Audience Test

This past Saturday afternoon, May 1, we asked some family and friends to attend an open rehearsal of the Pops group at the Music Room. It was the first time we've had more than a dozen people at one time in over a year, and we did it to see if we could keep the air as fresh for a large group as we have for small ones.

In addition to the measures outlined in a previous post, I took a third fan upstairs and placed it to blow air out of a second window; and besides propping open the front door, also opened the side door part way and the back door all the way.

We had 42 people total, and the CO2 readings were mostly in the 410 ppm to 440 ppm range, overlapping the 390 ppm to 440 ppm baseline readings I get on first entering the room after it's been unused for several days - and lower than the 450 ppm to 480 range I've been maintaining at rehearsals.

The extra fan and more open doors keeping the air fresher for total of 42 people than I had been managing for fewer than a dozen people at rehearsals was a very pleasant surprise. 

The caveat to all this is that we had perfect weather conditions. The outside temperature was 70 degrees, so all the air coming in was the same as what we wanted the inside temperature to be. Back in the winter it was sometimes tough to keep the air fresh and it still warm enough to play music - this summer it might be the case that on a hot day, we won't be able to keep the inside temperature as cool as we'd like.

The other weather condition in our favor was the wind being calm to breezy and from the WSW. Since the front door faces more to the south than north, winds from the south work more easily with the ventilation flow. 

Here is a pic is showing the CO2 detector on the newel post where I always put it so as to have comparable readings over time. 

And here is the other half the room where you can see how we distanced the audience.

In trying to assess the risk of indoor gatherings, this article lays out the variables very well. The reason being outside is safer is because,

it is very difficult, if not nearly impossible, to give the virus to others outdoors via the airborne spread of tiny floating droplets because those droplets are, in most circumstances, quickly dispersed as a result of wind, air, or a person’s movement. Thus, the exhaled particle clouds get quickly diluted to the extent that there is not enough of a concentrated inoculum to infect others nearby.

From the same article:

The four main risk factors that predict transmission within indoor spaces; Density, Duration, Dimensions, and Draft:

• Density – # of people in the room
• Duration – # of hours spent in the room
• Dimensions – # of square feet and ceiling height of the room
• Draft – amount of fresh air entry/speed of air flow

I'm thinking gatherings of around 60 people; with about an hour of music; being grateful for our wonderfully large, high ceilinged space; and with ventilation approximating outdoor freshness - we'll be as safe indoors as is practically possible.