scholarly journals Testing mobile air purifiers in a school classroom: Reducing the airborne transmission risk for SARS-CoV-2

2021 ◽  
pp. 1-18
Author(s):  
J. Curtius ◽  
M. Granzin ◽  
J. Schrod
Keyword(s):  
Transmission Risk ◽  
Airborne Transmission ◽  
School Classroom

scholarly journals Testing mobile air purifiers in a school classroom: Reducing the airborne transmission risk for SARS-CoV-2

2020 ◽  
Author(s):  
J. Curtius ◽  
M. Granzin ◽  
J. Schrod
Keyword(s):  
Exchange Rate ◽  
Transmission Risk ◽  
Aerosol Size Distribution ◽  
Airborne Transmission ◽  
Air Exchange Rate ◽  
Information Classification ◽  
School Classroom ◽  
Important Pathway ◽  
High School Classroom ◽  
Air Exchange

ABSTRACTAirborne transmission of SARS-CoV-2 through virus-containing aerosol particles has been established as an important pathway for Covid-19 infection. Suitable measures to prevent such infections are imperative, especially in situations when a high number of persons convene in closed rooms. Here we tested the efficiency and practicability of operating four air purifiers equipped with HEPA filters in a high school classroom while regular classes were taking place. We monitored the aerosol number concentration for particles > 3 nm at two locations in the room, the aerosol size distribution in the range from 10 nm to 10 µm, PM10 and CO2 concentration. For comparison, we performed similar measurements in a neighboring classroom without purifiers. In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90 % within less than 30 minutes when running the purifiers (air exchange rate 5.5 h-1). The reduction was homogeneous throughout the room and for all particle sizes. The measurements are supplemented by a calculation estimating the maximum concentration levels of virus-containing aerosol from a highly contagious person speaking in a closed room with and without air purifiers. Measurements and calculation demonstrate that air purifiers potentially represent a well-suited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially. Staying for two hours in a closed room with a highly infective person, we estimate that the inhaled dose is reduced by a factor of six when using air purifiers with a total air exchange rate of 5.7 h-1.Information ClassificationGeneral

scholarly journals Risk assessment for long and short range airborne transmission of SARS-CoV-2, indoors and outdoors, using carbon dioxide measurements.

2021 ◽  
Author(s):  
Florian Poydenot ◽  
Ismael Abdourahamane ◽  
Elsa Caplain ◽  
Samuel Der ◽  
Jacques Haiech ◽  
...  
Keyword(s):  
Public Health ◽  
Health Policy ◽  
Public Health Policy ◽  
Short Range ◽  
Epidemiological Data ◽  
Public Spaces ◽  
Viral Transmission ◽  
Transmission Risk ◽  
Reproduction Rate ◽  
Airborne Transmission

A quantitative analysis of the viral transmission risk in public spaces al- lows us to identify the dominant mechanisms that a proactive public health policy can act upon to reduce risk, and to evaluate the reduction of risk that can be obtained. The contribution of public spaces to the propa- gation of SARS-CoV-2 can be reduced to a level necessary for a declining epidemic, i.e. an overall reproduction rate below one. Here, we revisit the quantitative assessment of indoor and outdoor transmission risk. We show that the long-range aerosol transmission is controlled by the flow rate of fresh air and by the mask filtering quality, and is quantitatively re- lated to the CO2 concentration, regardless the room volume and the num- ber of people. The short-range airborne transmission is investigated ex- perimentally using dedicated dispersion experiments performed in two shopping malls. Exhaled aerosols are dispersed by turbulent draughts in a cone, leading to a concentration inversely proportional to the squared dis- tance and to the flow velocity. We show that the average infection dose, called the viral quantum, can be determined from epidemiological data in a manner consistent with biological experimental data. Practical implications. The results provide quantitative guidance useful for making rational public health policy decisions to prevent the dominant routes of viral transmission through reinforced ventilation, air purification, mechanical dispersion using fans, and incentivizing the wear- ing of correctly fitted, quality facial masks (surgical masks, possibly cov- ered by another fabric mask, or non-medical FFP2 masks). Taken to- gether, such measures significantly reduce the airborne transmission risk of SARS-CoV-2.

The Potential for Airborne Transmission of SARS-CoV-2 in Sport: A Cricket Case Study

2021 ◽  
Author(s):  
Rory England ◽  
Nicholas Peirce ◽  
Thamindu Wedatilake ◽  
Joseph Torresi ◽  
Simon Kemp ◽  
...  
Keyword(s):  
Risk Factors ◽  
Relative Orientation ◽  
Transmission Risk ◽  
Risk Category ◽  
Airborne Transmission ◽  
Event Duration ◽  
Factors Affecting ◽  
Video Footage ◽  
Compound Effect

AbstractA review of risk factors affecting airborne transmission of SARS-CoV-2 was synthesised into an ‘easy-to-apply’ visual framework. Using this framework, video footage from two cricket matches were visually analysed, one pre-COVID-19 pandemic and one ‘COVID-19 aware’ game in early 2020. The number of opportunities for one participant to be exposed to biological secretions belonging to another participant was recorded as an exposure, as was the estimated severity of exposure as defined from literature. Events were rated based upon distance between subjects, relative orientation of the subjects, droplet generating activity performed (e. g., talking) and event duration. In analysis we reviewed each risk category independently and the compound effect of an exposure i. e., the product of the scores across all categories. With the application of generic, non-cricket specific, social distancing recommendations and general COVID-19 awareness, the number of exposures per 100 balls was reduced by 70%. More impressive was the decrease in the most severe compound ratings (those with two or more categories scored with the highest severity) which was 98% and the reduction in exposures with a proximity <1 m, 96%. Analysis of the factors effecting transmission risk indicated that cricket was likely to present a low risk, although this conclusion was somewhat arbitrary omitting a comparison with a non-cricketing activity.

scholarly journals Airborne dispersion of droplets during coughing: a physical model of viral transmission

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hongying Li ◽  
Fong Yew Leong ◽  
George Xu ◽  
Chang Wei Kang ◽  
Keng Hui Lim ◽  
...  
Keyword(s):  
Social Protection ◽  
Flow Simulation ◽  
Droplet Evaporation ◽  
Transmission Risk ◽  
Focused Attention ◽  
Droplet Dispersion ◽  
Airborne Transmission ◽  
Transmission Potential ◽  
Droplet Sizes ◽  
Low Humidity

AbstractThe Covid-19 pandemic has focused attention on airborne transmission of viruses. Using realistic air flow simulation, we model droplet dispersion from coughing and study the transmission risk related to SARS-CoV-2. Although this model defines most airborne droplets as 8–16 µm in diameter, we infer that larger droplets of 32–40 µm in diameter may potentially be more infectious due to higher viral content. Use of face masks is therefore recommended for both personal and social protection. We found social distancing effective at reducing transmission potential across all droplet sizes. However, the presence of a human body 1 m away modifies the aerodynamics so that downstream droplet dispersion is enhanced, which has implications on safe distancing in queues. At 1 m distance, we found that an average of 0.55 viral copies is inhaled for a cough at median loading, scalable up to 340 copies at peak loading. Droplet evaporation results in significant reduction in droplet counts, but airborne transmission remains possible even under low humidity conditions.

scholarly journals The role of classroom volume, natural ventilation and voice reduction in transmission risk of SARS-CoV2 in schools

2021 ◽  
Author(s):  
Alessandro Zivelonghi ◽  
Massimo Lai
Keyword(s):  
Natural Ventilation ◽  
Risk Model ◽  
Emission Rate ◽  
Winter Season ◽  
Transmission Risk ◽  
Outdoor Temperature ◽  
Airborne Transmission ◽  
Air Exchange Rate ◽  
Theoretical Risk

School classrooms are enclosed settings where students and teachers spend prolonged periods of time and therefore risky environments for airborne transmission of SARS-CoV2. While countries worldwide have been pursuing different school reopening strategies, most countries are planning to keep schools open during the whole winter season 2020/21. This poses a controversial issue: ventilation of classrooms (an essential mitigation factor for airborne transmission) is expected to sensibly decrease due to outdoor temperatures getting colder and regulators going to allow less restrictive policies on windows closure. Moreover, most schools are not provided with mechanical ventilation/filtartion systems to date. Fundamental and urgent questions to be addressed are therefore: to which extent can we contain the airborne transmission risk in schools through natural ventilation only? can we reduce the airborne risk with easy to implement countermeasures like lowering the speaking volume? To answer these questions a theoretical risk model based on the emission rate of viral charge from an infective subject has been developed extending previous models for tubercolosis and influenza. The case of an infective student or an infective teacher in a classroom, as well as an infective teacher with microphone have been investigated and compared with infection thresholds for different group sizes. The model also considers the influence of indoor-outdoor temperature difference on the air exchange rate, which seems to be particularly strong during winter.

scholarly journals The Facility Infection Risk Estimator™: A web application tool for comparing indoor risk mitigation strategies by estimating airborne transmission risk

2021 ◽  
pp. 1420326X2110395
Author(s):  
Marcel Harmon ◽  
Josephine Lau
Keyword(s):  
Web Application ◽  
Risk Mitigation ◽  
Infection Risk ◽  
Mitigation Strategies ◽  
Transmission Risk ◽  
Physical Parameters ◽  
Airborne Transmission ◽  
Risk Mitigation Strategies ◽  
Risk Estimator ◽  
Number Of Individuals

The COVID-19 pandemic created needs for (a) estimating the existing airborne risk of infection from SARS-CoV-2 in existing facilities and new designs and (b) estimating and comparing the impacts of engineering and behavioural strategies for contextually reducing that risk. This paper presents the development of a web application to meet these needs, the Facility Infection Risk Estimator™, and its underlying Wells–Riley based model. The model specifically estimates (a) the removal efficiencies of various settling, ventilation, filtration and virus inactivation strategies and (b) the associated probability of infection, given the room physical parameters and number of individuals infected present with either influenza or SARS-CoV-2. A review of the underlying calculations and associated literature is provided, along with the model's validation against two documented spreading events. The error between modelled and actual number of additional people infected, normalized by the number of uninfected people present, ranged from roughly –18.4% to +9.7%. The more certain one can be regarding the input parameters (such as for new designs or existing buildings with adequate field verification), the smaller these normalized errors will be, likely less than ±15%, making it useful for comparing the impacts of different risk mitigation strategies focused on airborne transmission.

scholarly journals Monitoring carbon dioxide to quantify the risk of indoor airborne transmission of COVID-19

Flow ◽  
2021 ◽  
Vol 1 ◽  
Author(s):  
Martin Z. Bazant ◽  
Ousmane Kodio ◽  
Alexander E. Cohen ◽  
Kasim Khan ◽  
Zongyu Gu ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Infected Individual ◽  
Face Mask ◽  
The United States ◽  
Transmission Risk ◽  
National Academy Of Sciences ◽  
Airborne Transmission ◽  
Infectious Dose ◽  
Indoor Space ◽  
Using Data

Abstract A new guideline for mitigating indoor airborne transmission of COVID-19 prescribes a limit on the time spent in a shared space with an infected individual (Bazant & Bush, Proceedings of the National Academy of Sciences of the United States of America, vol. 118, issue 17, 2021, e2018995118). Here, we rephrase this safety guideline in terms of occupancy time and mean exhaled carbon dioxide ( ${\rm CO}_{2}$ ) concentration in an indoor space, thereby enabling the use of ${\rm CO}_{2}$ monitors in the risk assessment of airborne transmission of respiratory diseases. While ${\rm CO}_{2}$ concentration is related to airborne pathogen concentration (Rudnick & Milton, Indoor Air, vol. 13, issue 3, 2003, pp. 237–245), the guideline developed here accounts for the different physical processes affecting their evolution, such as enhanced pathogen production from vocal activity and pathogen removal via face-mask use, filtration, sedimentation and deactivation. Critically, transmission risk depends on the total infectious dose, so necessarily depends on both the pathogen concentration and exposure time. The transmission risk is also modulated by the fractions of susceptible, infected and immune people within a population, which evolve as the pandemic runs its course. A mathematical model is developed that enables a prediction of airborne transmission risk from real-time ${\rm CO}_{2}$ measurements. Illustrative examples of implementing our guideline are presented using data from ${\rm CO}_{2}$ monitoring in university classrooms and office spaces.

Measuring interpersonal transmission of expiratory droplet nuclei in close proximity

2021 ◽  
pp. 1420326X2110296
Author(s):  
Linzhi Fu ◽  
Peter V. Nielsen ◽  
Yi Wang ◽  
Li Liu
Keyword(s):  
Disease Transmission ◽  
Short Range ◽  
Close Contact ◽  
Measurement Techniques ◽  
Transmission Risk ◽  
Interpersonal Distance ◽  
Airborne Transmission ◽  
Face To Face ◽  
Close Proximity ◽  
Droplet Nuclei

Increasing evidence supports the significant role of short-range airborne transmission of viruses when in close contact with a source patient. A full-scale ventilated room (Cleanliness: ISO 14644–1 Class 5) and two face-to-face standing breathing thermal manikins were used to simulate a source individual and a susceptible person. Monodisperse particle generation and measurement techniques were used to evaluate the effect of virus-laden droplet nuclei size on short-range airborne transmission risk. We analysed four particle sizes (1.0, 1.5, 2.5, and 5.0 µm) to simulate the transport of exhaled droplet nuclei within an interpersonal distance of 0.5 m. The results indicated that the size distribution of airborne droplet nuclei could significantly influence transmission, with the inhalation fraction decreasing with increasing droplet nuclei size. Additionally, results showed that proximity to the source manikin could influence transmission. Inhalation fraction decreased with increasing interpersonal distance, fitting well with the 1/ d rule of droplet nuclei concentration decay. Our findings improve the understanding of the mechanism of the disease transmission.

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