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Filter classes and filter standards

Particle filters are, in Europe, rated according to the European standard EN 779. HEPA and ULPA filters, particular high-efficient air filters, are rated according to another method which is described in the European standard 1822. Depending on the standard, either initial filtration efficiency or fraction filtration efficiency is used for classifying filter performance.

Here, filtration efficiency means the ratio of collected and feeded material; fraction filtration efficiency means filtration efficiency as far as a certain fraction, i.e. particles of a certain size range, is concerned.

The subsequent table shows the common standards and respective ratings.