Ozone generated in situ from oxygen is a "biocidal" active substance under review under BPR2 as a surface disinfectant (PT2 and PT4) and drinking water disinfectant (PT5) and for use in industrial plant cooling towers (PT11). Although the evaluation has not been completed, an extensive database is available confirming its microbicidal efficacy also on viruses (20-27). Pending authorisation at European level, marketing in Italy as a PMC with a "disinfectant" claim is not allowed due to the impossibility (in situ generation - off-site production) to identify a specific site to be authorised as required by national legislation. Therefore, at this stage, ozone can be considered a "sanitizer".
The use of ozone is currently allowed at international level in food, surface sanitation and drinking water (FDA, USDA, US-EPA, CNSA) (36,37,38,40).
Ozone virucidal activity occurs rapidly following ozonization (28-30). As with many other products used in disinfection, there is no specific information on the efficacy against SARS VOC-2. On the other hand, several studies are available to support its virucidal (Norovirus) efficacy in health and non-healthcare environments (29). Even at low concentrations, with high humidity, ozone has a high virucidal disinfecting effect in air (30).
The International Ozone Association (www.ioa-pag.org) confirms the efficacy of ozone for the inactivation of many viruses even though it is not aware of specific research on SARS-CoV-2.
At industrial level, ozone is generated in situ by means of ozonators, which must be adapted from time to time in relation to spaces (dimensions, materials involved) and targets (11,19,20,21,22,23,24,25). Ozone generators must comply with the Low Voltage Directive (Directive 2014/35/EC), Electromagnetic Compatibility Directive (Directive 2014/30/EC) and the Restriction of Hazardous Substances Directive 2011/65/EC (RoHS).
Ozone is an unstable gas and spontaneously decays to oxygen (31,32,33). The time required for ozone decay depends on temperature, humidity and chemical and biological contamination, and always depends on the concentrations of use.
In real conditions the natural decay time necessary to make the premises accessible is at least 2 hours. If possible, it is preferable to carry out the treatments at night so that the amount of ozone in the environment is within the health safety limits when resuming work.
Avoid eliminating residual ozone by using forced ventilation to convey it to the external environment: DL.vo 155/2010 (67) sets limit values and quality objectives also for ambient air concentrations of ozone.
On the basis of CLP and REACH (34,35), registrants have classified ozone as: a substance that can cause or aggravate a fire; lethal if inhaled, causes severe skin burns and serious eye injuries, causes damage to organs in case of prolonged or repeated exposure through inhalation, very toxic for the aquatic environment with long lasting effects. Some notifiers identify ozone as a suspected mutagen. The German competent authorities indicated to ECHA in 2016 their intention to propose a harmonised classification and labelling for ozone also as a category 2 mutagen and a category 21 carcinogen.