A scientific approach to orchestra staging
In the early stages of planning our return to the stage, Utah Symphony musicians were actively searching for information regarding airflow and aerosols from wind instruments. There were some very preliminary aerosol studies, but none seemed sufficient to answer our most important question: how safe is it to be onstage at Abravanel Hall? We began to wonder if a study could be done here, to give us specific information that we could use to help form our safety plan.
Utah is a state with very few restrictions on holding live concerts, but we also have limited access to testing and a virus that has moved through the community unabated. The lack of government restrictions meant that we had the opportunity to return to work (and paychecks), but the burden of determining how to do so safely fell directly on the musicians’ “COVID” committee, elected for this purpose. Accurate scientific information would need to be a part of our safety plan if it were to have any chance of standing up to record-high case counts and overwhelmed hospitals.
The musicians initially inquired about an airflow study for Abravanel Hall, but it was our acting CEO Pat Richards who first made contact with the University of Utah. She was directed to the chemical engineering department, specifically to two scientists, James Sutherland and Tony Saad, who work in fluid dynamics. Tony and James were hired to design a study that could help us arrange the orchestra onstage at Abravanel Hall and at our opera venue, Capitol Theater, in such a way as to mitigate aerosol spread and buildup as much as possible. They arranged times to have the halls to themselves and set up sensitive equipment to track the airflow from the air vents across the stage and out through the returns. They also experimented with different arrangements of the HVAC system, and opening and closing the stage doors. They did not use any Plexiglas barriers and instead relied solely on the HVAC system and the space.
After taking measurements in the space, Tony and James entered this information into a computer simulation that tracked the airflow and air speed for the entire stage area. Then, they inserted markers into the simulation that represented individual ‘musicians’ playing different instruments. Included in this simulation were three each of clarinets, flutes, oboes, bassoons, and horns, two each of trumpets and trombones, and one tuba. Each of these instruments was assigned an amount of aerosol production for a 15-minute period, which was calculated using the University of Minnesota study, “Aerosol Generation from Different Wind Instruments”. By combining airflow information and the amount of aerosols generated, and by moving the wind instruments around in the simulation, they were able to calculate just how many aerosols would build up around individual instruments on specific parts of the stage, all the way down to one aerosol particle per liter of air.
So, what were the findings? The scientists observed that at center stage at Abravanel Hall, (precisely where the winds would normally sit), there is a ‘vortex’ where the air circulates between the floor and the ceiling but not out of the return vents for 40 minutes or more. The study suggested ways to mitigate this problem: placing wind instruments over air vents and near the doors; and opening the stage doors and making a few adjustments to the HVAC system, by which we can move nearly four times as much air off the stage over a 15-minute interval compared to leaving the doors closed.
At Capitol Theater a scrim placed at the front of the stage between the vocalists and the orchestra (which would be seated onstage behind the singers, not in the pit) was effective at keeping aerosols from the vocalists from washing over the orchestra. However, the scrim caused any aerosols produced by winds onstage (behind the scrim) to build up around the musicians, requiring an additional mitigation. To achieve this, Tony and James designed a ‘plenum’. The plenum acts as a sort of air duct by directing air pushed onstage by the HVAC system out the back doors. Its design is so effective that aerosols produced from the wind instruments can be removed from the space in less than a second.
The study did not consider the use of Plexiglas shields. These shields can actually disrupt airflow onstage in ways that may be dangerous by collecting aerosols in certain areas, directing them towards other musicians, or blocking them from moving out through return vents. I strongly urge any orchestra using Plexiglas shields to reconsider their use until an airflow analysis can be completed. Tony and James explained that they would need significantly more time to analyze how shields might change the airflow onstage, and that it is much easier to use the existing air patterns to our advantage. Shields would best be used to correct serious airflow problems that already exist in the space.
As a result of the airflow study, the Utah Symphony Safety Plan includes an extra layer of safety and allows us to make informed decisions about how to properly stage the orchestra during services, giving us greater confidence in our ability to keep musicians safe. We share many safety requirements seen in other safety plans around the country: symptom checks, staggered arrivals, distancing, shorter services, and testing, and it would be my hope that airflow studies will become routine as well.
Note: the author is an ICSOM Member-at-Large and a percussionist in the Utah Symphony