Aerosol dispersal in wind instruments

The pandemic has presented serious challenges for education. As a clarinet and saxophone teacher, I have become very much aware in the last year of the drawbacks and limitations of online music teaching. I have been trying to evaluate the relative safety of teaching in person again. I am fully vaccinated, and would expect that of any students I see in person, but that doesn't guarantee total safety.

Opinions of my fellow teachers span the full range. Although my community (Santa Clara County, California) has a high vaccination rate and relatively low incidence of infection, conditions are constantly changing.

One piece of the puzzle is to what degree we should be concerned about aerosol dispersal from wind instruments. Here are links to four studies available on the internet, with some takeaways. 

I am not implying any conclusion as to the safety of in-person lessons, as there are other important considerations besides just aerosol dispersal and safe distancing.

1)  https://www.bristol.ac.uk/news/2021/june/perform2-study.html - University of Bristol 

"Aerosol generated by playing woodwind and brass instruments is less than that produced when vocalising (speaking and singing) and is no different than a person breathing, new research has found."

2)  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7492159/ - University of Minnesota 

"Specifically, tuba produces fewer aerosols than normal breathing, while the concentrations from bassoon, piccolo, flute, bass clarinet, French horn, and clarinet stay within the range of normal breathing and speaking. Trumpet, oboe, and bass trombone tend to generate more aerosols than speaking."

A second phase of this project is described in this article, with an interesting observation:

"In the second phase of the study, Hong’s team used probes to measure how far the aerosols travel from each instrument inside Orchestra Hall. They found that the flow was very confined, and the aerosols dispersed quickly. At only 10 centimeters (about 4 inches) away from the instrument outlet, the aerosol concentration was less than 10 percent of what it was at the source, and no instruments showed an appreciable influence of flow beyond 30 centimeters (about 1 foot).

Part of this, the researchers said, is due to the human thermal plume effect, which refers to the upward air flow created by a person’s temperature being higher than the air around them. The majority of the aerosols are carried upward by this draft.
 
“The second part of the study is to help understand where the aerosols go,” Hong explained. “They’re not necessarily spreading horizontally—they are rising vertically. So, this will help us to optimize the placement of filters and the social distancing between individuals.”
 
Because of the thermal plume effect, they found the most efficient placement of filters would likely be above the musicians—resulting in a 95 percent particle extraction rate. Another strategy could be to reduce the temperature inside Orchestra Hall, which would increase the temperature difference between the people and the environment, ultimately making the plume stronger and the filters more effective."

3)  https://www.medrxiv.org/content/10.1101/2021.01.25.20248984v1.full - Bavarian Symphony Orchestra (measured extent of aerosol cloud) (preliminary paper, not peer-reviewed) 

"A distance of 2 m to the front and 1.5 m to the side should be recommended for trumpet and clarinet, 3 m to the front for the cross flutes in an orchestral formation. Our findings could be applied to other orchestral instruments, so other brass instruments such as tuba, trombone or horn may be similar to the trumpet. It could be expected that an oboe and a bassoon have the same or less dispersion than a clarinet. The largest distance occurred during playing the cross flutes. For the risk assessment, the individual playing style, different instrument-specific playing techniques as well as convectional flows in the specific rooms and at least the accumulation of aerosols during playing should also be taken into account."

4)https://www.makingmusic.org.uk/sites/makingmusic.org.uk/files/Measurement%20of%20aerosol%20from%20brass%20and%20woodwind%20instruments%20.pdf - University of Southern Denmark

"The emission of aerosol measured from brass and woodwind instruments was very low, and almost at the same level as background concentrations. Other experiments have shown very little airflow and very small aerosol concentrations at short distances from brass and woodwind instruments. Based on the actual measurements and the other studies mentioned 1 meter distance playing brass and woodwind instruments seems to be safe with respect to the risk of spreading aerosol from the instruments. This assumes that musicians blow towards the back of fellow musicians.


Please note: To be clear, I'm listing these studies for the benefit those who may be interested, but I am not trying to make a case for immediately resuming in-person instruction. Other factors would influence that decision, and teachers will weigh these factors as they see fit. The papers listed above have more detailed information than the short quotes I have provided. If you are interested, please follow the links and read the articles more carefully.