"How high can indoor levels of CO2 go? In a reported study, it was found that in a substantial number of poorly ventilated classrooms and workplaces, CO2 levels can average 1000 ppm, a significant proportion of these exceeded 2000 ppm and some even reached 3000 ppm. Keep in mind we are all currently living in an outdoor environment of 405 ppm with no sign that these levels will be abated for decades."
"How high can indoor levels of CO2 go? In a reported study, it was found that in a substantial number of poorly ventilated classrooms and workplaces, CO2 levels can average 1000 ppm, a significant proportion of these exceeded 2000 ppm and some even reached 3000 ppm. Keep in mind we are all currently living in an outdoor environment of 405 ppm with no sign that these levels will be abated for decades."
http://www.advancedsciencenews.com/co2-on-the-brain-and-the-brain-on-co2/