“When you observe the flow, you see these puffs and eddies, and we know that they spread, but we didn’t know if there was going to be anything general at all between these instruments,” says Jerolmack. The flute was an outlier but still only reached flow speeds of around 0.7 meters per second. Thus, measuring their concentration and the flow became important to understand the potential risk of a musician potentially passing SARS-CoV-2 to another person.Įvaluating the velocity of the flow, the researchers measured speeds of roughly 0.1 meters per second, orders of magnitude slower than that of a cough of sneeze, which can travel 5 to 10 meters per second.
Particles of this size, the researchers say, are small enough to travel far through the air, provided the air flow is strong enough to take them there. It proved somewhat surprising to the researchers to find that the wind instrument musicians produced aerosols that were similar in concentration to those emitted during normal breathing and speaking, from about 0.3 to 1 micrometer in diameter. The musicians played scales continuously for two minutes.
“It’s just like on a rainy day you will see the water drops if the sun shines through,” Arratia says. The researchers then shone a laser beam through the “fog” created by the humidifier, lighting up the aerosol particles and allowing them to be captured by a high-speed camera and particle counter. This arrangement was only shifted for the flute player, for whom the humidifier was placed near the musician’s mouth instead of the bell, since air travels over the mouthpiece while playing that instrument. In order to visualize and track the aerosols flowing out of the instruments as the musicians played, the researchers operated a humidifier that emitted water vapor droplets at the bell end of the instruments. To gather data, the researchers invited Orchestra musicians to campus, bringing along their wind instruments, including flutes, tubas, clarinets, trumpets, oboes, and bassoons. Those things are important to understand.” “Or you can have a lot of aerosols that get concentrated in a narrow beam. “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 and Penn Engineering. The research hinged on the questions of how many aerosol particles the musicians generated, how densely the particles were emitted from the instruments, and how fast they traveled through the air. As they gathered this information, along with the testing and case tracking that Penn Medicine was doing, it helped us make decisions with confidence.” Experimental approach “Those decisions included the spacing between players, the distancing between sections, who needed to mask. “Having experts like Paulo and Doug, who could measure particle size and trajectory and distance and velocity, were really valuable in making decisions for the orchestra,” says Brennan, who now serves on the Orchestra’s Board of Directors. The results not only informed the arrangement of the Philadelphia Orchestra as they resumed performances in the summer of 2020 but also laid the groundwork for how other musical groups might think about safely gathering and playing. Now, in a publication in Physics of Fluids, Arratia, Jerolmack, and colleagues report on their findings, which suggest the aerosols musicians produce dissipate within about six feet. “The challenge was, how can we get away from this to the point where they can play unobstructed but still safely,” Arratia says. “And yet, if they needed to be separated with plexiglass, that also posed a problem.” The musicians reported problems hearing one another and poor sightlines with plexiglass dividers. “The Orchestra director didn’t want the musicians to be far apart they needed to be close together to produce the best sound,” says Arratia, of the School of Engineering and Applied Science. Brennan, chief medical officer of the University of Pennsylvania Health System, the Orchestra sought expertise to help understand whether its musicians could return to playing in a safe physical arrangement that would minimize the chances of exposing one another, or their audiences, to SARS-CoV-2. It was 2020, and the Philadelphia Orchestra, like so many cultural institutions, had suspended performances due to the COVID-19 pandemic.
The latest research from the labs of Penn scientists Paulo Arratia and Douglas Jerolmack was an answer to “a call for help,” says Arratia.
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