ScienceDaily: Music-making and aerosol flow

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Arratia said that the most recent research from Penn scientists Douglas Jerolmack (Paulo Arratia) was an answer “to a call for help.”

It was 2020, and Philadelphia Orchestra, as many other cultural institutions, had temporarily suspended performances because of the COVID-19 epidemic. P.J. Brennan, chief medical officer of University of Pennsylvania Health System, was asked by the Orchestra to provide expertise in order to determine if its musicians could be allowed to return to playing in a safe arrangement that would reduce the risk of them being exposed to SARS-CoV-2.

Arratia of School of Engineering and Applied Science explains that “the Orchestra director didn’t want the musicians far apart. They needed them to be close together to make the best sound,” she said. However, it was a problem if the musicians needed to be separated by plexiglass. With plexiglass partitions, the musicians had difficulty hearing each other and poor sightlines. Arratia says, “The challenge is how can we get rid of this to the point that they can safely play unobstructed.”

Here’s the link to the publication. Nature CommunicationsArratia and Jerolmack along with colleagues present their findings. It appears that the aerosols musicians use dissipate within six feet. These results informed the Philadelphia Orchestra’s arrangement for their summer 2020 performances, and also provided the basis for other musical groups to gather safely.

Brennan, who is now a member of the Orchestra’s Board, says that having experts such as Doug and Paulo, who could measure particle size, trajectory, distance, velocity and trajectory, was really helpful in making decisions. These decisions involved the spacing between players and the distance between sections. Who needed to mask? It helped us make confident decisions as they gathered all this information along with the testing and case monitoring that Penn Medicine was doing.

Experimental approach

The research focused on three questions: how many aerosol particles did the musicians produce, how densely the particles were released from the instruments and how fast they moved through the air.

“You can have a big jet of air coming out, but if the aerosol concentration is very low it doesn’t much matter,” says Jerolmack, of the School of Arts & Sciences. Or, you can have many aerosols that are concentrated into a narrow beam. These are all important things to know.

Researchers invited Orchestra musicians on campus to gather data. They brought their wind instruments, which included flutes, clarinets (clarinets), trumpets, clarinets, trumpets and bassoons.

Researchers installed a humidifier at the bell end to track and visualize the aerosols that flowed out of the instruments during musicians’ playing. The humidifier was not moved for the flute player. Instead, the humidifier was placed next to the musician’s mouth. Air travels above the mouthpiece during the instrument’s play.

The researchers then used a laser beam to lighten the fog created by the humidifier. This lit up aerosol particles, which were then captured using a high-speed camera with a particle counter.

Arratia says, “It’s like a rainy morning; you will see water drops if there is sun shining through.”

The musicians played scales for two minutes continuously. Researchers were somewhat surprised to discover that aerosols produced by musicians playing wind instruments were comparable to those released during normal breathing. They ranged in size from 0.3 to 1 millimeter.

Researchers say particles this small can travel through the air at speeds of up to 2,000 miles per hour, provided that the airflow is strong enough. It was therefore important to measure their concentrations and determine the risk that a musician could transmit SARS-CoV-2.

The researchers measured the flow velocity at speeds of around 0.1 meters per sec. This is orders of magnitude slower that a cough or sneeze which can travel 5-10 meters per sec. The flute was an exception, but it still reached flow speeds of approximately 0.7 meters per second.

Jerolmack states, “When you look at the flow, there are these puffs or eddies. And we know that they spread. But we didn’t know what would happen if anything general between these instruments.” We found that we can predict how far aerosols travel by measuring only flow, aerosol concentration, and counts.

Music is flowing

The researchers found that the aerosols generated by these “miniconcerts,” dissipated into the background air stream, and settled within about two meters or six feet. This is similar to what was measured for speaking or breathing. Only trombone and flute-generated aerosols traveled further than that, perhaps because the air travels above the instrument rather than acting as a mask to stop the spread of aerosols.

Researchers speculate that woodwind instruments emit slightly lower levels of aerosols than brass instruments. This could be because they absorb some humidity, and the many holes in the instrument might reduce some of the aerosols’ flow.

The researchers did not measure any quality of SARS CoV-2. However, the results can be used to predict how music may affect the transmission of other respiratory diseases.

Arratia states, “Now you have something that you can use for future concerns, such as an outbreak of flu or something similar.” You can take our flow findings and plug them in to your own numbers about infectiousness or viral loads and adapt it for understanding risk.

He said, “This was not a problem that we deal with regularly, but it was something we felt compelled on.” It was great fun and made a significant difference in the difficult times during the pandemic.

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