It might not be a health risk, but I found this study [1] interesting. It showed impaired decision making at CO2 levels that you could encounter indoors.

[1] "Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance" . https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548274/