# Glycol, Far UVC, and CFM Measurement at BIDA

We planned to trial [far UVC and glycol vapors](https://blog.bidadance.org/2025/08/trialing-far-uvc-and-glycol-vapors.html) at the BIDA contra dance last night: these are two options (beyond masks and ventilation) for reducing infectious aerosol inhalation. Both worked without issues.

I set up the far UVC [Aerolamp](https://aerolamp.net/) on the stage, slightly angled down, primarily aiming to clear the air above the dancers:

[![](https://www.jefftk.com/far-uvc-at-bida-2025-09-07.jpg)](https://www.jefftk.com/far-uvc-at-bida-2025-09-07-big.jpg)

And the glycol vapor, [1 part TEG to 3 parts water](https://www.jefftk.com/p/calibrating-an-ultrasonic-humidifier-for-glycol-vapors) by weight, in an ultrasonic humidifier. This went right in front of the intake fan: \[1\]

[![](https://www.jefftk.com/bida-glycol-vapor-ultrasonic-humifier.jpg)](https://www.jefftk.com/bida-glycol-vapor-ultrasonic-humifier-big.jpg)

Logistically neither was much hassle, and we didn't get complaints about either. I would really like to measure how well they're working, but all the experiments I can think of (measuring the decrease in viable airborne bacteria?) are serious investments.

I also measured CO2 levels with my [M2000](https://temtopus.com/collections/pm2-5-monitor/products/temtop-m2000-air-quality-detector-co2-sensor-professional-hcho-co2-pm2-5-pm10-monitor?variant=40628808876080) \[2\]:

[![](https://www.jefftk.com/bida-co2-2025-09-07.png)](https://www.jefftk.com/bida-co2-2025-09-07-big.png)

These are high CO2 levels: this was our first dance back after the summer and attendance was high. Looking at our attendance sheet, I count 265; I'd guess occupancy peaked at ~230 since some people leave early, others arrive late, and some people are in the entryway and bathroom.

One thing you'll notice on that chart is that we kept the hall for some extra time at the end to measure longer. We'd like to estimate how much fresh air we're bringing in with the fans, and one way to do this is to fill the air with something (in this case, the CO2 people exhale) and then measure how quickly it decays:

[![](https://www.jefftk.com/co2-decrease-bida.png)](https://www.jefftk.com/co2-decrease-bida-big.png)

I had Gemini and GPT-5 fit an exponential decay constant, and both gave me k=0.095. You can see it's not a perfect fit: it decays more quickly initially, and then decreases. I think this is because while the room has some mixing (with ceiling fans), it's not perfectly mixed.

With primary dimensions of 62x47ft and a height of ~20ft, I get ~5,600 CFM (62 * 47 * 20 * 0.095). At last night's (higher than usual) attendance this is 24 CFM/person.

The actual amount of fresh air people experience will vary a lot across the hall: I measured in the corner farthest from the incoming air. Overall, then, I think this is an underestimate of the amount of ventilation the typical person is experiencing.

(A different reason why I'd like to know how many CFM we're getting is to estimate how much [TEG](https://en.wikipedia.org/wiki/Triethylene_glycol) to vaporize. I'd previously guessed [8,000 CFM](https://www.jefftk.com/p/calibrating-an-ultrasonic-humidifier-for-glycol-vapors) which still seems plausible: some portion of the air we're bringing in is going to go in one door and out the other without very thorough mixing.)

Next step will probably be a survey to understand how the community feels about applying these regularly going forward.

  
\[1\] We lent the fan out during the summer, which we've never done before and generally try to avoid with our gear. It came back with a busted switch. Thanks to Al for fixing it, in about 25 minutes before the dance started!

\[2\] I also tried using [Harris](https://chromamine.com/)' Aranet4, but because I didn't realize I needed to switch it to 1-min sampling I didn't get very useful results.

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