Filter Specifications and Standards
Following a review by the CEN (European Committee for Standardisation), there have been changes to the following European Standards providing changes to the classifications of filters, allowing clear definition and clarity to the specification and efficiency calculations for filter classes;
EN779: 2012 ‘Particulate Air Filters For General Ventilation – Determination of the Filtration Performance’.
EN1822-1: 2009 ‘High Efficiency Air Filters (EPA, HEPA & ULPA) – Part 1: Classification, Performance Testing, Marking’.
Revised European Standard for General Ventilation Filters
The European Committee for Standardization (CEN) has established a new standard for general ventilation air filters, EN779:2012. Where the existing EN779:2002 was already widely accepted as a standard for testing and classifying coarse and fine filters based on average efficiency, the revised standard is again an important step forward.
The EN779:2012 introduces an air filter classification for fine filters F7 to F9 based on Minimum Efficiency (ME). ME is defined as the lowest value of three different tests for 0.4 µm particles; initial efficiency, efficiency throughout the test’s loading procedure and discharged efficiency. Those air filters that do not meet the ME requirements will lose their original efficiency classification and will automatically drop one or more classes.
With this revised methodology, the new EN779 will address the negative effects on Indoor Air Quality (IAQ) caused by underperforming air filters that currently exist in the market. Although many air filters have demonstrated compliant average efficiencies, some do lose their particulate collection functionality over time and therewith become a gateway for airborne contamination in buildings. With the implementation of ME requirements in EN779:2012, the industry is now stimulated to develop fine filters with an improved efficiency throughout the entire installation cycle.
Revised Filter Classifications
Fine filters previously rated as F5 or F6 to EN779:2002 are not required to meet an ME value in the new situation. To clearly differentiate these from those that do, filter classes F5 and F6 have been renamed to M5 and M6 as part of a new medium filter category. The revised filter class descriptions are;
- G1 – G4: Course Filters
- M5 – M6: Medium Filters
- F7 – F9: Fine Filters
The following table shows the classification and efficiencies of filters as per EN 779:
|-||Class||Final Pressure Drop (Pa)||Average arrestance (Am) of synthetic dust %||Average efficiency (Em) of 0.4 µm particles %||Minimum Efficiency (ME) for 0.4 µm particles %|
|G1||250||50 < Am < 65||-||-|
|G2||250||65 < Am < 80||-||-|
|G3||250||80 < Am < 90||-||-|
|G4||250||90 < Am||-||-|
|M5||450||-||40 < Em < 60||-|
|M6||450||-||60 < Em < 80||-|
|F7||450||-||80 < Em < 90||35|
|F8||450||-||90 < Em < 95||55|
|F9||450||-||95 < Em||70|
Note: The characteristics of atmospheric dust vary widely compared to those of the synthetic dust used in the EN779 tests. Because of this, the test results do not provide a completely accurate basis for predicting either operational performance or service life. Loss of media charge or shedding of particles or fibres can also adversely affect efficiency.
The re-grading of the M5 & M6 filters and removal of the ME test requirements may have an impact on cleanroom design and the selection of pre-filters for ISO 14644 environments. This change should be considered during the design phase to ensure that the appropriate testing can be completed and documented to prove the integrity of the environment that the filter is supporting.
Revised European Standard for High-Efficiency Ventilation Filters
This new European standard is based on particle counting methods that actually cover most needs for different applications. EN 1822-1:2009 differs from its previous edition (EN 1822-1:1998) by including the following:
- An alternative method for leakage testing of Group H filters with shapes other than panels
- An alternative test method for using a solid, instead of a liquid, test aerosol
- A method for testing and classifying of filters made out of membrane-type media
- A method for testing and classifying filters made out of synthetic fibre media
Revised Filter Classifications
HEPA filters previously rated as H10 to H12 to EN1822-1:1998 are not required to meet a Local Value in the new situation. To clearly differentiate these from those that do, filter classes H10 to H12 have been renamed as E10 to E12 as part of a new EPA filter category. The revised filter class descriptions are;
- E10 – E12: Efficiency Particulate Air (EPA) Filters
- H13 – H14: High Efficiency Particulate Air (HEPA) Filters
- U15 – U17: Ultra Low Penetration Air (ULPA) Filters
The following table shows the various classifications of high-efficiency filters per EN 1822-1:
|-||Integral Value||Local Value|
|Filter Class||Collection Efficiency %||Penetration %||Collection Efficiency %||Penetration %|
The re-grading of the E10 to E12 filters and removal of the Local Value test requirements may have an impact on cleanroom design and filter selection for ISO 14644 environments. This change should be considered during the design phase to ensure that the appropriate testing can be completed and documented to prove the integrity of the environment that the filter is supporting.
Testing per EN 1822 is normally done with an aerosol probe which can be moved over the entire surface of the filter. This moving of the aerosol probe, or scanning, results in the measurement of many local collection efficiencies. These local efficiencies can be used to calculate the overall efficiency of the filter or the leak rate of a specific area of the filter. The overall efficiency calculation is often termed the integral value, while the leak rate is often termed the local value.
Tests are performed on new filters at specified nominal volumetric air flow. Filters of U15 or above must be scanned with a particle counter probe designed for this purpose. An oil thread test can be utilized on filters of H13 and H14 grade.
Filter testing includes the following measurement:
- Pressure drop at nominal air flow
- Overall collection efficiency at most penetrating particle size (MPPS)
- Local collection efficiencies at MPPS
- For filters with a specification of H13 and above, the Local Value has to be met to ensure that there are no leaks.