CU-Boulder researchers investigate aerosols from wind instruments

Original article published on Sharps & Flatirons here.

Is playing wind instruments safe during COVID-19?

It can be. But it requires a layered safety approach.

Researchers at CU-Boulder recommend masks with mouth slits, bell covers, efficient ventilation and social distancing protocols. These guidelines are intended to reduce wind instrument’s aerosols, a key to safe music-making during the pandemic.

The CU team, led by mechanical engineering professor Shelly Miller, began researching aerosols and music earlier this year. Miller’s initial research focused on the Skagit Valley choir rehearsal in Washington State as a COVID-19 super-spreader in March, showing that singing unmasked indoors spreads COVID-19 via aerosols.

In June, Miller and her team began to study wind instruments and aerosols in collaboration with researchers at the University of Maryland. This study was commissioned by an international coalition of over 120 performing arts organizations. Lead funders for the study include the NAMM Foundation, National Federation of State High School Associations, D’addario Foundation and College Band Directors National Association.

The study’s preliminary results, released in October, include aerosol research for four instruments, clarinet, flute, horn and trumpet, and a soprano singer. Analyzing aerosol emission concentrations and flow pathways, the researchers confirmed that wind instruments produce aerosols as predicted.

“What we have been seeing in our data recently has been confirming what we saw earlier,” Tehya Stockman, a graduate student in mechanical engineering and clarinetist, says. “We just have more data now.”

Stockman has been working in Miller’s lab since the study began. She measures quantities of aerosol emissions, often using her own clarinet as she works, and compares different risk mitigation strategies including bell covers. She admits creating guidelines to reduce risk of aerosol transmission has been challenging with so many unknown factors.

“When you are thinking about the risk of getting COVID-19 from people playing music, there are so many different factors,” Stockman says. “It’s not just how far away you are from someone else. What does the ventilation system look like? Are you playing inside or outside? Are people wearing masks? There are so many factors that you can’t know for each situation. These guidelines are more strict, so it can be applied to a wider range of situations.”

Whether rehearsing indoors or outdoors, basic guidelines apply: six feet of distance, masks and bell covers. Using computational fluid dynamics (CFD), meaning air flow simulations, researchers in Maryland confirmed the effectiveness of social distancing with six feet apart. Twelve feet for wind instruments and singers is a conservative estimate, to keep musicians even safer.

In order to reduce aerosols, two types of masks are recommended for rehearsals. A mask with a slit should be used when playing, and at all other times, especially when moving or talking, a normal mask should be worn.

Nylon bell covers decrease aerosols significantly, according to Stockman. Larger aerosols, which usually move in a straight line, are trapped by bell covers. Bell covers are especially important for straight-shaped instruments, such as a trumpet or clarinet, which have higher aerosol emission than curved instruments. Although smaller aerosols can follow air streamlines out of key holes, the quantity is much lower. 

Further research on key hole aerosols will be included in the next round of results.

In terms of location, outdoor rehearsals are recommended. However, as winter arrives, this is no longer possible. When indoors, musicians should have HEPA filters installed and must consider the efficiency of the room’s HVAC systems. HVAC efficiency will affect the air exchange rate—the number of times air is replaced in a room each hour. 

To calculate the risk of a specific indoor rehearsal space, musicians can use CU’s Risk Estimator Tool. On average most spaces will have three air exchanges per hour. Using this assumption, researchers in Maryland created CFD simulations of risk for an hour in an indoor space. They found that infection risk increases little from 0 to 30 minutes, followed by a sharp increase of risk from 30 to 60 minutes. Thus, they recommend rehearsals should include 30 minutes of playing, followed by a 15 minute break, where musicians leave the room, allowing for nearly an entire air exchange to take place.

At CU’s College of Music, musicians are following these guidelines for the fall semester. For band and chamber music rehearsals, students can be seen with two masks and bell covers, playing six to 12 feet away from each other.

For Stockman, seeing the impact of her research for CU and the broader music community has been encouraging. As a musician herself, she knows the importance of in-person music-making and is happy that her research can help facilitate that.

“Some music programs were going to be cut completely from schools,” Stockman says. “Once they are cut, they are hard to bring back. But now quite a few of them didn’t have to be cut.

“Our research showed there are ways to play music safely.”