As colder weather forces people to spend more time in public spaces, blocking the transmission of COVID-19 is becoming more difficult. At the 73rd Annual Meeting of the American Physical Society, scientists presented a series of studies on the aerodynamics of infectious diseases to reduce transmission risk.
Research at the start of the pandemic focused on large, rapidly falling droplets from coughs and sneezes and their effect on the spread of the new type of coronavirus. However, later, the transfer of tiny particles through the air is also dangerous and requires careful study.
William Ristenpart, a chemical engineer at the University of California, Davis, found that when people speak or sing loudly, they produce significantly more micron-sized particles than when they use a normal voice. The amount of particles produced during screaming is significantly higher than the amount released during coughing.
While many former office workers continue to work from home, employers explore ways to safely open their jobs while maintaining sufficient social distance between people. Using 2D modeling, Carnegie Mellon University’s Kelby Cramer and Gerald Wang have identified conditions that can help avoid crowding in confined spaces. In particular, engineers suggest paying attention to corridors in office buildings. There, the spread of the virus is especially dangerous.
Traveling to and from office buildings in light vehicles, including taxis, is also dangerous. Kenny Breuer and his collaborators at Brown University have performed numerical simulations of how the air travels through passenger car cabins. If air enters the space and exits at locations away from passengers, it reduces transmission risk.
MIT mathematicians Martin Bazant and John Bush have proposed new safety guidelines based on existing airborne disease transmission models to determine maximum exposure levels in different rooms. Their recommendations depend on a metric called “cumulative exposure time.” It is determined by multiplying the number of people in a room by the duration of the potential exposure to the virus.
The maximum depends on the size and intensity of ventilation in the room, whether people wear a mask, and on the infectivity of aerosol particles and other factors. To make it easier to implement the guideline, the researchers worked with chemical engineer Qasim Khan to develop an app and spreadsheet that people can use to assess transmission risk in different settings. Scientists’ materials will become available after December 3.
As Bazant and Bush wrote in an upcoming paper on the work, the 2-meter distance “provides little protection against pathogen-carrying aerosol droplets.” A better flow dynamics-based understanding of how contaminated particles move around a room may ultimately lead to smarter transmission reduction strategies.