect on the predicted mass loss rate at both scales (±1 g/m2-s) and a negligible effect on the predicted temperatures (±16 K) across different depths, heat fluxes, and oxygen concentrations at the mesoscale. These results prove, for the first time, that the variation in kinetics is negligible for predicting charring across scales. A kinetic model of charring derived for one wood species should be valid for all wood species within softwood or hardwood. Modellers should, t
Bonner M, Rein G, 2018, Flammability and multi-objective performance of building façades: Towards optimum design, International Journal of High-Rise Buildings, Vol: 7, Pages: 363-374, ISSN: 2234-7224
The façade is an important, complex, and costly part of a building, performing multiple objectives of value to the occupants, like protecting from wind, rain, sunlight, heat, cold, and sound. But the frequency of façade fires in large buildings is alarming, and has multiplied by seven times worldwide over the last three decades, to a current rate of 4.8 fires per year. High-performing polymer based materials allow for a significant improvement across several objectives of a facade (e.g., thermal insulation, weight, and construction time) thereby increasing the quality of a building. However, all polymers are flammable to some degree. If this safety problem is to be tackled effectively, then it is essential to understand how different materials, and the façade as a whole, perform in the event of a fire. This paper discusses the drivers for flammability in facades, the interaction of facade materials, and current gaps in knowledge. In doing so, it aims to provide an introduction to the field of façade fires, and to show that because of the drive for thermal efficiency and sustainability, façade systems have become more complex over time, and they have also become more flammable. We discuss the importance of quantifying the flammability of different façade systems, but highlight that it is currently impossible to do so, which hinders research progress. We finish by putting forward an integral framework of design that uses multi-objective optimization to ensure that flammability is minimized while considering other objectives, such as maximizing thermal performance or minimizing weight.
Richter F, Rein G, 2018, The role of heat transfer limitations in polymer pyrolysis at the microscale, Frontiers in Mechanical Engineering, Vol: 4, Pages: 1-13, ISSN: 2297-3079
Pyrolysis of synthetic or natural polymers is an important process in many industries such as fire safety, thermal recycling, and biomass power generation. The kinetics of pyrolysis is usually studied by thermogravimetric analysis (TGA), which is based on measuring the mass loss of a microscale sample and measuring the temperature of the surrounding fluid during controlled heating. The literature is rich in TGA measurements, which are often assumed to be governed solely by chemical kinetics. Heat and mass transfer effects, however, can occur when the sample mass is too large. Only a few studies in the literature quantify the threshold for the initial mass, above which heat transfer effects are significant. Here, we systematically analyse the role of heat transfer in TGA measurements, review existing formulations, and provide a novel threshold for the maximum sample mass. We focus on the natural polymer cellulose, a surrogate for biomass, and split the problem into heat transfer within the sample (intraparticle) and between the sample and the fluid (interparticle). Using dimensional analysis we derive two upper bound thresholds for the initial sample mass as a function of heating. One threshold is calculated based on interparticle heat transfer and depends on flow and heating conditions as well as material and fluid properties. The other is calculated based on intraparticle heat transfer and depends on heating conditions and material properties. Both thresholds were validated with measurements and previous studies from the literature. Comparing both thresholds shows that the maximum sample mass in a TGA is dictated by interparticle heat transfer and rapidly reduces with heating rate from 1.8 mg at 10 K/min to 0.15 mg at 50 K/min. These results enable the selection of appropriate sample masses and heating conditions in TGA measurements, which in turn will lead to a better understanding of polymer pyrolysis.
Wang Z, You F, Rein G, et al., 2018, Flammability hazards of typical fuels used in wind turbine nacelle, Fire and Materials, Vol: 42, Pages: 770-781, ISSN: 0308-0501
This study aims to develop a complete methodology for assessing flammability hazards of typical fuels (ie, transformer oil, hydraulic oil, gear oil, and lubricating grease) used in a wind turbine nacelle by combining different experimental techniques such as thermogravimetric analysis and cone calorimetry. Pyrolysis properties (onset temperature, temperature of maximum mass loss rate, and mass residue) and reaction‐to‐fire properties (ignition time, heat release rate, mass loss rate, and smoke release rate) were determined and used for a preliminary assessment of thermal stability and flammability hazards. Additional indices, for ignition and thermal behavior (effective heat of combustion, average smoke yield, and smoke point height, heat release capacity, fire hazard parameter, and smoke parameter, were calculated to provide a more advanced assessment of the hazards in a wind turbine. Results show that pyrolysis of transformer oil, lubricating grease, hydraulic oil, and gear oil occur in the range of 150°C to 550°C. Lubricating grease and transformer oil show the higher and lower thermal stabilities with maximum pyrolysis rate temperatures of 471°C and 282°C, respectively. The measured relation between ignition time and radiant heat flux agrees well with Janssens method (a power of 0.55). The aforementioned indices appear to provide a reasonable prediction of performance under real fire conditions according to a full‐scale fire test documented by Declercq and Van Schevensteen. The results of the study indicate that transformer oil is the easiest to ignite while lubricating grease is the most difficult to ignite but also has the highest smoke production rate; that transformer oil has the highest heat release rate while gear oil has the lowest; and that the fire hazard parameter is the highest for transformer oil and the smoke parameter is the highest for lubricating grease. The potential of this type of work to design safer wind turbines under perfor
Vermesi I, Restuccia F, Walker-Ravena C, et al., 2018, Carbon monoxide diffusion through porous walls: evidence found in incidents and experimental studies, Frontiers in Built Environment, Vol: 4, Pages: 1-8, ISSN: 2297-3362
It has been reported recently that carbon monoxide (CO) diffuses through gypsum board at a surprisingly high rate (Hampson et al., 2013). Because CO is poisonous and a by-product of systems typically present in residential housing such as boilers, generators and automobile engines, this finding could have a significant impact on the safety standards published by the National Fire Protection Association (NFPA) and International Code Council (ICC). In the USA, state legislation mandates the requirements for CO detection and warning equipment to be installed, but currently only enforces CO detection if there are communicating openings between the garage and occupied areas of a building. Therefore, there is a need to find out whether CO indeed diffuses through porous walls. In addition to investigating the validity of the experiments by Hampson (Hampson et al., 2013), this paper also collects a series of instances in the literature that show the diffusion of CO or other carbon-based gases. We have found a number of actual incidents and laboratory experiments which confirmed the transport of CO through other types of porous walls. We also found studies on the transport of other hydrocarbon gases with larger molecules than CO that can also diffuse through porous walls. We have also analyzed in detail the data from the recent experiments with a mass transfer model and confirm the validity of the findings for gypsum board. After 200 min, the CO concentration in the control chamber was around 200 ppm, which is high enough to affect people. Our analysis independently confirms that CO can diffuse through porous walls at a fast rate and that the phenomena merits further research for consideration in life safety standards.
Ayala P, Cantizano A, Rein G, et al., 2018, Factors affecting the make-up air and their influence on the dynamics of atrium fires, Fire Technology, Vol: 54, Pages: 1067-1091, ISSN: 0015-2684
In case of fire, constructive features of typical atria could favor the spread of smoke. This makes the design of their smoke control and management systems a challenging task. Five full-scale fire experiments in the literature have been analyzed and numerically compared in FDS v6 to explore the influence of the make-up air. However, these fire experiments cover only a limited number of set-ups and conditions, and require further numerical modeling to obtain a deeper understanding of the makeup air influence. Subsequently, 84 simulations with FDS v6 have been carried out, considering different vent areas (air velocity from 0.4 to 5.3 m/s) and configurations, two heat release rates (2.5 and 5 MW), and two pan locations. It is demonstrated that make-up air velocities lower than the prescribed limit of 1 m/s, by the international codes, may induce adverse conditions. Based on our results, we recommended fire engineers to numerically assess the fire scenario with even lower velocity values. The results also show that asymmetric configurations are prone to induce circulation around the flame which can contribute to the formation of longer flames and fire whirls. Thus, this numerical study links two fire types allowing the connection of pool fires to fire whirls, which completely differ in behaviour and smoke filling, for the sake of design of fire safety.
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