Preparation and Characterization of Chitosan/Hydroxypropyl Methylcellulose Temperature-Sensitive Hydrogel Containing Inorganic Salts for Forest Fire Suppression.

Effective forest fire suppression remains a critical challenge, necessitating innovative solutions. Temperature-sensitive hydrogels represent a promising avenue in this endeavor. Traditional firefighting methods often struggle to address forest fires efficiently while mitigating ecological harm and optimizing resource utilization. In this study, a novel intelligent temperature-sensitive hydrogel was prepared specially for forest fire extinguishment. Utilizing a one-pot synthesis approach, this material demonstrates exceptional fluidity at ambient temperatures, facilitating convenient application and transport. Upon exposure to elevated temperatures, it undergoes a phase transition to form a solid, barrier-like structure essential for containing forest fires. The incorporation of environmentally friendly phosphorus salts into the chitosan/hydroxypropyl methylcellulose gel system enhances the formation of temperature-sensitive hydrogels, thereby enhancing their structural integrity and firefighting efficacy. Morphological and thermal stability analyses elucidate the outstanding performance, with the hydrogel forming a dense carbonized layer that acts as a robust barrier against the spread of forest fires. Additionally, comprehensive evaluations employing rheological tests, cone calorimeter tests, a swelling test, and infrared thermography reveal the multifaceted roles of temperature-sensitive hydrogels in forest fire prevention and suppression strategies.

Multiple social and environmental factors affect wildland fire response of full or less-than-full suppression.

Wildland fire incident commanders make wildfire response decisions within an increasingly complex socio-environmental context. Threats to human safety and property, along with public pressures and agency cultures, often lead commanders to emphasize full suppression. However, commanders may use less-than-full suppression to enhance responder safety, reduce firefighting costs, and encourage beneficial effects of fire. This study asks: what management, socioeconomic, environmental, and fire behavior characteristics are associated with full suppression and the less-than-full suppression methods of point-zone protection, confinement/containment, and maintain/monitor? We analyzed incident report data from 374 wildfires in the United States northern Rocky Mountains between 2008 and 2013. Regression models showed that full suppression was most strongly associated with higher housing density and earlier dates in the calendar year, along with non-federal land jurisdiction, regional and national incident management teams, human-caused ignitions, low fire-growth potential, and greater fire size. Interviews with commanders provided decision-making context for these regression results. Future efforts to encourage less-than-full suppression should address the complex management context, in addition to the biophysical context, of fire response.

A Review on Safety Practices for Firefighters During Photovoltaic (PV) Fire.

In recent years, it is evident that there is a surge in photovoltaic (PV) systems installations on buildings. It is concerning that PV system related fire incidents have been reported throughout the years. Like any other electrical power system, PV systems pose fire and electrical hazards when at fault. As a consequence, PV fires compromised the safety of emergency responders. Therefore, the objective of this review is to evaluate the elements of firefighters' safety practices and subsequently collate the best safety practices for local fire rescue and firefighters in the event of PV fires. Out of 264 documents, only 20 publications were identified as 'closely related' and were systematically reviewed to evaluate firefighter safety practices from a scholarly perspective. Only 3% of the 20 publications reviewed, discussed the safety practices during PV fires. Thirteen safety practice key points were extracted from the reviewed documents, with nine critical findings highlighted as the hallmark of safety practices during PV fire for firefighters. The lack of academic journals discussing the fire safety aspects proves that there is a low interest in this field which is in dire need of further study and exploration to adhere with the PV population in ensuring a reliable emergency operation to minimize losses or injuries due to accidents.

The Ground-Dwelling Ant Fauna from a Cerrado Reserve in Southeastern Brazil: Vegetation Heterogeneity as a Promoter of Ant Diversity.

Ants represent one of the most diverse and ecologically important group of insects in tropical ecosystems, including in highly threatened ones such as the Brazilian Cerrado. Yet, a detailed understanding of the species diversity and composition of local Cerrado ant assemblages is lacking in many cases. Here we present the results of a comprehensive ant inventory performed within a region of the Cerrado (in São Paulo state) where most of the original vegetation has already been lost and where few conservation units exist. We performed consecutive surveys of the ant fauna that forage on the ground in replicated plots established in open savanna (campo sujo), dense savanna (cerrado sensu stricto), and forest (cerradão). Our surveys, with an estimated sample coverage of 99.4%, revealed a total of 219 species of ants from 60 genera, of which 36.1% were found in all the three vegetation types and 29.7% in just one. Rarefied species richness did not differ between vegetation types, but species composition differed markedly, especially between the two savannas in one hand and the forest in the other. Several species (60.1% of the 128 species analyzed) were significant "indicator" species due to their strong association with a given vegetation type. Overall, our findings reinforce the idea that habitat heterogeneity enhances ant diversity and that the mosaic of vegetation types that characterizes the Cerrado biome is one of the main factors explaining the elevated number of species that can be found at relatively small scales.

The Role of Wildfires in the Interplay of Forest Carbon Stocks and Wood Harvest in the Contiguous United States During the 20th Century.

Wildfires and land use play a central role in the long-term carbon (C) dynamics of forested ecosystems of the United States. Understanding their linkages with changes in biomass, resource use, and consumption in the context of climate change mitigation is crucial. We reconstruct a long-term C balance of forests in the contiguous U.S. using historical reports, satellite data, and other sources at multiple scales (national scale 1926-2017, regional level 1941-2017) to disentangle the drivers of biomass C stock change. The balance includes removals of forest biomass by fire, by extraction of woody biomass, by forest grazing, and by biomass stock change, their sum representing the net ecosystem productivity (NEP). Nationally, the total forest NEP increased for most of the 20th century, while fire, harvest and grazing reduced total forest stocks on average by 14%, 51%, and 6%, respectively, resulting in a net increase in C stock density of nearly 40%. Recovery from past land-use, plus reductions in wildfires and forest grazing coincide with consistent forest regrowth in the eastern U.S. but associated C stock increases were offset by increased wood harvest. C stock changes across the western U.S. fluctuated, with fire, harvest, and other disturbances (e.g., insects, droughts) reducing stocks on average by 14%, 81%, and 7%, respectively, resulting in a net growth in C stock density of 14%. Although wildfire activities increased in recent decades, harvest was the key driver in the forest C balance in all regions for most of the observed timeframe.

Double-Layered Polymer Microcapsule Containing Non-Flammable Agent for Initial Fire Suppression.

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a degradation of fire extinguishing performance. To improve the durability of the fire suppression microcapsules and the stability of the ouster shell, a complex coacervation was used, which could be microencapsulated at a lower temperature, and the polymer shell was coated with urea-formaldehyde (UF) resin. The outermost UF resin formed elaborate bonds with the gelatin-based shell, and thus, the structure of the outer shell became denser, thereby improving the loss resistance of the inner substance and thermal stability. The double-layered microcapsules had an average particle diameter of about 309 µm, and a stable outer shell formed with a mass loss of 0.005% during long-term storage for 100 days. This study confirmed that the double-layered microcapsules significantly improved thermal stability, resistance to core material loss, core material content and fire suppression performance compared to single wall microcapsules. These results indicated that the double-layered structure was suitable for the production of microcapsules for initial fire suppression, including highly volatile non-flammable agents with a low boiling point.

Optimum Efficiency of a Steam Ejector for Fire Suppression Based on the Variable Mixing Section Diameter.

The steam ejector is valuable and efficient in the fire suppression field due to its strong fluid-carrying capacity and mixing ability. It utilizes pressurized steam droplets generated at the exit to extinguish the fire quickly and the steam droplet strategy allows for an expressive decrease in water consumption. In this regard, the fire suppression process is influenced by the steam ejector efficiency, the performance of the pressurized steam, and the ejector core geometry, which controls the quality of the extinguishing mechanisms. This study investigated the impact of different mixing section diameters on the pumping performance of the ejector. The results showed that change in the diffuser throat diameter was susceptible to the entrainment ratio, which significantly increased, by 4 mm, by increasing the throat diameter of the diffuser and improved the pumping efficiency. Still, the critical back pressure of the ejector reduced. In addition, the diameter effect was studied and analyzed to evaluate the ejector performance under different operating parameters. The results revealed a rise in the entrainment ratio, then it diminished with increasing primary fluid pressure. The highest entrainment ratio recorded was 0.5 when the pressure reached 0.36 MPa at the critical range of back pressure, where the entrainment ratio remained constant until a certain back pressure value. Exceeding the critical pressure by increasing the back pressure to 7000 Pa permitted the entrainment ratio to reduce to zero. An optimum constant diameter maximized the ejector pumping efficiency under certain operating parameters. In actual design and production, it is necessary to consider both the exhaust efficiency and the ultimate exhaust capacity of the ejector.

Perceptions of Heat Stress, Heat Strain and Mitigation Practices in Wildfire Suppression across Southern Europe and Latin America.

This study aimed to assess current perceptions of heat stress, heat strain, acclimatisation and recovery practices in wildland fire suppression. A total of 1459 wildfire and structural firefighters, all involved in wildland fire suppression, completed an 18-question survey. Most participants (81.3%) reported heat strain as one of the main risks faced during wildland firefighting. Thermal strain is considered an important risk for health and safety in wildland firefighting. The best-valued heat strain mitigation strategies were those traditionally recommended in wildland fire suppression: (i) an adequate work/rest ratio (79.0%), (ii) acclimatisation (71.6%), (iii) enhancing body ventilation by opening protective clothing or removing helmets or gloves (63.5%), and (iv) drinking water and food supplementation (52.1%). Despite these results, only 22% of the participants reported carrying out acclimatisation in the workplace. The vast majority of the respondents (87.4%) consider active cooling strategies (i.e., ice slurry ingestion, ice vests, etc.) impractical in combating heat strain during wildfire suppression. We identified a gap between knowledge about heat strain, its mitigation strategies and the level of actual implementation of these practices in the workplace. Our results highlight the need to improve heat strain management and implement operational directives for acclimatisation and active cooling interventions.

High-temperature decomposition chemistry of trimethylsiloxane surfactants, a potential Fluorine-Free replacement for fire suppression.

Per- and polyfluoroalkyl substances (PFAS) have become global environmental contaminants due to being notoriously difficult to degrade, and it has become increasingly important to employ suitable PFAS alternatives, especially in aqueous film-forming foams (AFFF). Trimethylsiloxane (TriSil) surfactants are potential fluorine-free replacements for PFAS in fire suppression technologies. Yet because these compounds may be more susceptible to high-temperature decomposition, it is necessary to assess the potential environmental impact of their thermal degradation products. Our study analyzes the high-temperature degradation of a truncated trimethylsiloxane (TriSil-1n) surfactant based on quantum mechanical methods. The degradation chemistry of TriSil-1n was studied through radical formation and propagation initiated from two prominent pathways (unimolecular and bimolecular reactions) at both 298 K and 1200 K, a relevant temperature in flames and thermal incinerators. Regardless of the pathway taken and temperature, all radical intermediates stemmed from the polyethylene glycol chain and primarily formed stable polydimethylsiloxanes (PDMS) and small organics such as ethylene, formaldehyde, and acetaldehyde, among other products. The major degradation products of TriSil-1n resulting from high-temperature thermal degradation as predicted by this study would be relatively less harmful to the environment compared to PFAS incineration/combustion products from previous research, supporting the replacement of PFAS with TriSil surfactants.

Development and Validation of Earthquake Fire Response Simulation Protocol for Korean College Students in Health Programs.

The purpose of this study is to evaluate the adequacy of the developed protocol by verifying the validity of the expert group for the earthquake and fire response simulation protocol. A protocol development team consisting of one emergency rescue professor, one counseling psychology professor, three paramedics, and one firefighter developed the study's protocols to promote the core response and capabilities required at an earthquake fire site. We checked the content validity for the appropriateness of the contextual connection for each stage for the protocol. We also created an evaluation checklist to measure the items for each stage. The protocol developed in this study consists of earthquake response, fire response, evacuation, and fire suppression. We set the situation for each stage and composed learner activities and learning performance goals. The earthquake response stage included (1) shout "it's an earthquake," (2) protect yourself, (3) turn off electricity and gas, and (4) evacuate to a safe place. In the fire response stage, (1) shout "fire," (2) press the emergency bell and call 119, (3) close the door of a dangerous place where fire can spread, and (4) evacuate to a safe place. In the evacuation stage, (1) open the emergency exit, (2) cover your nose and mouth, (3) lower your posture, and (4) evacuate quickly in one direction. Lastly, in the firefighting stage, (1) pull out the safety pin, (2) hold the nozzle and face the fire, (3) grab the handle, and (4) spray the powder evenly. The protocol contributes to the development of systematic and elaborate simulation education materials in the future. Furthermore, it provides basic data for future disaster simulation operation and protocol development through continuous training and practical exercises.

The effects of high-severity fires on the arboreal ant community of a Neotropical savanna.

Fire-suppression is of concern in fire-prone ecosystems because it can result in the loss of endemic species. Suppressing fires also causes a build-up of flammable biomass, increasing the risk of severe fires. Using a Before-After, Control-Impacted design, we assessed the consequences of high-severity fires on Neotropical savanna arboreal ant communities. Over a 9-year period, we sampled the ant fauna of the same trees before and after two severe fires that hit a savanna reserve in Brazil and the trees from an unburned savanna site that served as a temporal control. The ant community associated with the unburned trees was relatively stable, with no significant temporal variation in species richness and only a few species changing in abundance over time. In contrast, we found a strong decline in species richness and marked changes in species composition in the burned trees, with some species becoming more prevalent and many becoming rare or locally extinct. The dissimilarity in species richness and composition was significantly smaller between the two pre-fire surveys than between the pre- and post-fire surveys. Fire-induced changes were much more marked among species with strictly arboreal nesting habits, and therefore more susceptible to the direct effects of fire. The decline of some of the ecologically dominant arboreal ant species may be particularly important, as it opens substantial ecological space for cascading community-wide changes. In particular, severe fires appear to disrupt the typical vertical stratification between the arboreal and ground-dwelling faunas, which might lead to homogenization of the overall ant community.

Land management objectives and activities in the face of projected fire regime change in the Sonoran desert.

As a multi-jurisdictional, non-fire-adapted region, the Sonoran Desert Ecoregion is a complex, social-ecological system faced increasingly with no-analogue conditions. A diversity of management objectives and activities form the socioecological landscape of fire management. Different managers have different objectives, resources, and constraints, and each therefore applies different activities. As a result, it can be difficult to predict the regional consequences of changing fire regimes. We interviewed and surveyed managers of 53 million acres of government-managed lands across the Sonoran Desert Ecoregion of Arizona, asking them to describe their management objectives and activities as well as expected changes in the face of projected fire regime change across the region. If current activities were deemed unlikely to meet objectives into the future, this represents a likely adaptation turning point, where new activities are required in order to meet objectives. If no potential activity will meet an objective, it may be necessary to select a new objective, indicating an adaptation tipping point. Here, we report which current objectives and activities are deemed by managers most likely and least likely to succeed. We also discuss constraints reported by managers from different jurisdictions. We find that agriculture, military, and resource extraction objectives are perceived by managers as most likely to be met, whereas conservation of natural and cultural resources is considered least likely to be achieved. Federal land managers reported higher likelihood of both achieving current objectives and adopting new activities than did non-federal land managers. This study illustrates how rapid global change is affecting the ability of land managers differing in missions, mandates, and resources to achieve their central objectives, as well as the constraints and opportunities they face. Our results indicate that changing environmental conditions are unlikely to affect all management entities equally and for some jurisdictions may result in adaptation turning points or tipping points in natural and cultural resource conservation.

Fire Suppression Agents Combined with Gasoline in Aquatic Ecosystems: A Mixture Approach.

Fire suppression agents are recommended for extinguishing fires by flammable liquids and frequently end in water bodies, combined with the fuels. There is a lack of toxicity information on these commercial formulations and the effects of mixtures of fire suppression agents and fuels. The aim of the present study was to evaluate the toxic effects of different fire suppression agents, the gasoline water-soluble fraction (GWSF), and mixtures of each fire suppression agent and GWSF. Individual tests were performed with Daphnia similis and Artemia sp.; the most toxic fire suppression agents to D. similis and Artemia sp. were F-500®, Cold Fire®, Agefoam®, and Kidde Sintex® 1%; the GWSF was the least toxic. The concentration addition model was used to predict the mixture effects and evaluate synergism/antagonism, dose ratio dependence, and dose level dependence. Cold Fire with GWSF showed dose level deviation to D. similis, marked mainly by synergism; for Artemia sp., the dose ratio pattern was predicted, with a synergistic response mainly by Cold Fire. Agefoam and GWSF behaved additively for D. similis and dose ratio for Artemia sp., with synergism being caused by Agefoam. Kidde Sintex 1% with GWSF were dose ratio for both organisms, with Kidde Sintex 1% being responsible for synergism. Our results show that some mixtures of fire suppression agents and GWSF may cause toxicity to aquatic organisms, posing risk in a real environmental scenario, such as a major fire combat. Environ Toxicol Chem 2021;40:767-779. © 2020 SETAC.

An experimental method to investigate the water-based suppression of smoldering peat fire.

Smoldering wildfire in peatlands is one of the largest and most persistent fire phenomena on Earth, which contributes importantly to global carbon emissions. However, very few studies are available on how to extinguish these smoldering wildfires. Herein, we develop an experimental method to explore the effectiveness of the water-based suppression on smoldering peat fire, and the proposed method can also be used to simulate fire suppression by rain. The low-temperature drying process avoids the variation of hydrophobicity of peat soil. The validation shows that the proposed approach can provide a wide range of water-spray intensities with time variation, and two examples of successful suppression of smoldering peat fire and flaming wood crib fire were presented.•The design of small-scale combustion reactor for peat can mimic the smoldering peat fire in the field.•The effectiveness of water-based fire suppression technologies on peat fire are explored in the lab.•The proposed method can evaluate the effect of rain and weather on suppressing the smoldering wildfire.

Geospatial Modeling of Containment Probability for Escaped Wildfires in a Mediterranean Region.

Despite escalating expenditures in firefighting, extreme fire events continue to pose a major threat to ecosystem services and human communities in Mediterranean areas. Developing a safe and effective fire response is paramount to efficiently restrict fire spread, reduce negative effects to natural values, prevent residential housing losses, and avoid causalties. Though current fire policies in most countries demand full suppression, few studies have attempted to identify the strategic locations where firefighting efforts would likely contain catastrophic fire events. The success in containing those fires that escape initial attack is determined by diverse structural factors such as ground accessibility, airborne support, barriers to surface fire spread, and vegetation impedance. In this study, we predicted the success in fire containment across Catalonia (northeastern Spain) using a model generated with random forest from detailed geospatial data and a set of 73 fire perimeters for the period 2008-2016. The model attained a high predictive performance (AUC = 0.88), and the results were provided at fine resolution (25 m) for the entire study area (32,108 km2 ). The highest success rates were found in agricultural plains along the nonburnable barriers such as major road corridors and largest rivers. Low levels of containment likelihood were predicted for dense forest lands and steep-relief mountainous areas. The results can assist in suppression resource pre-positioning and extended attack decision making, but also in strategic fuels management oriented at creating defensive locations and fragmenting the landscape in operational firefighting areas. Our modeling workflow and methods may serve as a baseline to generate locally adapted models in fire-prone areas elsewhere.

A benchmark dataset for ensemble framework by using nature inspired algorithms for the early-stage forest fire rescue.

This paper introduces a benchmark dataset to the research article entitled "Ensemble framework by using nature inspired algorithms for the early-stage forest fire rescue - a case study of dynamic optimization problems", by Zhang et al. [7]. Rescue ensemble that consists of rescue simulator and rescue algorithm is characterized by supporting the dynamic simulation of forest fire rescue. The purpose of rescue algorithm is to minimize the longest flight time of aircraft group II and the newly-increased burnt forest cost in one period, simultaneously. The map information in our dataset is from Google map and relevant parameters are also from the actual situation data. The benchmark contains 10 different maps that researchers can use to evaluate their own algorithms and compare their performance with our algorithm.

Can rain suppress smoldering peat fire?

Smoldering wildfire in peatlands contributes significantly to global carbon emissions and regional haze events. Smoldering fire in peatlands is one of the largest and most persistent fire phenomena on Earth. Here we assess the underlying mechanism of rain in suppressing the smoldering peat fire in the shallow soil layer up to 15 cm deep through laboratory experiments. We show that the minimum rainfall intensity to extinguish the peat fire is roughly 4 mm/h, so that the persistent light rain cannot suppress such smoldering wildfire. The required rain duration, ∆t (min), for extinguishing smoldering peat fire decreases with the rainfall intensities, I (mm/h), as log10∆t = - 1.15log10I + 3.3, and is much longer than that for extinguishing flaming wildfire. We also identify that the required rainfall depth for extinguishing peat fire gradually decreases with the rainfall intensity and approaches a minimum value of 13 mm under violent rain. As rainfall intensity increases, the carbon emission flux from peat fire decreases. Therefore, we conclude that the short-term violent rain is most effective for suppressing the persistent smoldering peat fire. This research helps evaluate the impact of weather on the development of peat fire and improve the prediction of carbon emissions from peat fire with the use of regional weather models.

Mesophication in temperate Europe: A dendrochronological reconstruction of tree succession and fires in a mixed deciduous stand in Bialowieza Forest.

The shift from shade-intolerant species to shade-tolerant mesophytic species in deciduous and mixed forests of the temperate zone is well described in studies from North America. This process has been termed mesophication and it has been linked to changes in fire regime. Fire suppression results in the cessation of establishment of heliophytic, fire-dependent tree species such as oak (Quercus) and pine (Pinus). Due to the scarcity of old-growth forests in Europe, data on long-term compositional changes in mixed forests are very limited, as is the number of studies exploring whether fire played a role in shaping the dynamics.The aim of this study was to reconstruct tree succession in a 43-ha natural mixed deciduous forest stand in Bialowieza Forest (BF), Poland using dendrochronological methods. In addition, the presence of aboveground fire legacies (charred and fire-scarred deadwood) enabled the fire history reconstruction.Dendrochronological data revealed tree establishment (Quercus) back to the end of the 1500s and fires back to 1659. Under a regime of frequent fires until the end of the 18th century, only oak and pine regenerated, sporadically. A shift in the fire regime in the first half of the 19th century triggered oak and pine cohort regeneration, then gradually spruce (Picea) encroached. Under an increasingly dense canopy and less flammable conditions, regeneration of shade-tolerant Carpinus, Tilia, and Acer began simultaneously with the cessation of oak and pine recruitment. Synthesis. The study reports the first evidence of mesophication in temperate Europe and proves that fire was involved in shaping the long-term dynamics of mixed deciduous forest ecosystems. Our data suggest that fire exclusion promoted a gradual recruitment of fire-sensitive, shade-tolerant species that inhibited the regeneration of oak and pine in BF.

High-severity wildfire leads to multi-decadal impacts on soil biogeochemistry in mixed-conifer forests.

During the past century, systematic wildfire suppression has decreased fire frequency and increased fire severity in the western United States of America. While this has resulted in large ecological changes aboveground such as altered tree species composition and increased forest density, little is known about the long-term, belowground implications of altered, ecologically novel, fire regimes, especially on soil biological processes. To better understand the long-term implications of ecologically novel, high-severity fire, we used a 44-yr high-severity fire chronosequence in the Sierra Nevada where forests were historically adapted to frequent, low-severity fire, but were fire suppressed for at least 70 yr. High-severity fire in the Sierra Nevada resulted in a long-term (44 +yr) decrease (>50%, P < 0.05) in soil extracellular enzyme activities, basal microbial respiration (56-72%, P < 0.05), and organic carbon (>50%, P < 0.05) in the upper 5 cm compared to sites that had not been burned for at least 115 yr. However, nitrogen (N) processes were only affected in the most recent fire site (4 yr post-fire). Net nitrification increased by over 600% in the most recent fire site (P < 0.001), but returned to similar levels as the unburned control in the 13-yr site. Contrary to previous studies, we did not find a consistent effect of plant cover type on soil biogeochemical processes in mid-successional (10-50 yr) forest soils. Rather, the 44-yr reduction in soil organic carbon (C) quantity correlated positively with dampened C cycling processes. Our results show the drastic and long-term implication of ecologically novel, high-severity fire on soil biogeochemistry and underscore the need for long-term fire ecological experiments.

The reaction pathway analysis of phosphoric acid with the active radicals: a new insight of the fire-extinguishing mechanism of ABC dry powder.

Dry powder fire-extinguishing agent is one of Halon substitutes due to its superior fire-extinguishing performance, non-toxicity, and environmental friendliness. As one of the most widely used dry powders, ABC dry powder has attracted wide attention. Understanding its reaction mechanism is important to the design of more efficient compound dry powder based on it. When ABC dry powder was applied to the flame, ammonium dihydrogen phosphate (the main fire-extinguishing component of ABC dry powder) would rapidly decompose into phosphoric acid (H3PO4) and ammonia. Therefore, in order to figure out the chemical reaction mechanism of ABC dry powder and active radicals, the main focus of this paper is on the H3PO4. Analysis of the electrostatic potential on van der Waals surface of H3PO4 was carried out. Besides, detailed theoretical investigation has been performed on the mechanism, kinetics, and thermochemistry of the reactions of H3PO4 with H, OH, and CH3 radicals and further decomposition of H3PO4 using M06-2X/6-311G(d,p)//CCSD(T)/cc-pVTZ level of theory. Mayer bond order for all intrinsic reaction coordinate points was also calculated. Finally, it is theoretically proved that ABC dry powder extinguishes the fire mainly by chemical inhibition on H and OH radicals. Grapical Abstract .