I taught a university course this last semester. In person. Up to 100 students in the lecture theatre. I managed to avoid catching #COVID19, or any kind of virus, actually. Here's the scoop: /1
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#CleanAir: The lecture theatre was in a very old building, luckily it had windows. But they were up REALLY high, so I took my own ladder and climbed up and opened all of the windows. I also propped open the doors at the front and back. I warned the students to bring a jacket /2
This dropped the CO2 from around 2000ppm to around 700ppm in ~ 10 mins. I also ran an air purifier at the lectern, on full. I kept my mask on until the CO2 dropped below 800ppm. /3