Ozone Risk mitigation measures


Due to the frequent use of ozone for sanitation purposes, because of Covid19, it seems appropriate to elaborate on the characteristics of this gas and the precautions concerning its use.

Ozone is a gas made up of 3 atoms of oxygen (O3), with a penetrating smell and a pale blue color.

It is naturally present in the stratosphere (15 to 60 km above sea level) where it forms an important protective belt, shielding ultraviolet radiation from the sun, which is harmful to living beings.

In the lower layers of the atmosphere, ozone is a result of pollution situations (internal combustion engines, industrial plants, heating systems, etc.), in which solar radiation reacts with pollutants already present in the air, typically nitrogen oxides and volatile organic compounds. In confined environments, ozone can therefore be significantly emitted by polluting sources such as: high voltage electrical instruments (electric engines, laser printers and fax machines), devices that produce ultraviolet rays, electronic filters to clean the air that are not correctly installed and maintained, chemical solvents.

Due to its oxidizing properties against microorganisms (bacteria, molds, viruses, spores and mites), ozone is used in many fields, especially to sanitize and sterilize indoor environments, such as workplaces.

It is an hazardous substance for people’s health. Prolonged exposure to high concentrations of ozone can cause headache, weakness, irritation to the ocular mucous membranes and respiratory tract, with long-term consequences that can lead to a reduction in lung function and chronic bronchitis. In addition, if inhaled can be lethal.

The Report of the Italian Institute of Health (ISS) “Focus on: the professional use of ozone also in reference to COVID-19″ of 23 July 2020 describes advantages, dangers and risk prevention in the use of ozone for sanitization.

The report specifies that the use of ozone in the workplace requires the adoption of specific precautions. In particular, it is necessary to assess the risk of exposure of the operators in charge of sanitisation treatments and of the workers who have to carry out their work in the treated environments.

As this is a hazardous substance used in a workplace, it is necessary to apply the provisions of Legislative Decree 81/2008, Title IX – Dangerous substances, Chapter I – Protection from chemical agents, by carrying out a risk assessment and adopting general and specific protection and prevention measures, providing provisions in case of accidents or emergencies, and carrying out proper information and training of workers.

Due to its toxicological properties and its ability to oxidize some materials, the sanitization of environments must take place with no people in. Ozone must be dispersed according to concentrations and times of use sufficient for the elimination of microorganisms and viruses, but minimizing the deterioration of oxidation materials.

It is also necessary to adopt all possible precautions, including operations aimed at reducing the residual concentration of ozone and the concentrations of pollutants that can be develop from the secondary reaction between ozone and volatile organic compounds (VOCs) (e.g. formaldehyde and other substances of particular hygienic-sanitary interest). To this regard, some ozone generators are equipped with a catalyst which, after treatment, transforms all residual ozone into oxygen.

The risk to which treatment operators and persons occupying treated environments are exposed must be assessed in advance. In addition, appropriate technical and organizational prevention and protection measures must be put in place to mitigate the risk of exposure, both with regard to treatment operators and workers working in ozone-treated environments. These include the use of personal protective equipment (PPE), the use of signs when using ozone-generating systems, the possibility of monitoring O3 concentration by means of measuring systems that allow air quality to be verified, or the guarantee of at least 3 air changes per hour.

More in detail, the technical and organizational measures for risk mitigation in working environments indicated by the Italian Institute of Health (ISS) are the following:

Technical measures 

  • Ozone generation systems must be placed in closed, lock-in rooms.
  • The premises where ozone generation systems are located should not be used as permanent workplaces. If this is not possible for reasons related to the process, it is necessary to ensure that the concentration of ozone in the air in the workplace does not exceed the limit value of occupational exposure.
  • The rooms, where ozone loss can occur in the event of a failure, should be monitored with optical and acoustic ozone detectors that stop ozone generation when triggered. This is not necessary for rooms where ozone-containing pipes contain no removable connections, which have been examined for possible losses by a qualified person.
  • In premises with ozone generation systems, appropriate signage must be present.
  • The rooms where the ozone generation systems are placed must be equipped with an installed ventilation exhaust so that the suction is positioned at floor height and automatically ignites when the gas detector is activated; at least three air parts must be guaranteed per hour.
  • Use ozone destruction units (thermal and/or catalytic) to remove residual ozone from the air after treatment.
  • Ability to monitor ozone concentrations in the air: control in air quality rooms through gas concentration measurement systems.

Organizational measures 

  • Instructions for the use of ozone generators must be provided before use and then at least once a year.
  • An escape and rescue plan must be put in place if the workplace requires it.
  • Only procedure workers can access the areas during treatment or after completion to ensure that the conditions for the return of workers in these areas are met.
  • Replace garments that have been in contact with or absorbed ozone and aerate clothing away from any source of ignition.
  • People with heart pacemakers or other electrical devices do not have to log into an environment with an ozone generation system.
  • Given the length of the treatment procedure and the time required for the complete decay and/or elimination of residual ozone, interventions must be planned in such a way as to ensure the safe return of the workers occupying the premises and treated areas. This can be achieved, for example, by using programmable automated systems that allow operations during the downtime of production activities.

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