Test methods for air filters

Test method for filters for general ventilation - Laser particle counting test method (EUROVENT4/9)

1. measurement of low-efficiency filters (EU1-EU4) by manual dust counting weighting method;

2. Measurement of high-efficiency filters by laser particle counter (EU5-EU9);

3. determination of dust particle size, upstream and downstream concentrations of different particle sizes by laser particle counter;

4. particle size range (0.2 - 5.0 um);

5. the dust source is a polydisperse phase liquid aerosol (DEHS: hexyl sebacate)

The efficiency of the air filter varies with the particle size of the dust, with the lowest efficiency at a certain particle size point, i.e. the maximum penetration rate, this point is called the most permeable particle size (MPPS). the MPPS point varies with the filter material and the filter airspeed.
For high-efficiency (HEPA) and ultra-high-efficiency (ULPA) air filters, the MPPS is generally between 0.1 and 0.25 μm.


In addition to normal penetration of the filter media, dust may also leak through breaks in the filter media or poor sealing of the cartridge to the outer frame.
A HEPA/ULPA filter with an acceptable total efficiency may not always have an acceptable point-by-point efficiency.
For HEPA and ULPA filters used at the end of unidirectional flow cleanrooms, both the total and point-by-point efficiencies must meet the specified values.
Traditional methods of total efficiency testing such as the sodium flame method, the oil mist method, the DOP method, as well as smoke or variable air volume leak detection methods, are not sensitive and precise enough to meet this increasingly demanding requirement.



In 1999, the European Committee for Standards (CEN) developed and promulgated EN1822, the latest standard for scanning testing and classification of HEPA/ULPA filters based on MPPS efficiency.

(1) The MPPS is determined by testing the classification count efficiency of the filter media used at different particle sizes at the filter air velocity of the filter to be tested, using either a Condensation Nucleus Particle Count (CNC) or laser particle counting equipment.

(2) At the specified surface air velocity (typically 0.45m/s), the air outlet surface of the filter is scanned and the point-by-point MPPS efficiency is tested.

(3) Based on the point-by-point MPPS efficiency, the total MPPS efficiency of the filter is calculated.

(4) Based on the total MPPS efficiency and the point-by-point efficiency, the filter is judged to be of the required grade.

Organic liquids such as DOP, DEHS, paraffin oil, etc. tend to produce high concentrations of artificial aerosols and are therefore often used to test HEPA/ULPA filters.