Smoke Temperature Research Articles

Application of the high-pressure water mist system in a railway tunnel rescue station

• Full-scale fire suppression experiments and numerical simulations in a rescue station were performed. • Suppression effect inside and outside train increased with increasing droplet size. • Convective cooling was the main controlling mechanism on suppressing a train fire. • Radiation heat flux received by the floor exponentially decayed with the distance from fire. • Longitudinal ventilation could effectively improve the suppression effect of water mist system. The fire safety of the rescue station as an important issue has not been well concerned. This study investigated the suppression performance of the high-pressure water mist system in a railway tunnel rescue station through CFD (Computational Fluid Dynamics) simulation and full-scale experiments. Eleven groups of numerical simulations and full-scale experiments were designed with various working pressures (5 and 8 MPa), mist droplet diameters (173.2, 178, and 192.9 μm), and longitudinal ventilation velocities (0, 1.5, and 2.5 m/s), in which the simulations were carried out by employing SIMTEC (Simulation of Thermal Engineering Complex) software. Results show that the temperature control effect both in the carriage and above the platform increases along with a bigger mist droplet diameter, in which convective cooling is found to be the main controlling mechanism. However, with increasing mist droplet diameter, smoke concentration increases, and oxygen concentration decreases. Moreover, the radiant heat flux received by the floor presents an increasing first and then decreasing tendency with the increase of distance away from the fire source (denoted by l ). Furthermore, in the region of l ≥ 2.5 m, radiant heat flux has an exponential attenuation with l . In addition, it is also found that the longitudinal ventilation system can effectively improve the suppression performance of the water mist system on a shielded fire. With increasing ventilation velocity, smoke temperature and radiant heat flux in the region of l ≥ 2.5 m decrease. In all cases, numerical results match well with experimental results, which validates the effectiveness of the CFD simulation. This study provides a significant reference for the fire safety design of the railway tunnel rescue station.

Numerical study on the impact of wall thermal inertia on maximum smoke temperature and longitudinal attenuation in long channel fires

In order to better understand the law of smoke propagation in long channel fires and enhance the fire protection of channel structure with different lining materials, a series of fire simulations were carried out by Fire Dynamics Simulator (FDS) to investigate the impact of wall thermal inertia on the maximum smoke temperature and longitudinal attenuation under the channel ceiling. Five wall materials corresponding from the foam concrete to the steel with thermal inertia ranging from 0.1 to 165 kW2•s/(m4·K2) and four heat release rates (5 MW, 7.5 MW, 10 MW and 12.5 MW) were employed. The maximum smoke temperature above the fire source and the temperature distribution under the ceiling along the channel longitudinal centerline were attained and analyzed. The results show that the maximum smoke temperature is significantly affected by the channel wall thermal property and increases with the decrease of wall thermal inertia. Based on the simulative data, a modified model taking the influence of wall thermal inertia into consideration is put forward to predict the maximum gas temperature below the ceiling. Further, the effect of channel wall thermal inertia on the longitudinal smoke temperature decay can be negligible when the thermal inertia is greater than or equal to 1.21 kW2•s/(m4·K2), however, the foam concrete wall with the thermal inertia of 0.1 kW2•s/(m4·K2) results in a smaller attenuation rate due to less heat conducted into the channel wall. Meanwhile, the smoke temperature distribution along the channel longitudinal centerline is also related to the heat release rate (HRR), and the larger the HRR, the slower the temperature decay. The investigation indicates that the temperature distribution along the longitudinal direction follows an exponential attenuation in the near fire field but presents a form of the sum of two exponential functions in the one-dimensional smoke propagation stage. Then taking the effect of wall thermal inertia and heat release rate into account, two novel models characterizing the law of longitudinal temperature attenuation were developed near fire source and in the one-dimensional smoke spread stage respectively.

Pengabut Semprot Bergerak untuk Pemberantasan Hama Kelapa Sawit

Palm oil (Elaeis guineensis) is a tropical plant that can be attacked by various pests, start from nurseries to plantations, so it is necessary to eradicate pests. Generally, the pests is eradicated by applying pesticides using fogging machines brought down by farmers so that they are ineffective in reaching high plants, and hot smoke from fogging machines can damage oil palm leaves. This study aims to design a tool that can optimize the application of pesticide fog to oil palm plants at a certain height. The tool's design in the form of a mobile spray fogger also aims to facilitate the operator in applying pesticide fog at various heights of oil palm and, simultaneously, can reduce the impact of damage to oil palm leaves. The research method was carried out by testing the performance of pesticide fog spraying in the laboratory and the performance test of applying pesticide fog using mobile spray foggers on the land. Furthermore, pesticide smoke from fogging machines was optimized by combining electric sprayers and air blowers so that pesticide fog is formed, reducing the temperature of pesticide smoke, and increasing the range of fogging. The performance of the combination of outputs from fogging machines, electric sprayers, and air blowers on mobile spray fogger produces a droplet diameter of 94.41 μm, droplet density of 365.44 droplet/cm2, effective fogging range of 8.63 m, effective fogging width of 0.91 m, and an average temperature decrease of 4°C.
 
 Keywords: air blower, electric sprayer, fogging machine, palm oil, pests

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.

Research on the Risk Classification of Cruise Ship Fires Based on an Attention-Bp Neural Network

Abstract Due to the relatively closed environment, complex internal structure, and difficult evacuation of personnel, it is more difficult to prevent ship fires than land fires. In this paper, taking the large cruise ship as the research object, the physical model of a cruise cabin fire is established through PyroSim software, and the safety indexes such as smoke temperature, CO concentration, and visibility are numerically simulated. An Attention-BP neural network model is designed for realizing the intelligent identification of a cabin fire and dividing the risk level, which integrates the diagnosis results of multiple neural network models through the self-Attention mechanism and adaptively distributes the weight of each BP neural network model. The proposed model can provide decision-making reference for subsequent fire-fighting measures and personnel evacuation. Experimental results show that the proposed Attention-BP neural network model can effectively realize the early warning of the fire risk level. Compared with other machine learning algorithms, it has the highest stability and accuracy and reduces the uncertainty of early cabin fire warning.

The effect of PhIP precursors on the generation of particulate matter in cooking oil fumes at high cooking temperatures and the inflammation response in human lung cells

Cooking Oil Fumes (COFs) contain carcinogenic organic substances such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs), of which 2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) is known as mainly meat-borne carcinogens. In this work, to identify the mechanisms to induce the inflammation response in human lung cells (A549) exposed to COFs, we investigated the physicochemical and biological characteristics of COFs generated with PhIP precursors (L-phenylalanine, creatinine, and glucose) at high cooking temperatures (300 °C and 600 °C). Interestingly, we found that PhIP was not formed both at 300 °C and 600 °C, while a large number of carbon nanoparticles were generated from soybean oil containing the PhIP precursors at 600 °C. From the biological analysis, COFs generated with the PhIP precursors at 600 °C induced the most significant pro-inflammatory cytokine (IL-6). This result indicates that the particulate matter in COFs generated with the PhIP precursors above the smoke temperature is the primary factor directly affecting the lung inflammatory response rather than PhIP. This study demonstrates for the first time a novel principle of the inflammatory response that the PhIP precursors can aggravate lung injury by affecting the physical properties of COFs depending on cooking temperature. Therefore, our finding is a significant result of overcoming the bias in previous studies focusing only on the chemical toxicity of PhIP in the inflammatory response of COFs.

Study on the Effect of Bridge Deck Spacing on Characteristics of Smoke Temperature Field in a Bridge Fire

The numerical simulation method is used to simulate the distribution characteristics of the smoke temperature field of a double-deck bridge smoke temperature field during tanker fire under natural ventilation. The influence of the distance between double decks on the truss and ceiling temperature field change in the double-deck bridge is investigated. The results show that the range of high-temperature area gradually decreases with the increase in bridge deck spacing. The maximum excess temperature function of the tunnel ceiling is also applicable to the bridge, but the coefficient is smaller than that of the tunnel experimental formula. An equation is proposed to predict the maximum excess temperature of the truss under different bridge deck spacings. As the bridge deck spacing increases, the maximum excess temperature decreases. The excess temperature of the truss increases along the truss, and the maximum excess temperature appears at the top of the truss. Based on the energy equation, an equation for the excess temperature of the truss is established. As the vertical height increases, the excess temperature of the truss above the fire source exponentially increases. The research results will contribute to the fire hazard evaluation and safety design of bridges.

Numerical study on the critical criterion for predicting the plug-holing under lateral mechanical exhaust in tunnel fires: Considering the effect of smoke flow in longitudinal direction

This paper has analyzed the phenomenon of plug-holing under lateral mechanical exhaust in tunnel fires by conducting large eddy simulations (LES) with Fire Dynamics Simulator (FDS). The lateral mechanical smoke exhaust is a method of smoke controlling in tunnel fires with exhaust vents set in the tunnel sidewall. The results show that the phenomenon of plug-holing occurs at the lateral exhaust vent as the exhaust rate increases. The occurrence of plug-holing will lead more fresh air discharged through the vent, thereby reducing the smoke exhaust efficiency. The smoke layer thickness and temperature downstream the vent in the tunnel are analyzed to evaluate the exhaust effectiveness of lateral mechanical exhaust. When the plug-holing does not occur, increasing exhaust rate can effectively reduce the smoke layer thickness. While the plug-holing occurs, the increasing exhaust rate will increase the smoke layer thickness on the contrary. In terms of reducing smoke temperature in the tunnel, increasing exhaust rate has very limited effect in this study. Therefore, it is not the case that the higher the exhaust rate, the better the smoke exhaust efficiency and effectiveness. There is a critical exhaust rate under which the plug-holing can be avoided. Furthermore, considering the horizontal and vertical inertial forces of the smoke beneath the vent, a critical criterion (Ri'critical) for predicting the occurrence of plug-holing of lateral mechanical exhausting is proposed. Based on the results of different exhaust rates, heat release rates and vent sizes, the critical criterion (Ri'critical) that corresponds to the occurrence of plug-holing can be determined as 0.6.

Numerical Simulation on the Effect of Fire Shutter Descending Height on Smoke Extraction Efficiency in a Large Atrium

In this study, a series of numerical simulations were carried out to investigate the effect of fire shutter descending height on the smoke extraction efficiency in a large space atrium. Based on the full-scale fire experiments, this paper carried out more numerical simulations to explore factors affecting the smoke extraction efficiency in the atrium. The smoke flow characteristics, temperature distribution law and smoke extraction efficiency of natural and mechanical smoke exhaust systems were discussed under different heat release rates and fire shutter descending heights. The results show that the smoke spread rate and the average temperature of the smoke are higher with a greater heat release rate. After the mechanical smoke exhaust system is activated, the smoke layer thickness and smoke temperature decrease, and the stable period of heat release rate is shorter. In the condition of natural smoke exhaust, the smoke extraction efficiency increases exponentially with the increase of heat release rate and the descending height of the fire shutter, and the maximum smoke extraction efficiency is 48.8%. In the condition of mechanical smoke exhaust, the smoke extraction efficiency increases with the increase of mechanical exhaust velocity. When the velocity increases to the critical value (8 m/s), the smoke extraction efficiency is essentially stable. The smoke extraction efficiency is increased first with the increase of fire shutter descending height and then has a downward trend when the descending height drops to half, and the maximum smoke extraction efficiency is 70.3% in the condition of mechanical smoke exhaust. Empirical correlations between the smoke extraction efficiency and the dimensionless fire shutter descending height, the dimensionless heat release rate and the dimensionless smoke exhaust velocity have been established. The results of this study can provide a reference for the design of smoke prevention and exhaust systems in the atrium.

Effect of bifurcation angle and fire location on smoke temperature profile in longitudinal ventilated bifurcated tunnel fires

The maximum ceiling temperature and longitudinal temperature distribution were investigated in bifurcated tunnels with different bifurcation angles under longitudinal ventilation. A series of experiments were carried out in a 1:10 small-scale bifurcated tunnel with a bifurcation angle of 60°, considering different longitudinal fire locations. Furthermore, 44 cases including 2 fire locations with bifurcation angles between 20°∼90° were simulated by FDS. The results indicated that: (1) The longitudinal fire location would affect the maximum temperature rise in the bifurcated tunnel. When the fire was in the bifurcated zone, the maximum temperature was lower than that in the non-bifurcated zone under a same condition. (2) The bifurcation angle had little effect on the maximum ceiling temperature. (3) The longitudinal temperature distribution of the main tunnel in the downstream from the fire source was independent of the bifurcation angle, while the attenuation rate of longitudinal temperature of the branch tunnel increased with the increasing of bifurcation angle. In addition, prediction models of the maximum ceiling temperature rise and the longitudinal temperature distribution in the main tunnel and branch tunnel were proposed, which could well predict the smoke temperature profile in T-shaped bifurcated tunnels with bifurcation angles between 20° and 90° under the dimensionless ventilation velocity greater than 0.19.

Numerical study on fire-induced smoke temperature characteristics in small curvature radius UTLT-like tunnels under emergency state

Extensive studies have usually focused on an ordinary single straight or large curvature radius tunnel fire. However, the curvature effect of small curvature radius curved tunnel on the fire-induced smoke temperature characteristics still needs to clarify. Therefore, a three-dimensional transient computational fluid dynamics (CFD) fire model for small curvature radius urban traffic link tunnel (UTLT)-like tunnel was established to understand the scope and extent of curvature effect on the fire-induced smoke under emergency state. The results show that, in the curved tunnel area, small curvature radius or large critical ventilation velocity results in stronger centrifugal force of the fire smoke, readily destabilizing the fire smoke downstream of the fire source. Compared with large radius of curvature and straight tunnels, due to the greater resistance of curved walls in small curvature radius tunnel, the length of smoke back-layering is longer. Simultaneously, the temperature of the high-temperature smoke on the outer wall of the ceiling cross section is higher than the inner wall. Prediction mathematical models for the maximum temperature and longitudinal temperature profiles were further developed by taking the curvature and ventilation velocity effect, which is basically consistent with experimental and simulated results.

Full-scale experimental study on thermal smoke movement characteristics in an indoor pedestrian street

Indoor pedestrian street, a common architecture scheme, brings both convenience and fire risk in the meantime. Full-scale tests were carried out to study thermal smoke movement characteristics, including smoke development, longitudinal temperature distribution in the room, and horizontal temperature distribution in the ring corridor, in an indoor pedestrian street under different mechanical smoke exhaust modes. Results showed that smoke movement characteristics were mainly influenced by the smoke exhaust mode and building structure. Under natural ventilation, thermal smoke spread along the two crossed channels of the room and entered the adjacent ring corridor and atrium. When the smoke exhaust system was activated, the smoke spread was effectively restricted. As the smoke exhaust was enhanced, the heat release rate of the ventilation controlled fire in the room was increased, resulting in the higher smoke temperature. In addition, the smoke temperature rise decreased exponentially with the increasing longitudinal distance from the fire in the room under all smoke exhaust modes. The stronger smoke exhaust and larger building space leaded to the higher decay rate. In the ring corridor, the decrease of smoke temperature rise with the horizontal distance was exponential under natural ventilation but was linear when the smoke exhaust system was activated. • Thermal smoke spread characteristics in indoor pedestrian street investigated. • Room fire scenarios under four mechanical smoke exhaust modes designed. • Smoke development and temperature distribution in room and ring corridor analyzed. • Effect of different mechanical smoke exhaust modes on smoke spread revealed. • Dimensionless exponential and linear smoke temperature decay models established.

Fuzzy-logic modelling for quality prediction of smoked Tilapia (Oreochromis niloticus) fish

Statistical modelling of hot smoke processing of pre-treated Tilapia (Oreochromis niloticus) fish was reportedly inaccurate, making it difficult to design, predict, and reproduce the finished product’s quality; hence, accurate modelling of this process is a gap in study. This study filled this gap and extended the literature by investigating the accuracy of artificial intelligent based model for the same process. Fuzzy inference system (FIS) model was developed using the already presented dataset in the literature from where inaccurate statistical models were reportedly derived. The dataset is on the effect of smoke temperature (80, 90 and 100OC) and smoke time (2.00, 2.50 and 3.00 h) on the gross energy value (GEV) (Kcal/g) and the overall acceptability (OA) properties of brined pre-solar dried and brined non-dried Tilapia (Oreochromis niloticus) fish. The efficiency of FIS membership function types (pimf, trimf and gbellmf) on the accuracy of the developed FIS model was also investigated. Coefficient of determination, root mean square error, individual percentage error and model accuracy were used to discern the model accuracy. Results showed that FIS had a modelling accuracy (𝑅2 value) between 0.9873 and 0.9999 as against 0.1072 and 0.5800 reported for the statistical model. The results suggested that FIS model outperformed the statistical model of Tilapia (Oreochromis niloticus) smoke processing and it is recommended for process/product design, control, and standardization.

The Influence of Air Curtains on Fire Smoke in Tunnels

To figure out the influence of smoke-proof air curtains on the law of tunnel fire smoke spread, this paper set a simulated fire scene of passenger bus with a fire source power of 25 MW in Fire Dynamics Simulator (FDS), a software for stimulating fire dynamics, to study the law of fire smoke spread in tunnels. At first, this paper analyzed the distribution of smoke temperature, visibility, and CO concentration in each area of the tunnel under the conditions of different jet velocities and angles of the air curtain, and explored the influence of air curtain on the law of fire smoke spread in the tunnel. The research results showed that, when the fire source power was 25MW and the smoke exhaust rate was 100m3/s, in order to effectively control the spread of smoke, the jet velocity of the air curtain should not be less than 7m/s. With the increase of jet velocity, the smoke-proof effect of the air curtain exhibited a trend of increasing first and decreasing later, and the optimal effect was reached at a jet angle of 20°. The influence of jet velocity on the smoke-proof effect was more significant, in case of a fire source power of 25MW and a smoke exhaust rate of 100m3/s, after comprehensively considering the effect and economy of smoke-proof, it’s determined that the best smoke-proof effect could be achieved under the conditions of a jet velocity of 10m/s, and a jet angle of 20°. Our research results proposed reasonable parameters for the smoke-proof of air curtain, which had improved the economy and provided useful guidance for smoke-proof in tunnels.

Influence of Ambient Pressure over Natural Smoke Ventilation in Shaft Tunnel Fire

This paper aims to disclose the influence of different ambient pressures over the smoke flow and smoke ventilation in the shaft tunnel. For this purpose, numerical simulations were carried out on the shaft tunnel, using Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) software package. The results show that: Under the same fire power, the smoke of tunnel fire spread faster and faster, with the falling ambient pressure. The longitudinal temperature curves of tunnel fire have basically the same features, at different ambient pressures. With the increase of ambient pressure, the longitudinal smoke temperature on the roof of the shaft tunnel gradually declines. The declining rate is positively correlated with the proximity to the fire source. Compared with that in small power fire, the roof temperature difference between low pressure and normal pressure is large in large power fire. The CO concentration in the shaft falls with the rise of ambient pressure. The smoke ventilation efficiency is better in the low-pressure environment, which facilitates the ventilation of fire smoke. The increase of fire power enhances the horizontal inertial force of smoke, and reduces the probability of plug holing. In addition, the ambient pressure has a small effect on the shaft smoke ventilation in small power fire.

Temperature Distribution of Coal Mine Tunnel Fire During Dynamic Sealing Process: A Numerical Study

ABSTRACT Implementing a sealing measure on both ends of the mine tunnel fire is an important approach for fire extinguishing. In order to explore the effect of different sealing velocities on the temperature distribution of mine tunnel fire during dynamic sealing, a series of full-scale mine tunnel fire models were built using Pyrosim, and Fire Dynamics Simulator (FDS) was carried out to investigate the smoke temperature beneath the tunnel ceiling in symmetrical sealing on both ends. The results show the sealing method led to a substantial increasement of the mine tunnel ceiling temperature when the HRR was relatively small (2 MW). And with the acceleration of the sealing velocity, the time to reach the maximum temperature was earlier. However, the HRR was greater than 6 MW, the sealing velocities have less impact on the maximum ceiling temperature. Due to dynamic sealing of the mine tunnel fire with natural ventilation conditions, the ceiling temperature expressed an exponential decay along the longitudinal direction. Meanwhile, with the increase of the HRR, fire extinguishing time was generally advanced. When the sealing velocity was relatively slow, the maximum ceiling temperature exhibited a hysteresis, and the temperature of outside the sealing wall declined slowly. The research has great significance for mine tunnel fire control and rescue.

Study on smoke temperature profile in bifurcated tunnel fires with various bifurcation angles under natural ventilation

A 1:10 small-scale bifurcated tunnel including main tunnel and branch tunnel was built, and the bifurcation angle was set to 60°. 21 tests with 7 possible fire locations were carried out in the small-scale tunnel under natural ventilation. Furthermore, 32 numerical simulation cases with 8 bifurcation angles were simulated by CFD. The results indicated that: 1) the maximum ceiling temperature in the bifurcated tunnel was independent of the fire location and bifurcation angle. Only when the fire was in the bifurcation area, the maximum smoke temperature rise was slightly higher than that located in other areas of the main tunnel. 2) the longitudinal temperature attenuation of the upstream and downstream from fire source in the main tunnel was independent of the bifurcation angle. 3) If the bifurcation angle varied between 20° and 160°, when the bifurcation angle ≤ 90°, the variation of bifurcation angle had a significant effect on the longitudinal temperature distribution in the branch tunnel. However, when the bifurcation angle > 90°, the longitudinal temperature distribution in the branch tunnel almost did not vary with the change of the bifurcation angle. A prediction model for the longitudinal temperature in the branch tunnel was established by considered the effect of bifurcation angle.

Distributions and trends of the global burden of COPD attributable to risk factors by SDI, age, and sex from 1990 to 2019: a systematic analysis of GBD 2019 data

BackgroundGlobal distributions and trends of the risk-attributable burdens of chronic obstructive pulmonary disease (COPD) have rarely been systematically explored. To guide the formulation of targeted and accurate strategies for the management of COPD, we analyzed COPD burdens attributable to known risk factors.MethodsUsing detailed COPD data from the Global Burden of Disease study 2019, we analyzed disability-adjusted life years (DALYs), years lived with disability (YLDs), years of life lost (YLLs), and deaths attributable to each risk factor from 1990 to 2019. Additionally, we calculated estimated annual percentage changes (EAPCs) during the study period. The population attributable fraction (PAF) and summary exposure value (SEV) of each risk factor are also presented.ResultsFrom 1990 to 2019, the age-standardized DALY and death rates of COPD attributable to smoking and household air pollution, occupational particles, secondhand smoke, and low temperature presented consistently declining trends in almost all socio-demographic index (SDI) regions. However, the decline in YLD was not as dramatic as that of the death rate. In contrast, the COPD burden attributable to ambient particulate matter, ozone, and high temperature exposure showed undesirable increasing trends in the low- and low-middle-SDI regions. In addition, the age-standardized DALY and death rates attributable to each risk factor except household air pollution and low temperature were the highest in the low-middle-SDI region. In 2019, the COPD burden attributable to smoking ambient particulate matter, ozone, occupational particles, low and high temperature was obviously greater in males than in females. Meanwhile, the most important risk factors for female varied across regions (low- and low-middle-SDI regions: household air pollution; middle-SDI region: ambient particles; high-middle- and high-SDI region: smoking).ConclusionsIncreasing trends of COPD burden attributable to ambient particulate matter, ozone, and high temperature exposure in the low-middle- and low-SDI regions call for an urgent need to implement specific and effective measures. Moreover, considering the gender differences in COPD burdens attributable to some risk factors such as ambient particulate matter and ozone with similar SEV, further research on biological differences between sexes in COPD and relevant policy-making of disease prevention are required.

Modelling fire smoke dynamics in a stairwell of high-rise building: Effect of ambient pressure

In a high-rise building fire, vertical shafts are the main paths for hot smoke to spread to multiple floors, posing a significant fire hazard. In this work, the large eddy simulation (LES) was applied to simulate smoke dynamics in a full-scale stairwell and study the influence of ambient pressure and heat release rate (HRR). The results have shown that the air mass flow rate into the stairwell decreases as ambient pressure drops on account of the lower air velocity and density and increases with HRR because of the stronger stack effect and increased smoke production. An equation incorporating ambient pressure and HRR is proposed for predicting the air mass flow rate. The temperature of hot smoke near the fire source increases with the reduced ambient pressure, while on the floors away from the fire source, the temperature decreases due to the higher temperature attenuation at a lower pressure. In addition, an empirical model is put forward for predicting the rising time of the smoke plume considering ambient pressure. The results could increase the basic understanding of smoke movement mechanisms and contribute to engineering applications of smoke control in high-rise building fires under reduced ambient pressure conditions.

Effect of altitude on vertical temperature distribution and longitudinal smoke layer thickness in long tunnel fires

SummaryBased on large eddy simulation, a series of long tunnel fire experiments with different heat release rates (HRRs) and altitudes were carried out. The vertical temperature and thickness of fire smoke are studied. The simulation results show that the higher the altitude, the lower the flame temperature rise, while the change of smoke plume temperature rise is opposite. The movement of smoke in the tunnel can be divided into four regions, and the smoke layer thickness in the longitudinal direction of the tunnel corresponds to the latter three regions. The thickness in Region II increases along the longitudinal direction, the thickness in Region III is a constant value, and the thickness in Region IV increases along the longitudinal direction. Besides, the change of altitude only has an effect on the smoke layer thickness in Region IV. Then, by considering the altitude, HRR, and smoke layer thickness, and using dimensional analysis, an empirical formula for predicting the smoke layer thickness under the influence of altitude in Region IV was established.