1.0 - EN779:2002 TO - EN779:2012 http://www.framindustrial.co.uk/products/EN779-2002-to-EN779-2012.aspx

EN779:2002 preceeds to the current release of EN779:2012 and the variation between

the two standards is significant. Included in the 2002 release is a test for the initial

electrostatic potential of media or filter, if tested this result is included in the 2002 report

but has no bearing on the filter grade. An explanation for electrostatic potential can be

found in the Fundamentals section.

In the 2002 edition only average arrestance or average efficiency defined the filtration

classification, the 2012 edition includes the result for electrostatic discharge and

grades the filter based around the minimum efficiency average arrestance, average

efficiency, new initial efficiency and discharged initial efficiency.

Although the report output appears the same, the filter grade can alter drastically with

the potential for an F9 to EN779:2002 filter dropping to M6 to EN779:2012. If a filter

which has an Average Efficiency of 98% making it F9 to EN779:2002, has an initial

discharged efficiency of 30% then it's new classification for EN779:2012 will be M6.

FRAM Industrial has created a straight forward chart explanation below, which

graphically explains the difference between the two standard revisions. The full

resolution image can be downloaded to clicking the image.

2.0 - FUNDAMENTALS: 2.1 - FILTRATION METHODS:

http://www.framindustrial.co.uk/filtration-industry-and-technology/Fundimental.aspx

Straining and inertial separation are the principle methods for filtration,

withinterception, diffusion (Brownian motion) and electrostatic charge being specific

forms of inertial separation.

These principles are used for contaminant filtration with varying levels of significance,

specific environmentally designed filters can be developed to strengthen each

characteristics where needed.

2.1.1 - FILTRATION ACCREDITATION:

Testing in the filtration industry is an esteemed and essential part of ensuring product

quality and customer satisfaction; the industry is heavily standardised and regulated

with globally and regionally popular testing methods.

FRAM Industrial has a pedigree of performing internal product quality testing

procedures from the most fundamental dimensional check confirmation to full product

life test standards such as the ARAMCO 32-SAMSS-008.

As a natural part of design and developement, products in the FRAM Industrial range

are independently tested to provide both manufacturing and market assurance. A

strong relationship is maintained with all of the industry related test laboratory houses

to ensure the highest quality products.

2.1.2 - FILTRATION METHOD: STRAINING

This method of filtration relates directly to the ratio of particle size to open area; if the

particles intended open pathway is smaller than the particle it will be blocked. This is

the least complicated and most common method of filtration, it’s apparent in all filter

types but depending on media pore size it’s typically the larger particles which are

affected by this method most.

Over time as contaminant blocks each pore or parts of a pore, the contaminant

begins to act as a filtration method helping to build up a contamainant layer known as

a ‘cake’.

2.1.3 - FILTRATION METHOD: INERTIAL SEPARATION

Contaminant separation takes place through particle and air stream inertia energy;

inertial separation generally describes a head on impact due to a lack of inertial

change. The air being filtered is forced through and around the fibres in the filter

pleat pack, if the contaminant particles are carrying too little or too much inertia to

make an effective change of direction around a fibre they will hit the fibre and stop.

Surface friction and areas of static low pressure air around the particle base prevent

the contaminant from moving back into the air stream.

Inertial separation is prevalent in all filter styles and will affect all contaminant particle

sizes; it’s effectiveness can be influenced by the saturation of other particles in the air

stream, particles can be both dislodged but also trap other particles.

2.1.4 - FILTRATION METHOD: INTERCEPTION

Turbulant boundary layers of air around contaminant particles in the airstream generate the

transfer of energy to create the inertial force moving the contaminant. Although contaminant

particles are pushed in the airstreams general direction their paths are heavily affected by their

inertia and mass. Interception is a form of inertial separation where the contaminant comes

into contact with any point around the filter media due to an inertial change.

After contact is made, surface friction and static low pressure areas around the particle will

prevent it from moving. This condition can affect all particle size, they can be disloged by

other particles in the area stream but stopped particles can also help to catch moving particles.

2.1.5 - FILTRATION METHOD: DIFFUSION (BROWNIAN MOTION)

Small contaminant particles can react dramatically through interaction with gas

molecules in the air stream. Although the gaseous elements of the air stream are

very small and light, (for example a hydrogen atom is estimated at around 0.1 nm),

the massive number of atoms the air stream (>1 yotta or 1024 per cubic metre of air)

is able to transfer is enough energy to influence objects with a 100 nm diameter into

Brownian motion.

The result of Brownian motion is a particle path which is considered random, also its

vector path length is in proportion to particle size. As contaminant particle size

reduces the probability of a particle hitting a fibre significantly increases.

Distance travelled by a particle decreases proportionally with particle size; the

smaller the particle the further it will travel, increasing the chance it will be inertially

separated, therefore particle removal efficiency is expected to increase for smaller

particles less than MPPS.

2.1.6 - FILTRATION METHOD: ELECTROSTIC

Inertial separation is significantly increased by electrostatic charge, positively or

negatively charged atoms in the filter attract contaminant particles of opposite

charge. Electrostic charge can be seen to temporarily improve filtration efficiency by

attracting particles with more or less charge to the filter media; this neutralises or

balances the filter system charge which after a short period reduces the number of

contaminant particles previously being attracted to the media fibres.

Filters can have electrostatic charge artificially induced into them, to improve initial

efficiency but over time due to dust loading this charge is balanced and the filter will

become less efficient. All filter products will have some level of electrostatic charge;

synthetic polymer based products are receptive to induced electrostatic charge where

as glass based products are not.

In the interest of fairness the industry tests for electrostatic charge as part of

theEN779 and EN1822 filtration tests, for more information click the standard links.

3.0 - Filter Specifications and Efficiencies: Fundamental Changes to Filter Standards

http://www.pharmout.net/blog/filter-specifications-and-efficiencies-fundamental-changes-to-filter-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’.

3.1 - EN 779:2012 3.1.1 - 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.

3.1.2 - 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 Final Pressure Drop (Pa)

Average arrestance (Am) of synthetic dust %

Average efficiency (Em) of 0.4 µm particles %

Minimum Efficiency(ME) for 0.4 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.

3.2 - EN 1822-1:2009 3.2.1 - 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

3.2.2 - 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 %

E10 85 15 – –

E11 95 5 – –

E12 99,5 0,5 – –

H13 99,95 0,05 99,75 0,25

H14 99,995 0,005 99,975 0,025

U15 99,9995 0,0005 99,9975 0,0025

U16 99,99995 0,00005 99,99975 0,00025

U17 99,999995 0,000005 99,9999 0,0001

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.

3.2.3n - Testing

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:

1. Pressure drop at nominal air flow

2. Overall collection efficiency at most penetrating particle size (MPPS)

3. Local collection efficiencies at MPPS

4. For filters with a specification of H13 and above, the Local Value has to be met to ensure that

there are no leaks.

Gordon Farquharson

Executive Consultant, is a Chartered Engineer with a unique blend of regulatory, technical and operational experience. He has conducted a broad spectrum of international audits, inspections and training assignments, encompassing technical aspects, GMP compliance and operational due diligence. Gordon is also active in developing standards and guidance within the global pharmaceutical industry (PIC/s, EU, FDA, WHO).

Posted on: March 26, 2013