- Proceedings of the National Academy of Sciences of the United States of America
- Published over 3 years ago
Fire whirls are powerful, spinning disasters for people and surroundings when they occur in large urban and wildland fires. Whereas fire whirls have been studied for fire-safety applications, previous research has yet to harness their potential burning efficiency for enhanced combustion. This article presents laboratory studies of fire whirls initiated as pool fires, but where the fuel sits on a water surface, suggesting the idea of exploiting the high efficiency of fire whirls for oil-spill remediation. We show the transition from a pool fire, to a fire whirl, and then to a previously unobserved state, a “blue whirl.” A blue whirl is smaller, very stable, and burns completely blue as a hydrocarbon flame, indicating soot-free burning. The combination of fast mixing, intense swirl, and the water-surface boundary creates the conditions leading to nearly soot-free combustion. With the worldwide need to reduce emissions from both wanted and unwanted combustion, discovery of this state points to possible new pathways for reduced-emission combustion and fuel-spill cleanup. Because current methods to generate a stable vortex are difficult, we also propose that the blue whirl may serve as a research platform for fundamental studies of vortices and vortex breakdown in fluid mechanics.
Although the energy densities of batteries continue to increase, safety problems (for example, fires and explosions) associated with the use of highly flammable liquid organic electrolytes remain a big issue, significantly hindering further practical applications of the next generation of high-energy batteries. We have fabricated a novel “smart” nonwoven electrospun separator with thermal-triggered flame-retardant properties for lithium-ion batteries. The encapsulation of a flame retardant inside a protective polymer shell has prevented direct dissolution of the retardant agent into the electrolyte, which would otherwise have negative effects on battery performance. During thermal runaway of the lithium-ion battery, the protective polymer shell would melt, triggered by the increased temperature, and the flame retardant would be released, thus effectively suppressing the combustion of the highly flammable electrolytes.
Here we see why humans unwittingly build fires that look the same: edifices of fuel, as tall as they are wide. The pile of fuel is permeable, air invades it by natural convection and drives the combustion. I show that the hottest pile of burning fuel occurs when the height of the pile is roughly the same as its base diameter. Future studies may address the shape effect of wind, material type, and packing. Key is why humans of all eras have been relying on this design of fire “unwittingly”. The reason is that the heat flow from fire facilitates the movement and spreading of human mass on the globe.
- Environmental science and pollution research international
- Published about 7 years ago
Volatile organic compounds (VOCs) and particles emitted by incense sticks and candles combustion in an experimental room have been monitored on-line and continuously with a high time resolution using a state-of-the-art high sensitivity-proton transfer reaction-mass spectrometer (HS-PTR-MS) and a condensation particle counter (CPC), respectively. The VOC concentration-time profiles, i.e., an increase up to a maximum concentration immediately after the burning period followed by a decrease which returns to the initial concentration levels, were strongly influenced by the ventilation and surface interactions. The obtained kinetic data set allows establishing a qualitative correlation between the elimination rate constants of VOCs and their physicochemical properties such as vapor pressure and molecular weight. The emission of particles increased dramatically during the combustion, up to 9.1(±0.2) × 10(4) and 22.0(±0.2) × 10(4) part cm(-3) for incenses and candles, respectively. The performed kinetic measurements highlight the temporal evolution of the exposure level and reveal the importance of ventilation and deposition to remove the particles in a few hours in indoor environments.
Surgical fires require an oxygen-enriched environment, a flammable substrate, and an ignition source. We hypothesized ambient oxygen concentration is proportional to the latency time to combustion and the incidence of surgical fires that are detected. We examined latency time and number of events, utilizing the VanCleave et al model of intraoral fire ignition under 60, 80, and 100% oxygen concentration and flow rates of 4 and 10 L/min. Results demonstrated that ambient oxygen concentration and flow rate correlated positively to the initiation of combustion. The number of combustion events with 60% oxygen was significantly lower than with both 80% ( p = .0168) and 100% ( p = .002). Likewise, the number of events with 80% oxygen was significantly lower than with 100% oxygen ( p = .0019). Flow rate has a significant effect on the time to the first event ( p = .0002), time to first audible pop ( p = .0039), and time to first flash or fire ( p < .0001). No combustion occurred at oxygen concentrations less than 60% or flows less than 4 L/min. We conclude that latency time to combustion is directly proportional to ambient oxygen concentration and flow rate. Minimum oxygen concentration and flow rate were identified in our model. Further research is indicated to determine the minimal clinical oxygen concentration and flow rate needed to support combustion of an intraoral fire in a patient.
Many houses are at risk of being destroyed by wildfires. While previous studies have improved our understanding of how, when and why houses are destroyed by wildfires, little attention has been given to how these fires started. We compiled a dataset of wildfires that destroyed houses in New South Wales and Victoria and, by comparing against wildfires where no houses were destroyed, investigated the relationship between the distribution of ignition causes for wildfires that did and did not destroy houses. Powerlines, lightning and deliberate ignitions are the main causes of wildfires that destroyed houses. Powerlines were 6 times more common in the wildfires that destroyed houses data than in the wildfires where no houses were destroyed data and lightning was 2 times more common. For deliberate- and powerline-caused wildfires, temperature, wind speed, and forest fire danger index were all significantly higher and relative humidity significantly lower (P < 0.05) on the day of ignition for wildfires that destroyed houses compared with wildfires where no houses were destroyed. For all powerline-caused wildfires the first house destroyed always occurred on the day of ignition. In contrast, the first house destroyed was after the day of ignition for 78% of lightning-caused wildfires. Lightning-caused wildfires that destroyed houses were significantly larger (P < 0.001) in area than human-caused wildfires that destroyed houses. Our results suggest that targeting fire prevention strategies around ignition causes, such as improving powerline safety and targeted arson reduction programmes, and reducing fire spread may decrease the number of wildfires that destroy houses.
Obligate seeder trees requiring high-severity fires to regenerate may be vulnerable to population collapse if fire frequency increases abruptly. We tested this proposition using a long-lived obligate seeding forest tree, alpine ash (Eucalyptus delegatensis), in the Australian Alps. Since 2002, 85% of the Alps bioregion has been burnt by several very large fires, tracking the regional trend of more frequent extreme fire weather. High-severity fires removed 25% of aboveground tree biomass, and switched fuel arrays from low loads of herbaceous and litter fuels to high loads of flammable shrubs and juvenile trees, priming regenerating stands for subsequent fires. Single high-severity fires caused adult mortality and triggered mass regeneration, but a second fire in quick succession killed 97% of the regenerating alpine ash. Our results indicate that without interventions to reduce fire severity, interactions between flammability of regenerating stands and increased extreme fire weather will eliminate much of the remaining mature alpine ash forest. This article is protected by copyright. All rights reserved.
Treatment of fuel (e.g. prescribed fire, logging) in fire-prone ecosystems is done to reduce risks to people and their property but effects require quantification, particularly under severe weather conditions when the destructive potential of fires on human infrastructure is maximised. We analysed the relative effects of fuel age (i.e. indicative of the effectiveness of prescribed fire) and logging on remotely sensed (SPOT imagery) severity of fires which occurred in eucalypt forests in Victoria, Australia in 2009. These fires burned under the most severe weather conditions recorded in Australia and caused large losses of life and property. Statistical models of the probability of contrasting extremes of severity (crown fire versus fire confined to the understorey) were developed based on effects of fuel age, logging, weather, topography and forest type. Weather was the primary influence on severity, though it was reduced at low fuel ages in Moderate but not Catastrophic, Very High or Low fire-weather conditions. Probability of crown fires was higher in recently logged areas than in areas logged decades before, indicating likely ineffectiveness as a fuel treatment. The results suggest that recently burnt areas (up to 5-10 years) may reduce the intensity of the fire but not sufficiently to increase the chance of effective suppression under severe weather conditions. Since house loss was most likely under these conditions (67%), effects of prescribed burning across landscapes on house loss are likely to be small when weather conditions are severe. Fuel treatments need to be located close to houses in order to effectively mitigate risk of loss.
Prescribed fires are a common nature conservation practice. They are executed by several parties with limited coordination among them, and little consideration for wildfire occurrences and habitat requirements of fire-dependent species. Here, we gathered data on prescribed fires and wildfires in Sweden during 2011-2015 to (i) evaluate the importance and spatial extent of prescribed fires compared to wildfires and (ii) illustrate how a database can be used as a management tool for prescribed fires. We found that on average only 0.006% (prescribed 65%, wildfires 35%) of the Swedish forest burns per year, with 58% of the prescribed fires occurring on clearcuts. Also, both wildfires and prescribed fires seem to be important for the survival of fire-dependent species. A national fire database would simplify coordination and make planning and evaluation of prescribed fires more efficient. We propose an adaptive management strategy to improve the outcome of prescribed fires.
- Environmental health : a global access science source
- Published over 4 years ago
Sugar cane harvesting by burning on Maui island is an environmental health issue due to respiratory effects of smoke. Volcanic smog (“vog”) from an active volcano on a neighboring island periodically blankets Maui and could confound a study of cane smoke’s effects since cane burning is not allowed on vog days. This study examines the association between cane burning and emergency department (ED) visits, hospital admissions, and prescription fills for acute respiratory illnesses.