If musical instruments were people, trumpets would be super spreaders. When a trumpeter blows into the mouthpiece, tiny droplets of breath, so-called aerosols, come out of the musician’s mouth, whiz through the brass tube and spray into the air.
During a deadly pandemic, when a musician unknowingly exhales an infectious virus, it presents a potential problem for orchestras. And the trumpet isn’t the only musical health hazard.
“Wind instruments are like machines for aerosolizing breath droplets,” says Tony Saad, chemical engineer and expert in computational fluid dynamics at the University of Utah.
A simple but radical change – reorganizing the musicians – could significantly reduce aerosol formation on stage, reported Dr. Saad and his colleagues in a new study published in Science Advances on Wednesday.
Work began last summer when the Utah Symphony began to wonder if and how they could safely perform again.
“They were looking for people who could provide insights into mitigation strategies that people would believe in.” said James Sutherland, a chemical engineer at the University of Utah and co-author of the study.
Researchers created a detailed computer model of the symphony’s concert hall and noted the location of each vent and the rate of air flow through the HVAC system.
Then they mapped the typical position of every musician. The Utah Symphony, like most modern orchestras, positioned its musicians in a standard pattern, with the stringed instruments at the front of the stage, followed by several rows of wood and brass instruments – the flutes and oboes, then the bassoons and clarinets, and then the trumpets and French horns. The trombones and drums were positioned at the very back of the stage.
To model the spread of aerosols during a concert, they incorporated the latest research led by Jiarong Hong, a mechanical engineer at the University of Minnesota. Working with the Minnesota Orchestra, Dr. Hong and his colleagues measured the concentration and size of aerosol particles emitted by various wind instruments. (Among their findings, trumpet, bass trombone, and oboe posed the greatest risk.)
With these parameters, Dr. Saad and Dr. Sutherland ran computational fluid dynamics simulations to model how the air and aerosols would flow through the Utah concert hall if all the musicians were playing.
The simulation revealed complex air flow patterns. In general, the air flowed down from the air vents in the ceiling to the air return vents in the floor at the back of the stage. But two different eddies also formed, in front and in the back of the stage, they found. “You see these big regions circulating like a big tornado,” said Dr. Saad.
Aerosols can get caught in these eddies, swirl around the stage, and build up over time.
June 23, 2021, 2:36 p.m. ET
The trumpets, which emitted large, concentrated clouds of aerosol, posed a particular problem. When the aerosol plumes from the instruments wandered to the ventilation slots in the back of the stage, they passed directly through the drummers’ breathing zone.
“We saw that and said, ‘Okay, this is a big problem, we have to fix it,'” said Dr. Sutherland. “And given the insight we had about how the river was moving, we said, ‘Well, let’s move some of these instruments.'”
They knew the idea could be controversial; For decades, orchestras have generally been arranged in the same way, for both acoustic and traditional reasons. “We asked them at the beginning of the project: ‘What restrictions do we have to work with? Can we move people? ‘”Said Dr. Sutherland. “And they said, ‘You are doing everything you think possible to reduce the risk.'”
They moved the trumpets all the way back to the stage, right next to the air return ducts. Then they relocated the other wind instruments from the center of the stage and moved them either closer to the rear vents or to the stage doors they suggested opening.
These movements, the team hoped, would allow the aerosols to flow straight out of the concert hall without passing through other musicians’ breathing zones or getting caught in a vortex on the stage. “You want the smoker to sit close to the window,” said Dr. Saad. “That’s exactly what we did here.”
Finally, they moved the instruments that don’t create aerosols at all – the piano and percussion section – into the center of the stage. Together, these optimizations reduced the average aerosol concentration in the musicians’ breathing zones by a factor of 100, the researchers calculated.
Although the exact airflow patterns will be different at each venue, the general principles should apply everywhere, the team said. Orchestras can reduce the risk of aerosol spread by placing the most risky instruments near open doors and air return ports. (Orchestras that can’t do their own computer modeling could put a fog machine on stage and watch the fog flow, the researchers suggested.)
Dr. Hong, who was not involved in the Utah study, praised the modeling work. “It’s not easy to simulate the flow in an orchestra hall,” he said. “You did a great job when it comes to characterizing the river.”
But he wondered if moving musicians was really a viable solution. “We work closely with musicians and they don’t like being rearranged,” he said. (He noted, however, that “I think that’s perfectly fine for a student band.”)
Instead, he suggested a different, albeit equally unconventional, solution: masks for the instruments. In a recent study, he found that covering the bell of a trumpet with a single layer of acoustic fabric can reduce particulate emissions by around 60 percent without compromising sound quality.
The Utah Symphony, on the other hand, was open to rethinking the seating. And when it took the stage last fall, it did so with the stage doors open and the wind instruments in the stern.
“That was a big challenge for the musicians,” said Steven Brosvik, President and CEO of the Utah Symphony and the Utah Opera. “But they all got into it and said, ‘Come on, let’s try.'”
It took the musicians a few weeks to familiarize themselves with the new arrangement, and they plan to revert to their traditional seating configuration in the fall, Brosvik said. But the simulations gave the musicians security and enabled them to get back on stage, he said: “For us it changed our lives.”
The researchers were pleased with the willingness of the musicians to embrace an unusual solution, although their findings may have hit some instrumentalists harder than others. Like Dr. Sutherland said, “We had to apologize to the trumpets in advance.”