Publications
219 results found
Roulston C, Paton-Walsh C, Smith TEL, et al., 2018, Fine particle emissions from tropical peat fires decrease rapidly with time since ignition, Journal of Geophysical Research: Atmospheres, Vol: 123, Pages: 5607-5617, ISSN: 2169-897X
Southeast Asia experiences frequent fires in fuel-rich tropical peatlands, leading to extremeepisodes of regional haze with high concentrations of fine particulate matter (PM2.5) impacting humanhealth. In a study published recently, the first field measurements of PM2.5 emission factors for tropical peatfires showed larger emissions than from other fuel types. Here we report even higher PM2.5 emission factors,measured at newly ignited peat fires in Malaysia, suggesting that current estimates of fine particulateemissions from peat fires may be underestimated by a factor of 3 or more. In addition, we use both field andlaboratory measurements of burning peat to provide the first mechanistic explanation for the high variabilityin PM2.5 emission factors, demonstrating that buildup of a surface ash layer causes the emissions of PM2.5 todecrease as the peat fire progresses. This finding implies that peat fires are more hazardous (in terms ofaerosol emissions) when first ignited than when still burning many days later. Varying emission factors forPM2.5 also have implications for our ability to correctly model the climate and air quality impacts downwindof the peat fires. For modelers able to implement a time-varying emission factor, we recommend an emissionfactor for PM2.5 from newly ignited tropical peat fires of 58 g of PM2.5 per kilogram of dry fuel consumed (g/kg), reducing exponentially at a rate of 9%/day. If the age of the fire is unknown or only a single value may beused, we recommend an average value of 24 g/kg.Plain Language Summary This paper provides evidence that peat fire emissions of fineparticulates are much larger than for other fires when the peat is newly ignited but decrease rapidly as thefire progresses. This is important because it means that newly ignited fires are particularly detrimental toambient air quality in impacted regions.
Hu Y, Fernandez-Anez N, Smith TEL, et al., 2018, Review of emissions from smouldering peat fires and their contribution to regional haze episodes, International Journal of Wildland Fire, Vol: 27, Pages: 293-312, ISSN: 1049-8001
Smouldering peat fires, the largest fires on Earth in terms of fuel consumption, are reported in six continents and are responsible for regional haze episodes. Haze is the large-scale accumulation of smoke at low altitudes in the atmosphere. It decreases air quality, disrupts transportation and causes health emergencies. Research on peat emissions and haze is modest at best and many key aspects remain poorly understood. Here, we compile an up-to-date inter-study of peat fire emission factors (EFs) found in the literature both from laboratory and from field studies. Tropical peat fires yield larger EFs for the prominent organic compounds than boreal and temperate peat fires, possibly due to the higher fuel carbon content (56.0 vs 44.2%). In contrast, tropical peat fires present slightly lower EFs for particulate matter with diameter ≤2.5 μm (PM2.5) for unknown reasons but are probably related to combustion dynamics. An analysis of the modified combustion efficiency, a parameter widely used for determining the combustion regime of wildfires, shows it is partially misunderstood and highly sensitive to unknown field variables. This is the first review of the literature on smouldering peat emissions. Our integration of the existing literature allows the identification of existing gaps in knowledge and is expected to accelerate progress towards mitigation strategies.
Boustras G, Ronchi E, Rein G, 2017, Fires: fund research for citizen safety, Nature, Vol: 551, Pages: 300-300, ISSN: 0028-0836
huang X, Rein G, 2017, Downward Spread of Smoldering Peat Fire: the Role of Moisture, Density, and Oxygen Supply, International Journal of Wildland Fire, Vol: 26, Pages: 907-918, ISSN: 1049-8001
Smouldering fires in peatland are different from the flames in wildland fires. Smouldering peat fire is slow, low-temperature and more persistent, releasing large amounts of smoke into the atmosphere. In this work, we experimentally and computationally investigate the vertical downward spread of smouldering fire in a column of 30 cm-tall moss peat under variable moisture content (MC) and bulk density. The measured downward spread rate decreases with depth and wet bulk density, and is ~1 cm h−1 equivalent to a carbon emission flux of 200 tonnes day−1 ha−1. We observe that downward spread increases as MC increases substantially at least inside the range from 10 to 70%, which is not intuitive and goes against the trend observed for the horizontal spread in the same peat. We also conduct one-dimensional computational simulations to successfully reproduce the experimental observations. The analysis shows that the spread rate increases with MC and decreases with density because smouldering spread is controlled by the oxygen supply. The volume of the porous peat expands when absorbing water, which reduces the density of organic matter and decreases the heat release rate. This shows that the widely assumed conclusion that the spread rate of wildfire decreases with MC is not universal when applied to smouldering fires.
Rackauskaite E, Kotsovinos P, Jeffers A, et al., 2017, Structural analysis of multi-story steel frames exposed to travelling fires and tradition design fires, Engineering Structures, Vol: 150, Pages: 271-287, ISSN: 1873-7323
Most of the current understanding of building behaviour in fire is based on the adoption of the standard and parametric temperature-time fire curves. However, these design fires are based on small scale tests and idealize the thermal environment as uniform. Thus, they have important limitations on their applicability to large enclosures. Instead, in large open-plan compartments, travelling fires have been observed. To account for such fires, a design tool called Travelling Fires Methodology (TFM) has been developed and used for design. The aim of the present study is to compare computationally the structural response of a multi-storey steel frame subjected to both uniform design fires (available in current standards) and travelling fires. A two-dimensional 10-storey 5-bay steel frame designed according to ASCE 7-02 is modelled in the general finite element program LS-DYNA. Different fire exposures are investigated. They include travelling fires, Eurocode parametric curves, ISO-834 standard fire and the constant compartment temperature curve from the SFPE standard. These fires are applied to different floors, one at a time, to explore the influence on the structural response, resulting in a total of 80 different scenarios. The development of deflections, axial forces and bending moments is analysed. Uniform fires are found to result in approx. 15–55 kN (3–13%) higher compressive axial forces in beams compared to small travelling fires. However, the results show irregular oscillations in member utilization levels in the range of 2–38% for the smallest travelling fire sizes, which are not observed for any of the uniform fires. Peak beam mid-span deflections are similar for both travelling fires and uniform fires and depend mainly on the fire duration, but the locations in the frame and times when these peak displacements occur are different. The results indicate that travelling fires and uniform fires trigger substantially different structural respons
Rein G, Huang X, Restuccia F, et al., 2017, Detection of landmines in peat soils by controlled smouldering combustion: Experimental proof of concept of O-Revealer, Experimental Thermal and Fluid Science, Vol: 88, Pages: 632-638, ISSN: 0894-1777
We study a novel landmine detection technology, called O-Revealer, which uses controlled smouldering combustion and is valid for minefields in peat soils. We have conducted laboratory experiments with two types of dummy landmines buried in peat, the plastic SB-33 and the metal PROM-1. The ignition and spread of a smouldering front was monitored under different soil moisture and wind conditions. Special attention was paid to the thermal conditions that could trigger thermal runaway of the explosive charge. In all experiments, the smouldering fire burned across the peat, leaving the dummy completely exposed to the open for easy identification and quick demining. The spread rate and peak temperature both decrease with soil moisture, and both increase with wind speed. The results show that for the SB-33 landmine, the heat damage to the shell can be significant, and the chance of thermal runaway ranges between low (moist peat and no wind) to high (dry peat and wind). For PROM-1 landmine, the damage and chance of runaway are always very low. In addition, using rock samples, we show that O-Revealer helps identify objects buried in the soil, thereby avoiding false detections. These experiments show the benefits of the technology and its feasibility for field application in peat minefields worldwide like Falkland Islands, Vietnam, Burma, Laos, Uganda, Zimbabwe or former Yugoslavia.
Roenner N, Hutheesing K, Fergusson A, et al., 2017, Simultaneous improvements in flammability and mechanical toughening of epoxy resins through nano-silica addition, Fire Safety Journal, Vol: 91, Pages: 200-207, ISSN: 0379-7112
Polymers in transport, and many other engineering applications, are required to be mechanically tough as well as resistant to ignition and flame spread. These demands are often for many polymer types in competition, especially when adding flame retardants. With nano-silica addition, we show that improvements in both properties of a polymer can be achieved simultaneously. In this study, an epoxy resin is evaluated for its flammability and mechanical properties with step wise additions of nano-silica. The fracture toughness was significantly improved. In the single edge notch bending test, the addition of 36% nano-silica particles doubled the toughness and increased the flexure modulus by 50%. Flammability was studied via time to ignition at constant irradiation, and via a UL94 test coupled with mass loss and surface temperature measurements. Modelling for the heat transport and chemical kinetics in Gpyro was done and yielded good agreement with the temperatures measured. Adding up to 36% nano-silica, the time to ignition increased by 38% although a sharp decrease was observed around 24% SiO2 addition. We show that the increased time to ignition is mostly due to a higher thermal diffusivity, increased inert content, as well as a strengthening of the residue outer skin, which acts as a mass barrier for pyrolysate. This outer skin was analysed using a scanning electron microscope coupled with an energy dispersive X-ray spectrometer. We found that in the skin the nano-silica particles agglomerate at the surface forming a strong continuous structure together with the char residue from the epoxy. Improvements in the flammability as seen in the UL94 test were measured with mass loss showing a 30% reduction after 20 s, and surface temperatures at the ignited end being up to 75 K lower compared to the pure epoxy. Modelling in Gpyro supported the temperature measurements taken. Despite the improvements seen, all samples ignited, failing the test with dripping and showing that
richter F, Rein G, 2017, Pyrolysis kinetics and multi-objective inverse modelling of cellulose at the microscale, Fire Safety Journal, Vol: 91, Pages: 191-199, ISSN: 1873-7226
The chemistry of pyrolysis, together with heat transfer, drives ignition and flame spread of biomass materials under many fire conditions, but it is poorly understood. Cellulose is the main component of biomass and is often taken as its surrogate. Its chemistry of pyrolysisis simpler and dominates the pyrolysis of biomass. Many reaction schemes with corresponding kinetic parameters can be found in the literature for the pyrolysis of cellulose, but their appropriatenessfor fire is unknown. This study investigated inverse modelling andthe blind prediction of six reaction schemes of different complexitiesfor isothermal and non-isothermal thermogravimetric experiments. We used multi-objective optimisation to simultaneously and separatelyinverse model the kinetic parameters of each reaction schemeto several experiments. Afterwards we tested these parameters with blind predictions. For the first time, we reveal a set of equally good solutions for the modelling of pyrolysis chemistry of different experiments. This set of solutions is called a Pareto front, and represents a trade-off between predictions of different experiments. It stems from the uncertainty in the experiments and in the modelling. Parameters derived from non-isothermal experiments compared well with the literature, and performed well in blind predictions of both isothermal and non-isothermal experiments. Complexity beyond the Broido-Shafizadeh scheme with seven parameters proved to beunnecessary to predict the mass loss of cellulose; hence, simplereaction schemes are most appropriate for macroscale fire models.Our results show that modellers should use simple reaction schemes to model pyrolysis in macroscale fire models.
vermesi I, Didomizio M, richter F, et al., 2017, Pyrolysis and spontaneous ignition of wood under transientirradiation: experiments and a-priori predictions, Fire Safety Journal, Vol: 91, Pages: 218-225, ISSN: 1873-7226
Wood is a material widely used in the built environment, but its flammability and response to fire are adisadvantage. Therefore, it is essential to have substantial knowledge of the behavior of wood undergoingexternal heating such as in a fire. The majority of studies in the literature use constant irradiation. Althoughthis assumption simplifies both modelling and experimental endeavors, it is important to assess the behaviorof materials under more comprehensive heating scenarios which might challenge the validity of solid-phaseignition criteria developed previously. These criteria are evaluated here for the spontaneous ignition undertransient irradiation by combining experimental measurements and a-priori predictions from a model of heattransfer and pyrolysis. We have applied a two-step transient irradiation in the cone calorimeter in the formof a growth curve followed by a threshold of constant irradiation. We used white spruce samples of size 100x 100 mm thickness of 38 mm measured the temperature at different depths and the mass loss. A one di-mensional model written in the open source code Gpyro is used to predict the pyrolysis behavior. The modelhas a chemical scheme in which the virgin components of wood (hemicellulose, cellulose, lignin) becomeactive, then decompose in two competing reactions: char and gas, and tar. The kinetic parameters, as wellas the thermal properties of the wood and char are taken from the literature, whileρand moisture contentare measured experimentally. A priori predictions of the temperature, made prior to the experiments, showexcellent agreement with the measurements, being within the experimental uncertainty range. The mass lossrate (MLR) predictions are qualitatively similar to the measurements, but there is a large uncertainty in themeasurements. For a-posteriori simulations, certain parameters are changed after having access to the mea-surements to improve the simulations. We found that the heat of reaction
Rackauskaite E, Kotsovinos P, Rein G, 2017, Structural response of a steel-frame building to horizontal and vertical travelling fires in multiple floors, Fire Safety Journal, Vol: 91, Pages: 542-552, ISSN: 1873-7226
During previous fire events such as the World Trade Centre Towers (WTC) 1, 2 & 7 in New York (2001), the Windsor Tower in Madrid (2005), and the Plasco building in Iran (2017), flames were observed to travel horizontally across the floor plate and vertically to different floors. Such fires are not considered as part of the traditional prescriptive structural design for fire. Recently, the Travelling Fires Methodology (TFM) has been developed to account for such horizontally travelling nature of fires. A dozen of studies have investigated the structural response of steel, concrete, and composite structures to a single-floor travelling fire. 5 out of 6 of the vertically travelling fire studies have been limited to the structures with a long span composite truss system as in the WTC Towers. The aim of this work is to investigate the response of a substantially different structural system, i.e. a generic multi-storey steel frame, subjected to travelling fires in multiple floors, and varying the number of fire floors, including horizontal and vertical fire spread. A two-dimensional 10-storey 5-bay steel frame is modelled in the finite element software LS-DYNA. The number of multiple fire floors is varied between 1 and 10, and for each of these scenarios, 5 different fire types are investigated. They include four travelling fire scenarios and the standard fire. In total, 51 fire simulations are considered. The development of deflections, axial forces, bending moments and frame utilization are analysed. Results show that the largest stresses develop in the fire floors adjacent to cool floors, and their behaviour is independent of the number of fire floors. Results indicate that both the fire type and the number of fire floors have a significant effect on the failure time (i.e. exceeded element load carrying capacity) and the type of collapse mechanism. In the cases with a low number of fire floors (1–3) failure is dominated by the loss of material strength, while
Rackauskaite E, Kotsovinos P, Rein G, 2017, Model parameter sensitivity and benchmarking of the explicit dynamic solver of LS-DYNA for structural analysis in case of fire, Fire Safety Journal, Vol: 90, Pages: 123-138, ISSN: 1873-7226
Due to the complex nature of structural response in fire, computational tools are often necessary for the safe design of structures under fire conditions. In recent years, use of the finite element code LS-DYNA has grown considerably in research and industry for structural fire analysis, but there is no benchmarking of the code available in the fire science literature for such applications. Moreover, due to the quasi-static nature of structural response in fire, the majority of the computational structural fire studies in the literature are based on the use of static solvers. Thus, this paper aims at benchmarking the explicit dynamic solver of LS-DYNA for structural fire analysis against other static numerical codes and experiments. A parameter sensitivity study is carried out to study the effects of various numerical parameters on the convergence to quasi-static solutions. Four canonical problems that encompass a range of thermal and mechanical behaviours in fire are simulated. In addition, two different modelling approaches of composite action between the concrete slab and the steel beams are investigated. In general, the results confirm that when numerical parameters are carefully considered such as to not induce excessive inertia forces in the system, explicit dynamic analyses using LS-DYNA provide good predictions of the key variables of structural response during fire.
Restuccia F, Huang X, Rein G, 2017, Self-ignition of natural fuels: can wildfires of carbon-rich soil start by self-heating?, Fire Safety Journal, Vol: 91, Pages: 828-834, ISSN: 1873-7226
Carbon-rich soils, like histosols or gelisols, cover more than 3% of the Earth's land surface, and store roughly three times more carbon than the Earth's forests. Carbon-rich soils are reactive porous materials, prone to smouldering combustion if the inert and moisture contents are low enough. An example of soil combustion happens in peatlands, where smouldering wildfires are common in both boreal and tropical regions. This work focuses on understanding soil ignition by self-heating, which is due to spontaneous exothermic reactions in the presence of oxygen under certain thermal conditions. We investigate the effect of soil inorganic content by creating under controlled conditions soil samples with inorganic content (IC) ranging from 3% to 86% of dry weight: we use sand as a surrogate of inorganic matter and peat as a surrogate of organic matter. This range is very wide and covers all IC values of known carbon-rich soils on Earth. The experimental results show that self-heating ignition in different soil types is possible, even with the 86% inorganic content, but the tendency to ignite decreases quickly with increasing IC. We report a clear increase in ambient temperature required for ignition as the IC increases. Combining results from 39 thermostatically-controlled oven experiments, totalling 401 h of heating time, with the Frank-Kamenetskii theory of ignition, the lumped chemical kinetic and thermal parameters are determined. We then use these parameters to upscale the laboratory experiments to soil layers of different thicknesses for a range of ambient temperatures ranging from 0 °C to 40 °C. The analysis predicts the critical soil layer thicknesses in nature for self-ignition at various possible environmental temperatures. For example, at 40 °C a soil layer of 3% inorganic content can be ignited through self-heating if it is thicker than 8.8 m, but at 86% IC the layer has to be 1.8 km thick, which is impossible to find in nature. We estimate that th
Fernandez-Anez N, Christensen K, Rein G, 2017, Two-dimensional model of smouldering combustion using multi-layer cellular automaton: The role of ignition location and direction of airflow, Fire Safety Journal, Vol: 91, Pages: 243-251, ISSN: 0379-7112
Smouldering combustion is one of the most common and persistent fire hazards of reactive porous media, such as biomass. In this work, a two-dimensional multi-layer cellular automaton has been developed to study the process of smouldering and the roles of both the ignition location and the direction of airflow for generic biomass. Three different configurations are studied: line front, with forward and opposed airflow respectively, and radial front. The first two configurations simulate ignition of one edge of the sample, while the radial front simulates ignition of a spot at the centre of the sample. The resulting spread patterns of line vs. radial front are significantly different. Furthermore, when smouldering occurs with similar characteristics, where both line front and radial front are self-sustained, the smouldering radial front has a higher growth rate than the line front. However, in the studied cases where enough oxygen is always available for oxidation, the direction of the airflow does not influence the spread of the smouldering front, and the line front with forward and opposed airflow present similar behaviour. Finally, two non-zero minimum values have been detected for self-sustained spread according to the moisture of the fuel (probability of drying) and its tendency for thermal degradation (probability of pyrolysis). This model provides a powerful but simple way of reproducing the complex dynamics of smouldering processes which can be used to investigate different scenarios.
Vermesi I, Rein G, Colella F, et al., 2017, Reducing the computational requirements for simulating tunnel fires by combining multiscale modelling and multiple processor calculation, TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY, Vol: 64, Pages: 146-153, ISSN: 0886-7798
Multiscale modelling of tunnel fires that uses a coupled 3D (fire area) and 1D (the rest of the tunnel) model is seen as the solution to the numerical problem of the large domains associated with long tunnels. The present study demonstrates the feasibility of the implementation of this method in FDS version 6.0, a widely used fire-specific, open source CFD software. Furthermore, it compares the reduction in simulation time given by multiscale modelling with the one given by the use of multiple processor calculation. This was done using a 1200 m long tunnel with a rectangular cross-section as a demonstration case. The multiscale implementation consisted of placing a 30 MW fire in the centre of a 400 m long 3D domain, along with two 400 m long 1D ducts on each side of it, that were again bounded by two nodes each. A fixed volume flow was defined in the upstream duct and the two models were coupled directly. The feasibility analysis showed a difference of only 2% in temperature results from the published reference work that was performed with Ansys Fluent (Colella et al., 2010). The reduction in simulation time was significantly larger when using multiscale modelling than when performing multiple processor calculation (97% faster when using a single mesh and multiscale modelling; only 46% faster when using the full tunnel and multiple meshes). In summary, it was found that multiscale modelling with FDS v.6.0 is feasible, and the combination of multiple meshes and multiscale modelling was established as the most efficient method for reduction of the calculation times while still maintaining accurate results. Still, some unphysical flow oscillations were predicted by FDS v.6.0 and such results must be treated carefully.
Restuccia F, Ptak N, Rein G, 2016, Self-heating behavior and ignition of shale rock, Combustion and Flame, Vol: 176, Pages: 213-219, ISSN: 1556-2921
The combustion of shale, a porous sedimentary rock, has been reported at times in outcrop deposits and piles. However, the initiating event of most of these fires is unknown. It could be that, under the right conditions, shale rock undergoes spontaneous exothermic reactions in the presence of oxygen. This work studies experimentally and for the first time the self-heating behavior of shale rock. As shale has high inert content, novel diagnostics such as mass loss measurements and observation ofcharring are introduced to the self-heating ignition criteria in respect to other self-heating materials.Using field samples collected from the outcrop at Kimmeridge Bay (UK) and the Frank-Kamenetskii theory of ignition, we determine the effective kinetic parameters for two particle-size distributions of shale. These parameters are then used to upscale the results to geological deposits and mining piles of different thicknesses. We show that for fine particles, with diameter below 2 mm, spontaneous ignition is possible for deposits of thickness between 10.7 m and 607 m at ambient temperatures between -20 ᵒC and 44 ᵒC. For the same ambient temperature range, the critical thickness is in excess of 30 km for deposits made of coarse particles with diameter below 17 mm. Our results indicate that shale rock is reactive, with reactivity highly dependent on particle diameter, and that self-ignition is possible for small particles in outcrops, piles or geological deposits accidentally exposed to oxygen.
Pereira P, Rein G, Martin D, 2016, Past and Present Post-Fire Environments, Publisher: Elsevier
Huang X, Restuccia F, Gramola M, et al., 2016, Experimental study of the formation and collapse of an overhang in the lateral spread of smouldering peat fires, Combustion and Flame, Vol: 168, Pages: 393-402, ISSN: 0010-2180
Smouldering combustion is the driving phenomenon of wildfires in peatlands, and is responsible for large amounts of carbon emissions and haze episodes world wide. Compared to flaming fires, smouldering is slow, low-temperature, flameless, and most persistent, yet it is poorly understood. Peat, as a typical organic soil, is a porous and charring natural fuel, thus prone to smouldering. The spread of smouldering peat fire is a multidimensional phenomenon, including two main components: in-depth vertical and surface lateral spread. In this study, we investigate the lateral spread of peat fire under various moisture and wind conditions. Visual and infrared cameras as well as a thermocouple array are used to measure the temperature profile and the spread rate. For the first time the overhang, where smouldering spreads fastest beneath the free surface, is observed in the laboratory, which helps understand the interaction between oxygen supply and heat losses. The periodic formation and collapse of overhangs is observed. The overhang thickness is found to increase with moisture and wind speed, while the spread rate decreases with moisture and increases with wind speed. A simple theoretical analysis is proposed and shows that the formation of overhang is caused by the spread rate difference between the top and lower peat layers as well as the competition between oxygen supply and heat losses.
Rackauskaite E, Rein G, 2016, Corrigendum to "Improved formulation of travelling fires and application to concrete and steel structures" [Structures 3 (2015) 250-260], Structures, Vol: 6, Pages: 182-182, ISSN: 2352-0124
Huang X, Rein G, 2016, Interactions of Earth's atmospheric oxygen and fuel moisture in smouldering wildfires, Science of the Total Environment, Vol: 572, Pages: 1440-1446, ISSN: 0048-9697
Vegetation, wildfire and atmospheric oxygen on Earth have changed throughout geological times, and are dependent on each other, determining the evolution of ecosystems, the carbon cycle, and the climate, as found in the fossil record. Previous work in the literature has only studied flaming wildfires, but smouldering is the most persistent type of fire phenomena, consuming large amounts of biomass. In this study, the dependence of smouldering fires in peatlands, the largest wildfires on Earth, with atmospheric oxygen is investigated. A physics-based computational model of reactive porous media for peat fires, which has been previously validated against experiments, is used. Simulations are conducted for wide ranges of atmospheric oxygen concentrations and fuel moisture contents to find thresholds for ignition and extinction. Results show that the predicted rate of spread increases in oxygen-rich atmospheres, while it decreases over wetter fuels. A novel nonlinear relationship between critical oxygen and critical moisture is found. More importantly, we show that compared to previous work on flaming fires, smouldering fires can be ignited and sustained at substantially higher moisture contents (up to 100% MC vs. 40% for 21% oxygen level), and lower oxygen concentrations (down to 13% vs. 16%). This defines a new atmospheric oxygen threshold for wildfires (13%), even lower than previously thought in Earth Sciences (16%). This finding should lead to reinterpretation of how the char remains observed in the fossil record constrain the lower concentration of oxygen in Earth's atmosphere in geological timescale.
Prat-Guitart N, Rein G, Hadden RM, et al., 2016, Effects of spatial heterogeneity in moisture content on the horizontal spread of peat fires, Science of the Total Environment, Vol: 572, Pages: 1422-1430, ISSN: 0048-9697
The gravimetric moisture content of peat is the main factor limiting the ignition and spread propagation of smouldering fires. Our aim is to use controlled laboratory experiments to better understand how the spread of smouldering fires is influenced in natural landscape conditions where the moisture content of the top peat layer is not homogeneous. In this paper, we study for the first time the spread of peat fires across a spatial matrix of two moisture contents (dry/wet) in the laboratory. The experiments were undertaken using an open-top insulated box (22. ×. 18. ×. 6. cm) filled with milled peat. The peat was ignited at one side of the box initiating smouldering and horizontal spread. Measurements of the peak temperature inside the peat, fire duration and longwave thermal radiation from the burning samples revealed important local changes of the smouldering behaviour in response to sharp gradients in moisture content. Both, peak temperatures and radiation in wetter peat (after the moisture gradient) were sensitive to the drier moisture condition (preceding the moisture gradient).Drier peat conditions before the moisture gradient led to higher temperatures and higher radiation flux from the fire during the first 6. cm of horizontal spread into a wet peat patch. The total spread distance into a wet peat patch was affected by the moisture content gradient. We predicted that in most peat moisture gradients of relevance to natural ecosystems the fire self-extinguishes within the first 10. cm of horizontal spread into a wet peat patch. Spread distances of more than 10. cm are limited to wet peat patches below 160% moisture content (mass of water per mass of dry peat). We found that spatial gradients of moisture content have important local effects on the horizontal spread and should be considered in field and modelling studies.
Prat-Guitart N, Rein G, Hadden RM, et al., 2016, Propagation probability and spread rates of self-sustained smouldering fires under controlled moisture content and bulk density conditions, International Journal of Wildland Fire, Vol: 25, Pages: 456-465, ISSN: 1448-5516
The consumption of large areas of peat during wildfires is due to self-sustained smouldering fronts that can remain active for weeks. We studied the effect of peat moisture content and bulk density on the horizontal propagation of smouldering fire in laboratory-scale experiments. We used milled peat with moisture contents between 25 and 250% (mass of water per mass of dry peat) and bulk densities between 50 and 150 kg m–3. An infrared camera monitored ignition, spread and extinction of each smouldering combustion front. Peats with a bulk density below 75 kg m–3 and a moisture content below 150% self-sustained smouldering propagation for more than 12 cm. Peat with a bulk density of 150 kg m–3 could self-sustain smouldering propagation up to a critical moisture content of 115%. A linear model estimated that increasing both moisture content and bulk density significantly reduced the median fire spread rate (which ranged between 1 and 5 cm h–1). Moisture content had a stronger effect size on the spread rate than bulk density. However, the effect of bulk density on spread rate depends upon the moisture content, with the largest effect of bulk density at low moisture contents.
Abbott BW, Jones JB, Schuur EAG, et al., 2016, Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment, ENVIRONMENTAL RESEARCH LETTERS, Vol: 11, ISSN: 1748-9326
Boustras G, Rein G, 2016, Special Issue in Fire Hazards in Energy Systems, Publisher: SPRINGER
Ang CDE, Rein G, Peiro J, et al., 2016, Simulating longitudinal ventilation flows in long tunnels: comparison of full CFD and multi-scale modelling approaches in FDS6, Tunnelling and Underground Space Technology, Vol: 52, Pages: 119-126, ISSN: 0886-7798
The accurate computational modelling of airflows in transport tunnels is needed for regulations compliance, pollution and fire safety studies but remains a challenge for long domains because the computational time increases dramatically. We simulate air flows using the open-source code FDS 6.1.1 developed by NIST, USA. This work contains two parts. First we validate FDS6’s capability for predicting the flow conditions in the tunnel by comparing the predictions against on-site measurements in the Dartford Tunnel, London, UK, which is 1200 m long and 8.5 m in diameter. The comparison includes the average velocity and the profile downstream of an active jet fan up to 120 m. Secondly, we study the performance of the multi-scale modelling approach by splitting the tunnel into CFD domain and a one-dimensional domain using the FDS HVAC (Heating, Ventilation and Air Conditioning) feature. The work shows the average velocity predicted by FDS6 using both the full CFD and multi-scale approaches is within the experimental uncertainty of the measurements. Although the results showed the prediction of the downstream velocity profile near the jet fan falls outside the on-site measurements, the predictions at 80 m and beyond are accurate. Our results also show multi-scale modelling in FDS6 is as accurate as full CFD but up to 2.2 times faster and that computational savings increase with the length of the tunnel. This work sets the foundation for the next step in complexity with fire dynamics introduced to the tunnel.
Huang X, Rein G, 2016, Thermochemical Conversion of Biomass in Smouldering Combustion across Scales: the Roles of Heterogeneous Kinetics, Oxygen and Transport Phenomena, Bioresource Technology, Vol: 207, Pages: 409-421, ISSN: 1873-2976
We investigate the thermochemical conversion of biomass in smouldering combustion bycombining experiments and modelling at two scales: matter (1 mg) and laboratory (100g) scales. Emphasis is put on the effect of oxygen (0 to 33 vol.%) and oxidation reactionsbecause these are poorly studied in the literature in comparison to pyrolysis. The results areobtained for peat as representative biomass supported by high-quality experimental data.Three kinetic schemes are explored, including various steps of drying, pyrolysis and oxidation.The kinetic parameters are found using the Kissinger-Genetic Algorithm method, andthen implemented in a 1D model of heat and mass transfer. The predictions are validated inthermogravimetric and bench-scale experiments to unravel the role of heterogeneous reaction.This is the first time that the influence of oxygen on biomass smouldering is explainedin terms of both chemistry and transport phenomena across scales.
McDermott RJ, Rein G, 2016, Special Issue on Fire Model Validation, Fire Technology, Vol: 52, Pages: 1-4, ISSN: 1572-8099
Stracher GB, Prakash A, Rein G, 2016, Coal and Peat Fires: A Global Perspective Volume 4: Peat - Geology, Combustion, and Case Studies, ISBN: 9780444595126
Coal and Peat Fires: A Global Perspective, Volumes 1–4, presents a fascinating collection of research about prehistoric and historic coal and peat fires. Magnificent illustrations of fires and research findings from countries around the world are featured—a totally new contribution to science. This last of four volumes in the collection, Peat--Geology, Combustion, and Case Studies, examines in detail peat fires chronicled in several countries. In addition, the geology of peat, peat megafires, infrared analysis of fires, and the mathematical modelling of fire hazards are presented. This essential reference includes a companion website with an interactive world map of coal and peat fires, collections of slide presentations, research data, additional chapters, and videos: booksite.elsevier.com/9780444595102.
Vermesi I, Roenner N, Pironi P, et al., 2016, Pyrolysis and ignition of a polymer by transient irradiation, Combustion and Flame, Vol: 163, Pages: 31-41, ISSN: 0010-2180
Pyrolysis is the thermochemical process that leads to the ignition of a solid fuel and a key mechanism in flame spread and fire growth. Because polymer materials are flammable and ubiquitous in the modern environment, the understanding of polymer pyrolysis is thus essential to tackle accidental fires. In this paper, we used transient irradiation as an external source of heat to study the process of pyrolysis and ignition of a polymer sample. While previous ignition studies use constant irradiation, transient irradiation is the most frequent condition found in accidental fires, but it lacks a theoretical framework since it has been largely ignored in the literature. Moreover, transient irradiation is a more comprehensive case for the understanding of pyrolysis where nonlinear heat transfer effects challenge the validity of solid-phase criteria for flaming ignition developed previously. We propose here that transient irradiation is the general problem to solid fuel ignition of which constant irradiation is a particular solution. In order to investigate how this novel heat source inuences polymer pyrolysis and flammability, numerical simulations and experiments have been conducted on Poly(methyl methacrylate) (PMMA) samples 100mm by 100mm and 30mm deep exposed to a range of parabolic pulses of irradiation. The 1D model, coded in GPyro, uses heat and mass transfer and single-step heterogeneous chemistry, with temperature dependent properties. The predictions are compared to experiments conducted in the Fire Propagation Apparatus using both constant and transient irradiation conditions. The experiments validate the temperature predictions of the model and also provide the time to ignition. The model then complements the experiments by calculating the mass loss rate. A series of 16 parabolic pulses (including repeats) are investigated with a range of peak irradiation from 25 to 45 kW/m2, while the time to peak ranges from 280 to 480s. For these pulses, the time to igniti
Rein G, 2016, Smoldering-Peat Megafires, Coal and Peat Fires: A Global Perspective Volume 4: Peat - Geology, Combustion, and Case Studies, Pages: 1-11, ISBN: 9780444595126
Smoldering megafires are the largest and longest burning fires on Earth. They destroy essential peat land ecosystems and are responsible for 15% of annual global greenhouse gas emissions. This is the same amount attributed to all the combustion engine vehicles in the world, yet it is not accounted for in global carbon budgets. Peat fires also induce surges of respiratory emergencies in the population and disrupt shipping and aviation routes for long periods, weeks, and even months. Despite their importance, we do not understand how smoldering fires ignite, spread, or extinguish, which impedes the development of any successful mitigation strategy. Megafires are routinely fought across the globe with techniques that were developed for flaming fires, and are thus ineffective for smoldering. Moreover, the burning of deep peat affects older soil carbon that has not been part of the active carbon cycle for centuries to millennia, and thus creates a positive feedback to the climate system.
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