OSHA guidelines for O3 in the workplace are based on time-weighted averages. Ozone levels should never exceed the following average: 0.10 ppm (parts per million) for 8 hours per day exposure.
For more detailed information on safe ozone levels, see the bullet points below.
The OSHA website cites several ACGIH (American Conference of Governmental Industrial Hygienists) guidelines for ozone in the workplace:
For more information, see the OSHA webpage regarding ozone: http://www.osha.gov/dts/chemicalsampling/data/CH_259300.html
Unlike OSHA, NIOSH safety and health standards are not enforceable under US law. However, NIOSH does "develop recommendations for health and safety standards" that may influence future law and OSHA regulations.
The NIOSH recommended exposure limit for ozone is 0.1 ppm (0.2 mg/m3). According to NIOSH, Ozone levels of 5 ppm or higher are considered immediately dangerous to life or health.
For more information: NIOSH Pocket Guide to Chemical Hazards: Ozone
Last Updated: July 8, 2014