University of Colorado Boulder
1111 Engineering Drive
Boulder, CO 80309
Popular version of 1pMU4 – Flow visualization and aerosols in performance
Presented Monday afternoon, May 23, 2022
182nd ASA Meeting in Denver, Colorado
Click here to read the abstract
Outbreaks from choir performances, such as the Skagit Valley Choir, showed that singing brought potential risk of COVID-19 infection. The risks of airborne infection from other musical performances, such as playing wind instruments or performing theater are less known. In addition, it is important to understand methods that can be used to reduce infection risk. In this study, we used a variety of methods, including flow visualization, aerosol and CO2 measurements to understand the different components that can lead to transmission risk from musical performance and risk mitigation. We have tested eight musical instruments, both brass and woodwinds, and also singing, with and without a mask/bell cover.
We started with the flow visualization of exhalations (from singers and voice actors) and resultant jets (from musical instruments) using (a) the schlieren method, and, (b) imaging with a laser sheet in a room filled with stage fog. These visualization tools helped identify the spatial location with maximum airflow (i.e. velocities) for aerosol and CO2 measurements, and showed the structure of the flows.
Figure 1: Schlieren method – proof of concept, opera singer. Courtesy: Flowvis.org
Figure 2: Laser sheet imaging – proof of concept, oboe. Courtesy: Flowvis.org
Our flow visualization velocity estimates indicated that using a barrier, such as a mask or a bell cover significantly reduced axial (exhaust direction) velocities. Keep in mind the jets observed using either method have the same composition as human exhalation, i.e. N2, O2, CO2, and trace gases.
Figure 3: Maximum measured axial velocities, with and without cover/mask Courtesy: Flowvis.org
We measured exhaled/exhausted CO2 and aerosol particles from the musicians. Our results indicate that aerosol spikes can be expected when there is a spike in CO2 measurements.
Figure 4: Combined Aerosol and CO2 time series for singing. Courtesy: Tehya Stockman
Figure 5: Aerosol data for performance with and without a mask/cover. Courtesy: Tehya Stockman
These results show that masks on instruments and singers while performing significantly decreases the amount of aerosols measured, thus providing one effective solution to reducing the risk of viral airborne transmission through aerosols. Musicians reported small differences in how the instruments felt, but very little difference in how they sounded.