The use of air purifiers operating on the electric discharge principle

Status:

completed 12/2005

Aims:

Equipment for purifying and conditioning indoor air is distributed commercially under a wide range of names. These products claim to remove airborne pollutants and odours completely and safely, and to kill microorganisms. They also have the function of increasing the comfort level for people present in the rooms concerned. These air purifiers operate on the principle of the Siemens Ozonizer, which employs silent electrical discharges, albeit with lower performance. In a reaction chamber, through which the room air is pumped, reactive oxygen species are produced. Their function is to ensure (oxidative) conversion of pollutants to harmless reaction products such as carbon dioxide and water. A project launched by the institutions for statutory accident insurance and prevention in the building trade and in the wholesale trade and warehousing industry was to assess the toxicological and occupational health aspects of such products.

Activities/Methods:

Since a plethora of terms, in some cases highly contradictory, are employed for the oxygen species produced in the air purifiers, the scientific principles were first established. Information on the technology employed and the reaction products created by its use was gained from study of the available technical and toxicological literature. Constructive dialogue was also sought with manufacturers.

Results:

Examination of the physical and chemical processes revealed that the desired complete purification of weakly contaminated indoor atmospheres cannot be attained by means of NTP technology. None of the reactive oxygen species which are potentially formed are able to degrade the constituent components of the atmosphere completely and to render them safe. On the contrary: the creation of reaction products must be anticipated which have a greater irritative effect than that of the initial substances. Independent preliminary measurements have since confirmed the theoretical suspected release of ozone. The literature survey also failed to produce any scientific evidence of the successful use of NTP reactors under indoor atmospheric conditions. Conversely, the predicted incidence of incompletely degraded compounds was confirmed by the literature data. The data at our disposal do not therefore permit a sound risk evaluation in the context of the German occupational health and safety legislation and the new Ordinance on Hazardous Substances. The use of these air purifiers for the decontamination of indoor atmospheres cannot be recommended. The use of such products should particularly be avoided in occupied rooms.

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