UV radiation is classified into three sub-categories on the basis of the radiation wavelength and photon energy: UV-A, UV-B and UV-C radiation. The wavelength of UV-C radiation is the shortest and photon energy the greatest. There is no UV-C radiation in nature since the atmosphere filters the UV-C radiation completely from solar radiation.

UV-C radiation is used to disinfect air, water and surfaces in hospitals and industry. It is dangerous for humans and burns the skin and damages the eyes easily.

UV-C radiation is well-suited for disinfecting air and water. However, it is less well suited for disinfecting surfaces. UV-C radiation does not penetrate deeply, which means that it will not pass through materials well. Even a thin layer of dirt or shading prevents UV-C radiation from reaching the object to be disinfected. UV-C radiation is poorly suited for disinfecting porous surfaces. Therefore, high radiation doses must be used when disinfecting surfaces. When disinfecting surfaces, UV-C disinfection supplements other disinfecting methods.

UV-C radiation is dangerous to humans, animals and plants

UV-C radiation burns the skin and damages the eyes. Damage can be inflicted quickly; with efficient lamps in seconds. Exposure limit values for UV-C radiation are set both for public and occupational exposure. It is not allowed to exceed these values when using the UV-C disinfection. The UV-C dose required for disinfection damages both the skin and eyes and clearly exceeds the exposure limit values. It is prohibited to direct UV-C lamps towards humans.  Skin and eyes must be protected in spaces that are being UV-C disinfected.

UV-C radiation is also harmful to animals and plants, so they should not be exposed to it.

UV-C radiation generates ozone. Ozone is a poisonous gas that causes respiratory symptoms and eye irritation. The amount of ozone depends on the UV-C lamp type. Sufficient ventilation should be ensured in spaces disinfected with UV-C. Ozone has a characteristic pungent odour, “electric odour”. If you can smell ozone, it is likely that there is too much ozone in the space.

UV-C radiation ages materials. It makes plastics, rubber and other materials yellow and brittle. When disinfecting with UV-C radiation, it must be ensured that the materials tolerate UV-C radiation.

A picture of UV-C lamp markings. In the lamp, there is sign warning about UV-C radiation and a sign warning about looking at the lamp.

Further information

Exposure limit values

• Occupational exposure limit values (tyosuojelu.fi)
• Public exposure limit values in Decree 1045/2018 of the Ministry of Social Affairs and Health (stuklex.fi)

Standards concerning devices

• SFS-EN 62471:en Photobiological safety of lamps and lamp systems (sfs.fi)
• SFS-EN ISO 15858:2016:en UV-C Devices. Safety information. Permissible human exposure (sfs.fi)

More extensive reports

• Opinion on UV-C lamps of the EU’s Scientific Committee on Health, Environmental and Emerging Risks SCHEER (ec.europa.eu)
• CIE Position Statement on the Use of Ultraviolet (UV) Radiation to Manage the Risk of COVID-19 Transmission (cie.co.at)
• IES’ report concerning UV-C disinfection (IES Illuminating Engineering Society, USA) (ies.org)

Indoor ozone

• Literature survey of the Finnish Institute for Health and Welfare: Ozonization in indoor environment (julkari.fi)