Numerical model and validation experiments of atrium enclosure fire in a new fire test facility

The use of computational fluid dynamics (CFD) as a tool for buildings, warehouses or factories design requirements fulfilling about fire safety is becoming more common and reliable. Performance-based fire safety assurance procedures make use of the CFD fire modelling to anticipate the evolution of fire, but they need always to be validated. This is especially difficult for big structures, with great clear volumes, where effects of natural and forced ventilation can be very scale dependent. A good opportunity to check the prediction capability of CFD codes to establish temperatures and velocities fields is the new full-scale fire test facility of the Technological Metal Centre in Murcia, Spain. It is an aluminium prismatic squared base building of 19.5 m×19.5 m×20 m, with several vents arranged in its walls and four exhaust fans at the roof. Series of experimental tests have been carried out using several heptane normalized pool-fires placed at the centre of the atrium. The data obtained from these experiments have been later used in a validation study of two CFD simulations implemented for temperature wall, ambient temperature prediction and exhaust fan assessment. The results show good agreement between experimental and numerical predictions and allow concluding that for a fire test of 1.6 MW of average heat release power, the exhaust and ventilation system is not enough to extract the hot combustion products. There is an excessive and dangerous accumulation of hot gases at the upper part of the atrium and the exhaust capacity of the roof fans must be increased. The CFD models can give the answer to that question.     

Experimental study of fire growth in a reduced-scale compartment under different approaching external wind conditions

In order to clarify the fire growth process in compartments under external wind conditions, detailed fire tunnel experiments were conducted in a reduced-scale compartment. The approaching external wind velocity was set to 0.0, 1.5 and 3.0 m/s, and the location of the fire source was changed between the downwind corner, upwind corner and center of the compartment. The experiments considered the effect of wind on a through-ventilation situation. The temperatures of the air and the wall surfaces in the compartment and the temperatures of the flames ejected from the opening were measured. The fuel mass loss rate and the heat flux from the opening were also recorded. Different fire growth characteristics are shown under different wind and fire source conditions. The temperature rises faster and burnout time is reduced under windy conditions. It is found that external wind has two opposing effects. One is to promote combustion within the compartment and thus raise the temperature, the other is to blow away and dilute the combustible gases in the compartment and decrease the temperature, or hasten its extinction. When the approaching wind velocity is high, the external plume is greatly inclined to the downwind side, and the flame becomes larger, thus increasing the risk of the fire spreading to neighboring buildings. The dimensionless temperature of the external flame was a little lower than the results indicated by Yokoi's experiments without wind.     

Wind effects on smoke motion and temperature of ventilation-controlled fire in a two-vent compartment

High-rise building fire is often influenced by the ambient wind. Study concerning fire behavior in the compartment of high-rise buildings in wind environment is needed for exploring some effective methods used for evaluation of compartment fire smoke movement and control. In this paper, smoke flowing direction and temperature of ventilation-controlled fire in a two-vent compartment are studied when ambient wind blows to the vent at higher altitude. It is found that there is a critical wind speed, above which the direction of smoke movement is dominated by wind rather than by buoyancy. It is also found that ambient wind has a complex influence on smoke temperature in the compartment. When wind speed exceeds another critical value, only one steady state appears in the smoke temperature rising curve. Otherwise three steady states appear. Heat transfer through the compartment walls has great influence on the second critical wind speed.     

A computational and experimental study of ultra fine water mist as a total flooding agent

Computational fluid dynamics (CFD) calculations were carried out to design total flooding fire tests in a 28 m³ compartment for an ultra fine water mist (<10 μm). The exit momentum of the mist produced by a proprietary ultrasonic generator technology was extremely low with a mist discharge velocity below 1 m/s. The mist was discharged with multiple floor outlets equally spaced around the centrally located 120 kW pool-like gas fire. The transport of mist and its interaction with the fire was simulated by Fluent, a commercial CFD model. Lagrangian Discrete Phase Model (DPM) was used for droplets. Simulation predicted extinguishment within 10 s with a mist delivery rate of 1 l/min. However, in total flooding fire tests conducted, extinction times were more than 5 min. Additional computations approximating the ultra fine mist (UFM) as a dense gas agreed well with the observed transport timescales of minutes indicating that UFM behaves like a gas. Further, the mist–fire interaction needs a multi-phase Euler–Euler approach with a droplet vaporization model.     

Microclimate and ventilation in Estonian and Finnish dairy buildings

A series of ventilation, thermal and indoor air quality measurements were performed in 14 different dairy buildings in Estonia and Finland. The number of animals in the buildings varied from 30 to 600. Measurements were made all year round with ambient temperatures ranging between −40 °C and +30 °C. The results showed that microclimatic conditions in the dairy buildings were affected by the design of the building, outside temperature, wind, ventilation and manure handling method. The average inside air concentration of carbon dioxide was 950 ppm, ammonia 5 ppm, methane 48 ppm, relative humidity 70% and inside air velocity was 0.2 m/s. Although occasionally exceeded, the ventilation and average indoor air quality in the dairy buildings were mainly within the recommended limits.     

Estimating the effects of ambient conditions on the performance of UVGI air cleaners

Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2 °C and an air velocity range of 0–3.25 m/s, measured cold spot temperature varied from 12.7 to 41.9 °C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17 °C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1 °C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.     

A smoke model and its application for smoke management in an underground mass transit station

This paper discusses the development of a smoke model for CFD. The model evaluates smoke visibility based on line of sight. Using a compartment fire, the deficiency in determining visibility by the conventional surface-based approach is first demonstrated. Smoke management in an underground rail station is investigated using the smoke model. For a medium growth rate fire, the results show that the platform is blocked by smoke within 2–3 min. On the mezzanine, the designed smoke exhaust controls the smoke only for a limited time of less than 4 min. The variations of smoke obscuration are quantified at three locations, which are used to start the tunnel ventilation at 4 min. This can be related to a video-based smoke detection. The smoke model would be useful in tenability, egress and other life safety assessments. Future development of the model includes local lighting effects and experimental validation.     

CO2, CO, and Hg emissions from the Truman Shepherd and Ruth Mullins coal fires, eastern Kentucky, USA

Carbon dioxide (CO₂), carbon monoxide (CO), and mercury (Hg) emissions were quantified for two eastern Kentucky coal-seam fires, the Truman Shepherd fire in Floyd County and the Ruth Mullins fire in Perry County. This study is one of the first to estimate gas emissions from coal fires using field measurements at gas vents. The Truman Shepherd fire emissions are nearly 1400 t CO₂/yr and 16 kg Hg/yr resulting from a coal combustion rate of 450-550 t/yr. The sum of CO₂ emissions from seven vents at the Ruth Mullins fire is 726 ± 72 t/yr, suggesting that the fire is consuming about 250-280 t coal/yr. Total Ruth Mullins fire CO and Hg emissions are estimated at 21 ± 1.8 t/yr and > 840 ± 170 g/yr, respectively. The CO₂ emissions are environmentally significant, but low compared to coal-fired power plants; for example, 3.9 × 10⁶ t CO₂/yr for a 514-MW boiler in Kentucky. Using simple calculations, CO₂ and Hg emissions from coal-fires in the U.S. are estimated at 1.4 × 10⁷-2.9 × 10⁸ t/yr and 0.58-11.5 t/yr, respectively. This initial work indicates that coal fires may be an important source of CO₂, CO, Hg and other atmospheric constituents.     

环境风作用下建筑开口溢流火焰拓展规律研究

建筑开口火溢流特征参数研究是火灾科学领域的基础研究内容之一,尤其是正交侧吹横向风影响下的开口火溢流特征更是影响到相邻建筑的火灾危险性。基于弗洛德相似准则,利用缩尺寸建筑燃烧腔室模型开展建筑溢流火灾实验,在正交侧吹横向风作用下,对不同火源功率和不同开口尺寸的建筑腔室溢流火焰扩展规律进行探究。重点分析风速对火焰形态的影响,建立环境风作用下建筑腔室开口溢流火焰长度的分段预测模型,为建筑外立面防火设计提供参考。     

Experimental data and numerical modelling of 1.3 and 2.3 MW fires in a 20 m cubic atrium

Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame.     

Experimental Investigation of Effect of External Side Wind on Fire Behaviors in a Corridor Connected to a Shaft

High-rise buildings are usually in a windy environment. The motion of fire-induced smoke and fire behaviors may be strongly affected by the external wind forces except by the stack effect. It turns out that wind with different directions and velocities can cause disparity in fire dynamics. Since most previous researches only focused on the cross wind conditions, this work investigated the effect of external side wind from 0 m/s to 1.21 m/s on the air flow behaviors, combustion characteristics of methanol pools and smoke temperature in a 1/6 scaled corridor connected to a 6-floor shaft. A remarkable observation is that the external side wind (parallel to top window, shown in Fig. 1) leads to pressure attenuation inside building and induces air to flow inside through bottom door. Therefore, the smoke spreads faster under the synergic effects of side wind and stack effect. At the steady stage, the supplement air flow velocity increases with wind velocity but remains proportional to 1/3 power of HRR. An equation incorporating the wind effect is proposed to predict the air flow velocity. Results also show that compared to cross wind conditions, the mass loss rates of methanol pools increase at high wind velocities. The wind effect on smoke temperature is obvious in cases with small pools. Here, the temperature first increases to a peak value and then decreases with increased wind velocity. However, the temperature remains the same in cases with large pools within our wind velocity range. The temperature in the shaft is also correlated with mass loss rate and wind velocity. This work shows that external side wind would increase the fire hazard of buildings by contributing to the combustion and spreading of smoke. Thus engineers should consider the effect of side wind carefully when designing smoke control system.

     

Numerical simulations on fire spread and smoke movement in an underground car park

The Fire Dynamic Simulator code is used to investigate fire spread and smoke movement in a large underground car park under different fire scenarios. Initially, by comparing with experimental results of heat release rate of a single car fire, the development of car fire is designed by letting surface densities of the fuel over the car. Fire spread and movement of smoke are then investigated under different ventilation conditions. Simulated results show that the development of car fire in the underground car park can be classified into four stages; namely an initial stage, a developed stage, an extinction and re-burning stage and another fast-developed stage. Affected by ventilation systems, fire develops rapidly resulting in consuming most oxygen quickly followed by early extinction of the fire. After extinction of the fire, with more ambient air drawn into the car park due to ventilation, re-ignition takes place with accelerated development. In addition, detailed field distributions of temperature and velocity vectors are given. It is found that the smoke layer decent to the top of the car after 15 min and the hot smoke flows in a disorderly manner resulting in the spread of fire more rapidly.     

Critical ventilation velocity for tunnel fires occurring near tunnel exits

Ventilation is an effective method for controlling smoke during a tunnel fire. The “critical ventilation velocity” u_cr is generally defined as the minimum velocity at which smoke is prevented from spreading against the longitudinal ventilation flow in tunnel fire situations. This study conducted small-scale experiments to investigate u_cr for situations when tunnel fire occurs near tunnel exits. The model tunnel was 4 m long, 0.6 m wide and 0.6 m tall, and the fires were located at 0.5 m, 1.0 m and 1.5 m from the tunnel exit. 6.3×6.3 cm² and 9.0×9.0 cm² square asoline fuel pans were used as fire source. Results show that u_cr decreases as the fire approaches the tunnel exit.     

Energy distribution analysis in full-scale open floor plan enclosure fires

Within a fast evolving built environment, understanding fire behaviour and the thermal exposure upon structural elements and systems is key for the continued provision of fire safe designs and solutions. Concepts of fire behaviour derived from research in enclosure fires has traditionally had a significant impact in general building design. At present, open floor plan enclosures are increasingly common – building design has drastically drifted away from traditional compartmentalisation. Nevertheless, the understanding of fire behaviour in open floor plan enclosures has not developed concurrently. The compartment fire framework, first conceived for under-ventilated fires in cubic compartments, has remained as standard practice. Although energy conservation within the enclosure was the basis for the current compartment fire framework that defines under-ventilated enclosure fires, little effort has been carried towards understanding the distribution of energy in design frameworks conceived for open floor plan enclosure fires. The work presented herein describes an analysis of the energy distribution established within an experimental full-scale open floor plan enclosure subjected to different fire modes and ventilation conditions. The results aim to enable the designer to estimate the fraction of the total energy released during a fire noteworthy to structural performance.     

机械加压送风防烟系统合理送风量的理论分析

从着火房间内外压力分布及烟气流动规律出发，分析加压送风与烟气蔓延之间的关系，并由此导出打开加压部位时，能够有效地阻止烟气进入疏散路线和避难场所的平均风速范围约为2.0m/s～2.5m/s，此值远大于《高层民用建筑设计防火规范》条文说明中推荐的风速范围0.7m/s～1.2m/s，机械加压送风防烟系统设计应综合考虑火灾区域烟气的有效排放。     

The assessment of the performance of a windcatcher system using computational fluid dynamics

Natural ventilation is increasingly being used in modern residential buildings to minimize the consumption of non-renewable energy and the reliance on active means for environmental control. Innovative green features such as the windcatcher has made use of natural ventilation in residential buildings for increasing ventilation rate. This paper presents a numerical study of assessment of the performance of windcatcher using computational fluid dynamics. A 500 mm square windcatcher system connected to the room has been modeled for different wind speeds in the range of 0.5–6 m/s and four different wind directions. The numerical results generally agree with the published experimental results of a wind tunnel experiment. The numerical results demonstrate that the windcatcher performance is greatly influenced by the external wind speed and direction with respect to the windcatcher quadrants. In all cases studied, the maximum velocity of air entering the room is close to the external wind speed and the windcatcher system is found to be an efficient way to channel fresh air into the room. The study also shows that the airflow rate of the air entering the room increases with the wind speed and slightly decreases with the wind incidence angle when the wind speed is lower than 3 m/s. In addition, the results show that the uniformity of air inlet decreases with increasing the wind speed and the incidence angle.     

COMPBRN III — A fire hazard model for risk analysis

COMPBRN III is a deterministic fire hazard computer code designed to be used in a probabilistic analysis of fire growth in a compartment. Its primary application to date has been the assessment of fire risk in the nuclear power industry. COMPBRN III follows a quasi-static approach to simulate the process of fire growth during the pre-flashover period in an enclosure. Physical models which quantify the thermal hazard (including temperature and heat fluxes) during a compartment fire are developed. Simulations of experiments are performed to test the accuracy of the improved hot gas layer model used in this version of COMPBRN in predicting the behavior of large-scale fires.     

Influence of different make-up air configurations on the fire-induced conditions in an atrium

In this paper, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. In the experiments, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke-layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. These data could be used as benchmark for future numerical validation studies. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDSv4). In the experiments, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. In the numerical simulations, the predictions agree well with the experiments for the cases with larger make-up air openings. Poor agreement has been found for the case with the smallest inlet openings.