It is an irritant to the respiratory system, but not toxic. It is also how nature itself cleans and sanitizes, but high levels of ozone will sting your nose and irritate your lungs.
That's why we NEVER start our ozone treatment unless the building is vacated of people and pets.
More than 1000 cities in the world use Ozone to purify city drinking water. It is used by the egg industry to remove salmonella and e-coli. It is used by the meat industry to kill mold, bacteria, and viruses. Dentists using ozone to kill bacteria on teeth rather than drill, and the cleaning industry uses ozonated water in place of harsh chemicals to clean and sanitize.