Limits for the concentration of ozone in ambient air are ruled by various guidelines in many countries.
According to ZH 1/474 (2005) section 4.7.1 from the German Employer’s Liability Insurance Association an ozone destruction unit must ensure a limit of 0,02 mg/m³. The European Union guideline 2002/3/EG sets a limit of 180 µg/Nm³ (= 90 ppbv) for ozone emissions.
Until 2005 the limit for ozone concentration in companies was 90 ppb according to the German BG-ETEM (Infopaper 526 dated 07/2013). Exceeding that limit was not permissible. Meaning: The concentration of substances that can cause irritations and odors (like ozone) cannot exceed the maximum permissible value at any time. Currently there is no workplace exposure limit. The committee for hazardous materials is working on defining an occupational limit value. Until this will be released it is recommended to meet the international standard of 60 ppb (0,12 mg/m³).
The Swiss Clean Air Act limits the emission of ozone to 120 µg/m³ bzw. 60 ppb.
In the USA workplace-related rules according to the Occupational Safety and Health Administration (OSHA) and the National Institute of Occupational Safety and Health (NIOSH) is < 0,1 ppm (= 100 ppbv).