Ventilation System Operation to Minimize the COVID-19 Airborne Transmission in Schools

Minimizing the SARS-CoV-2 virus transmission is essential to face the COVID-19 pandemic. This is even more important for highly crowded indoor environments, e.g. schools, where the mitigation solutions based on social distancing and hand washing seem to be not effective to reduce the virus airborne transmission mode, which is the main route of transmission. To minimize the airborne virus transmission a proper ventilation is necessary. In the study, a simplified mass balance equation (box-model) was applied to school scenarios in order to determine the required conditions to maintain the infection risk below an acceptable level. In particular, the required air exchange rates for mechanically-ventilated classrooms and the adequate airing procedures for naturally ventilated classrooms were determined. Moreover, for naturally ventilated classrooms, a control strategy based on the measurement of CO2 indoor concentration was also developed.

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Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph17082932 ◽

2020 ◽

Vol 17 (8) ◽

pp. 2932 ◽

Cited By ~ 105

Author(s):

Leonardo Setti ◽

Fabrizio Passarini ◽

Gianluigi De Gennaro ◽

Pierluigi Barbieri ◽

Maria Grazia Perrone ◽

...

Keyword(s):

Virus Transmission ◽

Field Studies ◽

University Hospital ◽

World Health ◽

Indoor Environments ◽

Airborne Transmission ◽

Surface Stability ◽

Air Samples ◽

Daily Life Activities ◽

The World

The COVID-19 pandemic caused the shutdown of entire nations all over the world. In addition to mobility restrictions of people, the World Health Organization and the Governments have prescribed maintaining an inter-personal distance of 1.5 or 2 m (about 6 feet) from each other in order to minimize the risk of contagion through the droplets that we usually disseminate around us from nose and mouth. However, recently published studies support the hypothesis of virus transmission over a distance of 2 m from an infected person. Researchers have proved the higher aerosol and surface stability of SARS-COV-2 as compared with SARS-COV-1 (with the virus remaining viable and infectious in aerosol for hours) and that airborne transmission of SARS-CoV can occur besides close-distance contacts. Indeed, there is reasonable evidence about the possibility of SARS-COV-2 airborne transmission due to its persistence into aerosol droplets in a viable and infectious form. Based on the available knowledge and epidemiological observations, it is plausible that small particles containing the virus may diffuse in indoor environments covering distances up to 10 m from the emission sources, thus representing a kind of aerosol transmission. On-field studies carried out inside Wuhan Hospitals showed the presence of SARS-COV-2 RNA in air samples collected in the hospitals and also in the surroundings, leading to the conclusion that the airborne route has to be considered an important pathway for viral diffusion. Similar findings are reported in analyses concerning air samples collected at the Nebraska University Hospital. On March 16th, we have released a Position Paper emphasizing the airborne route as a possible additional factor for interpreting the anomalous COVID-19 outbreaks in northern Italy, ranked as one of the most polluted areas in Europe and characterized by high particulate matter (PM) concentrations. The available information on the SARS-COV-2 spreading supports the hypothesis of airborne diffusion of infected droplets from person to person at a distance greater than two meters (6 feet). The inter-personal distance of 2 m can be reasonably considered as an effective protection only if everybody wears face masks in daily life activities.

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HVAC systems for environmental control to minimize the COVID-19 infection

Indoor and Built Environment ◽

10.1177/1420326x20951968 ◽

2020 ◽

Vol 29 (9) ◽

pp. 1195-1201

Author(s):

Junwei Ding ◽

Chuck Wah Yu ◽

Shi-Jie Cao

Keyword(s):

Thermal Comfort ◽

Disease Transmission ◽

Environmental Control ◽

Ventilation System ◽

Virus Transmission ◽

Hvac Systems ◽

Health Care Facilities ◽

Indoor Environments ◽

Healthy Environment ◽

And Control

The outbreak of pneumonia caused by 2019 Novel Coronavirus arises significant concern for virus transmission and control. The control of the indoor environment or public-enclosed environment is crucial to reduce the risk of infection. Heating, ventilation, air-conditioning (HVAC) systems are used to create a healthy, thermal-comfort indoor environments. Thus, the rational use of HVAC systems is of great importance for the environmental control to reduce infection risk and to improve human wellbeing in the pandemic. In order to satisfy the requirement of better healthy environment and more thermal comfort performance of indoor ventilation system, prevention of indoor pollution is essential, especially considering the purpose of disease transmission resistance. This paper investigated the collective contagion events in enclosed spaces as well as engineering control against virus spread with ventilation systems for health-care facilities and public vehicles. Future challenges of HVAC design and control were discussed.

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The impact of heating, ventilation, and air conditioning design features on the transmission of viruses, including the 2019 novel coronavirus: a systematic review of filtration

10.1101/2021.09.23.21264025 ◽

2021 ◽

Author(s):

Brian A Fleck ◽

Gail M. Thornton ◽

Lexuan Zhong ◽

Lisa A Hartling ◽

Dhyey Dandnayak ◽

...

Keyword(s):

Systematic Review ◽

Air Conditioning ◽

Virus Transmission ◽

Infection Risk ◽

Hvac Systems ◽

Airborne Transmission ◽

Virus Removal ◽

Filter Efficiency ◽

Novel Coronavirus ◽

The Impact

Historically, viruses have demonstrated airborne transmission. Emerging evidence suggests the novel coronavirus (SARS-CoV-2) that causes COVID-19 may also spread by airborne transmission. This is more likely in indoor environments, particularly with poor ventilation. In the context of potential airborne transmission, a vital mitigation strategy for the built environment is heating, ventilation, and air conditioning (HVAC) systems. HVAC features could modify virus transmission potential. A systematic review following international standards was conducted to comprehensively identify and synthesize research examining the effectiveness of filters within HVAC systems in reducing virus transmission. Twenty-three relevant studies showed that: filtration was associated with decreased transmission; filters removed viruses from the air; increasing filter efficiency (efficiency of particle removal) was associated with decreased transmission, decreased infection risk, and increased viral filtration efficiency (efficiency of virus removal); increasing filter efficiency above MERV 13 was associated with limited benefit in further reduction of virus concentration and infection risk; and filters with the same efficiency rating from different companies showed variable performance. Increasing filter efficiency may mitigate virus transmission; however, improvement may be limited above MERV 13. Adapting HVAC systems to mitigate virus transmission requires a multi-factorial approach and filtration is one factor offering demonstrated potential for decreased transmission.

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Ventilation procedures to minimize the airborne transmission of viruses at schools

10.1101/2021.03.23.21254179 ◽

2021 ◽

Author(s):

L. Stabile ◽

A. Pacitto ◽

A. Mikszewski ◽

L. Morawska ◽

G. Buonanno

Keyword(s):

Classroom Environment ◽

Ad Hoc ◽

Virus Transmission ◽

Transmission Risk ◽

Mitigation Measures ◽

Indoor Environments ◽

Airborne Transmission ◽

Transmission Potential ◽

Feedback Control Strategy ◽

Ventilation Rates

AbstractReducing the transmission of SARS-CoV-2 through indoor air is the key challenge of the COVID-19 pandemic. Crowded indoor environments, such as schools, represent possible hotspots for virus transmission since the basic non-pharmaceutical mitigation measures applied so far (e.g. social distancing) do not eliminate the airborne transmission mode. There is widespread consensus that improved ventilation is needed to minimize the transmission potential of airborne viruses in schools, whether through mechanical systems or ad-hoc manual airing procedures in naturally ventilated buildings. However, there remains significant uncertainty surrounding exactly what ventilation rates are required, and how to best achieve these targets with limited time and resources. This paper uses a mass balance approach to quantify the ability of both mechanical ventilation and ad-hoc airing procedures to mitigate airborne transmission risk in the classroom environment. For naturally-ventilated classrooms, we propose a novel feedback control strategy using CO2 concentrations to continuously monitor and adjust the airing procedure. Our case studies show how such procedures can be applied in the real world to support the reopening of schools during the pandemic. Our results also show the inadequacy of relying on absolute CO2 concentration thresholds as the sole indicator of airborne transmission risk.

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Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment

10.1101/2020.04.12.20062828 ◽

2020 ◽

Cited By ~ 1

Author(s):

G. Buonanno ◽

L. Stabile ◽

L. Morawska

Keyword(s):

Viral Load ◽

Research Area ◽

Infection Risk ◽

Activity Level ◽

Indoor Environments ◽

Emission Rates ◽

Airborne Transmission ◽

Emission Data ◽

Novel Approach ◽

Before And After

AbstractAirborne transmission is a pathway of contagion that is still not sufficiently investigated despite the evidence in the scientific literature of the role it can play in the context of an epidemic. While the medical research area dedicates efforts to find cures and remedies to counteract the effects of a virus, the engineering area is involved in providing risk assessments in indoor environments by simulating the airborne transmission of the virus during an epidemic. To this end, virus air emission data are needed. Unfortunately, this information is usually available only after the outbreak, based on specific reverse engineering cases. In this work, a novel approach to estimate the viral load emitted by a contagious subject on the basis of the viral load in the mouth, the type of respiratory activity (e.g. breathing, speaking), respiratory physiological parameters (e.g. inhalation rate), and activity level (e.g. resting, standing, light exercise) is proposed. The estimates of the proposed approach are in good agreement with values of viral loads of well-known diseases from the literature. The quanta emission rates of an asymptomatic SARS-CoV-2 infected subject, with a viral load in the mouth of 108 copies mL−1, were 10.5 quanta h−1 and 320 quanta h−1 for breathing and speaking respiratory activities, respectively, at rest. In the case of light activity, the values would increase to 33.9 quanta h−1 and 1.03×103 quanta h−1, respectively.The findings in terms of quanta emission rates were then adopted in infection risk models to demonstrate its application by evaluating the number of people infected by an asymptomatic SARS-CoV-2 subject in Italian indoor microenvironments before and after the introduction of virus containment measures. The results obtained from the simulations clearly highlight that a key role is played by proper ventilation in containment of the virus in indoor environments.

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Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their application to COVID-19 Outbreaks

10.1101/2021.04.21.21255898 ◽

2021 ◽

Author(s):

Z. Peng ◽

W. Bahnfleth ◽

G. Buonanno ◽

S. J. Dancer ◽

J. Kurnitski ◽

...

Keyword(s):

Disease Transmission ◽

Infection Risk ◽

Infection Model ◽

Indoor Environments ◽

Airborne Transmission ◽

Clear Trend ◽

Aerosol Generation ◽

Risk Parameter ◽

Risk Parameters ◽

Parameter Values

AbstractSome infectious diseases, including COVID-19, can be transmitted via aerosols that are emitted by an infectious person and inhaled by susceptible individuals. Although physical distancing effectively reduces short-range airborne transmission, many infections have occurred when sharing room air despite maintaining distancing. We propose two simple parameters as indicators of infection risk for this situation. They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and air cleaning rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend in relation to these parameters that is consistent with an airborne infection model, supporting the importance of airborne transmission for these outbreaks. The observed trends of outbreak size vs. risk parameters allow us to recommend values of the parameters to minimize COVID-19 indoor infection risk. All of the pre-pandemic spaces are in a regime where they are highly sensitive to mitigation efforts. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at much higher risk parameter values. Since both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include ventilation information, to allow expanding our knowledge of the circumstances conducive to airborne transmission of different diseases.

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Airborne bacteria concentrations and related factors at university laboratories, hospital diagnostic laboratories and a biowaste site

Journal of Clinical Pathology ◽

10.1136/jcp.2010.084764 ◽

2011 ◽

Vol 64 (3) ◽

pp. 261-264 ◽

Cited By ~ 22

Author(s):

Sung Ho Hwang ◽

Dong Uk Park ◽

Kwon Chul Ha ◽

Hyun Woo Cho ◽

Chung Sik Yoon

Keyword(s):

Sampling Site ◽

Ventilation System ◽

Airborne Bacteria ◽

Gram Negative Bacteria ◽

Indoor Environments ◽

Related Factors ◽

P Values ◽

Regular Control ◽

Number Of Bacteria

AimsTo evaluate concentrations of airborne bacteria in university laboratories, hospital diagnostic laboratories, and a biowaste site in Seoul, Korea. To measure total airborne bacteria (TAB), the authors assessed sampling site, type of ventilation system, weather and detection of Gram-negative bacteria (GNB), indoors and outdoors.MethodAn Andersen one-stage sampler (Quick Take 30; SKC Inc) was used to sample air at a flow rate of 28.3 l/min for 5 min on nutrient medium in Petri dishes located on the impactor. A total of 236 samples (TAB, 109 indoor and nine outdoor; GNB, 109 indoor and nine outdoor) were collected three times in each spot from the 11 facilities to compare airborne bacteria concentrations.ResultsTAB concentrations ranged from undetectable to 3451 CFU/m3 (mean 384 CFU/m3), and GNB concentrations from undetectable to 394 CFU/m3 (mean 17 CFU/m3). TAB concentrations were high in window-ventilated facilities and facilities in which GNB were detected; concentrations were also high when it was rainy (all p values <0.05). TAB concentrations correlated significantly with GNB (r=0.548, p<0.01), number of bacteria species (r=0.351, p<0.01) and temperature (r=0.297, p<0.01). The presence of heating, ventilating, and air conditioning (HVAC), the number of TAB species and the detection of GNB affect TAB concentrations in laboratories.ConclusionsIt is recommended that special attention be given to regular control of indoor environments to improve the air quality of university and hospital laboratories.

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Numerical Model for Prediction of Indoor COVID-19 Infection Risk Based on Sensor Data

Journal of Physics Conference Series ◽

10.1088/1742-6596/2069/1/012189 ◽

2021 ◽

Vol 2069 (1) ◽

pp. 012189

Author(s):

J Virbulis ◽

M Sjomkane ◽

M Surovovs ◽

A Jakovics

Keyword(s):

Numerical Model ◽

Low Cost ◽

Infection Risk ◽

Sensor Data ◽

Effect Of Temperature ◽

Indoor Environments ◽

Building Management ◽

Building Management System ◽

Predicted Risk ◽

Droplet Transmission

Abstract In addition to infection with SARS-CoV-2 via direct droplet transmission or contact with contaminated surfaces, infection via aerosol transport is a predominant pathway in indoor environments. The developed numerical model evaluates the risk of a COVID-19 infection in a particular room based on measurements of temperature, humidity, CO2 and particle concentration, the number of people and instances of speech, coughs and sneezing using a dedicated low-cost sensor system. The model can dynamically provide the predicted risk of infection to the building management system or people in the room. The effect of temperature, humidity and ventilation intensity on the infection risk is shown. Coughing and especially sneezing greatly increase the probability of infection in the room; therefore distinguishing these events is crucial for the applied measurement system.

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Airborne transmission of SARS-CoV-2 in indoor environments: A comprehensive review

Science and Technology for the Built Environment ◽

10.1080/23744731.2021.1977693 ◽

2021 ◽

pp. 1-60

Author(s):

Jialei Shen ◽

Meng Kong ◽

Bing Dong ◽

Michael J. Birnkrant ◽

Jianshun Zhang

Keyword(s):

Indoor Environments ◽

Airborne Transmission ◽

Comprehensive Review

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Impact of meteorological conditions and air pollution on COVID-19 pandemic transmission in Italy

Scientific Reports ◽

10.1038/s41598-020-73197-8 ◽

2020 ◽

Vol 10 (1) ◽

Cited By ~ 3

Author(s):

Simone Lolli ◽

Ying-Chieh Chen ◽

Sheng-Hsiang Wang ◽

Gemine Vivone

Keyword(s):

Air Pollution ◽

Metropolitan Areas ◽

Virus Transmission ◽

Quality Parameters ◽

Meteorological Conditions ◽

Decision Makers ◽

Indoor Environments ◽

Lombardy Region ◽

Autonomous Province

Abstract Italy was the first, among all the European countries, to be strongly hit by the COVID-19 pandemic outbreak caused by the severe acute respiratory syndrome coronavirus 2 (Sars-CoV-2). The virus, proven to be very contagious, infected more than 9 million people worldwide (in June 2020). Nevertheless, it is not clear the role of air pollution and meteorological conditions on virus transmission. In this study, we quantitatively assessed how the meteorological and air quality parameters are correlated to the COVID-19 transmission in two large metropolitan areas in Northern Italy as Milan and Florence and in the autonomous province of Trento. Milan, capital of Lombardy region, it is considered the epicenter of the virus outbreak in Italy. Our main findings highlight that temperature and humidity related variables are negatively correlated to the virus transmission, whereas air pollution (PM2.5) shows a positive correlation (at lesser degree). In other words, COVID-19 pandemic transmission prefers dry and cool environmental conditions, as well as polluted air. For those reasons, the virus might easier spread in unfiltered air-conditioned indoor environments. Those results will be supporting decision makers to contain new possible outbreaks.

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