Vacuum cleaners with high class HEPA filter
HEPA 13 or more
— vacuum cleaners equipped with advanced fine filters (HEPA) - class 13 or higher.For more information about such filters, see the relevant paragraph. A class describes the overall efficiency of air purification; it is estimated based on how many particles with a size of 0.1 - 0.3 microns the filter can hold. These particles are the worst retained by HEPA elements; larger and, to a certain extent, smaller contaminants are captured even more efficiently (for comparison, the size of most bacteria starts at 0.5 microns).
Specifically, class 13 means that the HEPA filter is capable of retaining at least 99.95% of the particles mentioned. It is a very solid indicator, but even more advanced elements can be found in vacuum cleaners - class 14, where this figure is already 99.995%.