Under conditions of weak social distance, simulation of a limited pedestrian counterflow (red and pink particles) in a wayway (blue boundary). Credit: Calby Kramer and Gerald J. Wang
Scientists studying the aerodynamics of infectious diseases share measures to prevent infection during indoor activities.
Wear a mask. Stay six feet away. Avoid large gatherings. As the world awaits safe and effective vaccines, control them COVID-19 Epidemics depend on comprehensive adherence to these public health guidelines. But, because cold weather forces people to spend more time indoors, blocking the spread of the disease will be more challenging than ever.
At the 73rd annual meeting of the American Physical Society’s Division of Fluid Dynamics, researchers presented a number of studies examining the aerodynamics of infectious diseases. Their results suggest a risk reduction strategy based on a strict understanding of how infected particles are absorbed into the air in a limited space.
Research at the onset of the epidemic focused on the role played by large, rapidly falling drops produced by coughing and sneezing. However, documented super spreader events have indicated that airborne transmission of small particles from everyday activities can also be a dangerous route of infection. Fifty-two of Washington’s 61 singers, for example, became infected after a 2.5-hour rehearsal in March. Of the 67 passengers who spent two hours on the bus with a COVID-19 infected person in China’s Zhejiang province, 24 later tested positive.
William Ristonpart, a chemical engineer at the University of California, Davis, observed that when people speak or sing loudly, they produce micron-sized particles dramatically compared to the normal sound they use. The particles produced when they screamed, they found, exceeded the number produced during coughing. In guinea pigs, they found that influenza was spread by contaminated dust particles. If the same is true for SARS-CoV-2Then the substances that release contaminated dust, such as tissues, can increase the risk, the researchers said.
Abhishek Kumar, Jean Hertzberg, and other researchers at Boulder, University of Colorado, focused on how the virus is transmitted during music performances. They discussed the results of experiments designed by instrumentalists to measure aerosol emissions.
“Everyone was concerned about the flute as early as possible, but it turned out that the flute is not produced that much,” Hertzberg said. Devices such as Clarinet and Obo, on the other hand, which have wet vibrating surfaces, produce abundant aerosols. The good news is that they can be controlled. “When you put a surgical mask on a clarinet or trumpet bell, it lowers the amount of aerosols down to the level in the normal tone of the sound.”
Engineers led by Ruishen Haney at the University of Minnesota examined their flow field and their strategy of similar risk reduction in their study of aerosols produced by different instruments. Despite the level of various aerosols produced by the musician and the instrument, they rarely travel more than one foot. Based on their findings, the researchers modeled an epidemic-sensitive meeting for a live orchestra and described where to place filters and audience members to reduce risk.
While many previous office feebound employees continue to work from home, employers are looking for ways to safely reopen their workplaces while maintaining sufficient social distance between individuals. Calby Kramer and Gerald Wang of Carnegie Mellon University modeled people as particles using two-dimensional simulations, identifying situations that would help avoid congestion and jamming in confined spaces such as Hall Loves.
Traveling and traveling to office fee buildings in passenger cars also carries a risk of infection. Kenny Brewer of Brown University and his colleagues performed statistical simulations of how air moves through a passenger car cabin to identify strategies that would reduce the risk of infection. If air enters and exits the room in places too far away from passengers, it can reduce the risk of transmission. In a passenger car, they said, it meant strategically opening some windows and closing others.
MIT Mathematicians Martin Besant and John Bush proposed new safety guidelines built on existing models of airborne decision transmission to identify maximum levels of exposure to a variety of indoor environments. Their guide is based on a metric, called “accumulated exposure time”, which is determined by multiplying the number of people in a room by the open period. The maximum depends on the size of the room and the ventilation rate, its occupant face cover, infectious infection of aerated particles and other factors. To facilitate easy implementation of the guidelines, the researchers worked with chemical engineer Qasim Khan to design an application and spread online spreadsheet, which people can use to measure the risk of transmission in different settings.
Bazant and Bush wrote in their next paper at work that, being six feet apart, “provides little protection against pathogenic aerosol drops that can be continuously absorbed by indoor space.” A better, flow-dynamics-based understanding of how infected particles move around the room can ultimately achieve a clever strategy of reducing transmission.
Published abstracts
Singing, Dust and Airborne Disease Transmission
Influenza transmission ventilation in guinea pig models is not sensitive to airflow speeds: evidence for the role of aerosolized foci
Aerosols in performance
Risk assessment of airborne disease transmission during wind instrument plays
Flow Physics of Social Distinctors: Patterns Emerging in Epidemic-Era Pedestrian Trends Using Particle-Based Simulations
Instructions for inbound flow and airborne disease transmission
Guide to limiting COVID-19 indoor airborne transmission
