Maximum Fire Temperature Research Articles

Influence of barrens restoration treatments on soil carbon, nitrogen, and mercury pools and emissions

AbstractCurrently barrens communities only represent about 1% of their original area in the Great Lakes region. To maintain or restore barrens vegetation, prescribed fire is often applied to limit the regeneration of undesirable species and shrubs. Vegetation community response is a combination of direct fire effects on the vegetation vitality and the indirect effect of soil nitrogen (N) loss that favors nutrient‐poor adapted barren communities. In this study, we assessed forest floor and upper mineral soil (0–5 cm) pools of carbon (C), N, and mercury (Hg) before and after prescribed fire of the Moquah Barrens in northwest Wisconsin. Although we took measurements in four distinct cover types, we found no relationship between cover type and soil pools. Across all cover types, prescribed fire led to considerable emissions of C, N, and Hg in the forest floor but only Hg in the upper mineral soils (0–5 cm), presumably because maximum fire temperatures were met for Hg volatilization. We classified fire severity and soil surface temperatures at the quadrat scale, but no discernable relationships with emissions were observed. The lack of detectable relationships is likely the result of a mismatch between the scales of response variables and predictors. As a result, we calculated ecosystem‐scale fire emissions based on the total area burned because we could not discern other smaller scale predictors. Overall emissions from dormant, spring season prescribed fires at the Moquah Barrens were approximately 11,000 Mg (5.5 Mg ha−1) for C, 350 Mg for N (0.17 Mg ha−1), and 4,500 g for Hg (2.3 g ha−1).

Vulnerability of Multistory RCC Framed Building with Shear Wall During Fire

Fire in a building is a casual phenomenon but cannot be completely ruled out in spite of the facts that buildings are provided with mandatory fire safety measures. A symmetrical in plan with 5 bays with 20 stories regular RCC building has been considered with fire at three different level that is at the bottom, middle and top. The building has been designed for gravity loads and lateral loads having three different configuration of shear walls and columns. Fire temperature of 700 0C was considered. The minimum value of maximum fire temperature for failure of vertical members has been found out by iterations. The worst verticals members due to fire has been identified and their displacement calculated. Best location of shear walls using commercial software etabs is used for the analysis and design.

Invasion of a non‐native forb reduces flammability in a fire‐dependent ecosystem

AbstractFire and grazing are two of the most common global disturbances that maintain and promote many grassland ecosystems worldwide. The presence of non‐native, invasive plant species can alter fire regimes through changes in fuel properties that affect native vegetation in many ecosystems and are a leading threat to biodiversity and ecosystem function. Sericea lespedeza (Lespedeza cuneata), a non‐native, invasive forb frequently present in many North American tallgrass prairies, may reduce flammability by altering the fuel bed moisture and structural characteristics to reduce fire in this fire‐dependent ecosystem. The goal of this research was to examine the influence of sericea lespedeza on fuel bed structure, moisture, and flammability compared to native grassland fuels. Fuel bed burning trials, conducted in a controlled laboratory setting, tested for the effect of fuel load mass of native grass and sericea lespedeza litter, proportion of sericea fuel load, and fuel moisture content on flammability metrics. Regardless of moisture content, sericea lespedeza reduced flammability and reduced maximum fire temperatures by as much as 500°C. Sericea lespedeza poses a major threat to North American tallgrass prairies by decreasing flammability of fuel beds through increased fuel bed density and moisture retention.

Comparison of the Performance of Biomass Briquette Stoves on Three Types of Stove Wall Materials

The performance analysis of the biomass briquette stove has been carried out. The research was conducted with three variations of stove wall materials (clay, steel, and aluminum) and with several variations of shell diameter of the burning chamber (140mm, 150mm, 160mm, 170mm, and 180mm). The fuel used is coconut shell briquettes. The results showed that the maximum fire temperature of clay, steel, and aluminum stoves was obtained, respectively 798℃, 617℃, 508℃ and thermal efficiency of 73.66% for clay followed by a steel stove of 38.98% and the lowest is obtained on an aluminum-based stove, which is only 11.49%. Furthermore, the diameter of the shell optimum is 180 mm for clay, 160 for steel, and 170 for aluminum.

EFFECT OF INLET AIR TEMPERATURE ON COMBUSTION, PERFORMANCE AND EMISSIONS OF GASOLINE DIRECT INJECTION (GDI) ENGINE FUELLED BY LPG FUEL

In the present work, the direct-injection petrol engine (GDI) combustion, emissions and performance at different engine speeds (1500, 2000, 2500 and 3000 rpm) with a constant throttle position have been studied. The fuel considered in this work is liquid petroleum gas (LPG) and gasoline. The software adopted in all simulations by the AVL BOOST 2016. A Hyundai 2.0 liter, 16 valves and 4 cylinders engine with a compression ratio 17.5:1 is used. The effect of several inlet air temperatures (0, 10, 20, 30, 40 and 50 oC) on the engine performance, combustion and emissions are also studied. The results show that the increase in the inlet air temperature leading to increase the peak fire temperature, brake specific fuel consumption (BSFC) and nitrogen oxide (NOx). However, this process results in a reduction in the peak fire pressure, combustion period (duration), brake power and brake torque. The maximum fire temperature and maximum specific fuel consumption can be achieved when the engine speed is 3000 rpm and the inlet air temperature is 50 ºC.

Quantifying Uncertainties in the Temperature–Time Evolution of Railway Tunnel Fires

Extreme fire events in tunnels can have catastrophic consequences, including loss of lives, structural damage, and major socioeconomic impacts. The fire scenario itself is one of the primary parameters that would influence the level of damage in a tunnel. Standard hydrocarbon fire temperature–time curves exist but they are idealized and do not consider the actual fire duration and potential for fire spread within the tunnel. Furthermore, risk-based decision-making frameworks and performance-based design of tunnel linings require realistic sets of fire scenarios to quantify damage. This paper focuses on quantifying uncertainties in the temperature–time evolution of railway tunnel fires considering fire spread between train cars. In this study, 540 numerical simulations are conducted in fire dynamics simulator by varying ventilation velocity, amount of fuel, tunnel slope, ignition point, and criteria for fire spread between railcars. Temporal and spatial distribution of fire temperature in the tunnel is studied. The resulting 540 temperature–time curves at sections with the highest temperature are analyzed and statistics of the maximum fire temperature and duration, heating rate, and decay rate are provided. Fires with heat release rates larger than 40 MW are categorized as high-intensity with mean maximum temperature of 1007°C. Fires with heat release rates smaller than 30 MW are categorized as low-intensity with a mean maximum temperature of 245°C. The proposed framework can be expanded in future to establish guidelines for temperature demands in the design of concrete tunnel linings within risk-based frameworks to achieve required performance levels in railway tunnel fire events.

On the possibility to simulate the operation of a SI engine using alternative gaseous fuels

A thermodynamic combustion model developed in AVL BOOST software was used in order to evaluate the pollutant emissions, performance and efficiency parameters of a spark ignition engine Renault K7M-710 fueled with compressed natural gas, hydrogen and blends of compressed natural gas and hydrogen (hythane). Multiple research studies have concluded that for the near future hythane could be the most promising alternative fuel because it has the advantages of both its components. In our previous work the model was validated for the performance and efficiency parameters by comparison of simulation results with experimental data acquired when the engine was fueled with gasoline. In this work the model was improved and can predict the values of pollutant emissions when the engine is running with the studied alternative fuels. As the percentage of hydrogen in hythane is increased, the power of the engine rises, the brake specific fuel consumption, carbon dioxide, carbon monoxide and total unburned hydrocarbon emissions decrease while nitrogen oxides increase. The values of peak fire pressure, maximum pressure derivative and peak fire temperature in cycle are higher, leading to an increased probability of knock occurrence. To avoid this phenomenon an optimum correlation between the natural gas-hydrogen blend, the air-fuel ratio, the spark advance and the engine operating condition needs to be found.

Numerical assessment of midrise multi-storey reinforced concrete framed structures subjected to fire

This research aims at numerical assessment of multistory reinforced concrete framed structures subjected to fire. The Applied Element Method (AEM) was selected for this study so that potential collapse, partial or total, can be predicted. The Extreme Loading for Structures (ELS) software was used in the current study. To consider the material deterioration due to fire, a modification to the constitutive models has been considered in ELS. Firstly, the AEM was validated to be a reliable tool for analyzing structures under the effect of fire loads. AEM was then used to perform a parametric study on a typical mid-rise multistory RC framed residential building, aiming at investigating the effect of different fire parameters on the damage of structural members. The studied parameters were: concrete compressive strength, steel yield stress, columns' reinforcement ratio, edge column orientation, location of fire, and maximum fire temperature. Numerical results revealed that framed reinforced concrete structures have a relatively good resistance to progressive collapse under the effect of fire loads, and that the effect of material deterioration due to fire should be considered in numerical analysis. Material deterioration could lead to an increase in deformation as high as 1000% at high temperatures (900 °C) which may lead to collapse.

Fragility analysis of R.C. seismically-isolated structures with residual mechanical properties after fire exposure

In seismically isolated reinforced concrete (r.c.) structures exposed to fire, significant damage to r.c. frame members of the superstructure and irreversible deterioration in the isolation system with elastomeric bearings (e.g. High-Damping-Rubber Bearings, HDRBs, and Lead-Rubber Bearings, LRBs) can occur. Note that the residual mechanical properties after fire can be lower or higher than during fire, depending on the maximum fire temperature and the heating and cooling rates. Earthquakes following fire may find load capacity notably reduced vis-à-vis the no fire condition, with an amplification in the structural response in the fire compartment. To evaluate seismic vulnerability following fire, a fragility analysis is performed on a six-storey r.c. seismically isolated framed structure designed in line with the current Italian code. Two fire scenarios are simulated assuming the fire compartment is confined to the area of the isolated level (i.e. F0) and the first level of the superstructure (i.e. F1). In particular, the nonlinear seismic response of the test structure in the no fire situation is compared with those during exposure to the heating phase (i.e. at 45, R45, and 60, R60, minutes of fire resistance) and after the cooling phase (i.e. Rcooling fire resistance). An isotherm method characterized by a fire-damage threshold calibrated on the basis of experimental results is proposed to evaluate reduced mechanical properties of HDRBs and LRBs. Finally, the residual seismic load capacity of the r.c. cross-sections after fire is assessed by means of experimental laws representing heating and cooling effects.

Seismic Performance of a Fire-Exposed Moment-Resisting Frame

Major earthquakes in urban areas often lead to building fires. Such earthquakes frequently damage buildings’ water sprinkler systems and diminish or strain firefighting capabilities. In such scenarios, buildings get exposed to fire for a long period of time, resulting in damage of spray-on-fire resistive materials. Consequently, steel frame temperature may reach as high as the maximum fire temperature, which subsequently cools slowly to ambient temperature. If the building frame does not deform severely after such a fire event, it is usually rehabilitated for continued occupation. The performance of such a fire-exposed steel building during a future earthquake is not known. This study investigates the seismic performance of a fire-exposed steel frame by performing finite-element analyses incorporating fire-exposed steel material properties. The simulation responses demonstrate vulnerability of fire-exposed steel buildings. A novel but startling observation made is that under seismic loading, a fire-damaged steel frame may form a soft-story mechanism at the story of fire exposure because of plastic hinge formation in the column instead of in the beams.

On the use of Bernstain-Bézier functions for modelling the post-fire stress-strain relationship of ultra-high strength steel (Grade 1200)

Ultra-high strength steels (UHSS) have significant potential applications in the engineering fields due to their unique specifications. In recent years, it has been experimentally shown that the post-fire stress-strain response of this material is highly dependent on the maximum steel temperature and the sustained load applied to it during fire. This paper employs the Bernstain-Bézier functions to present the relationship between the stress, strain, the maximum fire temperature and the sustained axial load ratio (β) for Grade 1200 UHSS cooled for fire temperatures to room temperature. The experimental results are used to verify and validate the proposed model throughout the paper. The model showed to be capable of not only interpolating the stress-strain curves, but also extrapolating them out of the range of the available experimental tests data. Also, taking advantage of the stress-strain-temperature response of the UHSS tested at elevated temperatures, the instantaneous stress-induced strain and consequently the creep strain of UHSS subjected to different constant sustained load values during transient fire are obtained.

Leaf and bark functional traits predict resprouting strategies of understory woody species after prescribed fires

In temperate forests, both deciduous and evergreen species with small or large leaves coexist in the understory and resprout after prescribed burnings. This diversity of traits suggests that there are different strategies operating after the initial resprout growth to re-acquire space, capture resources and resist additional stresses. This study aims to understand resprout vigor 3 years after burning of woody understory species with different leaf traits and bark investment (i.e., the ratio between bark thickness and basal stem diameter).In two temperate forests, we burned one stand in late spring and another in fall. After 3 years, we studied resprout number and resprout basal diameter and length of ten individuals of six species per stand. Three species were common in both forests and three were different. Therefore, species of both forests were grouped in three groups based on leaf traits and in three different groups according to their bark investment. Besides the expected positive effect of pre-fire plant size, resprout number and vigor were higher after burning in spring than in fall. The higher resprout volume in evergreens, with small specific leaf area (SLA), than in deciduous species, with large SLA, may be related to evergreens having a longer possible growing season than deciduous species. In addition, species in different leaf groups differed in the ratio of resprout length to diameter growth, suggesting that it is important for deciduous small-leaved species to grow tall rapidly before they are shaded by large leaved species. In contrast, no direct effect of light availability on resprout vigor was detected. Bark investment did not explain resprout vigor but did affect resprout number in the low bark investment group. In this group, resprout number decreased with increasing maximum fire temperature. Based on our results, burning in the fall is advisable when the management objective is to minimize the recovery of the understory. In addition, to reduce the dominance of understory woody species with low bark investment, our study suggests that understory fires must be performed with moderate to high intensity.

Temperature of post‐flashover compartment fires—Calculations and validation

AbstractThis paper describes and validates by comparisons with tests a one‐zone model for computing temperature of fully developed compartment fires. Like other similar models, the model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, ie, a ventilation‐controlled compartment fire. However, the mathematical solution techniques in this model have been altered. To this end, a maximum fire temperature has been defined depending on combustion efficiency and opening heights only. This temperature together with well‐defined fire compartment parameters was then used as a fictitious thermal boundary condition of the surrounding structure. The temperature of that structure could then be calculated with various numerical and analytical methods as a matter of choice, and the fire temperature could be identified as a weighted average between the maximum fire temperature and the calculated surface temperature of the surrounding structure as a function of time.It is demonstrated that the model can be used to predict fire temperatures in compartments with boundaries of semi‐infinitely thick structures as well as with boundaries of insulated and noninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. With these assumptions, fire temperatures could be calculated with spreadsheet calculation methods. For more advanced problems, a general finite element solid temperature calculation code was used to calculate the temperature in the boundary structure. With this code, it is possible to analyze surrounding structures of various kinds, for example, structures comprising several materials with properties varying with temperature as well as voids.The validation experiments were accurately defined and surveyed. In all the tests, a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions.

Improving tunnel resilience against fires: A new methodology based on temperature monitoring

Monitoring temperatures during tunnel fires is of major importance for both the firefighters extinguishing the fire, and the engineers in charge of the subsequent repair work. However, current methods of assessing fire damage have limitations when applied to tunnels and only provide estimates of the maximum fire temperatures at specific locations of the tunnel. This is not a desirable situation, as the temperature–time curves associated with the fire event should be available for use in assessing the residual strength of the tunnel structure. This is the key parameter in defining repair work and the length of time the tunnel will need to be closed and thus the socio-economic cost of the tunnel fire. In addition, real-time recording of the temperature–time curves would provide valuable information to the firefighters engaged in extinguishing the fire.This paper presents a new general methodology for the optimal placement of sensors in a tunnel to obtain the temperature evolution at any point along its lining during a fire. The methodology was applied to the Virgolo Tunnel in Italy, in which 100 potential high-temperature sensor configurations were tested and a set of optimal sensor configurations was proposed. The results of the analysis show that: (a) the proper location of the sensors is crucial; (b) it is possible to define a set of sensor configurations that minimize the cost of the monitoring system and maximize the accuracy of the estimated temperatures; (c) it is important to place at least three high-temperature sensors in each monitored cross section (at the crown and symmetrically on the haunches/side walls). The proposed methodology improves tunnel resilience against fires, as it enables safer infrastructure and a faster and more economic recovery of the tunnel after a fire event.

Growth and reproductive post-fire responses of two shrubs in semiarid Patagonian grasslands

Variation in fire intensity affects the post-fire survival and growth of shrubs. We examined effects of maximum fire temperature (a proxy for fire intensity) on the survival, growth and reproductive performance of the shrubs Mulinum spinosum and Senecio bracteolatus at 1 and 2 years post-fire in north-west Patagonian grasslands. We applied two fire temperature treatments to plants of each species. All M. spinosum plants survived fire treatments but high fire temperature notably decreased survival of S. bracteolatus. Bud position and plant architecture probably influenced shrub survival. During the first growing season, M. spinosum did not produce seeds whereas S. bracteolatus plants burned at low temperature produced three times more seeds and bigger seeds than unburned plants. Also, seeds from burned plants of S. bracteolatus had higher germinability than seed from unburned plants. High survival and resprouting capacity of M. spinosum even after high fire intensity indicate that this species might be less affected by changes in fire regime.

How can an invasive grass affect fire behavior in a tropical savanna? A community and individual plant level approach

Some invasive grasses have been reported to change fire behavior in invaded plant communities. Urochloa brizantha is an aggressive invasive grass in the Brazilian Cerrado, an ecosystem where fire is a common disturbance. We investigated the effects of U. brizantha on fire behavior in an open Cerrado physiognomy in Central Brazil. Using experimental burnings we compared fire behavior at both the community and the individual plant level in invaded (UJ) and non-invaded (NJ) areas burned in July. We also assessed the effect of fire season in invaded areas by comparing July (UJ) and October (UO) burnings. We evaluated the following variables: fuel load, fuel moisture, combustion efficiency, maximum fire temperature, flame height, and fire intensity. Additionally, we evaluated the temperatures reached under invasive and native grass tussocks in both seasons. Fuel load, combustion efficiency, and fire intensity were higher in NJ than in UJ, whilst flame height showed the opposite trend. Fuel amount and fire intensity were higher in October than in July. At the individual plant level, U. brizantha moisture was higher than that of native species, however, temperatures reaching ≥600 °C at ground level were more frequent under U. brizantha tussocks than under native grasses. At the community level, the invasive grass modified fire behavior towards lower intensity, lower burning efficiency, and higher flame height. These results provide essential information for the planning of prescribed burnings in invaded Cerrado areas.

Toward a “Molecular Thermometer” to Estimate the Charring Temperature of Wildland Charcoals Derived from Different Biomass Sources

The maximum temperature experienced by biomass during combustion has a strong effect on chemical properties of the resulting charcoal, such as sorption capacity (water and nonpolar materials) and microbial degradability. However, information about the formation temperature of natural charcoal can be difficult to obtain in ecosystems that are not instrumented prior to fires. Benzene polycarboxylic acids (BPCA) are molecular markers specific for pyrogenic carbon (PyC) which can provide information on the degree of aromatic condensation in charcoals. Here we apply the BPCA molecular marker method to a set of 10 charcoals produced during an experimental fire in a Pitch pine-scrub oak forest from litter and bark of pitch pine and inkberry plants in the Pinelands National Reserve in New Jersey, USA. We deployed temperature-sensitive crayons throughout the burn site, which recorded the maximum air temperature and made comparisons to the degree of thermal alteration recorded by BPCA molecular markers. Our results show an increase of the degree of aromatic condensation with monitored temperatures for bark biomass, while for needles no clear trend could be observed. For leaf-derived charcoals at increasing monitored fire temperatures, decreasing degree of aromatic condensation was obtained. This suggests that molecular markers can be used to roughly estimate the maximum fire temperatures experienced by bark and wood materials, but not based on leaf- and needle-derived materials. Possible applications include verifying declared pyrolysis temperatures of biochars and evaluating ecosystem fire temperature postburn.

Fire load: Survey data, recent standards, and probabilistic models for office buildings

To enable a probabilistic performance-based approach to fire design, probabilistic models to represent the fire load are needed. Such probabilistic models are presented in this paper for office buildings. First, a literature review of recent fire load density surveys is presented. These surveys indicate a large range of fire load density values, and strong correlation between fire load density, compartment area, and use. However, current codes and standards (such as Eurocode and a recent publication of NFPA 557) that are used to estimate fire load density do not account for these variables and specify constant values. Based on survey data, a Bayesian probability approach is used to develop probabilistic models to predict the fire load density in office buildings (one for light-weight use and one for heavy-weight use). The models consider the size of the compartment and the office room use (general office, library, storage, etc.). The proposed models correlate well to the data and have a better fit than that obtained, using the Eurocode and NFPA 557. The proposed models for fire load density are then used to develop probabilistic models for the maximum fire temperature in a given compartment. Several scenarios with different floor areas and openings are defined and the fire load models developed in this paper are used to investigate the range of possible maximum fire temperatures and their corresponding probabilities. It is found that the proposed maximum temperature model results in a range of temperatures that correlates well with the test data and the Refined Tanaka Method proposed by a recent SFPE standard. It is shown that both the fire load density and the maximum temperature probabilistic models are well suited for application in a probabilistic performance-based approach to fire design.

An approach for evaluating the residual strength of fire exposed bridge girders

This paper presents an approach for evaluating residual strength of fire exposed steel bridge girders. The approach involves three stages of analysis that is to be carried out at ambient conditions, during exposure to fire, and after cooling of the fire exposed bridge girder. In the first stage, load carrying capacity of the girder is evaluated at room temperature. In the second stage of analysis, thermal and structural response of the bridge girder is traced under specified fire exposure and loading conditions. In the third stage (after the bridge girder has cooled down), residual capacity of the girder is evaluated by incrementing load on the girder till failure occurs. The proposed approach is applied to carry out a set of numerical studies on a typical steel girder using finite element computer program ANSYS. Results from numerical studies indicate that the maximum fire temperature (and associated temperature in steel) is the most critical factor that influences residual strength of a fire exposed bridge girder. A girder exposed to typical “external” fire conditions, with maximum fire temperatures reaching to 600–700°C, retains about 70 to 80% of its strength on cooling. On the other hand, a steel bridge girder exposed to hydrocarbon fire, with a maximum temperature of about 1100°C, looses most of its strength during heating phase of the fire and experiences failure.

Effects of Prescribed Fire on the Buried Seed Bank in Mixed-Hardwood Forests of the Southern Appalachian Mountains

This study characterizes the seed bank prior to and immediately following dormant-season prescribed fire in mature, mixed-Quercus spp. (oak) forests in the south- ern Appalachian Mountains. Thirty samples from the litter/duff (LD) and the top 5 cm of the mineral soil (MS) were collected from five 5-ha burn units (6 plots per experimental unit) before and immediately after low-intensity prescribed fires, where maximum fire temperatures varied from <79 to 316 °C. A split-plot ANOVA and multi-response permu- tation procedures (MRBP) were utilized to assess the effects of burn treatment (pre- or post-fire) and seed bank layer (LD and MS) on the diversity and density of the buried seed bank. An average of 471 emergents/m 2 was observed in the buried seed bank compris- ing 133 identifiable taxa. No differences in total seed-bank density, Shannon-Weiner's diversity index (H'), or overall species composition between pre- and post-fire sampling or between the LD and MS layers were observed. Species richness (S) of the seed bank, however, was slightly greater pre-fire than post-fire, regardless of layer. Similarity, as defined by Sorenson's index, of species common to the seed bank and aboveground forest understory was low, with a slight increase in Sorenson's index observed during post-fire sampling of the seed bank and aboveground vegetation. Although we observed only neg- ligible effects of a once-applied, low-intensity prescribed fire on the buried seed bank, the effects of a low-intensity prescribed fire management regime—one that involves repeated low intensity burns—on the buried seed bank are unknown and should be a focus of fu- ture studies across mixed-oak forests in the eastern US.