CO2 is

Carbon dioxide is a colorless, tasteless gas that is heavier than air. The gas itself shows little toxicity, but suffocation is possible. If the amount of carbon dioxide is higher than the amount of oxygen circulating in the brain, there will be higher levels of respiratory disorders, headaches, tinnitus, and blood pressure will increase.

Riesgo de CO2

450 ppm or lessOutdoor air in ordinary everyday life.
450 - 1000 ppmThe air is clear and there is no big trouble in breathing.
1000 - 2000 ppmThe air becomes unhealthy and people may feel sleepy.
2000 - 5000 ppmThe environment is unhealthy and can cause headaches, a feeling of sleep, loss of concentration among other symptoms.
5000 ppm or moreIt can lead to permanent brain damage and even death in severe cases.