Fire Heat Research Articles

Heat flux assumptions contribute to overestimation of wildfire smoke injection into the free troposphere

Injections of wildfire smoke plumes into the free troposphere impact air quality, yet model forecasts of injections are poor. Here, we use aircraft observations obtained during the 2019 western US wildfires (FIREX-AQ) to evaluate a commonly used smoke plume rise parameterization in two atmospheric chemistry-transport models (WRF-Chem and HRRR-Smoke). Observations show that smoke injections into the free troposphere occur in 35% of plumes, whereas the models forecast 59–95% indicating false injections in the simulations. False injections were associated with both models overestimating fire heat flux and terrain height, and with WRF-Chem underestimating planetary boundary layer height. We estimate that the radiant fraction of heat flux is 0.5 to 25 times larger in models than in observations, depending on fuel type. Model performance was substantially improved by using observed heat flux and boundary layer heights, confirming that models need accurate heat fluxes and boundary layer heights to correctly forecast plume injections.

Investigation of the heat release rate and particle generation during fixed bed gasification of sweet sorghum stalk

Sweet sorghum (SS) is an agricultural crop that is produced commercially in Nigeria. The crop has a high biowaste energy in its stalk, which is an attractive source of bioenergy in rural areas where it is produced. The residue–to-produce ratio (RPR) of the crop is 1.25 kg of biowaste for 1 kg of SS produced. The solid residue that results from the crop can be subjected to gasification to produce combustible gases: carbon monoxide (CO), hydrocarbon gases (total hydrocarbons) and hydrogen. The combustible gases can be piped into a burner for heat or into a Compression Ignition (CI) engine for electricity generation. This will enhance energy security as well as energy equity in rural areas in Nigeria and sub-saharan African countries where the crop is also produced. This research was aimed at optimising the gasification of SS stalk residue to maximise the yield of combustible gases from the first stage of the process. The restricted ventilation cone calorimeter method was used to gasify SS stalks on a laboratory scale. The test was carried out at air flow rates per exposed flat surface area of 9, 11.2, 12.9, 14.3, 15.5, 16.3, and 19.2 g/s·m2 respectively, which controls the gasification rate or power output. The speciation of the gases that evolved from the gasification of the biomass samples was carried out by an FTIR that was calibrated for 60 species. Current uses of biomass residues in open fire heating generates toxic fine particulate emissions and this work aimed to show that this was not a greater problem with gasification. A dynamic electrical mobility particle spectrometer (DMS500) was used to measure the particulate size distribution and concentration, as an efficient gasifier should not be generating major yields of soot, which would be a problem for a downstream reciprocating engine. The optimum equivalence ratio (Ф) for the best energy transfer to the gaseous products was 2.1, which was similar to previous work on pine using this equipment where the optimum equivalence ratio was 2.8. The hot gases efficiency at the optimum Ф was 81%, which compares well to that of 78% for pine.

Reduced pressure effects on smoke temperature, CO concentration and smoke extraction in tunnel fires with longitudinal ventilation and vertical shaft

Nowadays, high-altitude tunnels at reduced pressure are emerging in the world's road network. A better understanding of the temperature and CO concentration distribution as well as the shaft extraction performance during tunnel fires with combined longitudinal ventilation and shaft exhaust under reduced ambient pressure is particularly crucial for the tunnel fire protection design. Series of tunnel fire simulations were carried out with ambient pressures of 50 kPa–101 kPa, fire heat release rates (HRRs) of 3 MW and 10 MW, and longitudinal ventilation velocities of 0 m/s to 2 m/s. The results show that the reduced ambient pressure enhances the difference in vertical and longitudinal distribution of CO concentration and smoke temperature, while the longitudinal ventilation gradually weakens this difference in longitudinal distribution. The natural exhaust shaft reduces the difference in vertical distribution but increases the difference in longitudinal distribution. As the reduction of ambient pressure, the smoke extraction efficiency of the shaft will increase slowly. Longitudinal ventilation can enhance the shaft's smoke extraction performance, but the general smoke extraction efficiency of the shaft deteriorates with the increasing longitudinal ventilation velocity. This study provides a fundamental reference for tunnel natural ventilation system under different ambient pressures, particularly in high-altitude tunnel fires.

Predicting real-time fire heat release rate by flame images and deep learning

The heat release rate (HRR) is the most critical parameter in characterizing the fire behavior and thermal effects of a burning item. However, traditional fire calorimetry methods are not applicable due to the lack of equipment in most fire scenarios. This work explores the real-time fire heat release rate prediction by using fire scene images and deep learning algorithms. A big database of 112 fire tests from the NIST Fire Calorimetry Database is formed, and 69,662 fire scene images labeled by their transient heat release rate are adopted to train the deep learning model. The fire tests conducted in the lab environment and the real fire events are used to validate and demonstrate the reliability of the trained model. Results show that regardless of the fire sources, background, light conditions, and camera settings, the proposed AI-image fire calorimetry method can well identify the transient fire heat release rate using only fire scene images. This work demonstrates that the deep learning algorithms can provide an alternative method to measure the fire HRR when traditional calorimetric methods cannot be used, which shows great potential in smart firefighting applications.

An integrated method for assessing passenger evacuation performance in ship fires

In order to assess effectively the passenger evacuation performance in ship fires, a quantitative method combining the computational fluid dynamics (CFD)-derived fire data and AnyLogic evacuation simulation is proposed in this paper. In this developed method, the speed reduction factor, instantaneous untenable conditions and fractional effective dose (FED) model are utilized to consider the effects of smoke visibility, heat and toxic gases in ship fires on the passenger walking speed, activity space and human health conditions. In order to demonstrate this proposed method, passenger evacuation analysis is performed in a hypothetical zone of the ship with obstacles for fast t-squared fires. The results indicate that the relationship between the required safe egress time (RSET) and fire heat release rate (HRR) is non-monotonic. However, the total FED increases with the increase of the fire HRR and the sequence of survivors. Compared with two existing methods, this proposed method is able to assess more rigorously the passenger evacuation performance in ship fires. The existing ASET/RSET method is more conservative, and the existing FED method with the Pathfinder underestimates the FED in ship fires. This work will provide a more accurate method for ship fire safety assessment and performance-based fire protection design.

Physical modeling and machine learning of ceiling maximum temperature rise induced by tandem heat sources with unequal heat release rates in a natural ventilation tunnel

The present work involved experimental studies of physical modeling as well as machine learning prediction of the characteristics of ceiling maximum temperature induced by adjacent heat sources with unequal fire heat release rates in a tunnel. The following are considered as variables in this study: separation distances between the adjacent heat sources, and unequal heat release rates between upstream fire sources (UFS) and downstream fire sources (DFS). It was found that, with the increasing separation distance between adjacent fires, the ceiling maximum temperature gradually decreases for the given total heat release rate (Q˙TFS). Meanwhile, with the increase in the ratio (Q˙UFS/Q˙TFS) of the upstream fire heat release rate (Q˙UFS) to the total heat release rate, the ceiling maximum temperature rise of the tunnel presents nonmonotonic changes: first a decrease and then an increase. From the dimensional analysis of adjacent tandem fires, a prediction model of ceiling maximum temperature rise induced by different separation distances and Q˙UFS/Q˙TFS ratios was proposed. The model has a good correlation with the experimental and previous research results. Furthermore, to perform the calculation quickly and facilitate rapid engineering design, we use machine learning methods to derive the maximum temperature rise of the tunnel ceiling. The fire heat release rate is predicted using a machine learning algorithm. The three parameters (Q˙UFS/Q˙TFS, ΔTmax, Hd) were paired with the maximum temperature rise of the ceiling and trained using the GRU neural network model. The results show that the machine learning algorithms has a good agreement with the verification experimental value, cmparisons with established physical models are also discussed. The research results can serve as a reference for an intelligent tunnel firefighting system.

Experimental study on temperature decay and smoke control in tunnel fires with combination of multi-point smoke exhaust and longitudinal ventilation

This paper investigates the longitudinal temperature distribution characteristics beneath the ceiling and smoke control of the tunnel with combination of multi-point smoke exhaust and longitudinal ventilation. Experiments are carried out in a model tunnel with dimensions of 60 m × 1.3 m × 0.67 m. The longitudinal wind speed is set to 0–0.5 m/s, the exhaust air volume to 0.34–1.09 m³/s and the fire heat release rates (HRR) are 30.7 kW and 61.4 kW. The results show that the tunnel fire with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel) causes the offset of flame, and the maximum temperature point beneath the tunnel ceiling appears in the upstream direction from the fire source. The large smoke exhaust air volume will cause smoke layering plug-holing at the smoke exhaust vents, and the temperature of the vents where plug-holing occurs is lower. Longitudinal ventilation combined with the top multi-point smoke exhaust system has a better smoke control effect, but the longitudinal wind speed cannot be greater than 0.5 m/s. The temperature decay beneath the tunnel ceiling is in accordance with the exponential attenuation law in a tunnel with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel), and the longitudinal temperature decay rate of the side close to the exhaust fan is smaller than that of the other side.

Important role of stratospheric injection height for the distribution and radiative forcing of smoke aerosol from the 2019–2020 Australian wildfires

Abstract. More than 1 Tg smoke aerosol was emitted into the atmosphere by the exceptional 2019–2020 southeastern Australian wildfires. Triggered by the extreme fire heat, several deep pyroconvective events carried the smoke directly into the stratosphere. Once there, smoke aerosol remained airborne considerably longer than in lower atmospheric layers. The thick plumes traveled eastward, thereby being distributed across the high and mid-latitudes in the Southern Hemisphere, enhancing the atmospheric opacity. Due to the increased atmospheric lifetime of the smoke plume, its radiative effect increased compared to smoke that remains in lower altitudes. Global models describing aerosol-climate impacts lack adequate descriptions of the emission height of aerosols from intense wildfires. Here, we demonstrate, by a combination of aerosol-climate modeling and lidar observations, the importance of the representation of those high-altitude fire smoke layers for estimating the atmospheric energy budget. Through observation-based input into the simulations, the Australian wildfire emissions by pyroconvection are explicitly prescribed to the lower stratosphere in different scenarios. Based on our simulations, the 2019–2020 Australian fires caused a significant top-of-atmosphere (TOA) hemispheric instantaneous direct radiative forcing signal that reached a magnitude comparable to the radiative forcing induced by anthropogenic absorbing aerosol. Up to +0.50 W m−2 instantaneous direct radiative forcing was modeled at TOA, averaged for the Southern Hemisphere (+0.25 W m−2 globally) from January to March 2020 under all-sky conditions. At the surface, on the other hand, an instantaneous solar radiative forcing of up to −0.81 W m−2 was found for clear-sky conditions, with the respective estimates depending on the model configuration and subject to the model uncertainties in the smoke optical properties. Since extreme wildfires are expected to occur more frequently in the rapidly changing climate, our findings suggest that high-altitude wildfire plumes must be adequately considered in climate projections in order to obtain reasonable estimates of atmospheric energy budget changes.

Investigation of the Temperature Beneath Curved Tunnel Ceilings Induced by Fires with Natural Ventilation

The distribution characteristics of the temperature below ceilings in curved tunnel fires have not been quantitatively studied. A small-scale tunnel was constructed in this work to study the maximum temperature and longitudinal attenuation of the temperature below ceilings induced by fires in a curved tunnel with natural ventilation. Different tunnel turning radiuses and fire heat release rates were taken into account. The results show that the distribution characteristics of temperature below the tunnel ceiling is hardly affected by the tunnel turning radius in a scenario where the flame plume impinges on the ceiling (strong-plume-driven). The fire-induced maximum temperature and longitudinal attenuation of temperature in curved tunnels are comparable to those of straight tunnels. Improved correlations are proposed for the condition of a strong-plume-driven ceiling jet, and the measured value of the temperature of the experiment collapsed well. This work may enhance the understanding of temperature distributions in curved tunnel fires.

Soil Heating in Fire (SheFire): A model and measurement method for estimating soil heating and effects during wildland fires.

Fire has transformative effects on soil biological, chemical, and physical properties in terrestrial ecosystems around the world. While methods for estimating fire characteristics and associated effects aboveground have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, biogeochemical cycling, and ecosystem recovery. In this paper, we present a novel framework for characterizing belowground heating and effects. The framework includes (1) an open-source model to estimate fire-driven soil heating, cooling, and the biotic effects of heating across depths and over time (Soil Heating in Fire model; SheFire) and (2) a simple field method for recording soil temperatures at multiple depths using self-contained temperature sensor and data loggers (i.e., iButtons), installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many logistical challenges associated with obtaining temperature profiles using thermocouples. Heating measurements provide inputs to the SheFire model, and modeled soil heating can then be used to derive ecosystem response functions, such as heating effects on microorganisms and tissues. To validate SheFire estimates, we conducted a burn table experiment using iStakes to record temperatures that were in turn used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by thermocouples, we co-located both types of sensors in the burn table experiment. We found that SheFire demonstrated skill in interpolating and extrapolating soil temperatures, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to thermocouples for recording soil temperatures during fires. Finally, we present a case study using iStakes and SheFire to estimate in situ soil heating during a prescribed fire and demonstrate how observed heating regimes would influence seed and tree root vascular cambium survival at different soil depths. This measurement-modeling framework provides a cutting-edge approach for describing soil temperature regimes (i.e., soil heating) through a soil profile and predicting biological responses.

Temperature variation inside a corridor-like enclosure under limited ventilation

This paper investigates the temperature variation inside a corridor-like enclosure (for example, high-speed train compartment) with persistent flame ejection through an opening (for example, window). The fire heat release rate and opening sizes are varied with 28 different experimental conditions. An exponential function is built and found to be able to describe the longitudinal temperature distribution, in which the decay rate has a power function with the window aspect ratio. The maximum temperature shows a considerable difference for various heat release rates (HRR), due to the mass flow rate of the fuel supply through the opening is comparable to or greater than the air mass inflow rate. A general model characterizing the longitudinal temperature distribution of various opening sizes and HRR is proposed with heat release to heat loss ratio inside the compartment, HRR and window aspect ratio, which shows a good agreement with the experimental results. This study provides important and new contributions over previous knowledge and has potential practical applications concerning the corridor-like enclosure fire safety and occupant evacuation.

Numerical study of the combustion regimes in naturally-vented compartment fires

Numerical simulations are performed to investigate the classical compartment fire problem involving a single door opening. Three different configurations were considered, namely a full-scale (ISO 9705), an intermediate and a small-scale enclosure with various opening heights and widths. A large number of numerical simulations was carried out using the CFD code Fire Dynamics Simulator (FDS)(version 6.7.0). Based on the variation of the average temperature inside the compartment, three combustion regimes were identified namely well-ventilated, transitional and under-ventilated regime. This variation also allowed us to identify the boundaries between regimes. Furthermore, by adopting a non-dimensional representation of the fire heat release rate inside the compartment as a function of the Global Equivalence Ratio (GER), a clear demarcation between these combustion regimes was obtained. A linear correlation has been established between the maximum heat release rate inside the compartment and the ventilation factor. The latter is expressed as Q̇inmax=850AH. A linear relation between the maximum air flow rate ṁin and the ventilation factor AH was found, i.e. ṁinmax=0.46AH where A is the door surface area and H its height.

Critical review of the common methods to determine the buoyancy-chimney effects in longitudinally-ventilated traffic tunnel fires

Determining the buoyancy-chimney effects (hot smoke stack effects) in the case of a fire in a traffic tunnel with a slope is of key importance in the process of sizing the ventilation system and smoke control. Given the complexity of the unsteady turbulent heated flow of air and combustion products mixture and the transient heat transfer by convection, radiation and tunnel wall conduction, various approximate methods, standards, guidelines, and numerical approaches are used, giving different values for the gas temperature distribution and pressure differences. Depending on the fire heat release rate, tunnel slope, and the length of the fire-affected zone, the differences in pressure can even reach values of over 100%, strongly affecting the ventilation sizing. To evaluate the reliability of available methods, a critical review of various methods is given, and a comparison analysis carried out in the case of a typical unidirectional-traffic tunnel equipped with a longitudinal ventilation system. The temperature field, the pressure rise, and the required number of fan units, required to provide the critical velocity for smoke control, are analyzed.

Modelling concrete slabs subjected to localised fire action with OpenSees

PurposeReinforced concrete slabs in fire have been heavily studied over the last three decades. However, most experimental and numerical work focuses on long-duration uniform exposure to standard fire. Considerably less effort has been put into investigating the response to localised fires that result in planarly non-uniform temperature distribution in the exposed elements.Design/methodology/approachIn this paper, the OpenSees for Fire framework for modelling slabs under non-uniform fire exposure is presented, verified against numerical predictions by Abaqus and then validated against experimental tests. The thermal wrapper developed within OpenSees for Fire is then utilised to apply localised fire exposure to the validated slab models using the parameters of an experimentally observed localised fire. The effect of the smoke layer is also considered in this model and shown to significantly contribute to the thermal and thus thermo-mechanical response of slabs. Finally, the effect of localised fire heat release rate (HRR) and boundary conditions are studied.FindingsThe analysis showed that boundary conditions are very important for the response of slabs subject to localised fire, and expansive strains may be accommodated as deflections without severely damaging the slab by considering the lateral restraint.Originality/valueThis work demonstrates the capabilities of OpenSees for Fire in modelling structural behaviours subjected to non-uniform fire conditions and investigates the damage pattens of flat slabs exposed to localised fires. It is an advancing step towards understanding structural responses to realistic fires.

Semi-empirical correlations for predicting hot gas layer temperature in pre-flashover compartment fires considering fire source location

A series of numerical experiments have been carried out through a CFD code, namely Fire Dynamics Simulator (FDS), to analyze the influence of the fire heat source location (transversal, longitudinal and vertical positions) on the hot gas layer temperature (HGLT) in pre-flashover compartment fires. Knowing the HGLT helps engineers to predict the onset of flashover and to design fire safety systems, which give more time for evacuation procedures. Using these numerical data, and based on an energy balance on the upper layer, new semi-empirical correlations were developed to predict the HGLT in pre-flashover compartment fires, as a function of the fire source location, heat release rate, ventilation factor, surface area, effective heat transfer coefficient and ambient thermal properties. As an external validation of the newly developed correlations, their outcomes were tested against several sets of experimental data available in the literature, showing a good agreement. So, it is concluded that these improved correlations are capable to predict the HGLT for different pre-flashover fire scenarios, accounting to the position where the fire started.

Experimental investigation on the effect of open fire on the tensile properties and damage evolution behavior of granite

The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock.

An exploration of equivalent scenarios for building facade fire standard tests

The building facade system is a key part of green buildings and carbon neutrality, but its fire safety is a global problem. Many large-scale facade fire standard tests are created to evaluate the fire risk of facade systems, but they are different from country to country, and their test results are difficult to compare. This study simulates five scenario-based facade fire standard tests, BS 8414-1 (UK), GB/T 29416 (China), ISO 13785-2, NFPA 285 (USA), and JIS A 1310 (Japan). Simulations explore the heat flux and temperature of spilled facade fire plume that controls the ignition and flame spread of facade fire. Under the default fire scenario, the BS 8414-1 and GB/T 29416 generate the largest heat flux (∼100 kW/m2) to ignite the facade above the opening. The facade fire plume in ISO 13785-2 produces a near-constant heat flux (∼50 kW/m2) for 2 m above the opening. The heat flux and plume temperature of NFPA 285 largely depend on the extra window burner, and JIS A 1310 can produce intensive heating on the facade by increasing the chamber fire heat release rate (HRR). The heat flux and temperature of spilled plume increase almost linearly with the outdoor fire HRR. Thus, by adjusting the total fire HRR, the values of facade surface heat flux, plume temperature, and ignition height can be matched to enable a fair comparison among different tests. This unique numerical work explores the equivalent façade fire scenarios for different standard tests that can guide future façade fire test development and optimization.

Противопожарные расстояния от наземных автостоянок до жилых зданий

Проанализированы нормативные требования к противопожарным разрывам от жилых зданий до границ открытых автостоянок. Рассмотрены особенности горения легковых автомобилей. На основе полевого моделирования изучены особенности распространения опасных факторов пожара (ОФП) и их воздействие на жилые здания при одновременном горении двух автомобилей. Моделирование проводилось при различных расстояниях до автостоянок и с учетом воздействия ветровой нагрузки. Показано, что на расстоянии от жилых зданий до автостоянок менее 10 м может потребоваться устройство огнестойких наружных стен здания с противопожарной защитой оконных проемов и применением негорючей облицовки фасада. The problem of parking lots and parking spaces is relevant in many large cities, which leads to the need to optimize parking space. The analysis of the regulatory framework in the field of fire safety of open parking lots has shown that the values of quenching distances from residential buildings to the boundaries of parking lots are associated with the fire hazard of the building, its number of storeys, fire resistance limits and characteristics of load-bearing and enclosing structures. In accordance with the new regulatory requirements, quenching distances from open storage areas, car parking to buildings and structures are not normalized. At the same time, when developing fire-fighting measures, it is necessary to take into account that the intensity of the fire impact on the building can significantly increase, for example, with the simultaneous ignition of two or more cars in the event of fuel spills, as well as arson. The purpose of this research is to study the peculiarities of fire hazards spread during simultaneous ignition of two or more cars on the basis of field modeling and to assess the possibility of fire-safe placement of an open parking lot in residential areas. To achieve the purpose of the study, field (CFD) modeling of fire dynamics using the FDS computer program was used. When modeling, calculations of fire hazards spread from an open parking lot and their impact on a residential building were carried out. As a result of modeling the fire development, temperature distributions, smoke and heat flows were obtained at different points in time at the window openings of a residential building at different points in time. The simulation was carried out at different distances and taking into account the impact of wind load. The results of the study showed that with the simultaneous ignition of two cars, the value of quenching distance of 10 m to open parking lots provides a condition for non-proliferation of fire on a residential building. With a decrease in the distance of less than 10 m, the values of the heat flux density and temperature at the window openings of apartments in the lower floors of the building under the influence of wind load may exceed critical values. In the residential areas of the lower floors, there may also be an excess of the values of fire hazards. To exclude this effect it is necessary to install fire-resistant exterior walls of the building with fire protection of window openings, as well as the use of finishes, facade cladding made of non-combustible materials. The simulation also showed that for residential buildings with a stylobate with a width of at least 5 m, quenching distances may not be observed when applying appropriate fire protection to the exterior walls and openings of the stylobate.

Representing low-intensity fire sensible heat output in a mesoscale atmospheric model with a canopy submodel: a case study with ARPS-CANOPY (version 5.2.12)

Abstract. Mesoscale models are a class of atmospheric numerical model designed to simulate atmospheric phenomena with horizontal scales of about 2–200 km, although they are also applied to microscale phenomena with horizontal scales of less than about 2 km. Mesoscale models are capable of simulating wildland fire impacts on atmospheric flows if combustion byproducts (e.g., heat, smoke) are properly represented in the model. One of the primary challenges encountered in applying a mesoscale model to studies of fire-perturbed flows is the representation of the fire sensible heat source in the model. Two primary methods have been implemented previously: turbulent sensible heat flux, either in the form of an exponentially-decaying vertical heat flux profile or surface heat flux; and soil temperature perturbation. In this study, the ARPS-CANOPY model, a version of the Advanced Regional Prediction System (ARPS) model with a canopy submodel, is utilized to simulate the turbulent atmosphere during a low-intensity operational prescribed fire in the New Jersey Pine Barrens. The study takes place in two phases: model assessment and model sensitivity. In the model assessment phase, analysis is limited to a single control simulation in which the fire sensible heat source is represented as an exponentially decaying vertical profile of turbulent sensible heat flux. In the model sensitivity phase, a series of simulations are conducted to explore the sensitivity of model–observation agreement to (i) the method used to represent the fire sensible heat source in the model and (ii) parameters controlling the magnitude and vertical distribution of the sensible heat source. In both phases, momentum and scalar fields are compared between the model simulations and data obtained from six flux towers located within and adjacent to the burn unit. The multi-dimensional model assessment confirms that the model reproduces the background and fire-perturbed atmosphere as depicted by the tower observations, although the model underestimates the turbulent kinetic energy at the top of the canopy at several towers. The model sensitivity tests reveal that the best agreement with observations occurs when the fire sensible heat source is represented as a turbulent sensible heat flux profile, with surface heat flux magnitude corresponding to the peak 1 min mean observed heat flux averaged across the flux towers, and an e-folding extinction depth corresponding to the average canopy height in the burn unit. The study findings provide useful guidance for improving the representation of the sensible heat released from low-intensity prescribed fires in mesoscale models.

수동화재보호 재료가 적용된 구조부재의 화재하중에 대한 강도 특성

In offshore installations, fires cause the structure to lose its rigidity and it leads to structural integrity and stability problems. The Passive Fire Protection (PFP) system slows the transfer rate of fire heat and helps prevent the collapse of structures and fatality. Especially, intumescent epoxy coating is widely used in the offshore industry, and not only is the material cost expensive, but it also takes a lot of time and cost for construction. Several studies have been conducted on the efficient application and optimal design of the PFP system. However, the mechanical properties and the strength of the PFP material have not been considered. In addition, researches on the correlation between the thickness of PFP and the structural behavior were insufficient. Therefore, this study aims to analyze the thermal and mechanical effects of the PFP on the structure when it is applied to the structural member. In particular, it is intended to resolve the change in strength characteristics of the structural members as the thickness of the PFP increases.