Wildland-urban Interface Fire Research Articles

The rising threats of wildland-urban interface fires in the era of climate change: The Los Angeles 2025 fires

The rising threats of wildland-urban interface fires in the era of climate change: The Los Angeles 2025 fires

Experimental Study of Heat Transfer Through Windows Exposed to a Radiant Panel Heater

AbstractStructure hardening is a key strategy to help mitigate building destruction during wildland-urban interface fires. Windows represent an important vulnerability for structure failure by allowing heat transfer to interior combustibles, and in cases of mechanical failure, an entry point for flames and/or embers. The purpose of this study is to characterize heat transfer through windows with various common construction variables (plain (annealed) versus tempered glass, single- versus double-pane, low-emissivity coating versus no coating, and air-filled versus argon-filled pane gap). Small-scale experiments were performed with 23 cm by 23 cm windows exposed to a radiant panel producing centerpoint incident heat fluxes of 10 $$\hbox {kW/m}^{2}$$ kW/m 2 , 20 $$\hbox {kW/m}^{2}$$ kW/m 2 , 30 $$\hbox {kW/m}^{2}$$ kW/m 2 , 40 $$\hbox {kW/m}^{2}$$ kW/m 2 , and 50 $$\hbox {kW/m}^{2}$$ kW/m 2 . Total heat flux was measured 5.1 cm behind the window glass. Times of pane cracking and other failure events were recorded. Double-pane designs reduced heat transfer through a window more than the single-pane design (measured 13% to 43% and 39% to 60% of the incident heat flux, respectively). Heat transfer was further reduced when a low-emissivity coating was present (measured 5 to 14% of the incident heat flux). The differences in measured heat flux behind plain glass versus tempered glass windows and air-filled versus argon-filled windows were not statistically significant. Tempered glass performed better than plain glass, and double-pane argon-filled windows consistently survived longer than double-pane air-filled windows. In some cases, heat fluxes measured behind the windows surpassed the critical heat flux required for ignition of some common household combustibles.

TOXIC HOMES AND COMMUNITIES? EXPOSURE TO URBAN FIRES AND INCREASED LIFE COURSE DEMENTIA RISK

Abstract Little is known about the health impacts of wildland urban interface (WUI) fires, which are increasingly common and mostly burn human-made materials. The Marshall Fire Community Health Research Study investigated a destructive WUI fire that affected communities of Superior and Louisville (CO) on December 30, 2021. Semi-structured seated and mobile interviews conducted July through November 2023 probed for perceived impacts on physical, mental, social, and cognitive health. Participants (n=44) were on average 52 years old (±16 years), 86% identified as Non-Hispanic White, 67% female, 86% homeowners, and 46.5% of participant homes were fully destroyed (53.5% smoke damaged). Reflexive thematic analysis identified behavioral and social pathways that may pose longer-term risk for Alzheimer’s Disease and Related Dementias across the life course. This includes early-life educational disruptions (e.g., displacement and stress/anxiety) and mid-life increased risk for hypertension, obesity, and alcohol consumption through heightened stress, lack of time and motivation for diet and exercise, maladaptive coping mechanisms, poor sleep quality, and reduced access to health-promoting services. Later life factors include increased risk for depression, social isolation, physical inactivity, diabetes, and exposure to poorer air quality. These risks varied by individual factors such as education, employment, insurance coverage, type of fire damage, and household composition. Individuals whose homes were smoke damaged may be particularly vulnerable. The study identifies novel behavioral and social pathways through which WUI fires may pose multifaceted and long-term cognitive health risks beyond the acute recovery phase.

Physical Health Symptoms and Perceptions of Air Quality among Residents of Smoke-Damaged Homes from a Wildland Urban Interface Fire.

The Marshall Fire was a wildland urban interface (WUI) fire that destroyed more than 1000 structures in two communities in Colorado. High winds carried smoke and ash into an unknown number of buildings that, while not incinerated, were significantly damaged. We aimed to understand whether smoke or ash damage to one's home was associated with physical health impacts of the fire event for people living in and around the fire zone whose homes were not completely destroyed. We analyzed data collected from participants who responded to Wave 1 (six months postfire; N = 642) or Wave 2 (one-year postfire; N = 413) of the Marshall Fire Unified Research Survey. We used self-reported exposure to smells and ash in their homes as measures of exposure and also created spatial exposure measures based on proximity to destroyed structures. Reporting a headache was statistically significantly associated with all exposure metrics (self-reported and spatial proximity), and reporting a strange taste in one's mouth was also significantly associated with having more destroyed buildings within 250 m of the home. Study findings can inform response planning for future WUI fires to protect the health of residents of smoke-damaged homes.

Volatile Organic Compounds Inside Homes Impacted by Smoke from the Marshall Fire.

Wildfires at the wildland-urban interface (WUI) have been increasing in frequency over recent decades due to increased human development and shifting climatic patterns. The work presented here focuses on the impacts of a WUI fire on indoor air using field measurements of volatile organic compounds (VOCs) by Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). We found a slow decrease in VOC mixing ratios over the course of roughly 5 weeks starting 10 days after the fire, and those levels decreased to ∼20% of the initial indoor value on average. The VOC composition could be described by a combination of biomass burning emissions and indoor air composition. Comparisons were made between polycyclic aromatic hydrocarbon (PAH) distributions in the gas phase and ash, with differences observed in their distribution between each other and when compared to fresh fuel inventory measurements. Mitigation tests were conducted running air cleaners with activated carbon and opening windows to promote indoor-outdoor air exchange, with both methods showing a decrease greater than 50% for average VOC levels indoors while active. We compare our results with simulated smoke impact experiments that show the slow decline in VOCs must be understood in the context of indoor reservoirs, beyond just on surfaces, leading to the slow release of VOCs to indoor air.

Modelling wildfire activity in wildland–urban interface (WUI) areas of Sardinia, Italy

Background Wildfire frequency, magnitude and impacts in wildland–urban interface (WUI) areas are increasing in the Mediterranean Basin. Aims We investigated the role played by socio-economic, vegetation, climatic, and zootechnical drivers on WUI wildfire patterns (area burned and wildfire ignitions) in Sardinia, Italy. Methods We defined WUI as the 100-m buffer area of the anthropic layers. We created a comprehensive and multi-year dataset of explanatory variables and wildfires, and then trained a set of models and evaluated their performances in predicting WUI fires. We used the best models to assess the single variable’s importance and map wildfire patterns. Key results Random Forest and Support Vector Machine were the best performing models. In broad terms, wildfire patterns at WUI were influenced by socio-economic factors and herbaceous vegetation types. Conclusions Machine learning models can be useful tools to predict wildfire ignitions and area burned at WUI in Mediterranean areas. Implications Improved knowledge of the main drivers of wildfires at WUI in fire-prone Mediterranean areas can foster the development or optimisation of wildfire risk reduction and prevention strategies.

Progress to Develop Globally Harmonized International Testing Standards for Large Outdoor Fires, Including Wildland‐Urban Interface Fires

ABSTRACTThe wildland‐urban interface (WUI) fire problem continues to perplex governments around the world. The WUI fire situation is not becoming better across the earth and globally harmonized test standards are required to help lessen the destruction in the event of WUI fire disasters. In this brief overview, a review of activities undertaken in ISO TC92/WG14, the Large Outdoor Fires and the Built Environment Working Group, under ISO TC92, is provided. Specifically, the genesis of how this working group came to be formed is provided as well as an overview of current documents that have been published by ISO TC92 and developed by ISO TC92/WG14. The review closes with recently added new work items in ISO TC92/WG14 and some possible future challenges.

Integrating an urban fire model into an operational wildland fire model to simulate one dimensional wildland–urban interface fires: a parametric study

Background Wildland fires that occur near communities, in the wildland–urban interface (WUI), can inflict significant damage to urban structures. Although computational models are vital in wildfires, they often focus solely on wildland landscapes. Aim We conducted a computational study to investigate WUI fire spread, encompassing both urban and wildland landscapes. Methods We developed a 1D landscape-scale semi-physical model by integrating a semi-physical urban fire spread model into an Eulerian level set model of wildfire. The model includes ignition and spread through radiation, direct flame contact and ember deposition. Key results Through a parametric study, we compare the relative change of spread rate from various structural properties and landscape layouts represented by model parameters, highlighting the significant impact of fire-resistant structure materials over surface treatments. Layout configurations play a pivotal role in fire spread, with isolated islands of combustibles effective in reducing spread rate, aligning with existing mitigation strategies. Conclusion Despite using a 1D domain and limitations on spatial and temporal variability, our model provides insights into underlying phenomena observed in WUI fires and their mitigation. It offers early-stage development of strategies for managing structure materials and landscape layouts. Implications Our model and findings provide insights into WUI fire dynamics, paving the way for advanced mitigation strategies.

Molecular Characterization and Photoreactivity of Organic Aerosols Formed from Pyrolysis of Urban Materials during Fires at the Wildland-Urban Interface.

Fires at the wildland-urban interface (WUI) are increasing in magnitude and frequency, emitting organic aerosol (OA) with unknown composition and atmospheric impacts. In this study, we investigated the chemical composition of OA produced through the 600 °C pyrolysis of ten urban materials in nitrogen, which were subsequently aged under UV light for 2 h. The analysis utilized ultrahigh-performance liquid chromatography (UHPLC) separation, coupled with a photodiode array (PDA) detector and a high-resolution mass spectrometer (HRMS) for molecular characterization. Hierarchical clustering analysis demonstrated that lumber-derived OA was the most diverse and distinct in composition. Unaged and aged OA (for each urban material) did not significantly differ in chemical identities. Potential aromatic brown carbon (BrC) chromophores (based on their degree of unsaturation) constituted 13-42% of all assigned compounds. PDA chromatograms revealed multiple BrC chromophoric species that were either enhanced or degraded as a result of UV aging, providing insights into specific BrC chromophores responsible for photobleaching and photoenhancement of the overall absorption coefficient. Thirty-six BrC chromophores were identified across the ten OA types, and their structures were confirmed using reference standards. Components of plasticizers and resins, such as phthalic and terephthalic acids, were structurally confirmed in the samples. We present potential species for WUI fires as components of resins, epoxies, dyes, and adhesives commonly used in manufacturing urban materials. Photolysis did not significantly impact the chemical composition of OA emitted from the burning of specific WUI materials.

Ignition limits of pine wood building material under the coupling effects of thermal radiation and cross winds

Ignition limits of pine wood building material under the coupling effects of thermal radiation and cross winds

Wildland-Urban Interface fire exposure of rural settlements: The case of Montesinho Natural Park

Wildland-Urban Interface fire exposure of rural settlements: The case of Montesinho Natural Park

Comparing Ignition of Fuel Beds to Firebrand Showers to Ignition of Fuel Beds by Non-Reacting Heaters

ABSTRACT The combustion of various fuels results in the release of firebrands during wildland-urban interface (WUI) fires. Firebrands represent a hazard, since the release of firebrands may lead to multiple ignitions at locations distant from the original combustion source. A newly developed experimental protocol using a non-reacting heater was used to simulate a firebrand. A direct comparison of this simplified non-reacting heater setup was undertaken to realistic fuel bed ignition to actual firebrand showers. Firebrand showers were generated using a custom experimental setup developed for this investigation. The novelty of this research is a detailed comparison for the first time to fuel bed ignition from non-reacting heaters to actual firebrand showers, for the same fuel bed type. The focus here is on smoldering ignition (SI) of the fuel beds, as this is seen as a complex and least understood aspect of firebrand ignition of actual WUI fires. Results indicate that the overall phenomenology of the ignition process is different between a non-reacting cartridge heater and a shower of firebrands. Complicated smoldering ignition phenomena of fuel beds by firebrand showers cannot be simulated by a simple non-reacting heater.

Environmentally persistent free radicals and other paramagnetic species in wildland-urban interface fire ashes

Wildland-urban interface (WUI) fires consume fuels, such as vegetation and structural materials, leaving behind ash composed primarily of pyrogenic carbon and metal oxides. However, there is currently limited understanding of the role of WUI fire ash from different sources as a source of paramagnetic species such as environmentally persistent free radicals (EPFRs) and transition metals in the environment. Electron paramagnetic resonance (EPR) was used to detect and quantify paramagnetic species, including organic persistent free radicals and transition metal spins, in fifty-three fire ash and soil samples collected following the North Complex Fire and the Sonoma-Lake-Napa Unit (LNU) Lightning Complex Fire, California, 2020. High concentrations of organic EPFRs (e.g., 1.4×1014 to 1.9×1017 spins g-1) were detected in the studied WUI fire ash along with other paramagnetic species such as iron and manganese oxides, as well as Fe3+ and Mn2+ ions. The mean concentrations of EPFRs in various ash types decreased following the order: vegetation ash (1.1×1017±1.1×1017 spins g-1)>structural ash (1.6×1016±3.7×1016 spins g-1)>vehicle ash (6.4×1015±8.6×1015 spins g-1)>soil (3.2×1015±3.7×1015 spins g-1). The mean concentrations of EPFRs decreased with increased combustion completeness indicated by ash color; black (1.1×1017±1.1×1017 spins g-1)>white (2.5×1016±4.4×1016 spins g-1)>gray (1.8×1016±2.4×1016 spins g-1). In contrast, the relative amounts of reduced Mn2+ ions increased with increased combustion completeness. Thus, WUI fire ash is an important global source of EPFRs and reduced metal species (e.g., Mn2+). Further research is needed to underpin the formation, transformation, and environmental and human health impacts of these paramagnetic species in light of the projected increased frequency, size, and severity of WUI fires.

After the Smoke Clears: Wildland-Urban Interface Fires and Residues in Nearby Homes.

Scientists are scrambling to fill major research gaps about the types of pollutants released when wildfires burn not just vegetation, but also structures and vehicles-and how nearby residents can protect themselves.

Predicting Wildfire Ember Hot-Spots on Gable Roofs via Deep Learning

Ember accumulation on and around homes can lead to spot fires and home ignition. Post wildland fire assessments suggest that this mechanism is one of the leading causes of home destruction in wildland urban interface (WUI) fires. However, the process of ember deposition and accumulation on and around houses remains poorly understood. Herein, we develop a deep learning (DL) model to analyze data from a series of ember-related wind tunnel experiments for a range of wind conditions and roof slopes. The developed model is designed to identify building roof regions where embers will remain in contact with the rooftop. Our results show that the DL model is capable of accurately predicting the position and fraction of the roof on which embers remain in place as a function of the wind speed, wind direction, roof slope, and location on the windward and leeward faces of the rooftop. The DL model was augmented with explainable AI (XAI) measures to examine the extent of the influence of these parameters on the rooftop ember coverage and potential ignition.

Firebrand burning under wind: an experimental study

Background Spot fires play a significant role in the rapid spread of wildland and wildland–urban interface fires. Aims This paper presents an experimental and modelling study on the flaming and smouldering burning of wood firebrands under forced convection. Methods The firebrand burning experiments were conducted with different wind speeds and firebrand sizes. Key results The burning rate of firebrands under forced convection is quantified by wood pyrolysis rate, char oxidation rate and a convective term. The firebrand projected area is correlated with firebrand diameter, char density, wind speed, and flaming or smouldering burning. A surface temperature model is derived in terms of condensed-phase energy conservation. We finally establish a simplified firebrand transport model based on the burning rate, projected area and surface temperature of firebrands. Conclusion The mass loss due to wood pyrolysis is much greater than that due to char oxidation in self-sustaining burning. The burning rate is proportional to U1/2, where U is wind speed. The projected area for flaming firebrands decreases more rapidly than that for smouldering ones. The firebrand surface temperature is mainly determined by radiation. Implications Knowledge about firebrand burning characteristics is essential for predicting the flight distance and trajectory in firebrand transport.

Assessing trends in wildland-urban interface fire research through text mining: a comprehensive analysis of published literature

Assessing trends in wildland-urban interface fire research through text mining: a comprehensive analysis of published literature

Global expansion of wildland-urban interface (WUI) and WUI fires: insights from a multiyear worldwide unified database (WUWUI)

Fires in the wildland-urban interface (WUI) are an important issue globally. To understand the change of WUI, we develop a 9 km worldwide unified wildland-urban interface database for 2001–2020 with Random Forest models and satellite data. We find that WUI has been increasing in all populated continents from 2001 to 2020 and the global relative increase is 24%, with the largest relative increase (∼59%) over Africa. Global total fire counts decrease by 10% from 2005 to 2020, whereas the WUI fraction of fire counts increases by 23%. The global total burned area decreases by 22% from 2005 to 2020, whereas the WUI fraction of burned area increases by 35%. These are mainly due to the expansion of WUI area. On all the populated continents, the WUI fractions of fire counts are higher than the WUI fractions of burned area, implying that WUI fires tend to have smaller sizes than wildland fires. We also project future WUI changes for the years 2030 and 2040, together with the projection of future fire burned area under different shared socioeconomic pathways (SSP) scenarios in the Community Earth System Model version 2 (CESM2). The projected global WUI fraction (excluding Antarctica and the oceans) is 5.9% in 2040 compared to 4.8% in 2020. The global WUI fraction of burned area is projected to increase from now to 2040 under most scenarios analyzed in this study, unless the WUI area stays at the 2020 level together with the projected burned area under SSP4-4.5. This study is a first step to understanding the changes of WUI fires at the global scale and demonstrates a growing importance of WUI fires. The global multi-year WUI and WUI fire datasets developed in this study can facilitate future work quantifying the impacts of WUI fires on air quality and climate.

Rapid Measurement of Magnetic Particle Concentrations in Wildland–Urban Interface Fire Ashes and Runoff Using Compact NMR

Wildfires are increasing in size, frequency, and intensity, releasing increased amounts of contaminants, including magnetic particles, into the surrounding environment. The aim of this paper is to develop a sensing method for the detection and quantification of magnetic particles (MPs) in fire ash and fire runoff using a compact Time-Domain Nuclear Magnetic Resonance (TD-NMR) system. The system is made up of custom NMR electronics with a compact and rugged permanent magnet array designed to enable future deployment as an in situ sensor. A signal-to-noise ratio of 25 dB was measured for a single scan, and sufficient data can be acquired in one minute. A linear relationship with an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 0.9699 was established between transverse relaxation rates and MP concentrations in ash samples. This was validated by testing known dilutions of pure magnetite particles and showing that they fit within the same linear curve. The developed approach was then applied to detect MPs in surface water, where changes in the relaxation rates as high as 400% were observed before and after a wildfire event. MPs were removed from the surface water using a magnetic particle separator to confirm that observed changes were solely due to the presence of MPs. The compact NMR system can be used as a simple and rapid approach to track and quantify the concentrations of magnetic particles released from fire ashes and also from other sources such as discharges from coal ash and other combustion ashes.

Firebrands Generated During WUI Fires: A Novel Framework for 3D Morphology Characterization

The goal of the present work is to establish a framework for firebrand morphology characterization. Central to this framework is the development of a simple firebrand shape classification model using multi-dimensional particle shape descriptors. This classification model is built upon a series of synthetically generated 3D particles whose shapes and sizes are chosen to be representative of actual firebrands typically encountered during vegetative and structural fuel burns. Principal Component Analysis (PCA) is applied to the synthetic dataset and used to structure the classification model. The model is then verified using 3D digital representations of real-world particles (firebrands collected during tree burns and unburned bark pieces from oak trees). The classification model, which will allow meaningful comparisons of firebrand morphological features by shape class, is expected to be gradually refined as more datasets are made available throughout the Wildland–Urban Interface (WUI) fire research community.