scholarly journals Beyond well-mixed: a simple probabilistic model of airborne disease transmission in indoor spaces

2021 ◽  
Author(s):  
Sijian Tan ◽  
Zhihang Zhang ◽  
Kevin Maki ◽  
Krzysztof J. Fidkowski ◽  
Jesse Capecelatro
Keyword(s):  
Disease Transmission ◽  
Risk Model ◽  
Ventilation Rate ◽  
Turbulent Dispersion ◽  
Balance Model ◽  
Wide Range ◽  
Ventilation Rates ◽  
Airborne Disease ◽  
Droplet Nuclei ◽  
Indoor Spaces

AbstractWe develop a simple model for assessing risk of airborne disease transmission that accounts for non-uniform mixing in indoor spaces and is compatible with existing epidemiological models. A database containing 174 high-resolution simulations of airflow in classrooms, lecture halls, and buses is generated and used to quantify the spatial distribution of expiratory droplet nuclei for a wide range of ventilation rates, exposure times, and room configurations. Imperfect mixing due to obstructions, buoyancy, and turbulent dispersion results in concentration fields with significant variance. The spatial non-uniformity is found to be accurately described by a shifted lognormal distribution. A well-mixed mass balance model is used to predict the mean, and the standard deviation is parameterized based on ventilation rate and room geometry. When employed in a dose-response function risk model, infection probability can be estimated considering spatial heterogeneity that contributes to both short- and long-range transmission.

scholarly journals Analytic modeling and risk assessment of aerial transmission of SARS-CoV-2 virus through vaping expirations in shared micro-environments

2021 ◽  
Author(s):  
Roberto Sussman ◽  
Eliana Golberstein ◽  
Riccardo Polosa
Keyword(s):  
Mechanical Ventilation ◽  
Risk Model ◽  
Case Scenario ◽  
Direct Exposure ◽  
Containment Measures ◽  
Nicotine Consumption ◽  
Contagion Risk ◽  
Droplet Nuclei ◽  
Respiratory Droplets ◽  
Indoor Spaces

Abstract Background. E-cigarettes are an important harm reduction tool that provides smokers an alternative for nicotine consumption that is much safer than smoking. It is important to asses its safety under preventive and containment measures undertaken during the COVID-19 pandemic. Methods. We develop a theoretical risk model to assess the contagion risk by aerial transmission of the SARS-CoV-2 virus carried by e–cigarette aerosol (ECA) in shared indoor spaces, a home and restaurant scenarios, with natural and mechanical ventilation, with and without face masks. We also provide the theoretical elements to explain the visibility of exhaled ECA, which has important safety implications. Results. In a home or restaurant scenarios bystanders exposed to ECA expirations by an infectious vaper (and not wearing face masks) face a 1% increase of risk of contagion with respect to a “control case” scenario defined by exclusively rest breathing without vaping. This relative added risk becomes 5 - 17% for high intensity vaping, 44 - 176% and over 260% for speaking for various periods or coughing (all without vaping). Mechanical ventilation significantly decrease infective emissions but keep the same proportionality in risk percentages. Face masks of common usage effectively protect wearers from respiratory droplets and droplet nuclei possibly emitted by mask-less vapers as long as they avoid direct exposure to the visible exhaled vaping jet. Conclusions. Vaping emissions in shared indoor spaces involve only a minuscule added risk of COVID-19 contagion with respect to the already existing (unavoidable) risk from continuous breathing, significantly less than speaking or coughing. Protection of bystanders from this contagion does not require extra preventive measures besides those already recommended (1.5 meters separation and wearing face masks).

scholarly journals A Computational Framework for Transmission Risk Assessment of Aerosolized Particles in Classrooms

2021 ◽  
Author(s):  
Kendrick Tan ◽  
Boshun Gao ◽  
Cheng-Hau Yang ◽  
Emily Johnson ◽  
Ming-Chen Hsu ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Disease Transmission ◽  
Ventilation Rate ◽  
Mitigation Strategies ◽  
Transmission Risk ◽  
Computational Framework ◽  
Seating Arrangement ◽  
K 12 ◽  
Education Administrators ◽  
Airborne Disease

Abstract The ongoing COVID-19 pandemic has rendered confined spaces as high-risk areas. There is an increasing push to resume in-person activities, for instance, teaching in K-12 and university settings. It becomes important to evaluate the risk of airborne disease transmission while accounting for the physical presence of humans, furniture, and electronic equipment, as well as ventilation. Here, we present a computational framework based on detailed flow physics simulations that allows straightforward evaluation of various seating and operating scenarios to identify risk factors and assess the effectiveness of various mitigation strategies. These scenarios include seating arrangement changes, presence/absence of computer screens, ventilation rate changes, and presence/absence of mask-wearing. This approach democratizes risk assessment by automating a key bottleneck in simulation-based analysis--creating an adequately refined mesh around multiple complex geometries. Not surprisingly, we find that wearing masks (with at least 74% inward protection efficiency) significantly reduced transmission risk against unmasked and infected individuals. The availability of such an analysis approach will allow education administrators, government officials (courthouses, police stations), and hospital administrators to make informed decisions on seating arrangements and operating procedures.

scholarly journals Numerical simulation of bioaerosol particle exposure assessment in office environment from MVAC systems

2017 ◽  
Vol 10 (2) ◽  
pp. 59-71 ◽  
Author(s):  
HC Yu ◽  
KW Mui ◽  
LT Wong
Keyword(s):  
Ventilation Rate ◽  
Two Phase ◽  
Maintenance Strategies ◽  
Office Environment ◽  
Particle Exposure ◽  
Mixing Chamber ◽  
Wide Range ◽  
Ventilation Strategies ◽  
Cooling Coils ◽  
Ventilation Rates

Bioaerosol (i.e. biological aerosol) exposures in the office environment are associated with a wide range of health effects. The potential bioaerosol emission from mechanical ventilation and air conditioning (MVAC) systems can endanger the building occupants in office, especially as over 90% of commercial buildings in Hong Kong that are equipped with MVAC systems, due to the microbial growths inside MVAC systems, such as cooling coils and mixing chamber, were reported. This study evaluated the exposure risk of the bioaerosol emission from the MVAC systems to the building occupants. A two-phase flow computational fluid dynamics approach was adopted to simulate the emission, dispersion, deposition, and exhaustion of bioaerosol particles from the MVAC systems in a typical office cubicle by altering the ventilation strategies with four ventilation rates, four emission concentrations, and two microorganism species. The results reported that about 5% contribution of concentration level from the MVAC system including the ventilation rate is sufficient to dilute the biocontainment. This study suggested the importance of the maintenance strategies of MVAC systems for minimizing bioaerosol exposures in offices.

scholarly journals Far-UVC efficiently inactivates an airborne pathogen in a room-sized chamber

2021 ◽  
Author(s):  
Ewan Eadie ◽  
Waseem Hiwar ◽  
Louise Fletcher ◽  
Emma Tidswell ◽  
Paul O’Mahoney ◽  
...  
Keyword(s):  
Disease Transmission ◽  
Environmental Control ◽  
Ventilation Rate ◽  
Control Measures ◽  
Delayed Effects ◽  
Pathogen Load ◽  
Regulatory Limits ◽  
Airborne Disease ◽  
Airborne Viruses ◽  
Scale Data

Abstract Many infectious diseases, including COVID-19, are transmitted by airborne pathogens. There is a need for effective environmental control measures which, ideally, are not reliant on human behaviour. One potential solution is Far-UVC which can efficiently inactivate pathogens, such as coronaviruses and influenza, in air. When appropriately filtered, and because of its limited penetration, there is evidence that Far-UVC does not induce acute reactions in the skin or eyes, nor delayed effects such as skin cancer. While there is laboratory evidence for far-UVC efficacy, there is limited evidence in full-sized rooms. In the first study of its type, we show that Far-UVC deployed in a room-sized chamber effectively inactivates aerosolised Staphylococcus aureus. At a room ventilation rate of 3 air changes per hour (ACH), with 5 filtered sources the steady-state pathogen load was reduced by 92.1% providing an additional 35 equivalent air changes (eACH). This reduction was achieved using Far-UVC intensities consistent with current regulatory limits. Far-UVC is likely to be more effective against common airborne viruses, including SARS-CoV-2, and should thus be an effective and “hands-off” technology to reduce airborne disease transmission. The findings provide room-scale data to support the design and development of safe and effective Far-UVC systems.

Regional Relative Risk, a Physics-Based Metric for Characterizing Airborne Infectious Disease Transmission

2021 ◽  
Author(s):  
Michael B Dillon ◽  
Charles F Dillon
Keyword(s):  
Infectious Disease ◽  
Relative Risk ◽  
Disease Transmission ◽  
Spatial Scales ◽  
Disease Outbreaks ◽  
Indoor Environments ◽  
Infectious Disease Transmission ◽  
Wide Range ◽  
Risk Metric ◽  
Airborne Disease

Airborne infectious disease transmission events occur over a wide range of spatial scales and can be an important means of disease transmission. Physics- and biology- based models can assist in predicting airborne transmission events, overall disease incidence, and disease control strategy efficacy. We develop a new theory that extends current approaches for the case in which an individual is infected by a single airborne particle, including the scenario in which numerous infectious particles are present in the air but only one causes infection. A single infectious particle can contain more than one pathogenic microorganism and be physically larger than the pathogen itself. This approach allows robust relative risk estimates even when there is wide variation in (a) individual exposures and (b) the individual response to that exposure (the pathogen dose-response function can take any mathematical form and vary by individual). Based on this theory, we propose the Regional Relative Risk – a new metric, distinct from the traditional relative risk metric, that compares the risk between two regions (in theory, these regions can range from individual rooms to large geographic areas). In this paper, we apply the Regional Relative Risk metric to outdoor disease transmission events over spatial scales ranging from 50 m to 20 km demonstrating that in many common cases, minimal input information is required to use the metric. Also, we demonstrate that it is consistent with data from prior outbreaks. Future efforts could apply and validate this theory for other spatial scales, such as indoor environments. This work provides context for (a) the initial stages of an airborne disease outbreak and (b) larger scale disease spread, including unexpected low probability disease “sparks” that potentially affect remote populations, a key practical issue in controlling airborne disease outbreaks. Importance Airborne infectious disease transmission events occur over a wide range of spatial scales and can be important to disease outbreaks. We develop a new physics- and biology- based theory for the important case in which individuals are infected by a single airborne particle (numerous infectious particles can be emitted into the air and inhaled). Based on this theory, we propose a new epidemiological metric, Regional Relative Risk, that compares the risk between two geographic regions (in theory, regions can range from individual rooms to large areas). Our modeling of outdoors transmission events predicts that for many scenarios of interest, minimal information is required to use this metric for locations 50 m to 20 km downwind. This prediction is consistent with data from prior disease outbreaks. Future efforts could apply and validate this theory for other spatial scales, such as indoor environments. Our results may a priori be applicable to many airborne diseases as these results depend on the physics of airborne particulate dispersion.

scholarly journals Analytic modeling and risk assessment of aerial transmission of SARS-CoV-2 virus through vaping expirations in shared micro-environments

2021 ◽  
Author(s):  
Roberto A Sussman ◽  
Eliana Golberstein ◽  
Riccardo Polosa
Keyword(s):  
Mechanical Ventilation ◽  
Risk Model ◽  
Case Scenario ◽  
Direct Exposure ◽  
Containment Measures ◽  
Nicotine Consumption ◽  
Contagion Risk ◽  
Droplet Nuclei ◽  
Respiratory Droplets ◽  
Indoor Spaces

Background. E-cigarettes are an important harm reduction tool that provides smokers an alternative for nicotine consumption that is much safer than smoking. It is important to asses its safety under preventive and containment measures undertaken during the COVID-19 pandemic.Methods. We develop a theoretical risk model to assess the contagion risk by aerial trans mission of the SARS-CoV-2 virus carried by e–cigarette aerosol (ECA) in shared indoor spaces, a home and restaurant scenarios, with natural and mechanical ventilation, with and without face masks. We also provide the theoretical elements to explain the visibility of exhaled ECA, which has important safety implications.Results. In a home or restaurant scenarios bystanders exposed to ECA expirations by an infectious vaper (and not wearing face masks) face a 1% increase of risk of contagion with respect to a “control case” scenario defined by exclusively rest breathing without vaping. This relative added risk becomes 5 - 17% for high intensity vaping, 44 - 176% and over 260% for speaking for various periods or coughing (all without vaping). Mechanical ventilation significantly decrease infective emissions but keep the same proportionality in risk percentages. Face masks of common usage effectively protect wearers from respiratory droplets and droplet nuclei possibly emitted by mask-less vapers as long as they avoid direct exposure to the visible exhaled vaping jet.Conclusions. Vaping emissions in shared indoor spaces involve only a minuscule added risk of COVID-19 contagion with respect to the already existing (unavoidable) risk from continuous breathing, significantly less than speaking or coughing. Protection of bystanders from this contagion does not require extra preventive measures besides those already recommended (1.5 meters separation and wearing face masks).

scholarly journals Splatters and Aerosols Contamination in Dental Aerosol Generating Procedures

2021 ◽  
Vol 11 (4) ◽  
pp. 1914
Author(s):  
Pingping Han ◽  
Honghui Li ◽  
Laurence J. Walsh ◽  
Sašo Ivanovski
Keyword(s):  
Particle Size ◽  
Disease Transmission ◽  
High Speed ◽  
Low Speed ◽  
Dental Procedures ◽  
Dental Equipment ◽  
Produce Contamination ◽  
Fluorescein Dye ◽  
Filter Papers ◽  
Airborne Disease

Dental aerosol-generating procedures produce a large amount of splatters and aerosols that create a major concern for airborne disease transmission, such as COVID-19. This study established a method to visualise splatter and aerosol contamination by common dental instrumentation, namely ultrasonic scaling, air-water spray, high-speed and low-speed handpieces. Mock dental procedures were performed on a mannequin model, containing teeth in a typodont and a phantom head, using irrigation water containing fluorescein dye as a tracer. Filter papers were placed in 10 different locations to collect splatters and aerosols, at distances ranging from 20 to 120 cm from the source. All four types of dental equipment produced contamination from splatters and aerosols. At 120 cm away from the source, the high-speed handpiece generated the greatest amount and size (656 ± 551 μm) of splatter particles, while the triplex syringe generated the largest amount of aerosols (particle size: 1.73 ± 2.23 μm). Of note, the low-speed handpiece produced the least amount and size (260 ± 142 μm) of splatter particles and the least amount of aerosols (particle size: 4.47 ± 5.92 μm) at 120 cm. All four dental AGPs produce contamination from droplets and aerosols, with different patterns of distribution. This simple model provides a method to test various preventive strategies to reduce risks from splatter and aerosols.

scholarly journals Proposing Alternative Solutions to Enhance Natural Ventilation Rates in Residential Buildings in the Cfa Climate Zone of Rasht

2021 ◽  
Vol 13 (2) ◽  
pp. 679
Author(s):  
Roya Aeinehvand ◽  
Amiraslan Darvish ◽  
Abdollah Baghaei Daemei ◽  
Shima Barati ◽  
Asma Jamali ◽  
...  
Keyword(s):  
Natural Ventilation ◽  
Residential Buildings ◽  
Residential Building ◽  
Ventilation Rate ◽  
Humid Climate ◽  
The Sustainable Development ◽  
Passive Strategies ◽  
Development Goals ◽  
Ventilation Rates ◽  
Ventilation Systems

Today, renewable resources and the crucial role of passive strategies in energy efficiency in the building sector toward the sustainable development goals are more indispensable than ever. Natural ventilation has traditionally been considered as one of the most fundamental techniques to decrease energy usage by building dwellers and designers. The main purpose of the present study is to enhance the natural ventilation rates in an existing six-story residential building situated in the humid climate of Rasht during the summertime. On this basis, two types of ventilation systems, the Double-Skin Facade Twin Face System (DSF-TFS) and Single-Sided Wind Tower (SSWT), were simulated through DesignBuilder version 4.5. Then, two types of additional ventilation systems were proposed in order to accelerate the airflow, including four-sided as well as multi-opening wind towers. The wind foldable directions were at about 45 degrees (northwest to southeast). The simulation results show that SSWT could have a better performance than the aforementioned systems by about 38%. Therefore, the multi-opening system was able to enhance the ventilation rate by approximately 10% during the summertime.

scholarly journals Extended Lifetime of Respiratory Droplets in a Turbulent Vapor Puff and Its Implications on Airborne Disease Transmission

2021 ◽  
Vol 126 (3) ◽  
Author(s):  
Kai Leong Chong ◽  
Chong Shen Ng ◽  
Naoki Hori ◽  
Rui Yang ◽  
Roberto Verzicco ◽  
...  
Keyword(s):  
Disease Transmission ◽  
Airborne Disease ◽  
Respiratory Droplets

Nitrification in bulk water and biofilms of algae wastewater stabilization ponds

2007 ◽  
Vol 55 (11) ◽  
pp. 93-101 ◽  
Author(s):  
M.A. Babu ◽  
M.M. Mushi ◽  
N.P. van der Steen ◽  
C.M. Hooijmans ◽  
H.J. Gijzen
Keyword(s):  
Model Equation ◽  
Bulk Water ◽  
Balance Model ◽  
Nitrification Rate ◽  
Relative Contribution ◽  
Activity Test ◽  
Stabilization Ponds ◽  
Wide Range ◽  
Water Columns ◽  
Wastewater Stabilization Ponds

Nitrogen removal in wastewater stabilization ponds is poorly understood and effluent monitoring data show a wide range of differences in ammonium. For effluent discharge into the environment, low levels of nitrogen are recommended. Nitrification is limiting in facultative wastewater stabilization ponds. The reason why nitrification is considered to be limiting is attributed to low growth rate and wash out of the nitrifiers. Therefore to maintain a population, attached growth is required. The aim of this research is to study the relative contribution of bulk water and biofilms with respect to nitrification. The hypothesis is that nitrification can be enhanced in stabilization ponds by increasing the surface area for nitrifier attachment. In order to achieve this, transparent pond reactors representing water columns in algae WSP have been used. To discriminate between bulk and biofilm activity, 5-day batch activity tests were carried out with bulk water and biofilm sampled. The observed value for Rnitrbulk was 2.7 × 10−1 mg-N L−1 d−1 and for Rbiofilm was 1,495 mg-N m−2 d −1. During the 5 days of experiment with the biofilm, ammonia reduction was rapid on the first day. Therefore, a short-term biofilm activity test was performed to confirm this rapid decrease. Results revealed a nitrification rate, Rbiofilm, of 2,125 mg-N m−2 d−1 for the first 5 hours of the test, which is higher than the 1,495 mg-N m−2 d−1, observed on the first day of the 7-day biofilm activity test. Rbiofilm and Rnitrbulk values obtained in the batch activity tests were used as parameters in a mass balance model equation. The model was calibrated by adjusting the fraction of the pond volume and biofilm area that is active (i.e. aerobic). When assuming a depth of 0.08 m active upper layer, the model could describe well the measured effluent values for the pond reactors. The calibrated model was validated by predicting effluent Kjeldahl nitrogen of algae ponds in Palestine and Colombia. The model equation predicted well the effluent concentrations of ponds in Palestine.

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