Concentrations Of Toxic Gases Research Articles

Graphene ribbons based THz toxic gas sensing

In this paper, an optical chemical sensor is proposed to detect some toxic gases such as Methane (CH4), Nitrogen (N2), Nitrogen dioxide (NO2), and Carbon monoxide (CO). This type of chemical sensor consists of graphene ribbons and Kapton materials as sensing elements. Also, exploits electromagnetic properties such as absorption in terms of signal transducing. These kinds of small-scale, flexible architectures and advanced detection techniques are in demand to identify toxic gases as well. To develop the proposed chemical sensor, this study describes the structure in the aspect of an equivalent circuit model (ECM) mathematically, while the full-wave simulation (FEM) is performed as the reference. Acceptable agreement between the ECM and FEM simulations is shown while an interesting tuning capability against external stimulation is obtained. It should be noted that the ECM approach is performed in just a few seconds while the FEM simulation takes more than 3 h to produce results. In addition, the maximum error is around the second absorption peak and is less than 4%.The main contribution of this work is introducing a simple structure to distinguish several toxic gases in the sub-THz gap (0.1–2 THz). Additionally, ample simulations are performed to verify the sensor's reliability. According to the simulation results, the proposed meta-structure can appropriately show different peak frequencies and even different numbers of absorption peaks against different concentrations of toxic gases. Additionally, due to the ultra-thin nature of the graphene and the flexibility of the Kapton, the proposed sensor can be wearable while it is considered non-invasive testing.

Tin Oxide Modification of Indium Oxide Gas Sensitive Layers to Increase Efficiency of Gas Sensors

Monitoring of air pollutions is one of actual trends in the development of industrial and domestic instrumentation. There are sets of tasks for improving gas analytical instruments because of increasing demand for control of a concentration of explosive and toxic gases on a level with maximum allowable concentration. The aim of the paper was to investigate the methods of formation and elemental composition of indium oxide films modified with tin oxide on the surface of gas sensor elements as one of the promising compounds for improving the detection efficiency of explosive and toxic gases in the environment. The processes of formation of gas-sensitive films deposited on the surface of nichrome alloy information electrodes were studied in this article. Substrates of anodic aluminum oxide with area of 10 × 10 mm2 and a thickness of 45 ± 0,5 μm were chosen for research. Two layers on the surface of the samples were formed. The first layer was formed from NiCr alloy (Ni – 80 %, Cr – 20 %) with a thickness of ≈ 0.3 μm by ion-plasma sputtering. The second layer was based on indium oxide with addition of tin oxide with thicknesses from ≈ 0.3 μm to ≈ 1.0 µm and coated with sol-gel technology. Five samples of gas-sensitive films were formed with different methods of deposition and heat treatment. Scanning electron microscopy was used for study of films’ morphology and elemental compositions of samples. The most perfect continuous semiconductor films were obtained by multilayer applying of a sol-gel paste. When semiconductor films were processed at annealing temperatures of 700 °C and higher in vacuum so there was observed cracking of semiconductor films up to a layer of NiCr alloy. The developed surface of gas-sensitive films allows to reach high sensitivity and affectivity of semiconductor sensors for control of air gas composition.

Respiratory distress in Holstein cows fed corn silage: case report

An outbreak of respiratory distress was observed in Holstein cows immediately after consuming a new batch of corn-silage, presumably due to the presence of pneumotoxic gases. Signs were observed in 10% of the cows, and characterized as tachypnea, orthopneic position, cough and notable anxiety a few minutes after offering the silage. No deaths were recorded. Mild leucocytosis was observed in the hemogram. Nutritional analysis and nitrate determination of the corn-silage revealed usual values. Nitrous oxide and methane concentration were evaluated by gas chromatography and nitrogen oxides concentration directly with a portable device, resulting in acceptable values. Although high concentrations of toxic gases could not be evidenced in the air sampled on farm, the clinical signs observed coincide with those reported in cases of exposure to gases formed during corn silage processes. A greater emphasis is required in the evaluation of the corn to be ensiled, given the possible existence of factors that can generate the accumulation of potentially toxic gases for cattle that affect negatively their health and productivity.

Data-driven modeling of downwind toxic gas dispersion in lithium-ion battery failures using computational fluid dynamics

Understanding the toxicity hazard associated with lithium-ion battery systems (electric vehicles, e-mobility devices, energy storage systems, etc.) is critical due to their increasing prevalence in densely populated areas. In this work, a meta-analysis of literature data on the main toxic gas species emitted by lithium-ion batteries was conducted. The aggregated data were used as inputs to computational fluid dynamics simulations to characterize the universe of potential toxic gas concentration profiles. These simulations were run for various ambient conditions and battery characteristics. Results are reported in terms of estimated minimum safety distances based on immediately dangerous to life or health (IDLH) values, which could help inform decisions regarding effective firefighting and evacuation recommendations. A sensitivity analysis was also run to identify the key factors that influence safety distances as well as the combination of factors that led to the largest and shortest safety distances. Additionally, using toxicity data from the literature, the downwind toxicity of an internal combustion engine vehicle fire was compared to that of an electric vehicle fire. A relatively simple simulation setup was used for all simulations to make the results as general as possible.

A Study on Numerical Model Uncertainty of Smoke Concentration in Fire Simulation

The prediction accuracy of smoke concentration related to visibility in fire hazard assessment using fire simulation contains a significant error compared to gas temperature and toxic gas concentration. However, the results are limited because the prediction uncertainty of smoke concentration was reviewed through specific fuels and experimental conditions. This study conducted experiments and simulations to evaluate the prediction uncertainty of smoke concentration in the numerical model using various fire conditions. Consequently, as various fuel and experimental conditions were applied, the predicted smoke concentration using fire simulation was confirmed to have a relative error from –45% to 520% based on the measurement data. Moreover, it was also confirm that the dependence on fuel types was significant.

Respiratory function of workers at some wood factories in Bac Tu Liem district, 2022

Objectives: This study aimed to assess the respiratory function status and associated factors among workers in wood factories in Bac Tu Liem district. Methods: A total of 80 workers from six woodworking establishments participated in this cross-sectional study. Respiratory symptom questionnaires based on ECCS-87 and ATS-DLD-78a were used to collect data on symptoms experienced within the past 12 months. Respiratory function measurements were also conducted during breaks and at the end of shifts. Results: Workers with 3-5 years of experience accounted for 63.8% of the total sample. The majority (92.5%) were exposed to harmful workplace factors for more than 8 hours per day. Only 13.8% reported using full personal protective equipment. Concentrations of respiratory particles and Total Suspended Particulate (TSP) in wood facilities exceeded allowable standards. Cough was the most commonly reported respiratory symptom, with a prevalence of 28.8%. Approximately 66.3% of subjects had normal respiratory function, while restrictive ventilation disorder accounted for the highest proportion of respiratory disorders at 21.3%. Statistical analysis revealed significant associations between respiratory dysfunction and work experience (OR=2.56, p<0.01), duration of exposure to hazardous factors (OR=1.8, p<0.05), use of personal protective equipment (OR=7.12, p<0.05), and the occurrence of respiratory symptoms (OR=1.73, p<0.01). Conclusions: workers in furniture manufacturing facilities in Bac Tu Liem district face exposure to high concentrations of total particles, respiratory particles, and toxic gases that surpass permissible standards. The study also found a significant relationship between respiratory dysfunction and employee characteristics. Keywords: Respiratory function, wood workers, wood factories.

О влиянии роста давления воздуха с глубиной на расчет требуемого количества воздуха в глубоких рудниках

The effect of increasing air pressure with the depth on the calculation of the required amount of air in the deep mines is analyzed in the work. It is established that with an increase in air pressure, the values of the volumetric maximum permissible concentrations of toxic and explosive gases in it decrease, while their maximum permissible mass concentrations remain unchanged. Failure to consider the decrease in volumetric maximum allowable concentrations of toxic and explosive gases with depth when calculating the required amount of air in the mines in some cases can lead to an underestimation of air flow rates in working areas and, as a result, to an excess of maximum allowable concentrations of harmful gases. To move the same volume of air, local ventilation fans at great depths need to expend more power than at the surface. Therefore, when working at depth, it is required to use local ventilation fans with electric motors of greater power. When air is supplied to a greater depth, it is compressed and the volume flow decreases. Therefore, in order to maintain the required volumes of air at depth, it is required to increase its flow rate at the main fan installation. This should be considered when calculating the required amount of air in deep mines. The results obtained in the work can be applied in the design of deep mines and the development of methods for calculating the required amount of air for them. Based on the conducted research, the method was adjusted for calculating the amount of air used at the Glubokaya mine of the Skalisty mine of the Polar Branch of PJSC MMC Norilsk Nickel.

Assessment the Air Pollution at the some Areas in Salahaddin Governorate - Iraq

The study was conducted in Salah al-Din Governorate - northern Iraq, during the period from 1/11/2021 to 30/3/2022, with the aim of evaluating the level of pollutants in the atmospheric air for three areas: Al-Boutama (rural area), Baiji refinery (oil industry area), and the city of Tikrit (a densely populated area), the concentrations of toxic gases were measured: sulfur dioxide (SO2), nitrogen oxide (NO), nitrite (NO2), hydrochloric acid (HCl), hydrogen fluoride (HF), carbon dioxide (CO2) and carbon monoxide. (CO), using the Wolf Pack Modular Area Monitor. The results were as follows: Significant differences were found between the study sites for all the variables tested, and Baiji refinery recorded the highest values for each of the variables SO2, NO, NO2, HCl and HF, which amounted to 2.54, 8.28, 6.4, 10.62 ppm and 0.42 mg/ m3, respectively. November 2021 recorded the highest concentrations of HCl and CO compounds with averages of 7.6 ppm and 18.37 mg/m3, respectively, while January 2022 recorded the highest averages of NO2, HF and CO2, which amounted to 5.27 ppm and 0.4 mg/m3 and 791 ppm, respectively, the interaction between Baiji refinery site and the months of November, December and January recorded the highest concentrations of pollutants amounting to 4.4 ppm for SO2 concentration, 11.2 ppm for NO concentration, 7.9 ppm for NO2 concentration, 13.8 ppm for HCl concentration, and 0.7 mg/m3 for HF concentration, and 16.5 ppm for VOCs concentration.

Numerical Evaluation of Wind Speed Influence on Accident Toxic Spill Consequences Scales

This study aims to evaluate numerically the influence of wind speed on scales of environmental harmful consequences caused by accidentally spilled toxic liquid evaporated from the surface of a free-form outlined spill spot. A coupled problem of the gas-dynamic movement of a toxic air-mixture cloud in the surface layer of the atmosphere under the influence of wind and a negative toxic inhalation impact on a human in an accident zone is solved by means of mathematical modelling and computer experiment. Physical processes of toxic liquid evaporation from the spill spot, formation of a mixture of toxic gas with the incoming air, and further dispersion of a hazardous gaseous chemical in the atmosphere under various wind speed conditions are investigated. A three-dimensional non-stationary mathematical model of the turbulent movement of a gas-air mixture is used for obtaining distribution of relative mass concentration of toxic gas impurities in time and space. The model takes into account the complex terrain, compressibility of the gas flow, three-dimensional and non-stationary nature of actual physical processes, different toxic properties of chemical substances, and arbitrary contour shape of the toxic spill spot. A probabilistic harmful impact model based on using a modernized probit analysis method is used to obtain fields of the conditional probability of a fatal human injury resulting from toxic gas inhalation. This model extracts relative mass concentration of toxic gas that could cause negative impact on humans at any control point during calculation time step exposition, collects integral toxic dose values from the multicomponent gas mixture dynamics model, calculates a value of the probit function for the corresponding toxic inhalation dose dangerous factor, and automatically assesses the human fatal injury conditional probability using partial cubic Hermitian spline. This technique allows environmental safety experts assessing the scale of considered type technogenic accident consequences numerically depending on wind speed conditions and elaborating the means to mitigate them to acceptable levels.

Study of gas hazard pattern in underground workings after blasting

Determining the sources of hazardous and toxic substances released into mine air, their gas composition, as well as providing each such source of pollution with the required amount of fresh air are important issues in terms of ensuring normal healthy and safe working conditions for miners. This paper studies blasting as one of the most dangerous sources of mine air pollution. The study was carried out for a long dead-end exploration working, and a development (preparatory) working of a copper-nickel mine. In accordance with the federal rules and regulations (FNiP), a number of requirements, including monitoring of gas hazard at a face, is applied to blasting operations.The study examined the behavior of gas-air mixture in dead-end mine workings after blasting. The findings are based on the experimental data obtained in the conditions of two dead-end workings at an operating coppernickel mine. A technique for the experimental studies of gas release after blasting in a dead-end working was developed. The main technical characteristics of the instruments involved in the in-situ measurements are given. Time dependences of the concentrations of toxic gases after blasting at the blasted working mouth, at the return ventilation current, and near a booster were established. In order to assess the reliability of the data obtained, the volume of released carbon oxides was calculated based on the data of gas analyzers and chemical reactions of explosives decomposition during detonation, depending on the types and weights of the explosives. A model of gas-air mixture transfer was described, constructed, and calibrated allowing for longitudinal dispersion. The Voronin model was used to simulate the gradual removal of toxic gases from the working face and solving the problem of boundary conditions. Based on experimental data, the coefficients of longitudinal dispersion, ventilation efficiency, and volume concentration of the considered gas admixture in the mixing zone at initial time were determined for a long dead-end mine working.The constructed gas-dynamic model and longitudinal dispersion coefficients obtained as a result of the analysis enabled the time required for long dead-end mine workings ventilation to be analysed and estimated. Based on the model, the algorithm for calculating the velocity of spreading the combustion products in a mine ventilation network in emergency situations is being improved. The value of longitudinal dispersion coefficient for different operating conditions is also being refined.Based on the gas distribution simulation within the interval of 1,500 m from a working face, the time required for the ventilation of a dead-end mine working was determined.

Establishment of Control Room Habitability Analysis Methodology Postulating the Event of Pressurized Tank/System of Hazardous Gas Release

A new methodology using a free turbulent flow model to evaluate control room habitability is developed, and the theoretical model can be applied to the postulated event of rupture or line break of the on-site hazardous gas pressurized tank/system. Based on the conservation of mass law and momentum equations, correlations of the control room ventilation hazardous gas intake concentration and the control room buildup toxic concentration were established and can be used to evaluate control room habitability. Compared with current methodology widely used in the industry (introduced by NUREG-0570), the developed theoretical analysis methodology is applicable to events occurring without any constraint on the distance between the site of toxic gas release and the inlet of the control room fresh air intake or the control room. With a given amount of hazardous gas release source, the analysis results indicate that maximum control room toxic gas concentration will depend on the mass release rate or its break size, the density of the hazardous gas, and the distance between the site of the toxic release and the control room fresh air intake. The limiting case of the control room habitability analysis will occur at the break size resulting in the highest control room toxic gas concentration. The control room toxic gas transient concentration at the limiting break size can be predicted by the model and compared with its acceptance criteria of short-term exposure limit and time-weighted average to evaluate the control room habitability whether protection actions of the control room operators are required to prevent incapacitation or death due to the postulated events of toxic gas release.

A Study on the Evacuation of an Extra-Long Highway Tunnel Fire—A Case Study of Chengkai Tunnel

The smoke from tunnel fires spreads over long distances and is difficult to vent. Smoke accumulation leads to high temperatures, low visibility, and high concentrations of toxic gases, which greatly hinders the evacuation of people inside the tunnel. In this paper, a representative extra-long highway tunnel—Chengkai Tunnel—is selected as the engineering background, and a tunnel model is built using FDS and Pathfinder software to simulate the fire scenario and evacuation scenario under different longitudinal wind speeds. The concept of safe evacuation reliability is proposed to describe the relationship between the ASET (available safe egress time) and the RSET (required safe egress time). The simulation results show that with the increase in longitudinal wind speed, the ASET upstream of fire source increases first and then remains unchanged, while ASET downstream of fire source increases first and then decreases. The ASET upstream of the fire source is affected by visibility, while the ASET downstream of the fire source is affected by visibility when the wind speed is low, and is affected by temperature as the wind speed increases. The bottleneck effect is an important reason for the long evacuation time of people. The blockage time is a power function of the evacuation movement time, and increasing the width of the cross passage can improve the evacuation efficiency of the tunnel. The increase in the number of evacuees will reduce the reliability of the safe evacuation of personnel. Among all simulated scenarios, a longitudinal wind speed of 2.5 m/s has the highest safe evacuation reliability, with 0.79, 0.92, and 0.99 for scenarios R1, R2, and R3, respectively. Excessive wind speed reduces the safe evacuation reliability downstream of the fire source.

Gas sensitive performance and mechanism of multiferroic BiFeO3 under thermal-magnetic synergetic excitation

In this study, multiferroic BiFeO3 particles with size of ∼ 50 nm and good crystallinity were prepared via a simple sol–gel method and annealing. And the volatile organic compounds (VOCs) sensing properties of BiFeO3 sensor were measured under both traditional thermal excitation and synergetic thermal-magnetic excitation. In particular, auxiliary magnetic field was first introduced into testing environment. The results shows that the optimum operating temperature of the sensor decreases 10℃ by introducing magnetic field, and the sensor shows three times faster response speed and diverse selectivity with best response to n-butanol under thermal excitation while butanone under thermal-magnetic excitation. In addition, the sensor has response value of 1.25 to 1 ppm n-butanol, indicating the possibility of detecting low concentration of toxic gases. The effect of magnetic field on multiferroic BiFeO3 sensor can be divided into three aspects: decrease of defects on domain wall, excitation of testing gas molecules with asymmetry electron cloud distributions and activation of surface-absorbed oxygen species with unpaired electrons.

Impact of fine particulate matter and toxic gases on the health of school children in Dhaka, Bangladesh

Background. Air pollution exposure has a detrimental effect on children who spend more than 17% of their weekdays inside a school building. The purpose of this study is to look into the effects of particulate matter (PM) and toxic gases on health of the school children. Between April and November 2018, samples were collected in real time from ten different schools (both indoor and outdoor) over four hours on two consecutive days at each school. During the first two hours, when students were present in the classroom, measurements were conducted inside the classroom. After that the measurements were conducted outside the classroom but within the school premises - when students were playing on the playground or eating breakfast outside of classroom. Method. To evaluate the impact of air pollution, 250 students (on average 20 students from each school) aged from 9 to 12 were selected from ten schools. Automatic monitors (AEROCET 531S, USA) were employed to measure PM1.0, PM2.5, and PM10 concentrations. NO2, TVOC, and CO2 concentrations were measured using an AEROQUAL (500S, New Zealand), and the respiratory rate is measured by BSMI Peak Flow Meter (Made: BSMI, Origin: China). Monitors were placed at about 2.0 meters above the floor at breathing height and no student wore the sensors. The ANOVA test was conducted to see the statistical significance between air quality parameters and peak flow meter readings. Results. The mean ± standard deviation of PM1.0, PM2.5, and PM10 concentrations were 19.1 ± 3.6, 34.2 ± 10.1, and 131.3 ± 58.6 μgm−3, respectively. PM2.5 and PM10 concentrations exceeded WHO standards (15 and 45 μgm−3 of 24 h) by 2.3 and 2.9 times. The highest concentrations of toxic gases were found on school campuses where vehicle densities (measured manually) were high. The mean Hazard Quotient (HQ) for PM10 (2.5 ± 2.2 indoor; 3.6 ± 2.6 outdoor) and PM2.5 (1.8 ± 0.8 indoor; 1.9 ± 1.0 outdoor) among all participating students was >1 indicating an unacceptable risk for human health. Lung function associated with the PEF value has a negative correlation with PM1.0 and PM2.5 concentrations in most cases. Conclusions. The findings of this study are useful in gaining a general understanding of the school environment in Dhaka. It aimed to understand how children were personally exposed in school and to develop effective control strategies to mitigate negative effects.

Development of a risk assessment method for the detailed consideration of the effects of liquid toxic substance leakage incidents on the human body: ethanol as a model substance.

To ensure safety in chemical plants handling a wide variety of liquid and gaseous hazardous substances, it is necessary to carry out highly accurate risk assessments and take appropriate measures. In this study, a risk assessment method was developed for the problem of the leakage of liquid hazardous substances. The risk assessment of toxic liquid leaks must consider the exposure of workers to the liquid and toxic gases produced by vaporization. The absorption and subsequent metabolism of hazardous substances in the body via multiple pathways after exposure to liquids and gases was calculated using a pharmacokinetic model. Estimation of exposure concentrations of toxic gases volatilized from leaked liquids was reproduced by computational fluid dynamics simulation. In this study, ethanol was selected as the hazardous substance and the risk of hazardous liquid leakage was assessed. The results of the analysis, which considered liquid and gas exposure under the conditions of the assumed scenario, showed that the maximum blood concentration of ethanol was 1640 µmol/L, which is sufficiently low compared to the concentration of 10,900 µmol/L at which acute toxic effects become apparent. These results suggest that work can be carried out safely under the conditions of the assumed scenario. The risk assessment methodology for liquid spills in this study confirms that risk assessment is possible under multiple scenarios, including individual differences, activity conditions, and the use of protective equipment.

Luminescent Silicon Nanowires for Light-Harvesting and Environmental Sensing Applications

Silicon nanowires (Si NWs) represent one of the most promising platforms to be integrated into modern nanodevices. The fabrication of a dense array of vertically aligned ultrathin Si NWs using a low-cost, maskless approach and compatible with Si technology will be here demonstrated. Si NWs with efficient light emission at room temperature (RT) represent a great advance industry, paving the way for a wide range of unexpected photonic applications. In this work I will show the realization of a new hybrid material based on the luminescence of Si NWs and two different dyes for light-harvesting antennas applications, without any surface functionalization and with energy transfer efficiencies higher than 90%. The luminescence of Si NWs has also been used for sensing applications by the realization of highly sensitive sensors for the detecting of low concentrations of toxic gases. These sensors allow the detection of toxic gases below the threshold limits for human health, through both optical and electrical transduction. The achievement of light emission from silicon-based materials represents a revolution in the industrial field, as it paves the way for new Si applications.

Numerical Study of the Factors Affecting Evacuation in Multi-Family House Fires

In this study, a numerical analysis was conducted on the factors affecting evacuation when fires occur in multi-family houses. The parameters of fire size, growth rate, and location, as well as open or closed corridor-window conditions were considered based on empirical factors, and the results using the CFAST model were evaluated according to the life safety code for evacuation. In the fire scenario considered in this study, the concentration of toxic gases in the area in front of the entrance to the stairwell, which is an evacuation route for a multi-family house, did not exceed the life safety code. However, it was confirmed that the temperature and height of the hot gas layer did exceed the life safety code. The height of the hot gas layer exceeded the life safety code the fastest when the fire was far from the entrance to the stairwell, and the opening of the hallway windows had a significant effect on reducing the temperature in the hallway and maintaining a high smoke layer.

The Development of the Toxic and Flammable Gases Concentration Monitoring System for Coalmines

Coal mining is still an important part of the global energy complex. Despite the active development of technologies and modern equipment, coal mining remains one of the most dangerous jobs in the world. The main danger is associated with a large number of the hard-predictable factors, such as the opening of a toxic and flammable gas blister, the collapse of a mine due to a violation of the mines’ structural integrity, etc. There are software and hardware systems capable of monitoring the necessary parameters, but the problem lies in the complexity and costliness of the implementation and maintenance, so even for the largest enterprises, the widespread implementation of such systems is unprofitable. Previously conducted studies have established that most of the developed coal mining monitoring systems are very expensive to implement and labor-consuming to use and support. This article proposes to consider the developed prototype of a system for toxic and flammable gases concentration real-time monitoring, capable of reading the information with sufficient speed and transferring it to a system which triggers the response mechanism in cases where the specified concentration limits would be exceeded.

ZnO/Ti3C2 composite with oxygen vacancies and Schottky barrier for effective detection of ppb-level NO2 at room temperature

Room-temperature detection of low concentrations of toxic and harmful gases is of great significance for the health and life of human being and contributes to long-term stability and low power consumption of gas sensors. In this work, we firstly prepared a ZnO1-x/Ti3C2 composite with rich oxygen vacancies by a hydrothermal process and subsequent annealing in hydrogen atmosphere. The experimental results reveal that the ZnO1-x/Ti3C2 composite exhibits very high responses (ΔR/Ra) of 0.03, 0.21 and 2.28 to 0.01, 1 and 10 ppm NO2 at room temperature, among which the response to 10 ppm NO2 is 2.3 and 14.2 times higher than those of ZnO/Ti3C2 composite and pristine Ti3C2, respectively. Moreover, the ZnO1-x/Ti3C2 composite presents good linear response (R2 = 0.99509), reproducibility and long-term stability to NO2. The outstanding NO2 sensing properties of ZnO1-x/Ti3C2 composite are mainly attributed to the presence of abundant oxygen vacancies and the formation of ZnO1-x/Ti3C2 Schottky barrier. Both the gas responses and calculated adsorption energies of ZnO1-x/Ti3C2 and ZnO/Ti3C2 composites to NO2, NH3, CO, HCHO and acetone demonstrate the high selectivity of the ZnO1-x/Ti3C2 composite to NO2. This work provides a new perspective on enhancing the room-temperature gas sensitivity of MOS-containing composites by constructing oxygen vacancies and heterojunction.

A 3D CFD modeling for assessing the effects of both longitudinal slope and traffic volume on user safety within a naturally ventilated road tunnel in the event of a fire accident

A 3D Computational Fluid Dynamics (CFD) model was set up to investigate the effects of the longitudinal slope on the risk level of users in naturally ventilated unidirectional road tunnels in the event of a fire accident. These tunnels, which in general do not require any mechanical ventilation system, have a length <1 km and their natural ventilation is due to the difference of pressure at the portals and/or the piston effect of the unidirectional traffic flow. Fire accidents related to vehicles characterized by different maximum Heat Release Rates (HRRsmax), situated at different locations from the entrance portal of the tunnel, were simulated by varying the longitudinal slope (i), as well as by applying both a positive and negative pressure difference (ΔP) between the entrance and exit portals to also consider any adverse wind conditions, or neglecting that (i.e., ΔP = 0). The combined effects of Peak Hourly Volumes (PHVs) were also investigated in the Quantitative Risk Analysis (QRA), which based on a probabilistic approach, considered as a risk indicator the annual cumulative frequency (F) of having a certain number of potential fatalities (N). The longitudinal profiles of temperature, radiant heat flux, toxic gases concentrations, and visibility distance upstream of the burning vehicle along the escape route (i.e., sidewalks) are reported and compared with the acceptability limits to verify if the environmental conditions are tolerable for user safety while escaping from the tunnel towards the entrance portal or the emergency exit located in the middle of the tunnel length. The results showed that the number of dangerous scenarios for user safety increased in the event of adverse wind (i.e., ΔP < 0) and/or negative gradients (i.e., i < 0). The QRA indicated the combinations of i, ΔP, and PHV for which the annual cumulative frequency (F) of having a given number of potential fatalities (N) was not acceptable. By providing additional points of knowledge in the field of fire safety engineering, this paper might serve in the design of the vertical alignment of naturally ventilated tunnels with a length <1 km, as well as in the strategies of management and traffic control.