Testing methods for air filters

Test types

We distinguish between the type test and the test in the manufacturing plant.


The type test of the filter is carried out by the standard procedure corresponding the given filter (see charter no 2). The tested filter should represent a set construction series. This condition is met provided the tested item is identical with the construction series in the following characteristics: the type description (1), the depth of the "filter complex" in the direction of the airflow, and the speed of the airflow through the filter medium. Other characteristics of the tested item can differ, e.g. the size, the shape of the reaction area. The type tests can be performed by all testing places accredited according to EN 45000. The class is allotted based on the valid attestation by some of the accredited testing places, which must include an explicit description of the tested product, the testing conditions and the test results. The type tests are important for coarse and mainly for the fine dust filters.


The test in the manufacturing plant
It applies to filters, which do not have the type tests, or to filters, which are, in accordance with the valid standards, subject to the respective test (e.g. the filters HEPA and ULPA). The classification of the filter can be done on the base of the tests in the manufacturing plant providing the manufacturer's testing equipment conforms to the valid standards, the test is carried out according to valid standards and the manufacturer has the quality assurance system in accordance with ISO 9000.

The tests in the manufacturing plant are performed using the manufacturer's testing equipment. The ground for the classification is the trial attestation, which includes an explicit description of the tested product, the testing conditions and the test results. The recognition of these tests is within the competence and responsibility of the buyer.

The testing procedure and classification of the air filters

Classification of the air filters into "categories" and "classes" (charter no 2) is done on the base of the results of the separation capacity measurements accomplished by the procedure described herein below. Detailed and binding information is provided by the respective standards.

Category is defined on the base of the unified measurement method and equal test parameters.
Class is defined on the base of one (lower) margin value or two (lower and upper) margin values of the separation capacity of the filter in relation to the method of the class measurement applying to the respective class.

Category G: Filters for coarse dust
Classes G1-G4

Gravimetrical test method according to EN 779 (2) for determination of the separation level:
Multiple dusting of the tested item by a given amount of standardized artificial testing dust. (3) in the flowing air up to the maximum end pressure loss 250 Pa. Determination of the separation level on the base of the weight rates by weighing the aerosol filters connected to the tested item. The mean value of the separation level (Am) is then calculated of all single measurements.

Category F: Filters for fine dust
Classes M5-F9

The test method based on the change of colour according EN 779 (2) for determination of the level of efficiency:
Multiple measuring of the level of efficiency concerning the natural atmospheric dust. After the first measurement the tested item is checked in the new condition by given amounts of of artificial testing dust (3) and after that the level of efficiency is determined again until reaching the end pressure loss 450 Pa. The measurement consists in comparing the tested air volumes, which are before and behind the tested item sucked through a white filter paper for micro-particles until they get the same colour. The mean value of the level of efficiency (Em) is calculated as the average of all single measurements.

Category H: HEPA filters for micro-particles
Classes E10-E12, H13-H14

Classes E10-E12 not tested for leak.
Classes H13 a H14 tested by "scanning" or visually (4) for leak elimination.

Testing procedure, see "category U".

Category U: ULPA filters for micro-particles
Classes U15-U17

Testing for elimination of untightness by "scanning".

The test method under EN 1822 (5). The test is carried out on non-polluted filters using fluid testing aerosol (e.g. DEHS) on the base of measured values for the particles diameter corresponding to maximum penetration factor (MPPS):

  • The first step of the test is to examine the flat samples of the filter medium for the size of particles to reach the maximum penetration factor (MPPS). The following evaluation and classification of the filter is performed for MPPS.
  • The second step is focused on measuring the integral penetration factor Di for MPPS (determined through the outlet surface) and the pressure loss of the filter, both at the rated volume flow.
  • The third step measures the topical penetration factor DL (leak penetration) for MPPS through the whole outlet filter surface and its frame (the method of scanning). For filter of the class E12 and higher the topical penetration factor must not exceed the value of the maximum integral penetration factor Di of the respective class (DL < 5·Di).

{en}For the filter classification the limit values of integral and topical penetration factors of the respective classes must not be exceeded.