3D multi-robot olfaction in naturally ventilated indoor environments: Locating a time-varying source at unknown heights

Source localization is significant for mitigating indoor air pollution and safeguarding the well-being and safety of occupants. While most study focuses on mechanical ventilation and static sources, this study explores the less-explored domain of locating time-varying sources in naturally ventilated spaces. We have developed an innovative 3D localization system that adjusts to varying heights, significantly enhancing capabilities beyond traditional fixed-height 2D systems. To ensure consistency in experimental conditions, we conducted comparative analyses of 2D and 3D methods, using a swinging fan to simulate natural ventilation. Our findings reveal a substantial disparity in performance: the 2D method had a success rate below 46.7% in cases of height mismatches, while our 3D methods consistently achieved success rates above 66.7%, demonstrating their superior effectiveness in complex environments. Furthermore, we validated the 3D strategies in real naturally ventilated settings, confirming their wider applicability. This research extends the scope of indoor source localization and offers valuable insights and strategies for more effective pollution control.

Working with cattle slurry on farms: emission and dispersion of hydrogen sulfide gas during stirring

Over the past 15 years, there have been numerous fatalities related to working with animal slurry. Working with cattle slurry releases toxic gases, in particular, hydrogen sulphide (H2S), which can cause acute central nervous system toxicity, breathing difficulties, and death if exposed to high concentrations. Real-time measurements of H2S gas were taken over distance and time, during the stirring of cattle slurry on farms. Gas was measured at eight slurry stores with differing typical configurations of indoor or outdoor stores and with or without slatted flooring. Highest H2S gas levels were measured from indoor stores under slatted floors, and generally at positions closest to the stirrer or the point of maximum stirring, with levels decreasing with distance from source. Most of the data indicate H2S gas levels increase very rapidly after stirring starts, and mostly decline to baseline levels within 30 min post start of stirring. There were, however, circumstances where gas levels remained high and only started to decline once the stirrer had stopped. H2S gas levels at all farms, at all positions measured were consistently below 10 ppm within 30 min of the stirrer being stopped. The current data highlight areas of the farm and ways of working that have the potential for workers and others to be at risk of exposure to toxic slurry gases. The area should be left to ventilate naturally for at least 30 min after the stirrer has been stopped before re-entering buildings. Influencing the design of stirring equipment and future slurry stores would likely reduce the risk of worker exposure to slurry gases.

Numerical performance of CO2 accumulation and droplet dispersion from a cough inside a hospital lift under different ventilation strategies

The impact of mechanical ventilation on airborne diseases is not completely known. The recent pandemic of COVID-19 clearly showed that additional investigations are necessary. The use of computational tools is an advantage that needs to be included in the study of designing safe places. The current study focused on a hospital lift where two subjects were included: a healthy passenger and an infected one. The elevator was modelled with a fan placed on the middle of the ceiling and racks for supplying air at the bottom of the lateral wall. Three ventilation strategies were evaluated: a without ventilation case, an upwards-blowing exhausting fan case and a downwards-blowing fan case. Five seconds after the elevator journey began, the infected person coughed. For the risk assessment, the CO2 concentration, droplet removal performance and dispersion were examined and compared among the three cases. The results revealed some discrepancies in the selection of an optimal ventilation strategy. Depending on the evaluated parameter, downward-ventilation fan or no ventilation strategy could be the most appropriate approach.

Influence of Ventilation on Formation and Growth of 1-20 nm Particles via Ozone-Human Chemistry

Ozone reaction with human surfaces is an important source of ultrafine particles indoors. However, 1-20 nm particles generated from ozone-human chemistry, which mark the first step of particle formation and growth, remain understudied. Ventilation and indoor air movement could have important implications for these processes. Therefore, in a controlled-climate chamber, we measured ultrafine particles initiated from ozone-human chemistry and their dependence on the air change rate (ACR, 0.5, 1.5, and 3 h-1) and operation of mixing fans (on and off). Concurrently, we measured volatile organic compounds (VOCs) and explored the correlation between particles and gas-phase products. At 25-30 ppb ozone levels, humans generated 0.2-7.7 × 1012 of 1-3 nm, 0-7.2 × 1012 of 3-10 nm, and 0-1.3 × 1012 of 10-20 nm particles per person per hour depending on the ACR and mixing fan operation. Size-dependent particle growth and formation rates increased with higher ACR. The operation of mixing fans suppressed the particle formation and growth, owing to enhanced surface deposition of the newly formed particles and their precursors. Correlation analyses revealed complex interactions between the particles and VOCs initiated by ozone-human chemistry. The results imply that ventilation and indoor air movement may have a more significant influence on particle dynamics and fate relative to indoor chemistry.

Study on infection risk in a negative pressure ward under different fresh airflow patterns based on a radiation air conditioning system

COVID-19 and other respiratory infectious viruses are highly contagious, and patients need to be treated in negative pressure wards. At present, many negative pressure wards use independent air conditioning equipment, but independent air conditioning equipment has problems such as indoor air circulation flow, condensate water accumulation, and improper filter maintenance, which increase the risk of infection for healthcare workers and patients. The radiation air conditioning system relies on the radiation ceiling to control the indoor temperature and uses new air to control the indoor humidity and air quality. The problems caused by the use of independent air conditioning equipment should be avoided. This paper studies the thermal comfort, contaminant distribution characteristics, contaminant removal efficiency, and accessibility of supply air in a negative pressure ward with a radiation air conditioning system under three airflow patterns. In addition, the negative pressure ward was divided into 12 areas, and the infection probability of healthcare workers in different areas was analyzed. The results show that the application of radiation air conditioning systems in negative pressure wards can ensure the thermal comfort of patients. Stratum ventilation and ceiling-attached jets have similar effects in protecting healthcare workers; both can effectively reduce the contaminant concentrations and the risk of infection of healthcare workers. Ceiling-attached jets decreases the contaminant concentrations by 10.73%, increases the contaminant removal efficiency by 12.50%, and decreases the infection probability of healthcare workers staying indoors for 10 min by 23.18%, compared with downward ventilation.

Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment

Upper-room ultraviolet germicidal irradiation (UVGI) system is recently in the limelight as a potentially effective method to mitigate the risk of airborne virus infection in indoor environments. However, few studies quantitatively evaluated the relationship between ventilation effectiveness and virus disinfection performance of a UVGI system. The objective of this study is to investigate the effects of ventilation strategy on detailed airflow distributions and UVGI disinfection performance in an occupied classroom. Three-dimensional computational fluid dynamics (CFD) simulations were performed for representative cooling, heating, and ventilation scenarios. The results show that when the ventilation rate is 1.1 h-1 (the minimum ventilation rate based on ASHRAE 62.1), enhancing indoor air circulation with the mixing fan notably improves the UVGI disinfection performance, especially for cooling with displacement ventilation and all-air-heating conditions. However, increasing indoor air mixing yields negligible effect on the disinfection performance for forced-convection cooling condition. The results also reveal that regardless of indoor thermal condition, disinfection effectiveness of a UVGI system increases as ventilation effectiveness is close to unity. Moreover, when the room average air speed is >0.1 m/s, upper-room UVGI system could yield about 90% disinfection effect for the aerosol size of 1 μm-10 μm. The findings of this study imply that upper-room UVGI systems in indoor environments (i.e., classrooms, hospitals) should be designed considering ventilation strategy and occupancy conditions, especially for occupied buildings with insufficient air mixing throughout the space.

Heating, ventilation, and air-conditioning systems in healthcare: a scoping review

Guidelines for heating, ventilation, and air-conditioning systems have been developed for different settings. However, there is a lack of up-to-date evidence providing concrete recommendations for the heating, ventilation, and air-conditioning systems of an isolation room, which is essential to appropriately guide infection control policies. To highlight the guidelines for heating, ventilation, and air-conditioning systems in isolation rooms to inform relevant stakeholders and policymakers. A systematic search was performed based on Joanna Briggs Methodology using five databases (CINAHL, Embase, Joanna Briggs Institute, Medline, and Web of Science) and websites. Eight articles published by government departments were included in this review. Most studies recommended controlled airflow without recirculation, 12 air changes per hour, high-efficiency particulate air filtrate to exhaust contaminated air from the airborne isolation room, humidity ≤60%, and temperature in the range of 18-30 °C. This review provides further evidence that there is a need for interdisciplinary collaborative research to quantify the optimum range for heating, ventilation, and air conditioning system parameters, considering door types, anterooms, and bed management, to effectively reduce the transmission of infection in isolation rooms.

Parametric modeling study for blown-dust secondary pollution and optimal ventilation velocity during tunnel construction

Tunnel construction often relies on drilling and blasting. High dust pollution is one of the primary problems of drilling and blasting construction. The level of secondary blown dust pollution caused by ventilation matches that of dust pollution caused by drilling construction. In this study, a critical flow model and blown dust rate model for deposited dust were established via force analysis, which was validated against the test data. The research results showed that the characteristic airflow velocity for blowing dust particles with a 100 μm diameter reached approximately 0.42 m/s for tunnel diameter is 10 m, and the ventilation Re values under smooth and rough conditions were 2.3 × 105 and 1.4 × 105, respectively. Furthermore, when ventilation Re reached 4 × 105, the blown dust pollution rate caused by ventilation under smooth conditions was approximately 1.8 × 10-2 kg/s. If dust particle size is more or less the critical dust particle size, the characteristic airflow velocity was increased. Moreover, the optimal velocity at which the deposited dust does not flow or move during tunnel construction was related to the tunnel size and roughness. For the smooth tunnel with a diameter of 10 m, the optimal ventilation velocity was 3.5 m/s. When the tunnel roughness was increased from 0.005 to 0.5 m, the optimal ventilation velocity decreased from 3.3 to 1.6 m/s. The deposited dust critical flow model and blown dust pollution rate model established in this study provide a sound theoretical basis for selecting the optimal velocity of tunnel ventilation and recognizing the risks of secondary blown dust pollution due to ventilation.

Refined design of ventilation systems to mitigate infection risk in hospital wards: Perspective from ventilation openings setting

To prevent respiratory infections between patients and medical workers, the transmission risk of airborne pollutants in hospital wards must be mitigated. The ventilation modes, which are regarded as an important strategy to minimize the infection risk, are challenging to be systematically designed. Studies have considered the effect of ventilation openings (inlets/outlets) or infected source locations on the airflow distribution, pollutant removal, and infection risk mitigation. However, the relationship (such as relative distance) between ventilation openings and infected sources is critical because it affects the direct exhaust of exhaled pollutants, which has not been thoroughly studied. To explore pollutant removal and infection prevention in wards, different ventilation modes (with varying ventilation openings) and infected patient locations must be jointly considered. This study investigated displacement ventilation (DV), downward ventilation (DWV), and stratum ventilation (SV) with 4, 6, and 10 scenarios of ventilation openings, respectively. The optimal ventilation mode and relative distance between outlets and infected patients were analyzed based on the simulated pollutant concentration fields and the evaluated infection risk. The pollutant removal effect and infection risk mitigation of SV in the ward were largely improved by 75% and 59% compared with DV and DWV, respectively. The average infection risk was reduced below 7% when a non-dimensional relative distance (a ratio of the actual distance to the cubic root of the ward volume) was less than 0.25 between outlets and infected patient. This study can serve as a guide for the systematic ventilation system design in hospitals during the epidemic.

Meta-Analysis of the Effect of Ventilation on Intellectual Productivity

Indoor air quality (IAQ) influences the health and intellectual productivity of occupants. This paper summarizes studies investigating the relationship between intellectual productivity and IAQ with varying ventilation rates. We conducted a meta-analysis of five studies, with a total of 3679 participants, and performed subgroup analyses (arithmetic, verbal comprehension, and cognitive ability) based on the type of academic performance. The task performance speed and error rate were evaluated to measure intellectual productivity. The effect size of each study was evaluated using the standardized mean difference (SMD). In addition, we calculated a dose-response relationship between ventilation rate and intellectual productivity. The results show that the task performance speed improved, SMD: 0.18 (95% CI: 0.10-0.26), and the error rate decreased, SMD: -0.05 (95% CI: -0.11-0.00), with an increase in ventilation rate. Converting the intervention effect size on the SMD into the natural units of the outcome measure, our analyses show significant improvements in the task performance speed: 13.7% (95% CI: 6.2-20.5%) and 3.5% (95% CI: 0.9-6.1%) in terms of arithmetic tasks and cognitive ability, respectively. The error rate decreased by -16.1% (95% CI: -30.8-0%) in arithmetic tasks. These results suggest that adequate ventilation is necessary for good performance.

Indoor air surveillance and factors associated with respiratory pathogen detection in community settings in Belgium

Currently, the real-life impact of indoor climate, human behaviour, ventilation and air filtration on respiratory pathogen detection and concentration are poorly understood. This hinders the interpretability of bioaerosol quantification in indoor air to surveil respiratory pathogens and transmission risk. We tested 341 indoor air samples from 21 community settings in Belgium for 29 respiratory pathogens using qPCR. On average, 3.9 pathogens were positive per sample and 85.3% of samples tested positive for at least one. Pathogen detection and concentration varied significantly by pathogen, month, and age group in generalised linear (mixed) models and generalised estimating equations. High CO2 and low natural ventilation were independent risk factors for detection. The odds ratio for detection was 1.09 (95% CI 1.03-1.15) per 100 parts per million (ppm) increase in CO2, and 0.88 (95% CI 0.80-0.97) per stepwise increase in natural ventilation (on a Likert scale). CO2 concentration and portable air filtration were independently associated with pathogen concentration. Each 100ppm increase in CO2 was associated with a qPCR Ct value decrease of 0.08 (95% CI -0.12 to -0.04), and portable air filtration with a 0.58 (95% CI 0.25-0.91) increase. The effects of occupancy, sampling duration, mask wearing, vocalisation, temperature, humidity and mechanical ventilation were not significant. Our results support the importance of ventilation and air filtration to reduce transmission.

The Influence of Ventilation Measures on the Airborne Risk of Infection in Schools: A Scoping Review

OBJECTIVES

To review the risk of airborne infections in schools and evaluate the effect of intervention measures reported in field studies.

BACKGROUND

Schools are part of a country's critical infrastructure. Good infection prevention measures are essential for reducing the risk of infection in schools as much as possible, since these are places where many individuals spend a great deal of time together every weekday in a small area where airborne pathogens can spread quickly. Appropriate ventilation can reduce the indoor concentration of airborne pathogens and reduce the risk of infection.

METHODS

A systematic search of the literature was conducted in the databases Embase, MEDLINE, and ScienceDirect using keywords such as school, classroom, ventilation, carbon dioxide (CO2) concentration, SARS-CoV-2, and airborne transmission. The primary endpoint of the studies selected was the risk of airborne infection or CO2 concentration as a surrogate parameter. Studies were grouped according to the study type.

RESULTS

We identified 30 studies that met the inclusion criteria, six of them intervention studies. When specific ventilation strategies were lacking in schools being investigated, CO2 concentrations were often above the recommended maximum values. Improving ventilation lowered the CO2 concentration, resulting in a lower risk of airborne infections.

CONCLUSIONS

The ventilation in many schools is not adequate to guarantee good indoor air quality. Ventilation is an important measure for reducing the risk of airborne infections in schools. The most important effect is to reduce the time of residence of pathogens in the classrooms.

Quantitative evaluation method of smoke exhaust performance and application on exhaust volume optimization in tunnel fires under lateral centralized mode

This study investigated the indicators in the quantitative method of evaluating the smoke exhaust performance, which provided a theoretical basis for the optimization of the smoke extraction system under the lateral centralized mode in tunnel fires. The criterion was proposed for plug-holing, and the theoretical models of smoke exhaust efficiency were established to distinguish whether the plug-holing occurs or not. The relationship between efficiency, effectiveness, and efficacy was analyzed from the perspective of smoke and heat exhaust. Meanwhile, this evaluation method was applied to the optimization of exhaust volume in a practical engineering through FDS numerical simulation. The results show that Ri is a vital basis for reflecting the movement form of smoke and the exhaust effect. The critical value of Ri is 1.09 when plug-holing occurs in a standard three-lane immersed tunnel, resulting in a significant reduction in the efficiency of smoke exhaust. The greater the exhaust volume of the exhaust fan, the greater the Ri value, the higher the total smoke and heat exhaust efficiency, and the better the exhaust effectiveness of smoke inlets without plug-holing. Under longitudinal ventilation, the optimal exhaust volume is 180 m³/s at 20 MW and 360 m³/s at 50 MW in the application case.

Response to the COVID-19 Pandemic in Classrooms at the University of the Basque Country through a User-Informed Natural Ventilation Demonstrator

The COVID-19 pandemic has generated a renewed interest in indoor air quality to limit viral spread. In the case of educational spaces, due to the high concentration of people and the fact that most of the existing buildings do not have any mechanical ventilation system, the different administrations have established natural ventilation protocols to guarantee an air quality that reduces risk of contagion by the SARS-CoV-2 virus after the return to the classrooms. Many of the initial protocols established a ventilation pattern that opted for continuous or intermittent ventilation to varying degrees of intensity. This study, carried out on a university campus in Spain, analyses the performance of natural ventilation activated through the information provided by monitoring and visualisation of real-time data. In order to carry out this analysis, a experiment was set up where a preliminary study of ventilation without providing information to the users was carried out, which was then compared with the result of providing live feedback to the occupants of two classrooms and an administration office in different periods of 2020, 2021 and 2022. In the administration office, a CO2-concentration-based method was applied retrospectively to assess the risk of airborne infection. This experience has served as a basis to establish a route for user-informed improvement of air quality in educational spaces in general through low-cost systems that allow a rational use of natural ventilation while helping maintain an adequate compromise between IAQ, comfort and energy consumption, without having to resort to mechanical ventilation systems.

Airplane cabin mixing ventilation with time-periodic supply: Contaminant mass fluxes and ventilation efficiency

Airplane cabin ventilation is essential to ensure passengers' well-being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time-periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time-periodic mixing ventilation in a section of a single-aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time-periodic supply strategies are evaluated. The induced time-periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.

Current and potential approaches on assessing airflow and particle dispersion in healthcare facilities: a systematic review

An indoor environment in a hospital building requires a high indoor air quality (IAQ) to overcome patients' risks of getting wound infections without interrupting the recovery process. However, several problems arose in obtaining a satisfactory IAQ, such as poor ventilation design strategies, insufficient air exchange, improper medical equipment placement and high door opening frequency. This paper presents an overview of various methods used for assessing the IAQ in hospital facilities, especially in an operating room, isolation room, anteroom, postoperative room, inpatient room and dentistry room. This review shows that both experimental and numerical methods demonstrated their advantages in the IAQ assessment. It was revealed that both airflow and particle tracking models could result in different particle dispersion predictions. The model selection should depend on the compatibility of the simulated result with the experimental measurement data. The primary and secondary forces affecting the characteristics of particle dispersion were also discussed in detail. The main contributing forces to the trajectory characteristics of a particle could be attributed to the gravitational force and drag force regardless of particle size. Meanwhile, the additional forces could be considered when there involves temperature gradient, intense light source, submicron particle, etc. The particle size concerned in a healthcare facility should be less than 20 μm as this particle size range showed a closer relationship with the virus load and a higher tendency to remain airborne. Also, further research opportunities that reflect a more realistic approach and improvement in the current assessment approach were proposed.

Effects of medical staff's turning movement on dispersion of airborne particles under large air supply diffuser during operative surgeries

The present study examines the effect of medical staff's turning movements on particle concentration in the surgical zone and settlement on the patient under single large diffuser (SLD) ventilation. A computational domain representing the operating room (OR) was constructed using computer-aided design (CAD) software. The airflow and particle models were validated against the published data before conducting the case studies. The airflow in the OR was simulated using an RNG k-ε turbulence model, while the dispersion of the particles was simulated using a discrete phase model based on the Lagrangian approach. A user-defined function (UDF) code was written and compiled in the simulation software to describe the medical staff member's turning movements. In this study, three cases were examined: baseline, SLD 1, and SLD 2, with the air supply areas of 4.3 m², 5.7 m², and 15.9 m², respectively. Results show that SLD ventilations in an OR can reduce the number of dispersed particles in the surgical zone. The particles that settled on the patient were reduced by 41% and 39% when using the SLD 1 and SLD 2 ventilations, respectively. The use of the larger air supply area of SLD 2 ventilation in the present study does not significantly reduce the particles that settle on a patient. Likewise, the use of SLD 2 ventilation may increase operating and maintenance costs.

Heating Control Strategy Based on Dynamic Programming for Building Energy Saving and Emission Reduction

Finding the optimal balance between end-user's comfort, lifestyle preferences and the cost of the heating, ventilation and air conditioning (HVAC) system, which requires intelligent decision making and control. This paper proposes a heating control method for HVAC based on dynamic programming. The method first selects the most suitable modeling approach for the controlled building among three machine learning modeling techniques by means of statistical performance metrics, after which the control of the HVAC system is described as a constrained optimization problem, and the action of the controller is given by solving the optimization problem through dynamic programming. In this paper, the variable 'thermal energy storage in building' is introduced to solve the problem that dynamic programming is difficult to obtain the historical state of the building due to the requirement of no aftereffect, while the room temperature and the remaining start hours of the Primary Air Unit are selected to describe the system state through theoretical analysis and trial and error. The results of the TRNSYS/Python co-simulation show that the proposed method can maintain better indoor thermal environment with less energy consumption compared to carefully reviewed expert rules. Compared with expert rule set 'baseline-20 °C', which keeps the room temperature at the minimum comfort level, the proposed control algorithm can save energy and reduce emissions by 35.1% with acceptable comfort violation.

A Study of the Plan and Performance Evaluation Method of an 8-m3 Chamber Using Ventilation Experiments and Numerical Analyses

With increases in the time spent on indoor activities, the interests and technological demands regarding indoor air quality (IAQ) have also increased. Indoor air pollution is often caused by furniture or construction materials and chemical substances, such as volatile organic compounds (VOCs). As a way to remove such pollutants, efforts have been made to promote the management of indoor air quality through emission experiments. To conduct an experiment, such as the pollutant emission experiment involving substances harmful to the human body, a chamber to control various factors should be developed. By using such chambers, experimental variables can be minimized, quantitative analyses may be conducted, and the basic theory may be discussed. When the chamber is installed, it is not easy to change the existing installed conditions. Therefore, it is necessary to review feasibility with an accurate design. However, there is limited research on both how to quantitatively design the chamber and evaluate it. Therefore, this study investigates suitable chamber design methods and performance through ventilation performance evaluation to discuss potential development methods. In the chamber design step, a computational fluid dynamics (CFD) analysis was performed to estimate the ventilation efficiency according to the inlet and outlet positions to develop an 8-m³ chamber. Next, a ventilation experiment was performed using the tracer gas method for the performance evaluation, while the chamber interior airflow was simulated based on the CFD analysis. In a ventilation experiment using a tracer gas, the variation in gas density leads to concentration imbalance; as a result of concentration imbalance at each point, errors may occur in ventilation efficiency depending on the measurement point, causing the accuracy of the performance evaluation to fall. An attempt was made to resolve this problem by performing the ventilation experiment with a ceiling fan. The result indicated that the performance evaluation could be conducted without altering ventilation efficiency, coinciding with the CFD analysis result. Furthermore, when the concentration field was examined according to time in the CFD analysis, uniform concentration of chamber interior air allowed the ventilation efficiency to be calculated irrespective of the measurement point. Based on the findings, this study suggests a quantitative method of performance evaluation with an experiment in an 8-m³ chamber and a concurrent CFD analysis.

Effects of Return Air Inlets' Location on the Control of Fine Particle Transportation in a Simulated Hospital Ward

The COVID-19 pandemic has made significant impacts on public health, including human exposure to airborne pathogens. In healthcare facilities, the locations of return air vents in ventilation systems may have important effects on lowering airborne SARS-CoV-2 transmission. This study conducted experiments to examine the influence of different return air vents' heights (0.7 m, 1.2 m, and 1.6 m) on the particle removal effects in a simulated patient ward. Three different ventilation systems were examined: top celling air supply-side wall return (TAS), underfloor air supply-side wall return (UFAS) and side wall air supply-side wall return (SAS). CFD simulation was applied to further study the effects of return air inlets' heights (0.3 m, 0.7 m, 1.2 m, 1.6 m, and 2.0 m) and air exchange rates. The technique for order of preference by similarity to ideal solution (TOPSIS) analysis was used to calculate the comprehensive scores of 60 scenarios using a multi-criterion method to obtain the optimal return air inlets' heights. Results showed that for each additional 0.5 m distance in most working conditions, the inhalation fraction index of medical staff could be reduced by about 5-20%. However, under certain working conditions, even though the distances between the patients and medical personnel were different, the optimal heights of return air vents were constant. For TAS and UFAS, the optimal return air inlets' height was 1.2 m, while for SAS, the best working condition was 1.6 m air supply and 0.7 m air return. At the optimum return air heights, the particle decay rate per hour of SAS was 75% higher than that of TAS, and the rate of particle decay per hour of SAS was 21% higher than that of UFAS. The location of return air inlets could further affect the operating cost-effectiveness of ventilation systems: the highest operating cost-effectiveness was 8 times higher than the lowest one.

Contaminant removal and contaminant dispersion of air distribution for overall and local airborne infection risk controls

Proper air distribution is crucial for airborne infection risk control of infectious respiratory diseases like COVID-19. Existing studies evaluate and compare the performances of different air distributions for airborne infection risk control, but the mechanisms of air distribution for airborne infection risk control remain unclear. This study investigates the mechanisms of air distribution for both overall and local airborne infection risk controls. The experimentally validated CFD models simulate the contaminant concentration fields in a hospital ward based on which the airborne infection risks of COVID-19 are evaluated with the dilution-based expansion of the Wells-Riley model. Different air distributions, i.e., stratum ventilation, displacement ventilation, and mixing ventilation, with various supply airflow rates are tested. The results show that the variations of the overall and local airborne infection risks under different air distributions and different supply airflow rates are complicated and non-linear. The contaminant removal and the contaminant dispersion are proposed as the mechanisms for the overall and local airborne infection risk controls, respectively, regardless of airflow distributions and supply airflow rates. A large contaminant removal ability benefits the overall airborne infection risk control, with the coefficient of determination of 0.96 between the contaminant removal index and the reciprocal of the overall airborne infection risk. A large contaminant dispersion ability benefits the local airborne infection risk control, with the coefficient of determination of 0.99 between the contaminant dispersion index and the local airborne infection risk.

Effectiveness of air-purifying devices and measures to reduce the exposure to bioaerosols in school classrooms

The SARS-CoV-2 pandemic, which suddenly appeared at the beginning of 2020, revealed our knowledge deficits in terms of ventilation and air pollution control. It took many weeks to realize that aerosols are the main route of transmission. The initial attempt to hold back these aerosols through textile masks seemed almost helpless, although there is sufficient knowledge about the retention capacity of fabric filters for aerosols. In the absence of a sufficient number of permanently installed heating, ventilation, and air conditioning systems, three main approaches are pursued: (a) increasing the air exchange rate by supplying fresh air, (b) using mobile air purifiers, and (c) disinfection by introducing active substances into the room air. This article discusses the feasibility of these different approaches critically. It also provides experimental results of air exchange measurements in a school classroom that is equipped with a built-in fan for supplying fresh air. With such a fan and a window tilted at the appropriate distance, an air exchange rate of 5/h can be set at a low power level and without any significant noise pollution. Heat balance calculations show that no additional heat exchanger is necessary in a normal classroom with outside temperatures above 10°C. Furthermore, a commercial mobile air purifier is studied in a chamber and a test room setup in order to examine and evaluate the efficiency of such devices against viable viruses under controlled and realistic conditions. For this purpose, bacteriophages of the type MS2 are used. Both window ventilation and air purifiers were found to be suitable to reduce the concentration of phages in the room.

Role of ventilation on the transmission of viruses in buildings, from a single zone to a multizone approach

In a virus pandemic context, buildings ventilation has been recognized as a solution for preventing transmission of the virus in aerosolized form. The impact of the widespread recommendation of window opening and sealing door on ventilation circuits needs to be considered with a multizone approach. We modeled the airflow distribution in a building where people are isolating in a pandemic context, including one infected person. We analyzed the impact of opening the window and sealing the door in the quarantine room on exposures and probability of infection for occupants of the flat and of adjacent flats. In order to study the sensitivity of the results, we tested three ventilation systems: balanced, exhaust-only, and humidity-based demand-controlled, and several window- and door-opening strategies. When the door of the quarantine room is sealed, we observe that opening the window in the quarantine room always results in increased exposure and probability of infection for at least one other occupant, including in neighbors' apartments. When all internal doors are opened, we observe moderate impacts, with rather an increase of exposure of the occupants of the same apartments and of their probability of infection, and a decrease for the occupants located in other apartments. Based on the analysis on the airflows distribution in this case study, we conclude that sealing the internal door has more influence than opening the window of the quarantine room, whatever the ventilation system. We observe that this widespread recommendation to open the window of a quarantine room and to seal the door is based on the consideration of a single zone model. We illustrate the importance of moving from such a single zone approach to a multizone approach for quantifying ventilation and airing impacts in multizone buildings as residences in order to prevent epidemics of viruses such as SARS-CoV-2. It highlights the need of air leakage databases.

Zonal model for predicting contaminant distribution in stratum ventilated rooms

Accurate prediction of the non-uniform contaminant distribution under stratum ventilation (SV) is crucial for optimal design for reducing contaminant exposure risks. Compared with experiments and computational fluid dynamics, zonal models are convenient to implement. This study proposes a zonal model for predicting dynamic non-uniform contaminant distribution in the stratum ventilated room. The zoning method is based on the unique airflow pattern under SV, and the room is divided into the jet zone, entrainment zone, and the mixing zone. The interzonal airflow rate is derived from the profile of the supply air jet. The results show that the proposed zonal model can predict the dynamic contaminant distribution in the stratum ventilated room. Compared with the experimental measurement, the predictions show good accuracy with the mean absolute error (MAE) at 0.51-2.36 ppm and root mean squared error (RMSE) at 0.64-2.53 ppm. The error of the proposed zonal model is influenced by the degree of mixing in each subzone. The proposed zonal model shows better accuracy for non-uniform air distribution under stratum ventilation compared with the existing zonal model.

Assessment of university classroom ventilation during the COVID-19 pandemic

Ventilation plays an important role in mitigating the risk of airborne virus transmission in university classrooms. During the early phase of the COVID-19 pandemic, methods to assess classrooms for ventilation adequacy were needed. The aim of this paper was to compare the adequacy of classroom ventilation determined through an easily accessible, simple, quantitative measure of air changes per hour (ACH) to that determined through qualitative "expert judgment" and recommendations from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and the American Conference of Governmental Industrial Hygienists (ACGIH)®. Two experts, ventilation engineers from facilities maintenance, qualitatively ranked buildings with classrooms on campus with regard to having "acceptable classroom ventilation." Twelve lecture classrooms were selected for further testing, including a mix of perceived adequate/inadequate ventilation. Total air change per hour (ACH) was measured to quantitatively assess ventilation through the decay of carbon dioxide in the front and rear of these classrooms. The outdoor ACH was calculated by multiplying the total ACH by the outdoor air fraction. The classrooms in a building designed to the highest ASHRAE standards (62.1 2004) did not meet ACGIH COVID-19 recommendations. Four of the classrooms met the ASHRAE criteria. However, a classroom that was anticipated to fail based on expert knowledge met the ASHRAE and ACGIH criteria. Only two classrooms passed stringent ACGIH recommendations (outdoor ACH > 6). None of the classrooms that passed ACGIH criteria were originally expected to pass. There was no significant difference in ACH measured in the front and back of classrooms, suggesting that all classrooms were well mixed with no dead zones. From these results, schools should assess classroom ventilation considering a combination of classroom design criteria, expert knowledge, and ACH measurements.

Changing Patterns of the Flow Ratio with the Distance of Exhaust and Supply Hood in a Parallel Square Push-Pull Ventilation

The method of flow ratio k is often used for designing parallel push-pull ventilation. The k value is mostly selected empirically and is difficult to determine accurately, resulting in an imprecise design of the push-pull ventilation system. Therefore, parallel push-pull ventilation was taken as the research object in this paper. The push-pull ventilation studied consists of a square uniform supply hood and a square uniform exhaust hood, and the side length of pull hood and pull hood was same. A workbench was set between the push hood and pull hood, and the source of toluene pollutions was set in the center of the worktable surface. The optimal k values for different distances between push hood and pull hood were studied by numerical simulation using Ansys Fluent, which were obtained base on the distribution of wind speed and toluene concentration. The results showed that parallel push-pull ventilation is not suitable for applications when L/a ≥ 6. The changing patterns of k value with L/a is proposed in the range of 1.5 ≤ L/a ≤ 5 for the parallel square push-pull ventilation, which can be used to estimate k value relatively accurately under the condition that L/a is known, so as to guide the determination of the exhaust air volume of the parallel push-pull ventilation system.

Effects of press-in airflow rate and the distance between the pressure duct and the side wall on ventilation dust suppression performance in an excavating tunnel

The efficiency of mine excavation has been significantly enhanced by continuing improvements in tunneling capabilities; however, this has also resulted in serious environmental pollution and greater safety risks for workers. To ensure safe production, the focus of this study is on the effect of varying the air pressure and the distance between the air pressure cylinder and the side wall settings on dust dispersion behavior and dust control in excavated tunnels. We also investigated temporal-spatial dust diffusion rules in tunnels by combining numerical simulation data with field measurement results. Through further analysis, when the pressure air volume and the exhaust air volume are both equal to 250 m³/min, the dust diffusion distance could be fitted as: [Formula: see text]. When the exhaust air volume is equal to 250 m³/min, dust control effects were improved as the pressure air volume decreased, becoming optimal when the pressure air volume dropped to 150 m³/min. Under these conditions, areas of high dust pollution were contained within 16 m of the cutting face, and the dust diffusion distance satisfied the formula: [Formula: see text]. When the pressure air volume is fixed, the change of the distance between the pressure air cylinder and the side wall has little effect on the dust diffusion. When the distance is 1.5 m, the dust control effect is the best, and the high dust pollution area is controlled within 14 m of the cutting surface. This alleviated dust pollution to a certain degree, thereby enhancing the air quality and ensuring safer production. This study provides a new understanding of the environmentally sustainable development of tunnels and is of great significance for clean production.

Combined effects of ventilation rates and indoor temperatures on cognitive performance of female higher education students in a hot climate

Impairment in mental functions attributed to the effects of indoor air quality and thermal conditions has received considerable attention in the past decade, particularly for educational buildings where students' cognitive performance is essential to foster learning. This study explores the combined effects of indoor temperatures and CO₂  levels as markers for ventilation rates on cognitive performance among female students (16-23 years old) in Saudi Arabia. The longitudinal experiments involved nine conditions combining three CO₂ concentration levels (achieved via changes in ventilation) and three temperature levels involving 499 participants, all exposed to the nine conditions. The study implemented a computer-based cognitive performance battery with "9Button" keyboards. Univariable and multivariable multilevel regression models explored the association of indoor temperature and CO₂  levels (as markers for ventilation rates) with cognitive performance after adjusting for potential confounders. Potential benefits were found on speed and accuracy of tasks of cognitive performance when indoor temperature was set between 20 and 23ºC and at CO₂  levels of 600 ppm compared to higher temperatures and poorer ventilation rates and that both ventilation and thermal environmental control are important and need to be improved for achieving optimum learning conditions. Nevertheless, the results are relevant for short-term exposures lasting no more than 2 h.

The risk of indoor sports and culture events for the transmission of COVID-19

Nearly all mass gathering events worldwide were banned at the beginning of the COVID-19 pandemic, as they were suspected of presenting a considerable risk for the transmission of SARS-CoV-2. We investigated the risk of transmitting SARS-CoV-2 by droplets and aerosols during an experimental indoor mass gathering event under three different hygiene practices, and used the data in a simulation study to estimate the resulting burden of disease under conditions of controlled epidemics. Our results show that the mean number of measured direct contacts per visitor was nine persons and this can be reduced substantially by appropriate hygiene practices. A comparison of two versions of ventilation with different air exchange rates and different airflows found that the system which performed worst allowed a ten-fold increase in the number of individuals exposed to infectious aerosols. The overall burden of infections resulting from indoor mass gatherings depends largely on the quality of the ventilation system and the hygiene practices. Presuming an effective ventilation system, indoor mass gathering events with suitable hygiene practices have a very small, if any, effect on epidemic spread.

The risk of indoor sports and culture events for the transmission of COVID-19

Nearly all mass gathering events worldwide were banned at the beginning of the COVID-19 pandemic, as they were suspected of presenting a considerable risk for the transmission of SARS-CoV-2. We investigated the risk of transmitting SARS-CoV-2 by droplets and aerosols during an experimental indoor mass gathering event under three different hygiene practices, and used the data in a simulation study to estimate the resulting burden of disease under conditions of controlled epidemics. Our results show that the mean number of measured direct contacts per visitor was nine persons and this can be reduced substantially by appropriate hygiene practices. A comparison of two versions of ventilation with different air exchange rates and different airflows found that the system which performed worst allowed a ten-fold increase in the number of individuals exposed to infectious aerosols. The overall burden of infections resulting from indoor mass gatherings depends largely on the quality of the ventilation system and the hygiene practices. Presuming an effective ventilation system, indoor mass gathering events with suitable hygiene practices have a very small, if any, effect on epidemic spread.

The application value of operating room ventilation with laminar airflow for surgical site infection: A protocol for a systematic review and meta-analysis

BACKGROUND

The presence of biological particles in the air inside operating theatres has the potential to cause severe surgical site infections. Recently, laminar airflow systems have been regarded as a means to reducing surgical site infections using airborne microbes. Still, other publications have argued the benefits of laminar airflow systems, stating the likelihood of adverse effects. Therefore, we will conduct this systematic study to evaluate the applicational value of adopting laminar airflow systems in operating theatres to minimize surgical site infections.

METHODS

Reporting of this study adheres to the guidelines of Preferred Reporting Items for Systematic Review and Meta-analysis Protocols. The authors will perform a systematic search on MEDLINE, Web of Science, EMBASE, the China national knowledge infrastructure, and the Cochrane Library from their commencement until June 2021. The search will identify relevant randomized and non-randomized controlled trials that evaluates the applicational value of using laminar airflow ventilation in surgical theatres to minimize surgical site infections. There are no restrictions on language. Two authors will independently screen the identified studies, perform data extraction, and use an appropriate method to evaluate the bias risk in the included studies.

RESULTS

The work done in the present study will enhance the existing literature on the applicational value of laminar airflow ventilation in surgical theatre to reduce surgical site infections.

CONCLUSION

The outcomes are a reference for healthcare practitioners and patients when making informed decisions regarding care during surgeries.

[Is it really an acute respiratory distress syndrome? : Current definitions, pathophysiology and differentiated diagnoses]

Although the Berlin definition of the acute respiratory distress syndrome (ARDS) is generally recognized, the differentiation from other diseases with severe gas exchange disturbances is often difficult in clinical practice. In particular, the assessment of radiological findings and identification of primary noncardiogenic lung edema pose problems. In ARDS typical inflammatory processes can be found with involvement of activated neutrophilic granulocytes. Anti-inflammatory treatment strategies were unsuccessful. Lung protective ventilation strategies and prone positioning are the only evidence-based treatment options. Identifying ARDS phenotypes according to the etiology or disease progression can possibly provide a targeted individualized treatment option. The control of various biomarkers for assessment and treatment is the main focus of scientific interest. The results of appropriate studies remain to be seen.

Modeling of aerosol transmission of airborne pathogens in ICU rooms of COVID-19 patients with acute respiratory failure

The COVID-19 pandemic has generated many concerns about cross-contamination risks, particularly in hospital settings and Intensive Care Units (ICU). Virus-laden aerosols produced by infected patients can propagate throughout ventilated rooms and put medical personnel entering them at risk. Experimental results found with a schlieren optical method have shown that the air flows generated by a cough and normal breathing were modified by the oxygenation technique used, especially when using High Flow Nasal Canulae, increasing the shedding of potentially infectious airborne particles. This study also uses a 3D Computational Fluid Dynamics model based on a Lattice Boltzmann Method to simulate the air flows as well as the movement of numerous airborne particles produced by a patient's cough within an ICU room under negative pressure. The effects of different mitigation scenarii on the amount of aerosols potentially containing SARS-CoV-2 that are extracted through the ventilation system are investigated. Numerical results indicate that adequate bed orientation and additional air treatment unit positioning can increase by 40% the number of particles extracted and decrease by 25% the amount of particles deposited on surfaces 45s after shedding. This approach could help lay the grounds for a more comprehensive way to tackle contamination risks in hospitals, as the model can be seen as a proof of concept and be adapted to any room configuration.

Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event

During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the aerosol route is likely; it appears unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases. It is vital to identify features of cases such as this to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was dominated by inhalation of respiratory aerosol generated by one index case, we use the available evidence to infer the emission rate of aerosol infectious quanta. We explore how the risk of infection would vary with several influential factors: ventilation rate, duration of event, and deposition onto surfaces. The results indicate a best-estimate emission rate of 970 ± 390 quanta/h. Infection risk would be reduced by a factor of two by increasing the aerosol loss rate to 5 h^-1 and shortening the event duration from 2.5 to 1 h.

Transmission of SARS-CoV-2 by inhalation of respiratory aerosol in the Skagit Valley Chorale superspreading event

During the 2020 COVID-19 pandemic, an outbreak occurred following attendance of a symptomatic index case at a weekly rehearsal on 10 March of the Skagit Valley Chorale (SVC). After that rehearsal, 53 members of the SVC among 61 in attendance were confirmed or strongly suspected to have contracted COVID-19 and two died. Transmission by the aerosol route is likely; it appears unlikely that either fomite or ballistic droplet transmission could explain a substantial fraction of the cases. It is vital to identify features of cases such as this to better understand the factors that promote superspreading events. Based on a conditional assumption that transmission during this outbreak was dominated by inhalation of respiratory aerosol generated by one index case, we use the available evidence to infer the emission rate of aerosol infectious quanta. We explore how the risk of infection would vary with several influential factors: ventilation rate, duration of event, and deposition onto surfaces. The results indicate a best-estimate emission rate of 970 ± 390 quanta/h. Infection risk would be reduced by a factor of two by increasing the aerosol loss rate to 5 h^-1 and shortening the event duration from 2.5 to 1 h.

Could the ductless personalized ventilation be an alternative to the regular ducted personalized ventilation?

This study investigates the performance of two systems: personalized ventilation (PV) and ductless personalized ventilation (DPV). Even though the literature indicates a compelling performance of PV, it is not often used in practice due to its impracticality. Therefore, the present study assesses the possibility of replacing the inflexible PV with DPV in office rooms equipped with displacement ventilation (DV) in the summer season. Numerical simulations were utilized to evaluate the inhaled concentration of pollutants when PV and DPV are used. The systems were compared in a simulated office with two occupants: a susceptible occupant and a source occupant. Three types of pollution were simulated: exhaled infectious air, dermally emitted contamination, and room contamination from a passive source. Results indicated that PV improved the inhaled air quality regardless of the location of the pollution source; a higher PV supply flow rate positively impacted the inhaled air quality. Contrarily, the performance of DPV was highly sensitive to the source location and the personalized flow rate. A higher DPV flow rate tends to decrease the inhaled air quality due to increased mixing of pollutants in the room. Moreover, both systems achieved better results when the personalized system of the source occupant was switched off.

Research on a personalized targeted air supply device based on body movement capture

Unlike general ventilation, personalized ventilation can improve thermal comfort and conserve energy based on individual differences. It can also provide every individual the ability to control fresh air exposure and ensure good indoor air quality. However, determining how to improve air supply efficiency while avoiding a draft sensation is still a difficult question. This paper introduces a body movement-based personalized targeted air supply device. Two indices, size target value Ts and velocity target value Tr , are introduced to evaluate the degree to which the created flow field reaches the desired level. Additionally, the air supply effect of the device is compared with that of other devices. This research shows that the personalized targeted air supply device can successfully deliver air to the target area and improve air supply accessibility in the target area. The multinozzle coupling air supply mode produces a flow field air velocity of approximately 0.3 m/s, thus effectively avoiding a draft sensation. Compared with that of other personalized nozzles, the energy consumption is reduced significantly, by 88.2%, while the air supply accessibility can be increased by 48% with equivalent energy consumption.

Laminar flow ventilation system to prevent airborne infection during exercise in the COVID-19 crisis: A single-center observational study

Particulate generation occurs during exercise-induced exhalation, and research on this topic is scarce. Moreover, infection-control measures are inadequately implemented to avoid particulate generation. A laminar airflow ventilation system (LFVS) was developed to remove respiratory droplets released during treadmill exercise. This study aimed to investigate the relationship between the number of aerosols during training on a treadmill and exercise intensity and to elucidate the effect of the LFVS on aerosol removal during anaerobic exercise. In this single-center observational study, the exercise tests were performed on a treadmill at Running Science Lab in Japan on 20 healthy subjects (age: 29±12 years, men: 80%). The subjects had a broad spectrum of aerobic capacities and fitness levels, including athletes, and had no comorbidities. All of them received no medication. The exercise intensity was increased by 1-km/h increments until the heart rate reached 85% of the expected maximum rate and then maintained for 10 min. The first 10 subjects were analyzed to examine whether exercise increased the concentration of airborne particulates in the exhaled air. For the remaining 10 subjects, the LFVS was activated during constant-load exercise to compare the number of respiratory droplets before and after LFVS use. During exercise, a steady amount of particulates before the lactate threshold (LT) was followed by a significant and gradual increase in respiratory droplets after the LT, particularly during anaerobic exercise. Furthermore, respiratory droplets ≥0.3 μm significantly decreased after using LFVS (2120800±759700 vs. 560 ± 170, p<0.001). The amount of respiratory droplets significantly increased after LT. The LFVS enabled a significant decrease in respiratory droplets during anaerobic exercise in healthy subjects. This study's findings will aid in exercising safely during this pandemic.

Preventing carbon monoxide poisoning in the Hudson River Tunnel in 1921: recounting history

The New York Bridge and Tunnel Commission began planning for a tunnel beneath the lower Hudson river to connect Manhattan to New Jersey in 1919. At 8,300 feet, it would be the longest tunnel for passenger vehicles in the world. A team of engineers and physiologists at the Yale University Bureau of Mines Experiment Station was tasked with calculating the ventilation requirements that would provide safety from exposure to automobile exhaust carbon monoxide (CO) while balancing the cost of providing ventilation. As the level of ambient CO which was comfortably tolerated was not precisely defined, they performed human exposures breathing from 100 to 1,000 ppm CO, first on themselves and subsequently on Yale medical students. Their findings continue to provide a basis for carbon monoxide alarm requirements a century later.

Impact of negative pressure system on microbiological air quality in a Central Sterile Supply Department

OBJECTIVE

Guidelines recommend that the cleaning area in a Central Sterile Supply Department (CSSD) maintain a negative pressure of the environmental air, but how much this system can impact the contamination of the air by bioaerosols in the area is not known. The objective of this study was to assess the impact of negative pressure on CSSD by evaluating the microbiological air quality of this sector.

METHODS

Microbiological air samples were collected in two CSSD in the same hospital: one with and one without a negative air pressure system. Outdoor air samples were collected as a comparative control. Andersen six-stage air sampler was used to obtain the microbiological air samples.

RESULTS

The concentration of bioaerosols in the CSSD without negative pressure was 273.15 and 206.71 CFU/m3 , while in the CSSD with negative pressure the concentration of bioaerosols was 116.96 CFU/m3 and 131.10 CFU/m3 . The number of isolated colonies in the negative pressure CSSD was significantly lower (P = .01541).

CONCLUSION

The findings showed that the negative pressure system in the CSSD cleaning area contributed to the quantitative reduction in bioaerosols. However, the concentration of bioaerosols was lower than that established in the guideline for indoor air quality of many countries. Therefore, it cannot be concluded that CSSDs which do not have a negative pressure system in their cleaning area offer occupational risk.

Simulation and experimental investigation of dust-collecting performances of different dust exhaust hoods

High-efficiency dust collection for open dust source has always been an important and difficult issue for air quality control at the workplace. This study performed simulations and experiments on three kinds of dust exhaust hoods, namely, updraft, side-draft and air-curtain exhaust hoods. Results show these three kinds of exhaust hoods varied significantly in dust-capturing efficiency. The dust-capturing efficiency of the updraft exhaust hood was the lowest (56.8%) while the air-curtain exhaust hood performed best in dust collection, with a dust-capturing efficiency of 93.8%. For a rectangular air-curtain exhaust hood with a size of 900 mm x 1200 mm, the dust-capturing efficiency first increased and gradually tended to stabilize with increasing air-curtain velocity and suction airflow rate. According to the present research results, the reasonable long-side air-curtain velocity and suction airflow rate were in the range 4 ~ 6.27 m/s and 5.4 ~ 9 m³/min, respectively. Under these conditions, dust-capturing efficiency can be as high as 79.6-86.5%. Implications: This study performed simulations and experiments on three kinds of dust exhaust hoods: updraft, side-draft and air-curtain. Simulation results show the dust-capturing efficiency of the air-curtain exhaust hood is best of 93.8%. Experimental results show under reasonable conditions, the dust-capturing efficiency of a rectangular air-curtain exhaust hood is 79.6-86.5%. This research is very meaningful, which not only has important innovation in the study of micro mechanism of dust collectors but provides powerful theoretical and experimental support for technological innovation.

Optimization of mine ventilation network feature graph

A ventilation network feature graph can directly and quantitatively represent the features of a ventilation network. To ensure the stability of airflow in a mine and improve ventilation system analysis, we propose a new algorithm to draw ventilation network feature graphs. The independent path method serves as the algorithm’s main frame, and an improved adaptive genetic algorithm is embedded so that the graph may be drawn better. A mathematical model based on the node adjacency matrix method for unidirectional circuit discrimination is constructed as the drawing algorithm may not be valid in such cases. By modifying the edge-seeking strategy, the improved depth-first search algorithm can be used to determine all of the paths in the ventilation network with unidirectional circuits, and the equivalent transformation method of network topology relations is used to draw the ventilation network feature graph. Through the analysis of the topological relation of a ventilation network, a simplified mathematical model is constructed, and network simplification technology makes the drawing concise and hierarchical. The rapid and intuitive drawing of the ventilation network feature graphs is significant for optimization of the ventilation system and day-to-day management.

Potential application of using vortex ring for personalized ventilation

A novel vortex ring personalized ventilation system (VRPV) is proposed for efficiently supplying fresh air to room occupants. A vortex ring generator with a piston-cylinder is developed for an experimental study of the formation, transportation, and ventilation characteristics of the VRPV. The translational velocity, volume, and fresh air ratio of the vortex rings are studied using high-speed cameras and tracer gas experiments. According to the results, the categories of the vortex ring volume in the formation stage are studied. It is observed that the velocity of the piston determines the initial translational velocity of the vortex ring, and a fitting equation is proposed to predict the evolution of the translational velocity. The deviation range of the VRPV over different distances is studied, and it is shown to be affected by interference from both the generator and the environment. Finally, the total volumes, fresh air volumes, and fresh air ratios of the VRPV are studied at different distances. The results indicate that, as a personalized ventilation system, the fresh air ratio of the VRPV is up to 159.3% higher than that of a symmetrical round jet within a 0-4 m range. This shows the excellent application potential of the VRPV for providing high-efficiency personalized ventilation with lower fresh airflow rates.

Coronavirus Disease 2019 (COVID-19): The Singapore Experience. A Review of the First Eight Months

As of 27 October 2020, there have been 57,980 confirmed cases of COVID-19 in Singapore, with 28 fatalities. To summarise the Singapore experience in managing and containing COVID-19 based on available published data and from relevant sources, a review of literature using research databases such as PubMed and OVID Medline, along with non-peer-reviewed articles and other sources, was conducted with the search terms 'COVID-19' and 'Singapore'. Research conducted in Singapore has provided insight into the clinical manifestations and period of infectivity of COVID-19, demonstrated evidence of pre-symptomatic transmission, linked infection clusters using serological tools, and highlighted aspects of hospital-based environmental contamination. It has also provided guidance for diagnostic testing and has described immune and virologic correlates with disease severity. Evidence of effectiveness of containment measures such as early border control, rigorous contact training, and calibrated social distancing measures have also been demonstrated. Singapore's multipronged strategy has been largely successful at containing COVID-19 and minimising fatalities, but the risk of re-emergence is high.

Effects of carbon-based additives and ventilation rate on nitrogen loss and microbial community during chicken manure composting

Aerobic composting is a sustainable method for chicken manure recycling, while its unsuitable porosity and carbon to nitrogen ratio (C/N) may result in high nitrogen loss and incomplete composting. With the aim to investigate the effects of carbon-based additives and two ventilation rates on chicken manure composting and microbial community, two series of treatments were set up for chicken manure composting, in order to investigate their effects on the biodegradation process, ammonia (NH₃) emission, nitrogen loss, physiochemical properties and microbial community. The results showed that additives and ventilation rates set in the current study influenced the carbon dioxide (CO₂) production from the 2^nd week and also the physiochemical parameters during the entire process, while no inhibitory effect on the maturity were observed. With woody peat as additive, the NH₃ emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02%, less than those in other treatments, 31.08–80.13 mg and 24.26–34.24%, respectively. The high aeration rate increased the NH₃ emission and nitrogen loss, which were varied when the additives were different. The terminal restriction fragment length polymorphism (T-RFLP) results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. It was concluded that woody peat could improve chicken manure composting more than other additives, especially on reducing nitrogen loss, meanwhile 0.18 L‧min^-1‧kg^-1 DM was suitable for various additives. Therefore, suitable additive and aeration rate could be used in practical application, which could significantly reduce nitrogen loss without influence on the compos maturity process.