Ozone is naturally present as a blue, pungent-smelling gas and its concentration in the atmosphere is around 0.04 ppm.
Humans’ exposure to ozone occurs by inhalation. As gas concentration and exposure time become more prolonged, ozone’s harmful effects on human health become more serious (concentrations over 50 ppm with exposure time exceeding 60 minutes can lead to coma).
Ozone’s concentration in the air: symptoms and effects on human health
| mg/m³ | ppm | |
| 0.02÷0.04 | 0.01÷0.02 | Odour threshold |
| 0.2 | 0.1 | Distinctive odour, burning nose and throat |
| 0.4÷1 | 0.2÷0.5 | Sight problems after a few hours of exposure |
| 1 | 0.5 | Severe tracheal problems |
| 2÷4 | 1÷2 | Headache, chest pain, persistent feeling of thirst and severe burning chest
Long exposure leads to poisoning |
| 10÷20 | 5÷10 | Feeling of chocking. Pulmunary edema |
| 30÷40 | 15÷20 | Small animals perish after two hours |
| ≥100 | ≥50 | Humans go into a coma after inhaling ozone for one hour |
Note: 1ppm = 2 mg/m³ - Source: ACGIH – American Conference of Governmental Industrial Hygienists
Ozone’s odour threshold for humans is set between 0.02 and 0.05 ppm.
Ozone is employed commercially, in order to, for instance, sanitise waters, prevent legionella and mold to spread in cured foods, process denim and sanitise clothes and spaces (hotels, companies, public establishments).
Ozonisers generate ozone from an oxygen gas stream, to which an electric, electrochemical or photochemical energy source is applied.
Safety in the workplace
In order to ensure safety and health at work, health standards and recommendations are in place to establish the Maximum Admitted Concentration (MAC) value:
- Employees cannot be exposed to an average concentration level exceeding 0.10 ppm over a time period of 8 hours (OSHA)
- The threshold set by the National Institute for Occupational safety and Health (NIOSH) is 0.10 ppm.
Ozone exposure limits for employees, such as TLV-TWA (Threshold Limit Values) are related to the physical activity performed (as the volumes of inhaled air change). Values set by ACGIH are the following:
- For heavy, moderate or light work carried out over a time period of less than 2 hours, TLV-TWA is set at 0.2 ppm.
- Over 2 hours: in case of light work, TLV-TWA is set at 0.1 ppm; in case of moderate work, TLV-TWA is set at 0.08 ppm; in case of heavy work, TLV-TWA is set at 0.05 ppm.
Complying with rules and preventing respiratory tract irritation:
- Ozone disinfection needs to take place in emptied out and properly confined spaces
- Any residual ozone in the environment needs to be eliminated by placing designated aspirators in the workspace provided with destructors or catalysts.
In order to protect employees’ health, Ferrarini & Benelli has applied a solution for years, which, owing to a system of catalysts, cuts down ozone generated by corona treatment. Such system now gets applied to spaces sanitised through ozone as well, in order to reduce residual concentration rapidly.
In Italy
The Italian Ministry of Health, through Protocol number 24482 dating back to 31st of July 1996, has recognised the use of ozone to treat air and water as a natural source to sanitise environments infested by bacteria, viruses, spores, mold and mites.
In addition to the Italian Legislative Decree 81/2008, which establishes that ozone is to be reduced below the threshold set in the above table, norms are in place in order to regulate emissions in the atmosphere (Directive 92/72 ECC of 21st/9/1992, Decree 15th/4/1994 and Decree 16th/5/1996 published by the Italian Ministry of Environment).
The Italian Food Safety National Committee’s report (CNSA - Comitato Nazionale per la Sicurezza Alimentare) on ozone air treatment in cheese-aging environments, states as follows: “ozone’s toxicity levels requires ozone operators to be continuously monitored and protected. In accordance with H.A.C.C.P rules, operators cannot be exposed to:
- More than 0.1 ozone ppm over 8 hours
- More than 0.3 ozone ppm twice a day over 15 minutes”.
Guidelines regarding ozone use to sanitise meat-processing plants establish that “ozone disinfecting needs to take place in emptied out and properly confined spaces. In order to reduce risks, sound and/or acoustic devices need to be placed at every access point during treatment”.
The Italian Ministry of Health’s pamphlet on ozone informs that: “epidemiological studies among urban population on ozone exposure have pointed out that ozone exposure levels starting at 0.2 mg/m³ (hourly average) over a couple of hours cause ocular mucous and the respiratory tract to be irritated. In children and young adults, temporary breathing problems due to ozone exposure starting at 0.12 mg/m³ (hourly average), have been detected. Only few studies on chronic exposure to ozone are currently available.
Ozone destruction systems bringing ozone levels below the danger threshold are therefore of the utmost importance.