Fire Plume Research Articles

The Impact of Oil Well Fires on the Free Space Optical Systems

Aerosol particles in oil fire plumes caused crucial air pollution. The smoke plumes from the blazes initially launched 200-400 m into the air and then continued to rise. The presence of liquid and solid aerosols may cause severe disturbance to the propagation of optical and infrared waves, thus can produce harmful effects on the wireless communication systems. In this paper, we analyze the bit error rate (BER), single to noise ratio (SNR), Q- factor and outage performance of single-input single-output (SISO) and multiple-input multiple-output (MIMO) FSO systems under attenuation of dense smoke conditions. Obtained results demonstrated that the performance of (SISO) FSO link is degraded from the Fog, Smoke and acid-rain Attenuation due to their chemical nature, their size and their concentration. As well, (MIMO) FSO link is a highly efficient way can be minimal smoke pollution effects

Open fires in Greenland in summer 2017: transport, deposition and radiative effects of BC, OC and BrC emissions

Abstract. Highly unusual open fires burned in western Greenland between 31 July and 21 August 2017, after a period of warm, dry and sunny weather. The fires burned on peatlands that became vulnerable to fires by permafrost thawing. We used several satellite data sets to estimate that the total area burned was about 2345 ha. Based on assumptions of typical burn depths and emission factors for peat fires, we estimate that the fires consumed a fuel amount of about 117 kt C and emitted about 23.5 t of black carbon (BC) and 731 t of organic carbon (OC), including 141 t of brown carbon (BrC). We used a Lagrangian particle dispersion model to simulate the atmospheric transport and deposition of these species. We find that the smoke plumes were often pushed towards the Greenland ice sheet by westerly winds, and thus a large fraction of the emissions (30 %) was deposited on snow- or ice-covered surfaces. The calculated deposition was small compared to the deposition from global sources, but not entirely negligible. Analysis of aerosol optical depth data from three sites in western Greenland in August 2017 showed strong influence of forest fire plumes from Canada, but little impact of the Greenland fires. Nevertheless, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar data showed that our model captured the presence and structure of the plume from the Greenland fires. The albedo changes and instantaneous surface radiative forcing in Greenland due to the fire emissions were estimated with the SNICAR model and the uvspec model from the libRadtran radiative transfer software package. We estimate that the maximum albedo change due to the BC and BrC deposition was about 0.007, too small to be measured. The average instantaneous surface radiative forcing over Greenland at noon on 31 August was 0.03–0.04 W m−2, with locally occurring maxima of 0.63–0.77 W m−2 (depending on the studied scenario). The average value is up to an order of magnitude smaller than the radiative forcing from other sources. Overall, the fires burning in Greenland in the summer of 2017 had little impact on the Greenland ice sheet, causing a small extra radiative forcing. This was due to the – in a global context – still rather small size of the fires. However, the very large fraction of the emissions deposited on the Greenland ice sheet from these fires could contribute to accelerated melting of the Greenland ice sheet if these fires become several orders of magnitude larger under future climate.

Impact of wildfires on particulate matter in the Euro-Mediterranean in 2007: sensitivity to some parameterizations of emissions in air quality models

Abstract. This study examines the uncertainties on air quality modeling associated with the integration of wildfire emissions in chemistry-transport models (CTMs). To do so, aerosol concentrations during the summer of 2007, which was marked by severe fire episodes in the Euro-Mediterranean region especially in the Balkans (20–31 July, 24–30 August 2007) and Greece (24–30 August 2007), are analyzed. Through comparisons to observations from surface networks and satellite remote sensing, we evaluate the abilities of two CTMs, Polyphemus/Polair3D and CHIMERE, to simulate the impact of fires on the regional particulate matter (PM) concentrations and optical properties. During the two main fire events, fire emissions may contribute up to 90 % of surface PM2.5 concentrations in the fire regions (Balkans and Greece), with a significant regional impact associated with long-range transport. Good general performances of the models and a clear improvement of PM2.5 and aerosol optical depth (AOD) are shown when fires are taken into account in the models with high correlation coefficients. Two sources of uncertainties are specifically analyzed in terms of surface PM2.5 concentrations and AOD using sensitivity simulations: secondary organic aerosol (SOA) formation from intermediate and semi-volatile organic compounds (I/S-VOCs) and emissions' injection heights. The analysis highlights that surface PM2.5 concentrations are highly sensitive to injection heights (with a sensitivity that can be as high as 50 % compared to the sensitivity to I/S-VOC emissions which is lower than 30 %). However, AOD which is vertically integrated is less sensitive to the injection heights (mostly below 20 %) but highly sensitive to I/S-VOC emissions (with sensitivity that can be as high as 40 %). The maximum statistical dispersion, which quantifies uncertainties related to fire emission modeling, is up to 75 % for PM2.5 in the Balkans and Greece, and varies between 36 % and 45 % for AOD above fire regions. The simulated number of daily exceedance of World Health Organization (WHO) recommendations for PM2.5 over the considered region reaches 30 days in regions affected by fires and ∼10 days in fire plumes, which is slightly underestimated compared to available observations. The maximum statistical dispersion (σ) on this indicator is also large (with σ reaching 15 days), showing the need for better understanding of the transport and evolution of fire plumes in addition to fire emissions.

Wildfire and Weather Radar: A Review

AbstractResearch in the pursuit of better understanding of fire behavior and fire‐atmosphere interaction has frequently encountered a dearth of observational data, especially from events that cause most impact. Here we show that meteorological radar has been demonstrated as an effective tool for profiling the microphysics, thermodynamics, and fire behavior feedback of wildfire plumes, including for cases with deep and moist convection occurring in the fire plume. A synthesis of knowledge on the use of radar for the analysis of wildfire is presented, and the new term pyrometeor is introduced to describe the range of scatterers observed by radar, the reflectivity signature of which is determined by interacting processes of wildfire behavior and atmospheric convection. The reflectivity theories of pyrometeors are compared, and it is shown that there are gaps in knowledge on the size distributions of pyrometeors as well as the complex dielectrics. Observational case studies are compared across plume microphysics, plume thermodynamics and deep pyroconvection, and operational usage of radar to monitor wildfire. The dominant hypothesis of reflectivity is scattering from ash particles, though theories for scattering such as from larger debris exist, although evidence is limited for any hypothesis. Vortices have also been identified using Doppler velocity radar data, but there is limited understanding of their cause and influence on fire‐atmosphere interactions. Recommendations are provided for methods and data sets to advance the application of radar for observing and understanding wildfires, including for plume microphysics and atmosphere‐fire interactions.

Experimental Study of Fire Plume Above a Fire Source with Simple Harmonic Oscillation in Horizontal Direction

In recent years, significant progress has been made in the development of maritime facilities such as floating storage and regasification units. In such offshore environments, the change in fire source position owing to temporal oscillation associated with maritime facilities affects fire plume properties. Because the properties of fire plumes in maritime facilities are important when dealing with problems related to fire detection, smoke filling, etc., we have focused attention on fire plume properties above a reciprocating fire source in an unconfined space as a first step. In particular, we experimentally investigated the characteristics of temperature rise and upward velocity along the fire plume axis formed above a 0.1 m square diffusion burner, which harmonically oscillates so as to simulate ship rolling motion under the condition of a small rolling angle. To clarify the time-averaged properties of such fire plumes, the temperature rise and upward velocity up to 5.8 m from the burner surface have been measured by varying the amplitude in three steps (0.1 m, 0.2 m, and 0.3 m) and the period in four steps (6 s, 8 s, 12 s, and 18 s). The results show that the time-averaged temperature rise and upward velocity changes from a two-dimensional plume to an axisymmetric plume. Such transition heights were determined from a simple theoretical model for predicting plume properties above a harmonically oscillating fire source. In addition, empirical correlations for effective heat release rates were also developed. These correlations allowed the existing engineering relationships for temperature rise and upward velocity along the plume axis formed above a fixed-point fire source to be utilised in order to estimate the characteristic properties of a plume formed over a harmonically oscillating fire source. This engineering knowledge can be useful for developing elemental models for the development of a two-layer zone model for ship fires.

Experimental Investigation on Lateral Temperature Profile of Window-Ejected Facade Fire Plume with Ambient Wind

The present study investigated experimentally the lateral temperature profiles of window-ejected facade fire plume from compartment with external ambient wind normal to the facade. The previous reports only focused on no wind conditions that the entrainment and diffusion of ambient air with the fire plume, which determines this lateral temperature profiles, is controlled solely by the buoyancy of the plume itself. This could be essentially affected by the external ambient wind, however, has not been revealed or quantified in the past. Hence, in this work, reduced-scale experiments were carried out employing a cubic compartment with an opening (window) and a facade wall, subjected to ambient wind provide by a wind tunnel. The lateral temperature profiles of the fire plume issued through the compartment opening was measured by thermocouples arrays installed along the facade, for various opening dimensions and ambient wind speeds. Results showed that with increasing of wind speed, the temperature at a fixed position decreased gradually, especially at those positions near the facade; while the lateral decay of temperature at a given height was faster as the wind speed was higher. This was interpreted by the physics that the ambient wind normal to the facade enhanced the entrainment and diffusion of ambient fresh air into the plume. Then, a formula (based upon classic Gaussian function) was put forward to characterize the lateral temperature profiles of the facade fire plume, by using the modified effective characteristic plume thickness (a horizontal diffusion length scale) to include wind effect. The obtained data and proposed formula in the present study provide a basic understanding for the window-ejected facade fire plume characteristics with ambient wind.

The FireFlux II experiment: a model-guided field experiment to improve understanding of fire–atmosphere interactions and fire spread

The FireFlux II experiment was conducted in a tall grass prairie located in south-east Texas on 30 January 2013 under a regional burn ban and high fire danger conditions. The goal of the experiment was to better understand micrometeorological aspects of fire spread. The experimental design was guided by the use of a coupled fire–atmosphere model that predicted the fire spread in advance. Preliminary results show that after ignition, a surface pressure perturbation formed and strengthened as the fire front and plume developed, causing an increase in wind velocity at the fire front. The fire-induced winds advected hot combustion gases forward and downwind of the fire front that resulted in acceleration of air through the flame front. Overall, the experiment collected a large set of micrometeorological, air chemistry and fire behaviour data that may provide a comprehensive dataset for evaluating and testing coupled fire–atmosphere model systems.

Association of flame-oscillation frequency under cross wind diffusion

Turbulent flame-oscillation frequency and combustion efficiency are the important parameters in combustion. It is a useful study to judge combustion efficiency by intuitive flame frequency. Based on a combustion wind tunnel experimental set-up, the variation law of combustion flame-oscillation frequency and combustion efficiency using external wind speeds was studied via the color flames image sequence of oil pan combustion and flue gas composition. The oscillation frequency was calculated with the upper edge of the fire plume which recorded flame image sequence using a high-speed video, combined the MATLAB image processing technique. The combustion efficiency was calculated combined with the C and H element mass of the liquid fuel in the oil pool and CO2 and H2O concentrations in the flue gas. The results show that the oscillation frequency of the flame revealed a tendency to increase followed by a decrease with increasing wind speed, while the overall trend of combustion efficiency increased first and then decreased. The combustion efficiency could be judged by observing the oscillation frequency of the flame image. In addition, the combustion efficiency may ensure in right way when the turbulence oscillation frequency of the oil pan flame ranged between 15 Hz and 18 Hz.

Comparison of single droplet impact behaviors on the burning shallow/deep pool

Abstract Dynamics of single water droplet impinging on burning heptane surface were investigated experimentally in shallow/deep pool. The pool regimes were newly defined and a translation region was found in burning pools. At low Weber numbers, the crater-jet only occurs for shallow pools while the crater-secondary jet does for deep pools. The bubble was observed at high Weber numbers for both pools. Compared to Weber number, liquid depth has a significant effect on the number of jet (jet and secondary jet). Some characteristic parameters, such as maximum crater depth, width and jet height were analyzed as a function of impacted dimensionless depth (1.9–11.1) and Weber numbers (246–638). Maximum crater depth and width are mainly determined by liquid depth in shallow pools, while they significantly depend on Weber number and impact behavior in deep pools. Maximum jet height is highly related to liquid depth and temperature. Additionally, the damping effect of fire plume on droplet impact velocity was explored and theoretical correlation between droplet impact velocity and impact height was proposed.

Experimental investigation on the effect of ambient pressure on entrainment coefficient of pool fires

Previous experiments at high-altitude environments have indicated that the ambient pressure has an effect on the entrainment coefficient, which further affects the axial temperature profile of a fire plume. However, their substantial relationship remains unclear as only a limited number of tests have been conducted. In this work, a reduced pressure compartment is employed to mimic the sequential low-pressure environments (40–101 kPa) for small-scale pool fires with diameters of 6, 8, and 10 cm, in order to determine the entrainment coefficient at different pressures based on the measurements of axial temperature profile. It is revealed that the entrainment coefficient relative to that at atmospheric pressure has a linear relationship with ambient pressure, which is validated in the pressure range of 40–101 kPa. By taking this relationship into consideration, all the plume temperature data can be correlated non-dimensionally with z-zo/D.

Virtual origin correction for a fire plume in a room under displacement ventilation regime

The paper examines experimentally and theoretically the virtual origin position of a fire plume in the so-called simultaneous filling and emptying box problem. Small-scale experiments are carried out with a pool fire placed into a rectangular box with an opening vent located at the ceiling. At steady state, a balance is achieved between the smoke mass flow rate supplied by the fire plume and the mass flow rate of smoke that escapes through the ceiling vent. A theoretical model for the simultaneous filling and emptying of a box is proposed, to predict the thickness and the temperature of the smoke layer. The model involves the conservation of mass and energy for the smoke layer as well as the calculation of the heat transfer through the walls. The characteristics of the fire plume at the layer interface are evaluated using the self-similar solutions including a correction of the virtual origin position. A new correction is suggested for the virtual origin position. The comparison of the model including the new virtual origin correction with the experimental data shows a good agreement.

Impact of the room geometry on the smoke filling time due to a fire plume

In this paper, the influence of a room geometry on the smoke filling time with a fire plume is studied by means of full-scale simulations with the CFD model Fire Dynamics Simulator (FDS) and two-zone models. The results show that the room aspect ratio has little impact on the smoke filling times in the case of small surface rooms. Consequently, the zone models can be used to predict the evacuation time. In the case of large surface rooms, such as atria and hangars, the dynamic of the ceiling jet when it hits the side walls cannot be neglected. In that case, the zone models overestimate the smoke filling time which directly impacts the evacuation time.

Discharge Characteristics of a Portable Compressed Air Foam System

Existing portable foam extinguishers generate fire-fighting foam at high pressures with the aid of an air aspirating nozzle. This system could encounter several limitations at the point of application such as poor foam quality due to the use of fire contaminated air for foam generation and insufficient momentum to reach the seat of fire. Research has shown that by incorporating compressed air into a portable foam system, the integrated foam system could generate superior quality foam with high momentum when properly installed with the right components. Several studies had been conducted on the extinguishing performance of compressed air foam systems on multiple fire types, both for small and large fires. Compressed air foam systems mitigate exposure of the operator to heat and provides faster knockdown of the fire plume as compared to air-aspirated foam because of its stronger stability and rheology. Since the expansion ratio of the foam can be regulated to combat specific fire types and sizes, compressed air foam systems can be utilized in protecting a variety of equipment of varied sizes.The aim of this study is to investigate the discharge characteristics of a portable compressed air foam at low pressure. For this study, the requirements of NFPA 10 and CAN/ULC-S508 for a new system were used to determine the feasibility of the system.The effect of air pressure on the expansion ratio of the foam was investigated with foam concentrate ranging from 2% to 4% for three different hoses with lengths of 1-m, 2-m and 3-m. Pressure used ranged from 1.72 bar to 5.52 bar. The 3% and 4% solution for the 2-m hose and 3-m hose exhibited similar trend of a rise and fall with pressure by generating fluid foam of medium expansion ratio in the range of 19 to 28. However, the expansion ratio of 3% solution and 4% solution for the 1-m hose increased monotonically with increasing pressure and generated wet foam of low expansion ratio in the range of 8 to 15. While low expansion foams are effective in extinguishing liquid pool fires, medium expansion foams are used for structural protection due to its slow drainage time and its ability to adhere to sloped, vertical, horizontal and slippery surfaces.Discharge range tests were conducted to investigate the horizontal projection of the foam from the nozzle at a height of 0.9m above the ground. The test was conducted in an open space with little interference of wind. Visual record of the maximum discharge range was taken at intervals. The foam from the 1-m hose projected from 1 m at 2.42 bar to 2.4 m at 5.52 bar while the foam from the 2-m hose projected from 1.8 m at 2.42 bar to 4.5 m at 5.17 bar. Likewise, the foam from the 3-m hose with an initial discharge of 1.85 m at 2.41 bar increased progressively to above 4.5 m at 4.83 bar. The tests demonstrated the relationship between pressure and the momentum of the foam, showing that an increase in pressure leads to an increase in the range covered. Furthermore, flow rates at different pressures were investigated using 3% foam solution with a 2 m hose. The flow rate of the foam ranged from 8 g/s to 20 g/s at 1.93 bar and 5.24 bar respectively, indicating linear progression with pressure. The flow rates correspond to application times of 244 and 102 seconds respectively for the 2-liter solution. Overall, all foams tested met the requirements of the CAN/ULC-S508 standard.

Experimental investigation of externally venting flames geometric characteristics and impact on the façade of corridor-like enclosures

Understanding of the physics and mechanisms of fire development and externally venting flames (EVF) in corridor-like enclosures is fundamental to studying fire spread to adjacent floors in high-rise buildings. This work aims to investigate the burning behaviour of a liquid fuel pool fire in a corridor-like enclosure and to identify the key factors influencing EVF characteristics and its impact on façades. A series of experiments is conducted in a medium-scale corridor-facade configuration using ethanol pool fires. A new fuel supply system has been developed to keep the fuel level constant to minimize lip effects. The influence of fuel surface area and ventilation factor on the fire development is also investigated. Experimental measurements consist of mass loss, heat release rate, temperatures and heat fluxes inside the corridor and on the facade. Three distinct burning regions are observed and their characteristics depend on both the pan size and ventilation factor. A power dependence of EVF height in relation to excess external heat release rate has been found. The impact of EVF on the façade is investigated by measuring heat flux on the façade using thin steel plate probes. It is found that the characteristics of EVF strongly depend on opening dimensions and for large opening widths EVF tend to emerge from the opening as two separate fire plumes.

Study on emergency ventilation for train fire environment in metro interchange tunnel

Metro interchange tunnels have been extensively constructed to meet the requirements of traffic organizations among travel lines. Fire safety issues remain a concern owing to the peculiar building structure and lack of special guidelines from current design standards and norms for ventilation. Focusing on this problem, and aiming to establish a safe evacuation environment, we carried out numerical simulations and full-scale experiment to investigate the efficiency of available co-work ventilation modes in eliminating smoke induced by train fire. The numerical model was constructed by Fire Dynamic Simulator 6.3.2, using the parameters of a real tunnel, ventilation systems containing tunnel ventilation fan (TVF), jet fan, ceiling duct, and the available co-work modes among these. The grid size and boundary conditions were verified through full-scale fire experiment and theoretical prediction by comparing the fire plume and ceiling jet flow temperature. The results demonstrate that, the semi-hybrid ventilation mode provides safe evacuation environment to the greatest extent, by utilizing the co-operation of TVFs, jet flow, and downstream ceiling extraction, compared to other modes. This mode effectively eliminated smoke and maintained the temperature, harmful gases, visibility and radiant heat flux at a safe level upstream of the fire. Furthermore, the optimized operation of the ceiling duct improved the smoke discharge efficiency as far as possible downstream of the middle carriage fire. An emergency response plan was eventually proposed for different fire scenarios, including equipment activation and passenger evacuation strategies, providing guidance for rapidly creating safe evacuation path in the interchange tunnel fire environment.

Critical velocity in ventilated tunnels in the case of fire plumes and densimetric plumes

We focus on the critical velocity in longitudinally ventilated tunnels and on its dependence on the power of the fire source. In particular we aim at identifying the reason for the appearance of the so-called ‘super-critical’ velocity, a ventilation velocity that becomes independent of the heat release rate as this latter becomes large. A critical review of existing literature studies allows us to point out possible explanations for this peculiar phenomenon. Among these, we focus here on effects related to heat fluxes (diffusive and radiative) and to the presence of large (compared to the tunnel height) flames. To enlighten the role of these phenomena, our approach is that of systematically compare the critical velocities as induced, for a given heat release rate, by densimetric plumes and fire plumes. The study is conducted by combining experimental, numerical and theoretical methods. The experiments were performed in a reduced-scale tunnel using densimetric plumes (air/helium mixture and hot air). Numerical simulations were performed with Fire Dynamics Simulator (FDS) and concerned densimetric plumes and fire plumes (propane). These show that the diffusive heat fluxes at the tunnel walls affect only marginally the critical ventilation. Similar conclusions can be drawn for the role of the radiative fluxes. The results also show that plumes arising from small fires can be reliably modelled as buoyant densimetric plumes released at ground level. In these cases the critical velocity increases with the one-third power of the heat release rate. The flow dynamics (and therefore the critical velocity) induced by larger fires is instead different. Notably, the occurrence of large flames (i.e. larger than the tunnel half-height) represent a source of distributed buoyancy, located downwind of the injection of flammable gases. Their presence induces the critical velocity to become almost independent on the heat release rate.

Effect of blockage-induced near wake flow on fire properties in a longitudinally ventilated tunnel

Effect of blockage-induced near wake flow on fire properties in a longitudinally ventilated tunnel was studied. Numerical simulation was conducted in a tunnel under longitudinal ventilation velocity in the range of 1.0–4.0 m/s. Vehicular blockage was positioned in the upstream of the fire source, with four kinds of blockage ratios (0.24, 0.40, 0.56, 0.72). Temperature contours were used to describe the fire plume region in the tunnel with longitudinal ventilation. It is found that the fire flame goes five stages and transits leaning direction from downstream to upstream of the fire with increasing blockage ratio and ventilation velocity, behaving differently from that in just a longitudinally ventilated tunnel without vehicular blockage. With the increasing ventilation velocity and blockage ratio, the vertical temperature 5 m downstream of the fire decreases and temperature difference in the vertical direction gradually weakens. However, in the upstream 2.5 m from the fire, after the temperature tending to be uniform in the vertical direction, it is high in the middle height and low at the top and bottom. At ventilation velocity larger than 2.5 m/s, the temperature beneath the tunnel ceiling decreases with the increasing blockage ratio downstream of the fire, while there is increase in the upstream. A new expression with the factor blockage ratio included is proposed to predict the maximum temperature beneath the tunnel ceiling, showing good agreement with simulation data.

Experimental Study on Flame Spread over Inclined PMMA and PE Slabs

The effects of orientation on flame spread over the upper surface of PMMA and PE slabs were studied through a series of experiments. For fuel inclined angles smaller than 75° in this study, flame spread would arrive a steady-state stage finally. The flame spread rate and the angle of the fire plume near pyrolysis front in the steady-state stage were measured to investigate the differences between flame spread over melting and non-melting solids. Compared to the flame spread over polymethyl methacrylate (PMMA), the melting behaviors of high density polyethylene (PE) significantly decrease the flame spread rate, which is mainly attributed to the decreased size of fire plume and reduced interactions between fire plume and solid surface. The angles of the fire plume in the steady-state stage under different fuel inclined angles were measured to better understand the melting effects on flame spread over the inclined solid surface.

An experimental study on the effect of fire growth in a lower-floor compartment on fire evolution and facade flame ejection from an upper-floor compartment

The present study investigated the effect of fire growth in a lower-floor compartment on fire evolution and the characteristics of facade flame ejection from an upper-floor compartment. Experiments were performed using two floors with identical compartments (0.4 m cubic with an opening of 0.2 m × 0.2 m). A 0.2-m square porous propane burner was used as fire source in each compartment. Results showed that the growth of facade fire plume from the lower-floor compartment significantly affected the ventilation conditions for the opening of upper-floor compartment hence its fire evolution and facade flame ejection characteristics. These evolutions were found to be of three distinct types with HRR increasing in the lower-floor compartment: (I) in the case of relatively small upper-floor compartment fires under well-ventilated conditions, the flame was gradually weakened and finally extinguished; (II) in the case of medium upper-floor compartment fires under well-ventilated conditions, the flame inside the compartment (well-ventilated) turned to eject through the opening (under-ventilated), and the facade flame height decreased slightly till the flame was extinguished; (III) in the case of relatively large upper-floor compartment fires in under-ventilated conditions, the facade flame was sustained, and once the lower-floor compartment fire was involved, the flame height first increased significantly, then decreased, and finally increased again after the two facade flames from the two floors merged. The critical HRR of lower-floor compartment for realising flame ejection from upper-floor compartment (type II) was lower as the HRR of the upper-floor compartment is higher. The critical HRR of the lower-floor compartment for realising flame extinction of upper-floor compartment was found to be independent of the HRR of upper-floor compartment for type-I evolution while it increased with the HRR of the upper-floor compartment for type-II evolution. These new observations are essential for understanding building fire involving compartments of two floors.

Thermodynamics of Pyrocumulus: A Conceptual Study

Abstract In favorable atmospheric conditions, fires can produce pyrocumulonimbus cloud (pyroCb) in the form of deep convective columns resembling conventional thunderstorms, which may be accompanied by strong inflow, dangerous downbursts, and lightning strikes that can produce dangerous changes in fire behavior. PyroCb formation conditions are not well understood and are difficult to forecast. This paper presents a theoretical study of the thermodynamics of fire plumes to better understand the influence of a range of factors on plume condensation. Plume gases are considered to be undiluted at the fire source and approach 100% dilution at the plume top (neutral buoyancy). Plume condensation height changes are considered for this full range of dilution and for a given set of factors that include environmental temperature and humidity, fire temperature, and fire-moisture-to-heat ratios. The condensation heights are calculated and plotted as saturation point (SP) curves on thermodynamic diagrams. The position and slope of the SP curves provide insight into how plume condensation is affected by the environment thermodynamics and ratios of fire heat to moisture production. Plume temperature traces from large-eddy model simulations added to the diagrams provide additional insight into plume condensation heights and plume buoyancy at condensation. SP curves added to a mixed layer lifting condensation level on standard thermodynamic diagrams can be used to identify the minimum plume condensation height and buoyancy required for deep, moist, free convection to develop, which will aid pyroCb prediction.