Singing and wind instruments are the most productive aerosol generating activities in church life and aerosols are the main method of transmitting an airborne virus. Large aerosol droplets at close range and small (long hang time) aerosol droplets in the air at long range. How much exposure to COVID-19 is the issue  and the longer that people stay inside with aerosol producers the more risk they incur in the process. Masks and distance dramatically reduce the risk  but nothing can eliminate it apart from hiding in a cave.
If you choose to meet in person and sing, what can you do to minimize exposure risk? The short answers are listed below, with paragraph length bullet explanations following.
- Increase ventilation … (in room air purifiers).
- Decrease service time.
- Wear masks … (they make a mask for singers now).
- Maintain 10 feet distance between family clusters.
- Decrease the number of singers and wind instruments.
- Monitor CO2 Levels. (Wut?)
- DO NOT recirculate the air in your HVAC system UNLESS you have HEPA filtration. Recirculation will only concentrate the aerosols and possibly tend towards a Skagit Valley Choir super spreading event.
- Purchase high CADR portable air purifiers [3,4]. Your goal is to get an air exchange rate (ACH) of 12 times an hour, which is equivalent to a hospital isolation room. In other words, entirely new/purified air once every 5 minutes. This is double the rate you need to beat the 10-minute limit on exposure time, which is the basis for all distancing guidelines. Place them between the stage and audience on short tables to optimize flow.
- If you can add additional HVAC ventilation, do so. However, each ton of AC only gives you 400 CFM for a 200 square foot room with 10 foot ceilings—and that gives you 12 ACH. It will be expensive to do this, and you’ll definitely want to add high MERV HEPA filtering as well.
- Upper Room Germicidal UV (GUV) lighting is likely to be the future for large spaces. This is pricey and requires highly-skilled labor for installation. This is a very long-range solution, but likely to be cheaper than copying hospital room ventilation systems.
Decreased Service Times
- Using models developed from super spreading events like the Skagit Valley Choir incident, scientists can estimate the risk of infection based on room size, ventilation rates, and physical distancing [5a,5b]. A 2500 square foot room with 40 people (50 sq ft each) and 1 infected singer singing through a 50% efficient mask for 30 minutes has a probability of infection of 1.6%, resulting in 0.65 COVID cases. See this video for tutorial on the spreadsheet by its author [5c].
- The case given above assumes only 3 ACH (air changes per hour), which is likely to be more than most buildings have. If you bump that ACH to 12, the risk drops to 0.7% and the number of infections to 0.3.
- Masks are essential in slowing the spread of the virus by means of reducing aerosol emissions at the source. For example, two people at close range wearing 50% efficient masks will reduce their emissions by 75%. Again, it’s not the exposure to COVID that’s the issue, but how much. Until we have a way to effectively detect and isolate the infected, masks and distance are our only options.
- Masks absolutely work. This video [6: https://youtu.be/CpbJFk311Lw] explains why, even for particles as small as the virus. The Internet is littered with misinformation about masks. The raw Physics of it demands that they work. Numerous random control trials prove that they work. Many countries have beaten COVID because of masks + distance + contact tracing.
- There is now a mask made just for singers that doesn’t destroy resonance and articulation . Check out this video of an operatic piece with and without that mask followed by an analysis of the vocal wave forms in software .
- The distance rule is largely for staying away from large droplets that tend to fall to the ground in 6 feet or less. However, loud talking, singing, coughing, etc will send those particles farther. Six feet really isn’t enough, but you do cut out about 90% of the emissions at that distance.
- The Lancet paper  actually shows the greatest risk reduction comes by distancing, but masks plus distance obviously reduce it even further.
Decrease the Number of Singers & Wind Instruments
- There is no better risk reduction than limiting the number of high emission sources. Singing and wind instruments produce substantial aerosols. The singers mask  mentioned above will be essential for singers.
- Simply cut a hole in the mask of all your wind instrumentalists. Though imperfect, it will help. Get creative about how to better seal that slot while playing.
Monitor CO2 Levels?
- The accumulation of CO2 (carbon Dioxide) in spaces occupied by people indicates poor ventilation.
- Poor ventilation means that exhaled aerosols are concentrating in the same space where persons are inhaling air.
- The main transmission pathway for COVID-19 is airborne inside of poorly ventilated spaces.
- Get a CO2 monitor and aim to maintain ~400ppm CO2, which is essentially what you’d find outdoors. When CO2 gets to 800ppm , either vacate the space or find a way to ventilate it.
- The National Federation of High Schools (NFHS) commissioned a study on singing and wind instruments currently underway at the University of Colorado at Boulder . Essentially ALL of the studies done on aerosol emission are for coughing, talking , breathing, etc.—but nothing on singing or wind instruments. The Physics of vocalization demands that there be more aerosol emissions for those activities, but it had not been measured before. Singing produces about 10 times what breathing does, and usually more than coughing. The difference is coughing produces lots of large droplets that fall to the grand quickly, whereas everything else produces aerosols that can’t be seen and hang in the air for minutes to hours and concentrate. On July 10, 2020 preliminary findings were released  with more to follow later in July and 2020.
- The vast majority of transmission events come from poorly ventilated indoor venues where one or more infected persons interact for long periods of time (30 minutes or more). Outdoor venues are as safe as it gets unless you’re yelling/singing directly into one another’s faces. It all boils down to dilution and wind simply carrying the danger away. However, if you remain downwind of an infected person long enough, such as in a drafty outdoor corridor or patio, then you can obtain enough viral load to become infected.
- There really is NO valid data supporting the notion that masks don’t work. For a short synopsis of that fact watch this 30-minute video. 
Finally, realize that these measures simply reduce risk rather than eliminate it. Moreover, ALL of these measures assume universal masking and distancing. Take those out of the equation and the risk starts to skyrocket. Until we get a vaccine and effective testing and contact tracing, this is the way we minimize risk for participating congregants.
Feel free to contact me with any questions that you might have. In addition to being a Physics Professor full time, I am a worship leader and former assistant pastor. I get it.
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