Toxicty of Ozone to Humans
This graph shows an indication of the ozone concentration and exposure time.
Example:
At an ozone concentration of 0.1 ppm (100 ppb), 1000 minutes of exposure causes no symptoms.
At an ozone concentration of 1 ppm (1000 ppb), 100 minutes of exposure can cause Nontoxic Symptomatic symptoms.
For more info click the links below
Source: Toxicity of ozone to humans (Langewerf, 1963; cited in Dimitriou, 1990)