Some more info.
Ozone Causes Cancer.
Ozone is Typically Produced by "Corona Discharge".
This is High Voltage Leaking into the Air. It is an Arc, But Quite often Invisable to the naked eye.
Below 5000 Volts, there is Still some Ozone Produced, But it is in Very Small Amounts because of Very Low Corona Discharge. That is why a air cleaner should be just under 5Kv.
Ozone has as "Half Life" of 20 minutes, so if only Small Amounts of Ozone are Produced, it will distroy itself Before it builds up to Dangerous Levels.
Ozone Exists Naturally in the Air.
In Canada:
The Desireable Level is 0.05 ppm.
The Maximim Acceptable level is 0.08 ppm.
Up to 0.15 ppm is Just Tollerable, but Long term Exposure is Dangerous.
Above that level is Not Recommended at all.
In a Room that has Considerable Bacteria, Ozone Will be Distroyed Faster than the above 20 minutes. Ozone is Often used to Distroy Bacteria or Bad Odors. But Usually in the Absence of People.
Hope this helps clear this up.