In Europe, standard EN 779 is almost exclusively used to classify coarse and fine dust filters (= particulate matter filters). EPA, HEPA and ULPA filters, particularly fine-pored particulate matter filters, are rated in accordance with standard EN 1822. Depending on the standard, either the initial separation efficiency or the fractional separation efficiency is used as the performance criterion for standard contamination.
The initial separation efficiency is the separation efficiency of the new filter, i.e. the relationship between the collected material and the supplied material. The fractional separation efficiency denotes the separation efficiency of a filter with regard to a fraction, meaning particles of a specific size class. The following table shows the usual standards and the corresponding classifications.