Search Results (125)

This paper is a contribution to the ongoing debate on the nature and drivers of the abrupt environmental shift at the onset of the Younger Dryas. The goal of this study is to identify key parameters that characterize the Allerød–Younger Dryas boundary, 12.9–12.8 ka in sedimentary sections, and are representative of broader paleobasin dynamics in the eastern Baltic region. Two new Late Glacial sediment archives, the Kulikovo and Sambian, provide data on this time interval. Geochronological and lithological (grain size and loss on ignition) analyses of the sequences indicate a change in sedimentation during 12.9–12.8 ka, which is manifested by a peak of terrigenous, coarser-grained material and an accompanying peak of organic matter in sediments. A review of the published data shows that this lithological situation is also characteristic of other paleobasins in the eastern Baltic region and beyond for layers dated to the onset of the Younger Dryas. This probably indicates an environmental event that caused a short-term increased input and deposition of organic matter, accompanied by a surge in erosional processes. The environmental shift triggered by the event is also recorded in a remarkable drop in pollen concentration and species diversity in the overlying layer. The sediment horizon in Late Glacial (Allerød–Younger Dryas) sequences corresponding to these parameters can be considered an important and reliable geochronological marker of the 12.9–12.8 ka interval. The organic-rich layer in the Kulikovo section, as well as other similar layers in the Baltic, can be considered a “black mat” phenomenon related to the onset of the Younger Dryas. Full article

Fire-driven land cover change has generated a paradox: while habitat fragmentation from agriculture, livestock, and urban expansion has reduced natural fire occurrences, human-induced ignitions have increased wildfire frequency and intensity. In northern Colombia’s Magdalena Department, most of the territory faces moderate to high wildfire risk, especially during recurrent dry seasons and periods of below-average precipitation. However, knowledge of wildfire spatiotemporal occurrence and its drivers remains scarce. This work addresses this gap by identifying fire-prone zones and analyzing the influence of climate and vegetation in the Magdalena Department. Fire-prone zones were identified using the Getis–Ord Gi* method over fire density and burned area data from 2001 to 2023; then, they were analyzed with seasonally aggregated hydroclimatic indices via logistic regression to quantify their influence on wildfires. Vegetation susceptibility was assessed using geostatistics, obtaining land cover types most affected by fire and their degree of fragmentation. Fire-prone zones in the Magdalena Department covered ~744.35 km² (3.21%), with a weak but significant (τ = 0.20, p < 0.01) degree of coincidence between classification based on fire density, as pre-fire variable, and burned area, as a post-fire variable. Temporally, fire probability increased during the dry season, driven by short-lagged precursors such as Dry Spell Length and precipitation from the preceding wet season. Fire-prone zones were dominated by pastures (62.39%), grasslands and shrublands (19.61%) and forests (15.74%), and exhibited larger, more complex high-risk patches, despite similar spatial connectedness with non-fire-prone zones. These findings enhance wildfire vulnerability understanding, contributing to risk-based territorial planning. Full article

Understanding environmental factors that control the ignition of fuel beds exposed to firebrands is necessary to help reduce the risk of losses of structures. Ignition by firebrands has been reported to be sensitive to wind, but identification and quantification of the physical cause(s) of such sensitivities are still limited. The objective of this study was to quantify the influence of wind speed and direction on the ignition of a fuel bed exposed to firebrands and to understand the causes of this sensitivity. Fuel beds of Douglas fir shavings were exposed to a firebrand surrogate (i.e., a resistive heater) to determine flaming ignition probability and time to ignition for three different wind speeds and three wind directions. Increases in wind speed above quiescent reduced the temperature required for flaming ignition. However, a wind speed threshold above which ignition probability decreased was observed for some wind directions. The temperatures required for flaming ignition to occur and the time to ignition were sensitive to the wind direction. High-speed images and corresponding CFD calculations indicated that ignition occurred in the regions with the most prominent recirculation zones. Thus, sensitivities to wind speed and direction are attributable to differences in the pyrolysate residence time as controlled by recirculation zones. The results indicate that the local flow characteristics can significantly influence ignition, and characterization of the freestream velocity alone may not be sufficient. Full article

Polyurethane (PUR)-based artificial leathers are often used as interior materials in public area, making flame retardants (FRs) necessary. The mode of action of different FRs varies depending on the chemical class and the structure of the supplied material. Usually, FRs are designed for bulk materials like foams, e.g., for upholstery, the main application of PUR. However, in thin materials, FRs act differently, thus leaving the PUR without sufficient flame resistance. In this study, PUR films and artificial leathers were equipped with twelve commercially available, halogen-free FRs in various concentrations and combinations. Fire resistance was tested with LOI measurements, cone calorimetry, horizontal burning behavior, and thermogravimetric analyses. An organophosphorus FR proved to be the most suited for flame-resistant artificial leather. The LOI was increased from 20 to 24.2%, the peak heat release rate was reduced by about 30%, and the sample was self-extinguishing in horizontal burning behavior. Phosphinates and aluminum trihydroxide were the least efficient FRs. Combinations of bentonite with phosphorus-based FRs showed synergistic effects in reducing the probability of igniting the material. The results demonstrate that sufficient flame retardancy for PUR-based thin materials can be achieved with commercially available halogen-free FRs, paving the way for more sustainable and greener materials by substituting ecologically harmful and health-damaging FRs. Full article

Statistics indicate that over 90% of large forest fires experience re-ignition after initial extinction. However, research on the mechanisms triggering forest fire rekindling remains largely empirical, lacking an intuitive 3D mathematical model to elucidate the process. To fill this gap, this study proposes a digital twin-based forest fire re-ignition trigger model to investigate the transition from smoldering to flaming combustion. Leveraging digital twin technology, a virtual forest environment was constructed to assess the influence of ambient wind conditions and terrain slope on the smoldering-to-flaming (StF) transition based on historical rekindling data. Subsequently, logistic regression was employed in a reverse iterative process to update the model parameters, thereby establishing a matching mechanism between the model predictions and the observed rekindling states. This approach enables the adaptive adjustment of the weights assigned to key variables (e.g., wind speed and slope) and facilitates the prediction of forest fire rekindling probability within the virtual environment. Additionally, digital twin simulations are employed to assess the 3D firefighting effectiveness of unmanned aerial vehicles (UAVs) deploying hydrogel and solidified foam extinguishing agents. This visualization of the firefighting process provides valuable insights, aiding in the development of more effective strategies for preventing and controlling fire re-ignition. Full article

The growing need to address natural and human-induced disasters while protecting territory remains a key focus for the scientific community. Effective emergency management, especially during wildfires, requires coordinated responses to safeguard lives and assets. This study develops hazard maps to aid emergency planning in Italy and estimate territorial resilience indicators. Focusing on wildfire ignition hazards in Ischia, the study uses a probabilistic model based on fifteen years of wildfire data (2009–2023). By analyzing ignition points and employing a Poisson distribution, it correlates ignition probabilities with vegetation types. The hazard maps reveal that wildfire risk is primarily influenced by the wildland–urban interface and vegetation characteristics, emphasizing the need to integrate territorial and urban factors into wildfire forecasting. The findings also suggest areas for refining the model to enhance risk mitigation strategies. Full article

Roll-on/Roll-off passenger vessels transporting electric vehicles (Ro-Ro EVs) face unique fire hazards, challenging traditional fire risk management strategies. This study integrates fault tree analysis (FTA) with Fuzzy Bayesian Network (FBN) to assess the fire risks of Ro-Ro EVs across the entire hazard chain. Given limited historical accident data, five experts familiar with the Shanghai Baoshan–Chongming ferry route refine fault tree models to visualize key fire hazard chain mechanisms and estimate risk probabilities. The FBN incorporates fault tree hierarchical structures, EV and Ro-Ro vessel-related risk factors, and applies a nine-level fuzzy scoring system to assess these risks. The FTA-FBN model offers a comprehensive framework for evaluating emerging fire risks specific to Ro-Ro EVs. Findings indicate that the highest risk occurs during the ignition phase. Primary triggers include external heat sources, improper vehicle securing, and vehicle collisions, leading to thermal runaway in lithium batteries. Failures in extinguishing and detecting lithium battery fires exacerbate fire spread. Effective fire compartmentalization and flammable material management are essential to prevent uncontrolled fires. Recommendations for fire prevention and control include shipboard battery level monitoring, charging restrictions, explosion-proof electrical installations, enhanced ventilation, lithium battery fire suppression systems, and vehicle securing. Full article

High-altitude relight is a critical challenge for aero-engines, directly impacting the safety and emergency response capabilities of aircraft. This paper systematically reviews the physical mechanisms, key factors, and relevant prediction models of high-altitude relight, highlighting the detrimental effects of extreme conditions such as low pressure and temperature on fuel evaporation rates, flame propagation speeds, and turbulent combustion processes. A comprehensive overview of the current state of high-altitude relight research is presented, alongside recommendations for enhancing the ignition performance of aero-engines under extreme conditions. This paper focuses on the development of ignition prediction models, including early empirical and semi-empirical models, as well as physics-based models for turbulent flame propagation and flame kernel tracking, assessing their applicability in high-altitude relight scenarios. Although flame kernel tracking has shown satisfactory performance in predicting ignition probability, it still overly relies on manually set parameters and lacks precise descriptions of the physical processes of flame kernel generation. Future studies on some topics, including refining flame kernel modeling, strengthening the integration of experimental data and numerical simulations, and exploring the incorporation of new ignition technologies, are needed, to further improve model reliability and predictive capability. Full article

The cleanliness of hydrogen energy throughout its life cycle has enabled its applications in transportation and buildings. However, such scenarios often involve the storage and use of hydrogen in enclosed spaces. Ensuring the facility’s safety during hydrogen accidental leakage through rapid detection and emergency measures has been a long-standing topic. In this work, we analyze hydrogen leakage in a hydrogen bus through CFD simulation. By extracting the hydrogen diffusion time and combining it with the leakage frequency and ignition probability, we quantitatively evaluate the placement of the sensors and propose an index for detection system assessment named the average detection delay index (ADDI). A near-field detection sensor was introduced to the system, which reduced the lower ADDI limit of the detection system by up to 10 times while reducing the system cost without changing the level of performance. Full article

In real road traffic, combustion engines of motor vehicles operate in dynamic conditions. Under such conditions, significant time variability in the values describing engine operations is observed, especially in terms of rotational speed and torque. Therefore, it is possible to model such conditions as probabilistic and to treat the properties of combustion engines in these conditions as stochastic processes. This paper presents a stochastic approach to the analysis of pollutant emission and fuel consumption test results of a motor vehicle driven in real traffic conditions. The empirical data were obtained from tests conducted on a car with a spark-ignition engine equipped with mobile on-board measuring equipment. The scope of the investigations covered the domains of time, frequency and process values. In the time domain, statistical characteristics of the processes were analyzed to explore potential correlations between them. In the frequency domain, the power spectral density of the processes was determined. In the process values domain, the emphasis was placed on examining the probability density of processes. A large diversification of the determined characteristics was found, in particular for vehicle velocity, engine operating states and the processes of pollutant emissions and fuel consumption. For practical reasons, the results of the correlation studies were particularly valuable, as they enabled assessment of the effects of taking action to reduce emissions of various pollutants. Full article

Background: Wildfire modelers rely on Monte Carlo simulations of wildland fire to produce burn probability maps. These simulations are computationally expensive. Methods: We study the application of importance sampling to accelerate the estimation of burn probability maps, using L2 distance as the metric of deviation. Results: Assuming a large area of interest, we prove that the optimal proposal distribution reweights the probability of ignitions by the square root of the expected burned area divided by the expected computational cost and then generalize these results to the assets-weighted L2 distance. We also propose a practical approach to searching for a good proposal distribution. Conclusions: These findings contribute quantitative methods for optimizing the precision/computation ratio of wildfire Monte Carlo simulations without biasing the results, offer a principled conceptual framework for justifying and reasoning about other computational shortcuts, and can be readily generalized to a broader spectrum of simulation-based risk modeling. Full article

The coal–oxygen composite reaction is a complex physicochemical reaction process, and different heating rates have a great influence on this reaction. In order to reveal the influence of different heating rates on the coal–oxygen composite reaction of coking coal, the TG-DSC experimental method was adopted to analyze the hysteresis effect of the characteristic temperature, inflection point temperature, and peak temperature under different heating rates. Furthermore, the KAS method was employed to calculate the apparent activation energy, and the Málek method was utilized to infer the most probable mechanism functions and determine the compensation effects at different stages of the coal oxidation process. The results show that with an increase in heating rate, the temperature values corresponding to each characteristic temperature point increase, the characteristic temperature exhibits a hysteresis phenomenon, and the heat flow rate and heat flux rate also show an increasing trend. The apparent activation energy gradually increases in Stages II and III, with a maximum value of 198.7 kJ/mol near the ignition point T₃, which first increases and then gradually decreases in Stage IV, where the maximum value is around the temperature point T₄ of the maximum mass loss rate, which is 170.02 kJ/mol. The variation trend in the pre-exponential factor is consistent with the apparent activation energy, and the dynamic compensation effect is greater in Stage IV. The three different oxidation stages have different mechanism functions: a three-dimensional diffusion mode is present in Stages II and III, which is ultimately transformed into an accelerated form α-t curve with E₁ and n = 1 in Stage IV. Full article

Wildfire ignitions are often linked to environmental and climatic factors, but human behavior plays a critical role, particularly in rural southern Europe. However, tools to quantify the probability of human-caused ignitions are lacking. This study addresses this by developing a human behavior wildfire ignition probability index focused on mainland Portugal, a region historically vulnerable to wildfires. Statistical analyses, including multicollinearity checks and a Generalized Linear Model, were used to analyze ignition data, while geospatial analyses estimated the ignition probabilities for 2021 and 2022. Inputs included human activity indicators, land use types, and proximity to residential roads. The resulting probability maps identified high-risk areas, particularly in forested zones and near residential roads. These maps closely aligned with documented human-caused ignitions, confirming the model’s reliability. The index is a robust tool for identifying high-risk areas and has significant potential to improve fire prevention strategies by targeting the most vulnerable regions. Future research should explore its integration into forecasting systems for real-time fire prevention and response strategies as well as its adaptation to other regions with similar wildfire risks. Full article

The ignition of combustible materials by electric welding spatters represents a significant cause of fires in welding operations, and the current intensity is a sensitive factor that affects the ignition capacity of welding spatters. In this work, the influence of different current intensities on the physical properties and ignition capacity of welding spatters on common combustible materials was investigated, and the ignition mechanism of electric welding spatter was also explained by means of the hot-spot theory. The results indicated that the splash range, the total generated quantity, the maximum diameter, and the temperature of electric welding spatters increased with the enhancement in current intensity. Furthermore, a higher current intensity was associated with a greater likelihood of producing irregular spatter particles. The probability of ignition of electrode welding spatters was found to be sensitive to their physical properties, exhibiting a non-linear increase with increasing current intensity. At a current intensity of 360 A, a surge in both the physical properties and ignition capacity of the spatters was observed, which is attributed to the coupling of a reduction in the critical hot-spot radius and an unstable pulsation in the arc. Full article

Accidental leakage from oil–gas storage tanks can lead to the formation of liquid pools. These pools can result in vapor cloud explosions (VCEs) if combustible vapors encounter ignition energy. Conducting accurate and comprehensive consequence analyses of such explosions is crucial for quantitative risk assessments (QRAs) in industrial safety. In this study, a methodology based on the SLAB-TNO model to calculate the overpressure resulting from a VCE is presented. Based on this method, the consequences of the VCE accident considering the gas cloud concentration diffusion are studied. The probit model is employed to evaluate casualty probabilities under varying environmental and operational conditions. The effects of key parameters, including gas diffusion time, wind speed, lower flammability limit (LFL), and environment temperature, on casualty diffusion are systematically investigated. The results indicate that when the diffusion time is less than 100 s, the VCE consequences are significantly more severe due to the rapid spread of the gas cloud. Furthermore, increasing wind speed accelerates gas dispersion, reducing the spatial extent of casualty isopleths. The LFL is shown to have a direct impact on both the mass and diffusion of the flammable gas cloud, with higher LFL values shifting the explosion’s epicenter upward. The environmental temperature promotes gas diffusion in the core area and increases the mass of the combustible gas cloud. These findings provide critical insights for improving the safety protocols in oil and gas storage facilities and can serve as a valuable reference for consequence assessment and emergency response planning in similar industrial scenarios. Full article