Fire Front Research Articles

Crown fire initiation of a thunderstorm

Understanding bushfire–atmosphere interactions is essential for accurate prediction of fire behaviour, and for the safe and effective strategic management of fires to mitigate risk to people and property. Bushfires with feedbacks to thunderstorms represent the most extreme form of fire–atmosphere interaction, with potential to initiate tornadoes, lightning and hazardous winds causing dangerous fire behaviour and new ignitions many kilometres from the fire front. However, there is very little evidence that links quantitative fire behaviour with observed thunderstorm dynamics. Here we combine stochastic modelling of fire behaviour with satellite and mobile weather radar data of a bushfire thunderstorm in Queensland, Australia. The results show the coupling between fire behaviour and thunderstorm development in a conditionally unstable atmosphere. The process by which the coupling occurs raises questions as to the cause and effect relationship of the bushfire-initiated thunderstorms and associated fire behaviour. Recommendations for future research are made, highlighting the need for understanding links between modelled and observed fire behaviour dynamics and atmospheric thermodynamics.

The effect of fuel bed structure on Rothermel model performance

Background Fifty years after its initial publication, Rothermel’s model continues to underpin many operational fire modelling tools. Past authors have, however, suggested a possible oversensitivity of the Rothermel model to fuel depth in certain fuel types. Aims To evaluate Rothermel model performance based on previous observations of the effect of fuel structure on flame spread through porous fuel beds. This is informed by the consideration of the effect of fuel structure on the physical mechanisms underpinning surface flame spread. Methods This study uses an existing dataset of flame spread experiments in pine needle beds to evaluate the effect of fuel structure on Rothermel model predictions of spread rate and reaction intensity. Key results Underpredictions of spread rate occurred for compressed fuel beds, apparently driven by an underprediction of the reaction intensity. Conclusions A greater understanding of the role of fuel structure on the energy release within the fire front region is therefore required. Implications The current tendency for spread rate to be underestimated in the studied fuel beds in quiescent (no wind or slope) conditions requires further consideration given the widespread use of Rothermel’s model in current operational modelling tools.

MECHANISM OF COAL AEROSOL EXPLOSION DEVELOPMENT IN AN EXPERIMENTAL MINE WORKING

Today there is not enough scientific data on the energy level and the velocity of an explosion in actual mine workings, which have a cross-sectional area larger than experimental mine workings. The objective of the paper is to justify the energy parameters of an explosion in actual mine workings based on the disclosure of the fire front development mechanism when coal dust explodes in an experimental mine working with a limited cross-sectional area. These studies can be the basis for choosing the speed of action and the strength of the means of the localization of dust explosions. The main research method is an experimental and analytical method, based on the analysis of the results of experimental explosions of coal dust in experimental mine workings and theoretical substantiation of the regularities of the development of the velocity and additional energy of the fire front with further extrapolation to the conditions of actual mine workings. It is proposed to supplement the mechanism of explosion development with an idea about the sections of development of explosion dynamics, i.e. initiation, dust explosion, crater, which determine the characteristic parameters of the explosive front velocity: maximum initiating velocity, average velocity, and maximum velocity in a crater. It was established that during methane initiation in the experimental mine working at the boundary between the initiation and dusting zones, there is a situation of a hybrid explosion of a mixture of methane and dust with air, which has its own velocity and energy indicators. A linear dependence of the energy generated during the coal aerosol explosion on the cross-sectional plane of the mine working was established. This makes it possible to use the results of testing the coal from certain deposits in small-scale experimental set-ups to justify the parameters of protective means for the actual mine workings.

Wildfire aerial thermal image segmentation using unsupervised methods: a multilayer level set approach

Background and aims Infrared thermal images of a propagating wildfire taken by manned or unmanned aerial vehicles can help firefighting authorities with combat planning. Segmenting these images into regions of different fire temperatures is a necessary step to measure the fire perimeter and determine the location of the fire front. Methods This work proposes a multilayer segmentation method based on level sets, which have the property of handling topology, making them suitable to segment images that contain scattered fire areas. The experimental results were compared using hand-drawn labels over a set of images provided by the Portuguese Air Force as ground truth. These labels were carefully drawn by the authors to ensure that they complied with the requirements indicated by the Portuguese National Authority for Emergency and Civil Protection. The proposed method was optimised to ensure contour smoothness and reliability, as well as reduce computation time. Key results The proposed method can surpass other common unsupervised methods in terms of intersection over union, although it has not yet been able to perform real-time segmentation. Conclusions Although falling out of use in relation to supervised and deep learning methods, unsupervised segmentation can still be very useful when annotated datasets are unavailable.

Physics-based simulations of grassfire propagation on sloped terrain at field scale: motivations, model reliability, rate of spread and fire intensity†

This study focuses on physics-based modelling of grassfire behaviour over flat and sloped terrains through a set of field-scale simulations performed using the Wildland–urban Interface Fire Dynamics Simulator (WFDS), with varying wind speeds (12.5, 6 and 3 m s−1) and slope angles (−30° to +30°). To ensure the accuracy of this Large Eddy Simulation (LES), a sensitivity study was carried out to select the converged domain and grid sizes. Fire isochrones, locations of fire front, dynamic and quasi-steady rates of spread (RoS), and fire intensity results from the simulations are presented. Within the simulations conducted, the RoS and fire intensity were found to be higher with increasing slope angles, as well as with wind velocity. RoS comparisons are made with various empirical models. At different slope angles and driving wind velocities, different empirical quasi-steady RoS broadly match with particular dynamic maximum, minimum and averaged RoS values from this study. It appears that the ideal nature of grassfire propagation simulation and challenges related to measuring quasi-steady values in experimental studies are likely reasons for the observed differences. Additionally, for lower wind velocities, the RoS–fire intensity relationship (Byram’s) deviates from linearity for greater upslopes.

Deterministic–Probabilistic Prediction of Forest Fires from Lightning Activity Taking into Account Aerosol Emissions

Forest fires arise from anthropogenic load and lightning activity. The formation of a thunderstorm front is due to the influence of a number of factors, including the emission of aerosol particles from forest fires. The purpose of this study is mathematical modeling of heat and mass transfer in vegetation firebrand carried out from a forest fire front, taking into account the formation of soot particles to predict forest fire danger from thunderstorm activity. Research objectives: (1) development of a deterministic mathematical model of heat and mass transfer in a pyrolyzed firebrand of vegetation, taking into account soot formation; (2) development of a probabilistic criterion for assessing forest fire danger from thunderstorms, taking into account aerosol emissions; (3) scenario modeling of heat and mass transfer and the formation of a thunderstorm front; (4) and the formulation of conclusions and proposals for the practical application of the developed deterministic–probabilistic approach to the prediction of forest fires from thunderstorms, taking into account aerosol emissions. The novelty of this study lies in the development of a new model of heat and mass transfer in a pyrolyzed vegetation firebrand and a new probabilistic criterion for forest fire danger due to thunderstorm activity, taking into account aerosol emission. The distributions of temperature and volume fractions of phases in a firebrand are obtained for various scenarios. Scenarios of surface fires, crown forest fires, and a fire storm are considered for typical types of coniferous vegetation. Cubic firebrands are considered in the approximation of a two-dimensional mathematical model. To describe the heat and mass transfer in the firebrand structure, a differential heat conduction equation is used with the corresponding initial and boundary conditions, taking into account the kinetic scheme of pyrolysis and soot formation. Variants of using the developed mathematical model and probabilistic criterion in the practice of protecting forests from fires are proposed. Key findings: (1) linear deterministic–probabilistic mathematical model to assess forest fire occurrence probability taking into account aerosol emission and lightning activity; (2) results of mathematical modeling of heat and mass transfer in firebrand taking into account soot formation; (3) and results of scenario modeling of forest fire occurrence probability for different conditions of lightning activity and aerosol emission.

Collective Effects of Fire Intensity and Sloped Terrain on Wind-Driven Surface Fire and Its Impact on a Cubic Structure

The combined effects of percent slope and fire intensity of a wind driven line fire on an idealized building has been numerically investigated in this paper. The simulations were done using the large eddy simulation (LES) solver of an open source CFD toolbox called FireFOAM. A set of three fire intensity values representing different heat release rates of grassland fuels on different inclined fuel beds have been modeled to analyze the impact of factors, such as fuel and topography on wind-fire interaction of a built area. An idealized cubic structure representing a simplified building was considered downstream of the fire source. The numerical results have been verified with the aerodynamic measurements of a full-scale building model in the absence of fire effects. There is a fair consistency between the modeled findings and empirical outcomes with maximum error of 18%, which acknowledge the validity and precision of the proposed model. The results show that concurrent increase of fire intensity and terrain slope causes an expansion of the surface temperature of the building which is partially due to the increase of flame tilt angle upslope on the hilly terrains. In addition, increasing fire intensity leads to an increase in the flow velocity, which is associated with the low-pressure area observed behind the fire front. Despite limitations of the experimental results in the area of wind-fire interaction the result of the present work is an attempt to shed light on this very important problem of fire behavior prediction. This article is a primary report on this subject in CFD modeling of the collective effects of fire intensity and sloped terrain on wind driven wildfire and its interaction on buildings.

Разработка средств локализации взрывов угольной пыли

The aim of the research was to increase the speed of the device for localizing coal dust explosions to reliably suppress the fire front by creating a barrier from a cloud of fire extinguishing agent and, as a result, stopping the spread of an explosion in a mine working. The result is an increase in the safety of a mine personnel. In the paper, an integrated approach was applied, including the following: analysis and generalization of statistical data on explosions of the methane-air and dust-air mixtures in the mines of Ukraine; critical analysis of means of localization of explosions of coal dust; computer simulation of stress propagation in a rock mass during an explosion. The obtained data on the propagation of stresses in a rock mass allowed to scientifically substantiate the new approach to obtaining information about a shock front approaching. The results of the study confirmed that the transfer of dust accumulations into a suspended state under the influence of seismic waves moving along the working with a significant advance of the explosion front creates conditions for the formation of an explosive concentration of dust ahead of the fire front. Earlier receipt of an explosion signal from a seismic sensor can contribute to the formation of an explosion-proof environment even before the fire front approaches, which will allow taking measures to prevent the creation of a combustible environment and the formation of a non-combustible zone in the path of the fire front. Thanks to the discovery of the mechanism of propagation of explosion energy in a mountain environment, a fundamentally new approach to detecting an explosion in a mine working was substantiated, and a new design of a device for localizing coal dust explosions was developed. The introduction of this device will speed up the localization of dust explosions by creating an efficient barrier from a cloud of fire extinguishing agents. At the same time, an explosion-proof environment will be formed in the mine working, which will lead to an increase in the level of protection of miners from the harmful and hazardous explosion factors.

Fifty years of progress in wildland fire modelling: from empirical to fully physical CFD models

The aim of this short review is to present the progress made in wildland fire modelling during the last 50 years and the intellectual track followed by wildland fires models, from fully empirical models in the 60s, to semi-empirical ones in the 70s, to fully physical models at the end of the 90s. During the last period, the large diffusion of HPC methods substantially contributed to the development of multiphase formulations applied to wildland fire modelling. Many studies have particularly focused on the effects of various parameters (vegetation, topography, atmosphere) affecting the behaviour of a fire front propagating through a forest fuel layer.

A hybrid stochastic Lagrangian – cellular automata framework for modelling fire propagation in inhomogeneous terrains

A stochastic model motivated by the Lagrangian transported probability density function method for turbulent reacting flows and the cellular automata approach for forest fires was put together to simulate propagation of fires in terrains with inhomogeneous composition. In contrast to the usual cellular automata models for fires where the probability of ignition is prescribed, here the ignition of cells is determined by a random walk that mimics turbulent convection and diffusion of the hot gases and firebrands from upwind and neighbouring fire fronts. Radiation is also included. The model is aimed at speed of computation while approximating the key physics through only a few terrain-related inputs and tunable parameters representing fire intensity, hot gas and ember decay timescales, cell ignition delay and local turbulence. These parameters were calibrated against controlled fire experiments and the model was then used to give reasonable predictions for fires of increasing complexity. The presented framework allows improvements for more accurate representation of the flammable material characteristics, fire-induced flow modifications, and most other phenomena present in fires, hence providing an extendable and simple yet physically-realistic novel modelling approach.

Measurements from inside a Thunderstorm Driven by Wildfire: The 2019 FIREX-AQ Field Experiment

Abstract The 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field experiment obtained a diverse set of in situ and remotely sensed measurements before and during a pyrocumulonimbus (pyroCb) event over the Williams Flats fire in Washington State. This unique dataset confirms that pyroCb activity is an efficient vertical smoke transport pathway into the upper troposphere and lower stratosphere (UTLS). The magnitude of smoke plumes observed in the UTLS has increased significantly in recent years, following unprecedented wildfire and pyroCb activity observed worldwide. The FIREX-AQ pyroCb dataset is therefore extremely relevant to a broad community, providing the first measurements of fresh smoke exhaust in the upper troposphere, including from within active pyroCb cloud tops. High-resolution remote sensing reveals that three plume cores linked to localized fire fronts, burning primarily in dense forest fuels, contributed to four total pyroCb “pulses.” Rapid changes in fire geometry and spatial extent dramatically influenced the magnitude, behavior, and duration of pyroCb activity. Cloud probe measurements and weather radar identify the presence of large ice particles within the pyroCb and hydrometers below cloud base, indicating precipitation development. The resulting feedbacks suggest that vertical smoke transport efficiency was reduced slightly when compared with intense pyroCb events reaching the lower stratosphere. Physical and optical aerosol property measurements in pyroCb exhaust are compared with previous assumptions. A large suite of aerosol and gas-phase chemistry measurements sets a foundation for future studies aimed at understanding the composition of smoke plumes lifted by pyroconvection into the UTLS and their role in the climate system.

Modeling the propagation of tumor fronts with shortest path and diffusion models—implications for the definition of the clinical target volume

Objective. The overarching objective is to make the definition of the clinical target volume (CTV) in radiation oncology less subjective and more scientifically based. The specific objective of this study is to investigate similarities and differences between two methods that model tumor spread beyond the visible gross tumor volume (GTV): (1) the shortest path model, which is the standard method of adding a geometric GTV-CTV margin, and (2) the reaction-diffusion model. Approach. These two models to capture the invisible tumor ‘fire front’ are defined and compared in mathematical terms. The models are applied to example cases that represent tumor spread in non-uniform and anisotropic media with anatomical barriers. Main results. The two seemingly disparate models bring forth traveling waves that can be associated with the front of tumor growth outward from the GTV. The shape of the fronts is similar for both models. Differences are seen in cases where the diffusive flow is reduced due to anatomical barriers, and in complex spatially non-uniform cases. The diffusion model generally leads to smoother fronts. The smoothness can be controlled with a parameter defined by the ratio of the diffusion coefficient and the proliferation rate. Significance. Defining the CTV has been described as the weakest link of the radiotherapy chain. There are many similarities in the mathematical description and the behavior of the common geometric GTV-CTV expansion method, and the definition of the CTV tumor front via the reaction-diffusion model. Its mechanistic basis and the controllable smoothness make the diffusion model an attractive alternative to the standard GTV-CTV margin model.

Mathematical simulation of inert heating and pyrolysis of forest fuel under the influence of a forest fire front, if the process of sooting is taken into account

Introduction. Large amounts of pollutants, including carbonaceous particles of soot, are released into the atmosphere during a forest fire. High concentrations of these particles in the air can lead to the development of cardiorespiratory diseases or death. It has been noticed that a certain number of soot particles is produced at the stage of forest fuel pyrolysis. In this regard, it is advisable to study the processes of pyrolysis and sooting to develop effective methods of their prediction and prevention.Goal of the study. The goal of this study is the mathematical simulation of heat transfer in an element of standard forest fuel (a birch leaf), taking into account the thermal decomposition of dry organic matter and sooting.Materials and methods. Within the framework of the work, scenario modeling of heat and mass transfer processes in an element of forest fuel (a birch leaf), subjected to the influence of a high-temperature environment, was conducted. A one-dimensional heat transfer equation and a kinetic equation, having respective initial and boundary conditions, were solved by means of numerical simulation. The finite difference method was employed to solve the resulting system of differential equations. The calculations were conducted using the RAD Studio software package. Graphical results were processed using the OriginPro software package.Results. Scenario modeling took into account the type of forest fire, the period of the fire hazard season, forest fuel properties, the degree of the forest fuel dispersion, and the initial moisture content in a forest fuel element. The authors have found that the major influence is made by the extent of dispersion and the type of forest fire. The similarity of qualitative characteristics of sooting has also been established for all types of forest fires.Conclusion. The proposed mathematical model can be used in conjunction with geoinformation systems to visualize the initial and output information in the process of assessment, monitoring and forecasting of forest fires and their environmental consequences.

Tools for the analysis and visualisation of distributions and vector fields in surface forest fires modelling

The problem of computer modelling of the spread of surface forest fires in a two-dimensional formulation is herein considered. We describe the initial-boundary value problem in the form of a system of partial differential equations in the accepted approximation of the corresponding physical and chemical processes with refinements of the mutually agreed defining functions and the coefficients included in the equations. The Wolfram Mathematica computer algebra system is used as a platform for developing the computer model, performing calculations, and creating a database with the outcomes of computations. The results of numerical experiments investigating possible scenarios of how a fire zone spreads in different directions and its behaviour near the fuelbreaks are presented. Several qualitative features of the structure, the evolution of the temperature front, and the vector fields of the oxygen concentration gradient over the forest area are identified and illustrated with multidimensional graphics in the presence of areas of the low content of combustible materials of various shapes and sizes, including the demonstration of the influence of the equilibrium wind speed in the forest canopy. Possible variants of the fire front movement in the direction of the wind velocity and against it are identified and explained using representative examples.

3d-reconstruction of destructive process models using remote sensing by a group of unmanned aerial vehicles

The paper presents a novel method of volumetric reconstruction of transient destructive processes using remote sensing by a group of unmanned aerial vehicles. The study is based on the most common class of such processes like forest fires, where a fire front is a determinant, and its propagation reflects the dynamics of the process. The effects of wind, smoke and fire, turbulence and vibration, interference, distortion, and obstacles lead to uncertainty of observations, to overcome which fuzzy sets, soft sets and gray numbers were combined. A spatial model based on a recursive eight-fold subdivision of space as well as on a hierarchical structure of virtual cells is proposed, which allowed to resolve the contradictions between the accuracy and rate of reconstruction. The set of possible states of virtual cells is determined and the algorithm of their classification based on the use of a five-channel image recognition system containing infrared, two main, and two additional optical channels is proposed. An algorithm for calculating a 3D observation vector, presented by an array of confidence vectors, is proposed, which can be used to determine the gray fuzzy state of virtual cells allowing a combination of observations from different observers and refining them sequentially. The terrain where the process evolves is represented by a soft gray fuzzy set of virtual cells, which belong to a specific state at the consideration time, allowing identification of convincing, uncertain, suspicious, and negative components. The first one defines a stable core of the fire front while the second one represents its variation caused by uncertainty. The proposed method allows the reconstruction of transient spatially distributed processes of other classes, smoothing the effects of distortions and noise and ensuring acceptable performance.

California wildfire spread derived using VIIRS satellite observations and an object-based tracking system

Changing wildfire regimes in the western US and other fire-prone regions pose considerable risks to human health and ecosystem function. However, our understanding of wildfire behavior is still limited by a lack of data products that systematically quantify fire spread, behavior and impacts. Here we develop a novel object-based system for tracking the progression of individual fires using 375 m Visible Infrared Imaging Radiometer Suite active fire detections. At each half-daily time step, fire pixels are clustered according to their spatial proximity, and are either appended to an existing active fire object or are assigned to a new object. This automatic system allows us to update the attributes of each fire event, delineate the fire perimeter, and identify the active fire front shortly after satellite data acquisition. Using this system, we mapped the history of California fires during 2012–2020. Our approach and data stream may be useful for calibration and evaluation of fire spread models, estimation of near-real-time wildfire emissions, and as means for prescribing initial conditions in fire forecast models.

MATHEMATICAL MODELING OF THE FOREST FIRE IMPACT ON THE BRANCH OF A CONIFEROUS TREE

It is necessary to develop quantitative methods to assess the formation of thermal burns in the morphological parts of coniferous trees. The purpose of the study is mathematical modeling of heat transfer in the layered structure of a coniferous tree branch under the influence of a forest fire front. The heat propagation in the «branch — needles — flame zone» system is described by a system of non-stationary differential equations of heat conduction with the corresponding initial and boundary conditions. As an object of research, a digital model of a branch of a coniferous tree for various species, namely, pine, larch and fir, was used. Temperature distributions are obtained for different variants of the branch structure and conditions of the impact of the forest fire front. Conclusions are made about the need for further modernization of the mathematical model. The developed model is the basis for creating software tools for specialized geographic information systems.

Prescribed grass fire evolution mapping and rate of spread measurement using orthorectified thermal imagery from a fixed-wing UAS

ABSTRACT Fire metrics such as fire front location and rate of spread (ROS) are critical to understanding the behavior of prescribed fires and wildfires. This paper proposes a new method for prescribed grass fire evolution mapping and ROS measurement using multitemporal thermal orthomosaics collected by a small fixed-wing Unmanned Aircraft System (UAS) at low altitudes. The proposed method provides a low-cost, safe, and effective solution for active grass fire monitoring and fire metric measurement in areas that may be challenging for a typical rotor-wing UAS to cover due to endurance and size constraints. The proposed method is demonstrated using a prescribed grass fire data set collected by the KHawk fixed-wing UAS over a 13 ha. Kansas tallgrass prairie field on 8 October 2019. Repeat-pass thermal images collected by the KHawk UAS during about 10 min of the burning were grouped and processed to produce multitemporal orthomosaics with a spatial resolution of about m and a horizontal position error of about 1.5 m. The resulting orthomosaics were further processed for fire front extraction and the measurement of fire front location and ROS. The head fire ROS of this grass burn was observed to be between 0.2 and 0.4 with a mean value of 0.27 .

Beyond migration: a critical review of climate change induced displacement

ABSTRACT Scholarship on displacement caused by the effects of climate change generally approaches displacement as the involuntary movement of people. However, in this article, we argue that there are uncertainties surrounding Climate Change Induced Displacement (CCID) that are partly caused by discursive ambiguity around the notion of ‘displacement’ – a concept that remains poorly defined in the context of climate change research – and a conflation between displacement due to quick-onset disaster events and the cumulative pressure of living in an environment marked by a disrupted climate. Reflecting on the impacts of the Australian bushfires in 2019–20, we conceptualise CCID beyond migration as an event and a physical relocation across geographical space. Even fast-onset disaster events, such as the Australian bushfires, can dispossess and displace beyond the immediate threat of the fire front; but this displacement is not necessarily aligned with movement and migration, nor is it evenly proportioned across populations. Based on a review of existing literature on CCID, we identify three key tensions shaping scholarship on CCID: conceptualisation; distribution of risk and impact; and discursive framing. Together, we contend, these tensions highlight the imperative of striving for conceptual clarity and awareness of distributional inequities of risk and vulnerabilities.

Simulating Potential Impacts of Fuel Treatments on Fire Behavior and Evacuation Time of the 2018 Camp Fire in Northern California

Fuel break effectiveness in wildland-urban interface (WUI) is not well understood during downslope wind-driven fires even though various fuel treatments are conducted across the western United States. The aim of this paper is to examine the efficacy of WUI fuel breaks under the influence of strong winds and dry fuels, using the 2018 Camp Fire as a case study. The operational fire growth model Prometheus was used to show: (1) downstream impacts of 200 m and 400 m wide WUI fuel breaks on fire behavior and evacuation time gain; (2) how the downstream fire behavior was affected by the width and fuel conditions of the WUI fuel breaks; and (3) the impacts of background wind speeds on the efficacy of WUI fuel breaks. Our results indicate that WUI fuel breaks may slow wildfire spread rates by dispersing the primary advancing fire front into multiple fronts of lower intensity on the downstream edge of the fuel break. However, fuel break width mattered. We found that the lateral fire spread and burned area were reduced downstream of the 400 m wide WUI fuel break more effectively than the 200 m fuel break. Further sensitivity tests showed that wind speed at the time of ignition influenced fire behavior and efficacy of management interventions.