even in the best case scenario of just sitting at your desk with a chill heartrate you will have a co2 concrentration of 2000-2500ppm.  when walking slowly its already nearly 3000 and so on. further down you see that 2000ppm and up are already very bad for you, especially for longer durations. dont forget people wore these things for months/years for hours each day, a lot of people even re-used their old fucking disgusting face diapers full of bacteria and mold
Austria