Filter tests are generally carried out in accordance with the filter test standards with so-called A2 fine dust (sand dust, dolomite dust). Ventilation filters, but also FFP2 or FFP3 protective masks are tested according to this procedure.
However, a filter test with a type of sand dust has little informative value about the filtration of microorganisms or viruses in the nano range.
Until now, there was no test method for measuring virus separation efficiency. Therefore, together with our research partners, we have developed a test procedure that makes it possible to test under real-life conditions.
In this process, viruses are applied to aerosols - just as happens in reality - and for the first time an entire filter element (not just a filter material sample) is exposed to the aerosol-virus mixture.
Finally, the viral load in the clean gas is analysed and the virus removal rate is determined from this. The test is repeated several times in order to obtain a valid result. The viruses used have a size of 28 nm (nanometre = 1 millionth of a millimetre) and are thus 5 times smaller than the coronavirus.
The test demonstrates a virus filtration efficiency of 97.2%, which is even higher for the SARS-CoV-2 virus.