Do wind instruments spread COVID aerosol droplets?

During the COVID-19 pandemic, many live music events and festivals were postponed and even canceled to protect musicians and the public. When they started performing again, many groups resorted to performing with secluded or limited crowds. They also adapted their repertoire to promote pieces with strings and made significant changes in the number of musicians and their positions in the hall.

Orchestral ensembles face a special challenge. Contamination is a major concern, particularly whether wind instruments are carriers of contamination from aerosol dispersion.

In Physics of liquidsResearchers from the University of Pennsylvania collaborated with musicians from the Philadelphia Orchestra to deepen our understanding of how much aerosol is produced and distributed by wind instruments.

“Ideally, musicians would sit close together to compose the best sound, but such an arrangement became a problem during the COVID pandemic,” said author Paulo Arratia of the University of Pennsylvania.

The researchers used visualization to characterize the flow and then tracked fog particles in the air with a laser. They also measured the aerosol concentration of wind instruments with a particle counter.

They then combined these two measurements to develop a simple equation to describe aerosol dispersion, where the aerosol velocity decreases with distance from the instrument. The idea is to help other researchers determine how far aerosols will travel by measuring the exhaust velocity. This indicates how quickly the current will decrease.

Aerosols emitted by wind instruments had a similar concentration and size distribution compared to normal speech and respiratory events.

“We were surprised that the amount of aerosol produced is of the same range as normal speech,” Arratia said. “I expected much higher flow rates and aerosol concentrations.”

Flow measurements (using particle frame rate measurement) showed that the jet velocities when exiting the air are much lower than when coughing and sneezing. For most instruments, the maximum decay length is less than 2 meters from the opening of the instrument. Therefore, wind musicians should keep a meter and a half apart, similar to the recommendation for individuals.

The researchers will then look at contamination from aerosol dispersion from a group standpoint to understand how much aerosol and flow is produced by the entire orchestra playing together.

“Hopefully this manuscript will guide health officials to develop protocols for safe, live music events,” Arratia said.