Air purifiers - tests to verify effectiveness

Air purifiers or air filters (mobile, stationary) are used to reduce the concentration of viable microorganisms in the air as a means of minimizing the risk of infection in enclosed spaces. For users, it is important that the air cleaning/disinfection carried out by these devices is highly effective and helps to protect against aerosol-based infections.

One of the services we offer as an independent scientific institution is an evaluation of the effectiveness of air cleaning/disinfection devices along with support for companies with regard to subsequent optimization work steps. Microbiological testing under realistic conditions is one of the core competences of Fraunhofer IVV and has been used for many years to validate disinfection and sterilization processes.

We determine the effectiveness of air purifiers by measuring the inactivation or depletion of airborne microorganisms in the room air. Microbial test aerosols are generated in order to artificially contaminate the room air with a defined concentration of selected microorganisms. By taking a comparative measurement of the viable test organisms with and without air treatment, the effectiveness of the air cleaning devices can be quantitatively determined. Depending on the objective, the impact on naturally occurring airborne microorganizms can also be established. We can carry out effectiveness testing on air purifiers based on various technologies – e.g., UV radiation, ionization or particle filters – even while the devices are still in the development phase.

Our employees use various systems in order to generate airborne microorganisms in a defined and careful manner. Different test organisms are applied for the generation of specific test aerosols, from vegetative bacteria and viral surrogates to resistant mold or bacterial spores. We use suitable surrogates (e.g., Pseudomonas phage phi6 bacteriophages) to assess effectiveness against coronaviruses. The impact of air cleaning and disinfection on the original airborne microbial concentration can also be investigated and evaluated.

In our laboratory and pilot plant, we have an aerosol chamber with a volume of 1.5 m³ and an office container with a volume of 30 m³ available for experiments. Both spaces can be used to test and evaluate the efficiency of air cleaning/disinfection devices under realistic conditions. The test involves generating defined bioaerosols with selected microorganisms, then running the test device for the relevant amount of time before taking air samples and subjecting them to microbiological analysis. The extent to which the test device reduces the amount of viable microorganisms in the room air is used to assess its effectiveness.