Search Results (841)

Geopolymer mortars made from various waste products can appreciably reduce carbon dioxide emissions and landfill-related issues, making them viable substitutes for ordinary Portland cement, a workhorse in the concrete industry. Thus, a series of ternary geopolymer mortars were made and characterized to determine the effects of exposure to elevated temperatures (from room temperature up to 900 °C) on their engineered (residual compressive strength, weight loss, and slant shear bond strength) and microstructural properties. These mortars, which contain fly ash, ground blast furnace slag, and a high volume of palm oil fuel ash, were designed to activate via the incorporation of an alkali activator solution at a low concentration (molarity of 4). The elevated temperature-mediated deterioration of the ternary geopolymer mortar was quantified using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The results revealed an improvement in the ternary geopolymer mortars’ resistance against elevated temperatures when the palm oil fuel ash level in the mortar matrix was raised from 50 to 70% and when slag was replaced by fly ash. It was asserted that the proposed ternary geopolymer mortars may contribute to the advancement of green concretes demanded by the construction sectors. Full article

In order to solve the defects of traditional coal spontaneous combustion prevention technology in a closed goaf, a strain of aerobic endogenous bacteria was isolated from coal and used as a blocking raw material. Based on the metabolic and reproductive characteristics of microorganisms, the experimental study on the inhibition of coal spontaneous combustion by microorganisms was carried out. The colonies were isolated and purified by the dilution concentration plate method and the scribing plate method. The growth morphology of microorganisms was analyzed, and the growth curve was determined. The strains were identified by seamless cloning technology for high-throughput sequencing. The surface morphology of coal was analyzed by SEM, the differences of oxidation characteristic temperature points were analyzed by TG–DTG–DSC images, a programmed heating experiment was used to analyze the concentration of the indicator gas CO, and the changes in microscopic groups before and after microbial action were analyzed by FTIR and XPS spectra. Therefore, the inhibition of coal oxidation by endogenous bacteria was verified from macroscopic and microscopic perspectives. The results show that the coal bacteria isolated from the coal is Lysinibacilus sp. After the culture of Lysinibacilus sp., the surface of the coal demonstrated less detritus, and was relatively smooth. In the early stage of low temperature oxidation of coal spontaneous combustion, the characteristic temperature point of coal oxidation and the reaction between coal and O₂ could be delayed by Lysinibacilus sp., and the total heat release was reduced in the combustion process. Not only that, Lysinibacilus sp. could also reduce the CO concentration during coal heating. After the coal was decomposed by Lysinibacilus sp., the C=C thick ring skeleton structure had little effect; however, the aromatic substitution pattern changed. This bacterium had an effect on the C-O bond, reducing the percentage of -CH₂- and increasing the percentage of -CH₃. It might also use the crystalline water in coal for life activities. The carboxyl carbon in coal changed the most, with a decrease of 12.03%, so it might become the carbon source required for microbial growth. The reproductive metabolism of microorganisms also affected the form of nitrogen, and the percentage of pyridine nitrogen in coal was reduced. The ratio of single-bond carbon to double-bond carbon in raw coal was about 3:2, but after this bacterial action, the ratio of the two was about 1:1. The analytical conclusions of XPS and FTIR spectra were consistent, and the results supported each other. Full article

Anyone who has tried lighting a campfire on a windy day can appreciate how difficult it could be. However, despite real-life experience and despite laboratory experiments which have demonstrated that fire ignition risk dramatically decreases beyond a certain wind threshold, current fire weather indices (FWIs) do not take this effect into account and assume a monotonic relation between wind velocity and ignition risk. In this paper, we perform a global analysis which empirically quantifies the probability of ignition as a function of wind velocity. Using both traditional methods (a logistic regression and a generalized additive model) and machine learning techniques, we find that beyond a threshold of approximately 3–4 m/s, the ignition risk substantially decreases. The effect holds when accounting for additional factors such as temperature and relative humidity. We recommend updating FWIs to account for this issue. Full article

Fire is a fundamental ecological process with a long history on Earth, determining the distribution of vegetation formations across the globe. Fire, however, does not only affect the vegetation but also the soil on which vegetation grows, creating a post-fire environment that differs significantly in terms of soil chemical and physical properties from the pre-fire environment. The duration of these alterations remains largely unknown and depends both on the vegetation condition and the fire characteristics. In the current study, we investigate the effect of fire on some chemical and physical properties 11 years after the event in four plant communities. Two of them constitute typical Mediterranean fire-prone plant communities, dominated by sclerophyllous Mediterranean shrubs, such as Quercus coccifera and Q. ilex, while the other two are not considered fire prone and are dominated by deciduous broadleaved species such as Q. petraea and Castanea sativa, respectively. The results indicate that fire affects the soil properties of the various communities in a different manner. Burned sites in the Q. coccifera community have a significantly lower concentration of organic matter, total nitrogen, and available magnesium. At the same time, they have a significantly higher concentration of sand particles and a lower concentration of clay particles. The effect of fire on the soil properties of the other three communities is less dramatic, with differences only in total phosphorus, organic matter, and total nitrogen. The results are discussed in relation to the site conditions and the post-fire regeneration of plant communities. Full article

Planning the analyses of the spatial distribution and driving factors of forest fires and regionalizing fire risks is an important part of forest fire management. Based on the Landsat-8 active fire dataset of the Liangshan Yi Autonomous Prefecture from 2014 to 2021, this paper proposes an optimal parameter logistic regression (OPLR) model, conducts forest fire risk zoning research under the optimal spatial analysis scale and model parameters, and establishes a forest fire risk prediction model. The results showed that the spatial unit of the optimal spatial analysis scale in the study area was 5 km and that the prediction accuracy of the OPLR was about 81%. The climate was the main driving factor of forest fires, while temperature had the greatest influence on the probability of forest fires. According to the forest fire prediction model, mapping the fire risk zoning, in which the medium- and high-risk area was 6021.13 km², accounted for 9.99% of the study area. The results contribute to a better understanding of forest fire management based on the local environmental characteristics of the Liangshan Yi Autonomous Prefecture and provide a reference for related forest fire prevention and control management. Full article

This paper presents the results of numerical simulation of a model combustion chamber of a pulse detonation engine using the authors’ developed software package. The main goal of the present study is to numerically investigate the effects of cyclic operation of pulse detonating chambers, as the former studies have been limited to simulating one cycle. To achieve this goal, a new mathematical model for heavy gas was applied simulating condensed fuel phase, which made it possible to accelerate computations and simulate multi-cycle operation of the device. Distributions of such characteristics as temperature, pressure, velocity, concentrations of reagents, intensity of reactions, and thrust force are obtained. A two-stage kinetic model of propellant combustion is proposed. Attention is paid to the main stages of PDE operation: filling of the chamber with reagents, ignition and transition to detonation, products exhaust, purification, and cooling the chamber with a neutral gas. The simulation of the working cycle with the shortest period for the specified system parameters was carried out, the execution time of each stage was obtained, and an assessment was carried out to minimize the main stages of the work cycle. Numerical results demonstrated that the characteristics of the engine cycle are stabilized already in the second cycle: the thrust in the first cycle differs from the thrust in the second by 5%, in the third from the second by 1%. Moreover, details of thrust dynamics in the second and third cycles were studied. Full article

Fire accidents have been reported frequently in Chinese townships over the past few years, where people’s lives and properties have been subjected to huge losses. As a result, a considerable number of traditional villages have disappeared. In this study, field surveys and on-site monitoring were used to study the village of Gao Tuan, while seven scenarios were set up in Pyrosim for simulation and analysis. As indicated by the results of this study, the hidden dangers of Dong traditional settlements in the western Hunan region were identified in terms of the construction materials, street width, and fire use. The Pyrosim simulation analysis results were as follows: scenarios 1/2 show that by utilizing the topography and layout, the wind speed was reduced layer by layer, which reduced the fire spreading disaster by nearly half; scenarios 3/4/5/6 show that, except for the 1000 mm wide street, the degree of fire spreading was negatively correlated with the width of the street, and the fire could no longer be spread to the other side of the street when it was 8000 mm; and scenario 7 shows that, in the case of a fire in a residential house, it is safer to evacuate the people in the building in a unit within 320 s. Based on the survey and Pyrosim simulation results of fire spreading, the strengths and weaknesses of Gaotuan Village in the face of fire events were analyzed, and targeted recommendations are made based on the study for the Dong traditional settlement in the western Hunan region for fire prevention. Full article

The shelf life of energetic materials (EMs) is directly associated with safety and functionality. Therefore, a priori knowledge of this parameter is essential. The standard approach for predicting the shelf life of EMs is tremendously time and money consuming. It involves massive accelerated aging tests at temperatures typically between 40 and 80 °C for relatively long time periods—from months to years—with different aging time intervals, followed by analysis of the aging-induced changes. A subsequent kinetic analysis with Arrhenius evaluation provides the effective activation energy for calculating shelf life at lower storage temperatures. In this work, a much less time- and resource-intensive approach based on the kinetic analysis of decomposition data gathered by using thermal analysis techniques is discussed as a possible alternative for the shelf life prediction of EMs. The discussion is placed in the context of the few but promising works of literature on the subject that provide evidence and examples. On the path towards the practical application of this approach, the definition of procedures that allow for a realistic simulation of storage conditions not only in the accelerated aging tests—still needed but limited to the validation of the decomposition kinetics—but also in the thermal analysis experiments is highlighted as one of the main issues to be addressed. Full article

Despite recent advances in both coupled fire modeling and measurement techniques to sample the fire environment, the fire–atmosphere coupling mechanisms that lead to fast propagating wildfires remain poorly understood. This knowledge gap adversely affects fire management when wildland fires propagate unexpectedly rapidly and shift direction due to the fire impacts on local wind conditions. In this work, we utilized observational data from the FireFlux2 prescribed burn and numerical simulations performed with a coupled fire–atmosphere model WRF-SFIRE to assess the small-scale impacts of fire on local micrometeorology under moderate wind conditions (10–12 m/s). The FireFlux2 prescribed burn provided a comprehensive observational dataset with in situ meteorological observations as well as IR measurements of fire progression. To directly quantify the effects of fire–atmosphere interactions, two WRF-SFIRE simulations were executed. One simulation was run in a two-way coupled mode in which the heat and moisture fluxes emitted from the fire were injected into the atmosphere, and the other simulation was performed in a one-way coupled mode for which the atmosphere was not affected by the fire. The difference between these two simulations was used to analyze and quantify the fire impacts on the atmospheric circulation at different sections of the fire front. The fire-released heat fluxes resulted in vertical velocities as high as 10.8 m/s at the highest measurement level (20 m above ground level) gradually diminishing with height and dropping to 7.9 m/s at 5.77 m. The fire-induced horizontal winds indicated the strongest fire-induced flow at the lowest measurement levels (as high as 3.3 m/s) gradually decreasing to less than 1 m/s at 20 m above ground level. The analysis of the simulated flow indicates significant differences between the fire-induced circulation at the fire head and on the flanks. The fire-induced circulation was much stronger near the fire head than at the flanks, where the fire did not produce particularly strong cross-fire flow and did not significantly change the lateral fire progression. However, at the head of the fire the fire-induced winds blowing across the front were the strongest and significantly accelerated fire progression. The two-way coupled simulation including the fire-induced winds produced 36.2% faster fire propagation than the one-way coupled run, and more realistically represented the fire progression. Full article

Separation Distances are used throughout the world to protect people and assets from the potential hazardous effects from propellants, explosives, and pyrotechnics. The current separation distances for Hazard Division (HD) 1.3 substances and articles used in the United States, in some cases, may not adequately protect against the effects from heat flux and debris when those substances and articles are ignited in a confined structure. Multiple tests in such a confined scenario with HD 1.3 substances have shown that the heat flux and debris hazards could result in injury at distances beyond the current specified explosives safety separation distance (ESSD). Herein are the recommended ESSDs for confined as well as unconfined HD 1.3 articles and substances based on the analysis of hundreds of tests. Recommended ESSDs include a smaller value for unconfined quantities less than 145 kg and ESSDs that are consistent with NATO distances for confined substances and articles. Full article

The steel column performance in realistic structures during a fire has yet to be fully understood because existing research emphasizes single-story performance, thereby disregarding the influence of continuous steel columns in multi-story configurations devoid of fire. This paper presents a numerical study to comprehend the overall structural fire performance of continuous steel columns, considering the effect of loading ratios, restraint ratios, column continuity, and single-sided lateral moments. An advanced numerical model was initially developed using ABAQUS and validated against experimental tests. The validated numerical model was subsequently employed to investigate the effects of several parameters, including axial restraint ratios (α = 0.05–0.35) and axial load ratios (n = 0.3–0.8). The study findings indicated that the restraint ratios within the designed range have a slightly beneficial impact on the fire resistance of continuous steel columns. The column continuity did not exert a significant impact on the performance of steel columns in fire. Additionally, the comparison showed that the current design approach in EN 1993-1-2 was conservative for predicting the limiting temperature of internal and edge columns. Full article

In fire-prone ecosystems, plant resilience to recurrent fires depends on certain fire-adaptive traits. However, how key functional and reproductive traits of graminoids respond to varying burning seasons is poorly understood. This meta-analysis, therefore, unpacks global perspectives on how resprouting, growth, reproductive, and productivity traits of graminoids (grasses and sedges) respond to different burning seasons. We recorded 569 observations from 80 experimental studies comparing graminoid plant trait responses in unburned vs. burned treatments over different seasons of burn. Weighted log response ratios and 95% confidence intervals (95%CI) were analyzed for each plant trait using random effects models and compared across burning seasons. Summer (0.35 (95%CI = 0.25 to 0.46)) and autumn burns (0.24 (95%CI = 0.16 to 0.31)) increased above-ground biomass m⁻², while biomass plant⁻¹ was increased only by spring burns (0.27 (95%CI = 0.22 to 0.32)). Bud production plant⁻¹ and tiller⁻¹ were reduced significantly by fire, especially spring, summer, and autumn burns. The shoot height (0.29 (95%CI = 0.17 to 0.41)), leaf length (0.15 (95%CI = 0.11 to 0.20)), and specific leaf area (0.08 (95%CI = 0.06 to 0.09)) increased only under summer burns, while flowering was enhanced by spring (0.19 (95%CI = 0.00 to 0.38)) and autumn burns [0.34 (95%CI = 0.02 to 0.66)]. However, seed production m⁻² was reduced by spring and summer burns and the opposite was true for seed production plant⁻¹. Overall, herbaceous plant trait responses to fire varied by the season of burn, disagreeing with the general principle that early spring burning is the best practice. We suggest that a decision on the season of burn should be informed by the objective of burning. Full article

An aspect of human responses to fires is perceiving changes in intensity. The nature of fires can make this challenging, as flames and smoke are dynamic and change with time. For developing fires, this is in addition to growth occurring vertically and sometimes horizontally, with the footprint of the fire either remaining the same or increasing in size. The present study investigated how precisely humans could visually detect differences in the intensities and growth rates of simulated fires. Using a similar approach to research with non-symbolic visual quantities, a series of experiments compared the precision of judgments regarding which of two simulated fires was greater in intensity or growing faster in intensity when the footprint was fixed or varied. In addition, participants reported what characteristics they used to make their judgments. Precision was significantly worse when comparing the growth rates versus the intensities of fires, and it was better when the fire footprint varied. This provides initial estimates of the precision of mental representations of fire intensity and growth. In addition, participants reported using multiple characteristics, including the size of flames and smoke produced. The present study indicates that humans can precisely detect differences in the intensities of fires using visual cues, but have difficulty when comparing growth rates. We discuss how this suggests that the growth rate may not be a reliable visual cue used by occupants when responding to fires. Full article

Wildfires burn millions of hectares of forest worldwide every year, and this trend is expected to continue growing under current and future climate scenarios. As a result, accurate knowledge of fuel conditions and fuel type mapping are important for assessing fire hazards and predicting fire behavior. In this study, 499 plots in six different areas in Portugal were surveyed by ALS and multisource RS, and the data thus obtained were used to evaluate a nationwide fuel classification. Random Forest (RF) and CART models were used to evaluate fuel models based on ALS (5 and 10 pulse/m²), Sentinel Imagery (Multispectral Sentinel 2 (S2) and SAR (Synthetic Aperture RaDaR) data (C-band (Sentinel 1 (S1)) and Phased Array L-band data (PALSAR-2/ALOS-2 Satellite) metrics. The specific goals of the study were as follows: (1) to develop simple CART and RF models to classify the four main fuel types in Portugal in terms of horizontal and vertical structure based on field-acquired ALS data; (2) to analyze the effect of canopy cover on fuel type classification; (3) to investigate the use of different ALS pulse densities to classify the fuel types; (4) to map a more complex classification of fuel using a multi-sensor approach and the RF method. The results indicate that use of ALS metrics (only) was a powerful way of accurately classifying the main four fuel types, with OA = 0.68. In terms of canopy cover, the best results were estimated in sparse forest, with an OA = 0.84. The effect of ALS pulse density on fuel classification indicates that 10 points m⁻² data yielded better results than 5 points m⁻² data, with OA = 0.78 and 0.71, respectively. Finally, the multi-sensor approach with RF successfully classified 13 fuel models in Portugal, with moderate OA = 0.44. Fuel mapping studies could be improved by generating more homogenous fuel models (in terms of structure and composition), increasing the number of sample plots and also by increasing the representativeness of each fuel model. Full article

Regulation (EU) No 305/2011 lays down harmonized conditions for marketing construction products in the European Union. One of its consequences has been the introduction of the product standard EN 50575 and standard EN 130501-6, concerning power, control, and communication cables permanently installed in buildings to prevent the risk of a fire and its consequences. EN 13501-6 provides the reaction to fire classifications for cables, the test methods to be performed, the requirements to meet a specific reaction to fire, and additional classifications for smoke production, flaming droplets, and acidity. It requires EN 60754-2 as the technical standard to assess acidity, and it defines three classes: a₁, a₂, and a₃ (the less performant). Due to the release of hydrogen chloride during the combustion, acidity is the weak point of PVC cables, which are not yet capable of achieving the a₁ or a₂ classes required for specific locations according to fire risk assessments. EN 13501-6 does not include EN 60754-1, used in harmonized standards outside the scope of Regulation (EU) No 305/2011. EN 60754-1 and EN 60754-2 are common standards for determining halogen gas content, and acidity/conductivity, respectively. While they involve the same type of test apparatus, they differ in heating regimes, final temperatures, and detection methods. In particular, EN 60754-2 requires testing at temperatures between 935–965 °C in the tube furnace, where the sample burns, the smoke is collected in bubblers, and pH and conductivity are measured as an indirect assessment of acidity. On the other hand, the temperature regime of EN 60754-1 is a gradual heating run, followed by isothermal heating at 800 °C. The paper shows that when potent acid scavengers are used in PVC compounds, performing EN 60754-2 with the thermal profile of EN 60754-1 or at 500 °C in isothermal conditions, the evolution of hydrogen chloride changes significantly up to 10 times less than the test performed in isothermal at 950 °C. The reason lies behind the kinetic of hydrogen chloride release during the combustion of PVC compounds: the higher the temperature or faster the heat release, the quicker hydrogen chloride evolution and the lower the probability for the acid scavenger to trap it. Thus, these findings emphasize the “fragility” of EN 60754-2 as a tool for assessing risks associated with the release of hydrogen chloride during fires. Full article