[ourlordcaffeine]

Levels above 1000ppm are shown to cause cognitive impairment. 3000ppm is absolutely harmful.

>our lungs are constantly dealing with much higher concentrations

After gas exchange. Not with inhaled air.

[voxelghost]

>After gas exchange. Not with inhaled air.

gas exchange is continuous, not a discrete event that only takes place just after fresh air enters the lungs.