Do wind instruments disperse COVID aerosol droplets? The measurement of the outflow velocity determines the distance traveled by the aerosols and, therefore, the decay rate of the outflow
During the COVID-19 pandemic, many live music events and festivals have been postponed and even canceled to protect musicians and audience members. When they started performing again, many bands resorted to performances with distant or limited crowds. They also adapt their repertoire to favor string pieces and considerably modify the number of musicians and their positions in the auditorium.
Orchestral ensembles faced a particular challenge. Contamination is a major concern: in particular, if wind instruments are vectors of contamination by dispersion of aerosols.
In Fluid physicsby AIP Publishing, researchers at the University of Pennsylvania worked with musicians from the Philadelphia Orchestra to further our understanding of the amount of aerosol produced and dispersed by wind instruments.
“Ideally, musicians would sit next to each other to compose the best sound, but such an arrangement has become a problem during the COVID pandemic,” said author Paulo Arratia, of the University of Pennsylvania.
The researchers used visualization to characterize the flow, then tracked the fog particles in the air with a laser. They also measured the aerosol concentration of wind instruments with a particle counter.
Next, they combined these two measurements to develop a simple equation to describe aerosol scatter, in which aerosol velocity decreases with distance from the instrument. The idea is to help other researchers determine the distance traveled by aerosols by measuring the speed of the outflow. This indicates how fast the flow will decrease.
Aerosols emitted from wind instruments shared a similar concentration and size distribution to normal speech and breathing events.
“We were surprised that the amount of aerosol produced was in the same range as normal speech,” Arratia said. “I expected much higher flow velocities and aerosol concentrations.”
Flow measurements (using particle image velocimetry) have shown that outflow jet velocities are much lower than cough and sneeze events. For most instruments, the maximum decay length is less than 2 meters from the opening of the instrument. Therefore, wind musicians should stay 6 feet apart, as the recommendation for individuals.
Researchers will then look at aerosol scatter contamination from a group perspective to understand the amount of aerosols and fluxes produced by the entire orchestra playing together.
“I hope this manuscript will guide health officials in developing protocols for safe, live music events,” Arratia said.
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Material provided by American Institute of Physics. Note: Content may be edited for style and length.