Friday , November 27 2020

Airflow studies reveal strategies to reduce COVID-19 internal transmission

The flow of social distance

Simulation of pedestrian flow (red and pink particles) confined in a corridor (blue boundary) under conditions of weak social distance. Credits: Kelby Kramer and Gerald J. Wang

Scientists studying the aerodynamics of infectious diseases share steps to prevent transmission in internal activities.

Wear a mask. There was a difference of six meters. Avoid big encounters. As the world waits for a safe and effective vaccine, it controls it COVID-19 pandemics is to comply with these public health guidelines. But as colder weather forces people to spend more time, it will be harder than ever to block the transmission of disease.

At the 73rd Annual Meeting of the Fluid Dynamics Division of the American Physical Society, researchers presented a number of studies to investigate the aerodynamics of infectious diseases. The results suggest risk reduction strategies based on a rigorous understanding of how infectious particles mix with air in confined spaces.

The role played by large drops falling from coughs and sneezes was studied at the beginning of the pandemic. However, documented super-proliferation events have warned that transmitting tiny particles in the air from daily activities can also be a dangerous route of infection. Forty-three of the 61 singers in Washington state, for example, became infected in March after a 2.5-hour choir rehearsal. Of the 67 passengers who spent two hours on the bus with a COVID-19 infected individual in Zhejiang Province (China), 24 were positive.

William Ristenpart Davis, a chemical engineer at the University of California, found that when people speak or sing loudly, they produce a vast number of micron-sized particles compared to those who use a normal voice. The number of particles produced by screaming far exceeds the number generated by coughing. In the cavities, they have seen the flu spread through contaminated dust particles. If the same thing happens SARS-CoV-2the researchers said that objects that release tissues such as contaminated dust can pose a risk.

Abhish, Kumar, Jean Hertzberg, and other researchers at Boulder University in Colorado looked at how the virus could spread during a music performance. The instrumentalists discussed the results of experiments designed to measure aerosol emissions.

“Everyone was very worried about the flutes at first, but it seems like the flutes don’t produce that much,” Hertzberg said. On the other hand, instruments such as clarinets and oboes, which have wet vibrating surfaces, produce a large number of aerosols. The good news is that they can be controlled. “When you put a surgical mask on the hood of a clarinet or trumpet, the number of aerosols drops to the levels in a normal tone of voice.”

Engineers led by Ruichen He of the University of Minnesota investigated a similar risk reduction strategy when studying the flow area and aerosols generated by various instruments. Despite the different levels of aerosols created by the musicians and instruments, they rarely traveled farther than on foot. Based on the findings, the researchers devised a pandemic-sensitive seat model for live orchestras and described where to place filters and audience members to reduce risks.

While many first office employees continue to work from home, employers are exploring ways to safely reopen their workplaces while maintaining a sufficient social distance between individuals. Using two-dimensional simulations that modeled people as particles, Kelby Kramer and Gerald Wang identified conditions that would help avoid congestion and obstruction in confined spaces such as the corridors of Carnegie Mellon University.

Traveling to and from office buildings also carries a risk of infection. Kenny Breuer and his collaborators at Brown University conducted numerical simulations to find out how air moves in passenger car cabins to identify strategies that can reduce the risk of infection. If air enters and leaves the room at points far from the passengers, then it can reduce the risk of transmission. That said, in a passenger car this means that some windows are strategically opened and others closed.

WITH ONE Mathematicians Martin Bazant and John Bush proposed a new safety guideline based on existing models of airborne disease transmission to identify the maximum level of exposure in different indoor environments. Their guideline depends on a metric called “accumulated exposure time,” which is determined by multiplying the number of people in a room by the duration of the exposure. The maximum depends on the size and ventilation rate of the room, the coverage of the occupant’s face, the contamination of the aerosolized particles, and other factors. To easily implement the guidelines, the researchers worked with chemical engineer Kasim Khan to design an application and online spreadsheet that people can use to measure transmission risk in various settings.

As Bazant and Bush wrote in a subsequent paper on the work, being six meters away “provides little protection from constantly falling from aerosol droplets containing pathogens that are small enough in an indoor space.” A better understanding of how contaminated particles move through the room, based on flow dynamics, can lead to faster strategies to reduce transmission.

Featured summaries

Singing, dust and transmission of airborne diseases

Influenza transmission in the guinea pig model is not sensitive to ventilation air velocity: Proof of the Function of Aerosolized Foam

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Risk Assessment of Airborne Diseases in Wind Instrument Games

Physics of social distance flows: Finding patterns in pedestrian flows during the Pandemic using particle-based simulations.

Internal flows of passenger cars and implications for the transmission of airborne diseases

Guideline for limiting indoor air transmission in COVID-19

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