SIST EN 779:2004

SLOVENSKI STANDARD
01-maj-2004
1DGRPHãþD
SIST EN 779:2000
Particulate air filters for general ventilation - Determination of the filtration
performance
Particulate air filters for general ventilation - Determination of the filtration performance
Partikel-Luftfilter für die allgemeine Raumlufttechnik - Bestimmung der Filterleistung
Filtres a air de ventilation général pour l'élimination des particules - Détermination des
performances de filtration
Ta slovenski standard je istoveten z: EN 779:2002
ICS:
91.140.30 3UH]UDþHYDOQLLQNOLPDWVNL Ventilation and air-
VLVWHPL conditioning
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 779
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2002
ICS 91.140.30 Supersedes EN 779:1993
English version
Particulate air filters for general ventilation - Determination of the
filtration performance
Filtres à air de ventilation générale pour l'élimination des Partikel-Luftfilter für die allgemeine Raumlufttechnik -
particules - Détermination des performances de filtration Bestimmung der Filterleistung
This European Standard was approved by CEN on 14 September 2002.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 779:2002 E
worldwide for CEN national Members.

Contents
page
Foreword.4
Introduction .5
1 Scope .6
2 Normative references .6
3 Terms and definitions.6
4 Symbols and abbreviated terms.9
5 Requirements .11
6 Classification.11
7 Test rig and equipment .12
7.1 Test conditions .12
7.2 Test rig .12
7.3 Aerosol generation .16
7.3.1 DEHS Test Aerosol .16
7.3.2 Neutralisation (conditioning) of aerosol.16
7.4 Aerosol sampling system .18
7.5 Flow measurement .20
7.6 Particle counter.20
7.7 Differential pressure measuring equipment .20
7.8 Dust feeder .20
8 Qualification of test rig and apparatus .23
8.1 Air velocity uniformity in the test duct .23
8.2 Aerosol uniformity in the test duct .23
8.3 Particle counter sizing accuracy.24
8.4 Particle counter zero test.25
8.5 Particle counter overload test .25
8.6 100 % efficiency test.25
8.7 Zero % efficiency test .26
8.8 Aerosol generator response time.26
8.9 Pressure equipment calibration .26
8.10 Pressure drop checking.26
8.11 Dust feeder air flow rate.27
8.12 Neutraliser .29
8.13 Summary of qualification requirements .29
8.14 Apparatus maintenance .30
9 Test materials.30
9.1 Test air - cleanliness, temperature and humidity .30
9.2 Test aerosol.30
9.3 Loading dust.31
9.4 Final filter.31
10 Test procedure .32
10.1 Preparation of filter to be tested.32
10.2 Initial pressure drop .32
10.3 Initial efficiency .32
10.3.1 Efficiency of discharged filter media .32
10.3.2 Efficiency measurement.32
10.4 Dust loading .33
10.4.1 Dust loading procedure.33
10.4.2 Arrestance .34
10.4.3 Efficiency .35
10.4.4 Average efficiency .35
10.4.5 Dust holding capacity.35
11 Uncertainty calculation of the test results .36
12 Reporting .37
12.1 General.37
12.2 Summary.38
12.3 Efficiency .39
12.4 Pressure drop and air flow rate.40
12.5 Arrestance and dust holding capacity.40
12.6 Marking .40
Annex A (normative)  Electrostatic discharging procedure .49
A.1 General.49
A.2 Test method for discharging of filter material .49
A.2.1 Equipment .49
A.2.2 Preparation of test samples.50
A.2.3 Measurement of the filter efficiency .50
A.2.4 Isopropanol test.50
A.3 Expression of results .50
Annex B (informative)  Shedding from filters.51
B.1 General.51
B.2 Shedding.51
B.2.1 Particle bounce .51
B.2.2 Release of fibres or particulate matter from filter material .51
B.2.3 Re-entrainment of particles .51
B.3 Testing .52
B.4 References.52
Annex C (informative)  Commentary .53
C.1 General.53
C.2 Classification.53
C.3 Test.53
C.3.1 Test aerosol.53
C.3.2 Loading dust .54
C.3.3 Distribution and sampling of aerosols .54
C.3.4 Particle counter characteristics .54
C.3.5 Flat sheet test.54
C.4 Filtration characteristics .55
C.4.1 General.55
C.4.2 Pressure drop.55
C.4.3 Discharged efficiency.55
Annex D (informative)  Pressure drop calculation.57
Annex E (informative)  Example of a completed test report .59
E.1 Example of test reports.59
E.2 Examples of calculations.67
A.3 Final results at 450 Pa .70
Bibliography .71
Foreword
This document (EN 779:2002) has been prepared by Technical Committee CEN/TC 195 "Air filters for general air
cleaning", the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by May 2003, and conflicting national standards shall be withdrawn at the latest by
May 2003.
This European Standard deals with the performance testing of particulate air filters for general ventilation and su-
persedes EN 779:1993, which describes an obsolete test method.
EN 779 is based on the test method according to Eurovent 4/9:1997. In addition, it contains extensive test rig quali-
fication procedures together with procedures which give some information regarding the real life behaviour of par-
ticulate air filters (see ”Introduction”).
Annex A is normative. Annexes B to E are informative.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following coun-
tries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Swe-
den, Switzerland and the United Kingdom.
Introduction
General
The procedures described in this standard have been developed from those given in EN 779:1993 and Eurovent
4/9:1997. The basic design of test rig given in EN 779:1993 is retained with the exception of the “dust-spot” atmos-
pheric aerosol opacity test equipment. Instead, a challenge aerosol of DEHS (or equivalent) is dispersed evenly
across the duct upstream of the filter being tested. Representative upstream and downstream samples are ana-
lysed by an optical particle counter (OPC) to provide filter particle size efficiency data.
Classification
The EN 779:1993 classification system (comprising groups F and G filters) has been retained; classification is now
determined from the average filtration efficiency with respect to liquid DEHS particles of 0,4 μm diameter. Classifi-
cation of F filters is based on performance with respect to 0,4 mm particles because of practical evidence that the
EN 779:1993 classification based on the “dust-spot” opacity test is very closely matched. Filters found to have an
average efficiency value of less then 40 % will be allocated to group G and the efficiency reported as
“< 40 %”. The classification of G filters is based on their average arrestance with the loading dust.
Test aerosol
A challenge aerosol of DEHS (or equivalent) was chosen for the efficiency test for the following reasons:
 experience has already been gained by users of the Eurovent 4/9 test method so that much suitable equip-
ment already exists;
 liquid aerosols are easy to generate in the concentrations, size range and degree of consistency required;
 the DEHS could be used as a neutral test aerosol without charge or be charged to the Boltzmann equilibrium
charge level. In this standard the aerosol should be brought to the Boltzmann charge distribution;
 spherical latex particles are used to calibrate particle counters. The determination of the particle size of spheri-
cal liquid particles using optical particle counters is more accurate than would be the case with solid particles
of nonspherical salt and test dusts.
The aerosol should be brought to the Boltzmann charge distribution to represent the charge distribution of aged
ambient atmospheric aerosol.
Filtration characteristics
Initiatives to address the potential problems of particle re-entrainment, shedding and the in-service charge neutrali-
sation characteristics of certain types of media have been included in annexes A and B.
Certain types of filter media rely on electrostatic effects to achieve high efficiencies at low resistance to air flow.
Exposure to some types of challenge, such as combustion particles in normal atmospheric air or oil mist, may neu-
tralise such charges with the result that filter performance suffers. It is important that the users are aware of the
potential for performance degradation when loss of charge occurs. It is also important that means be available for
identifying cases where the potential exists. The normative test procedure, described in annex A, provides tech-
niques for identifying this type of behaviour. This procedure is used to determine whether the filter efficiency is de-
pendent on the electrostatic removal mechanism and to provide quantitative information about the importance of
the electrostatic removal.
In an ideal filtration process, each particle would be permanently arrested at the first contact with a filter fibre, but
incoming particles may impact on a captured particle and dislodge it into the air stream. Fibres or particles from the
filter itself could also be released, due to mechanical forces. From the user’s point of view it might be important to
know this, but such behaviour would probably not be detected by a particle counter system according to this stan-
dard.
1 Scope
This European Standard refers to particulate air filters for general ventilation. These filters are classified according
to their performance as measured in this test procedure.
This European Standard contains requirements to be met by particulate air filters. It describes testing methods and
the test rig for measuring filter performance.
In order to obtain results for comparison and classification purposes, particulate air filters are tested against two
synthetic aerosols, a fine aerosol for measurement of filtration efficiency as a function of particle size within a parti-
cle size range 0,2 mm to 3,0 mm, and a coarse one for obtaining information about dust holding capacity and, in the
case of coarse filters, filtration efficiency with respect to coarse loading dust (arrestance).
This European Standard applies to air filters having an initial efficiency of less than 98 % with respect to 0,4 μm
3 3 3 3
particles. Filters should be tested at an air flow rate between 0,24 m /s (850 m /h) and 1,5 m /s (5 400 m /h).
The performance results obtained in accordance with this standard cannot by themselves be quantitatively applied
to predict performance in service with regard to efficiency and lifetime. Other factors influencing performance to be
taken into account are described in annex A (normative) and annex B (informative).
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN 1822-1, High efficiency air filters (HEPA and ULPA) - Part 1: Classification, performance testing, marking.
EN ISO 5167-1:1995, Measurement of fluid flow by means of pressure differential devices - Part 1: Orifice plates,
nozzles and Venturi tubes inserted in circular cross-section conduits running full (ISO 5167-1:1991).
ISO 2854, Statistical interpretation of data - Techniques of estimation and tests relating to means and variances.
ISO 12103-1, Road vehicles - Test dust for filter evaluation - Part 1: Arizona test dust.
3 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1
arrestance
weighted (mass) removal of loading dust (expressed in %)
3.2
average arrestance
ratio of the total amount of loading dust retained by the filter to the total amount of dust fed up to final pressure
drop. Average arrestance is used for classification of G-filters (expressed in %)
3.3
average efficiency - E
m
weighted average of the efficiencies for the different specified dust loading levels up to final pressure drop. Average
efficiency is used for classification of F-filters (expressed in %)
3.4
average efficiency - E
i,j
average efficiency for a size range ”i” at different dust loading intervals ”j” (expressed in %)
3.5
charged filter
filter which is electrostatically charged or polarised
3.6
coarse filter
filter classified in one of the classes G1 to G4
3.7
counting rate
number of counting events per unit of time
3.8
DEHS
liquid (DiEthylHexylSebacate) for generating the test aerosol
3.9
dust holding capacity
amount of loading dust retained by the filter up to final pressure drop (expressed in grams)
3.10
face area
area of the inside section of the test duct immediately upstream of the filter under test (nominal values
0,61 m · 0,61 m = 0,37 m )
3.11
face velocity
air flow rate divided by the face area (expressed in m/s)
3.12
final filter
air filter used to collect the loading dust passing the filter under test
3.13
final pressure drop - recommended
maximum operating pressure drop of the filter as recommended by the manufacturer at rated air flow (expressed in
Pa)
3.14
final pressure drop
pressure drop up to which the filtration performance is measured for classification purposes (expressed in Pa)
3.15
fine filter
filter classified in one of the classes F5 to F9
3.16
HEPA filter
High Efficiency Particulate Air Filter, classes H10 to H14 according to EN 1822-1. A filter intended to purify the air
upstream of the test circuit
3.17
ULPA filter
Ultra Low Penetration Air Filter, classes U15 to U17 according to EN 1822-1
3.18
initial arrestance
arrestance of the first 30 g loading dust increment (expressed in %)
3.19
initial efficiency
efficiency of the clean filter operating at the test air flow rate (expressed in % for each size range of selected parti-
cles)
3.20
initial pressure drop
pressure drop of the clean filter operating at its test air flow rate (expressed in Pa)
3.21
isokinetic sampling
sampling of the air within a duct such the probe inlet air velocity is the same as the velocity in the duct at the sam-
pling point
3.22
loading dust
synthetic test dust specifically formulated for determining the dust holding capacity and arrestance of the filter
3.23
mean diameter
geometric average of the size range diameter (expressed in μm)
3.24
media velocity
air flow rate divided by the net effective filtering area (expressed in m/s to an accuracy of three significant figures)
3.25
net effective filtering area
area of filter medium in the filter which collects dust (expressed in m )
3.26
neutralisation
bringing the aerosol to a Boltzmann charge distribution (same amount of positive as negative ions in the aerosol)
3.27
particle bounce
it describes the behaviour of particles that impinge on the filter without being retained
3.28
particle size
equivalent optical diameter of a particle
3.29
particle number concentration
number of particles per unit of volume of the test air
3.30
penetration
ratio of the particle concentration downstream to upstream of the filter (expressed in %)
3.31
re-entrainment
releasing to the air flow of particles previously collected on the filter
3.32
shedding
releasing to the air flow of particles due to particle bounce and re-entrainment effects, and to the release of fibres or
particulate matter from the filter or filtering material
3.33
synthetic test dust
dust specifically formulated for determining the dust holding capacity and arrestance of the filter
3.34
test air flow rate
volumetric rate of air flow through the filter under test (expressed in m /s for a reference air density of
1,20 kg/m )
3.35
test aerosol
aerosol used for determining the efficiency of the filter
3.36
test air
air to be used for testing purposes
4 Symbols and abbreviated terms
For the application of this European Standard, the following symbols and abbreviated terms apply.
A Arrestance
A Arrestance in loading phase ”j”, %
j
A Average arrestance during test to final pressure drop, %
m
CL Concentration limits of particle counter
CV Coefficient of variation
CV Coefficient of variation in size range ”i”
i
DHC Dust holding capacity, g
d Size range diameter or mean diameter, μm
i
d Lower border diameter in a size range, μm
l
d Upper border diameter in a size range, μm
u
E Initial efficiency, %
i
E The average efficiency for size range ”i” after dust loading phase ”j”, %
i,j
E , Average efficiency of size range ”i” during test up to final pressure drop, %
m i
E Average efficiency of 0,4 μm particles during test up to final pressure drop (used for classification),
m
%
Average efficiency, %
E
F5 to F9 Fine filter classes
G1 to G4 Coarse filter classes
M Mass of dust fed to the filter during loading phase ”j”, g
j
mean Mean value
mean Mean value in size range ”i”
i
m Dust in duct after filter, g
d
m Mass of dust passing the filter at the dust loading phase ”j”, g
j
m Cumulative mass of dust fed to filter, g
tot
m Mass of final filter before dust increment, g
m Mass of final filter after dust increment, g
N Number of particles in size range ”i” upstream of the filter
i
n Number of points
n Number of particles in size range ”i” downstream of the filter
i
OPC Optical particle counter
p Pressure, Pa
p Absolute air pressure upstream of filter, kPa
a
p Air flow meter static pressure, kPa
sf
q Mass flow rate at air flow meter, kg/s
m
q Air flow rate at filter, m /s
V
q Air flow rate at air flow meter, m /s
Vf
t Temperature upstream of filter, °C
t Temperature at air flow meter, °C
f
Distribution variablea
t
(1 - )
U Uncertainty, % units
Standard deviationd
nNumber of degrees of freedom
Air density of air, kg/mr
Relative humidity upstream of filter, %j
Dust increment, gDm
Dm Mass gain of final filter, g
ff
Filter pressure drop, PaDp
Air flow meter differential pressure, PaDp
f
Filter pressure drop at air density 1,20 kg/m , PaDp
1,20
ANSI American National Standards Institute
ASHRAE American Society of Heating, Refrigerating and Air Conditioning Engineers
ASTM American Society for Testing and Materials
CAS Chemical Abstracts
CEN European Committee for Standardisation
EN European Standard
EUROVENT European Committee of Air Handling and Refrigeration Equipment Manufacturers
ISO International Standards Organisation
NORDTEST Organisation for common test recommendations in Nordic countries
VTT Technical Research Centre of Finland
5 Requirements
The filter shall be designed or marked so as to prevent incorrect mounting. The filter shall be designed so that
when correctly mounted in the ventilation duct, no leak occurs at the sealing edge.
The complete filter (filter and frame) shall be made of material suitable to withstand normal usage and exposures to
those temperatures, humidities and corrosive environments that are likely to be encountered.
The complete filter shall be designed so that it will withstand mechanical constraints that are likely to be encoun-
tered during normal use. Dust or fibres released from the filter media by air flow through the filter shall not consti-
tute a hazard or nuisance for the people (or devices) exposed to filtered air.
6 Classification
Filters are classified according to their efficiency (arrestance) under the following test conditions:
3 3
 the air flow shall be 0,944 m /s (3 400 m /h) if the manufacturer does not specify any rated air flow rate;
 250 Pa maximum final pressure drop for Coarse (G) filters;
 450 Pa maximum final pressure drop for Fine (F) filters.
If the filters are tested at 0,944 m /s and at maximum final pressure drops, they are classified according to Table 1.
For instance G3, F7.
Filters tested at airflows and final pressure drops different from those above shall be classified according to
Table 1. The classification shall be qualified by test conditions in parentheses, e.g. G4 (0,7 m /s, 200 Pa), F7
(1,25 m /s).
Table 1 — Classification of air filters according to EN 779
Class Final pressure drop Average arrestance (A Average efficiency (E )
m) m
of synthetic dust of 0,4 μm particles
Pa % %
G1 250 -
50 £ A < 65
m
G2 250 -
65 £ A < 80
m
G3 250 -
80 £ A < 90
m
G4 250 -
90 £ A
m
F5 450 - 40 £ E < 60
m
F6 450 -
60 £ E < 80
m
F7 450 - 80 £ E < 90
m
F8 450 -
90 £ E < 95
m
F9 450 - 95 £ E
m
NOTE The characteristics of atmospheric dust vary widely in comparison with those of the synthetic loading dust used
in the tests. Because of this the test results do not provide a basis for predicting either operational performance or life. Loss
of media charge or shedding of particles or fibres can also adversely affect efficiency (see annexes A and B).
7 Test rig and equipment
7.1 Test conditions
Room air or outdoor air may be used as the test air source. Relative humidity shall be less than 75 %. The exhaust
flow may be discharged outdoors, indoors or recirculated. Requirements of certain measuring equipment may im-
pose limits on the temperature of the test air.
Filtration of the exhaust flow is recommended when test aerosol and loading dust may be present.
7.2 Test rig
The test rig (see Figure 1) consists of several square duct sections with 610 mm · 610 mm nominal inner dimen-
sions except for the section where the filter is installed. This section has nominal inner dimensions between 616
mm and 622 mm. The length of this duct section shall be at least 1,1 times the length of the filter, with a minimum
length of 1 m.
The duct material shall be electrically conductive and electrically grounded, have a smooth interior finish and be
sufficiently rigid to maintain its shape at the operating pressure. Smaller parts of the test duct could be made in
glass or plastic to see the filter and equipment. Provision of windows to allow monitoring of test progress is desir-
able.
HEPA filters may be placed upstream of section 1, in which the aerosol for efficiency testing is dispersed and mixed
to create a uniform concentration upstream the filter.
Section 2 includes in the upstream section the mixing orifice (10) in the centre of which the dust feeder discharge
nozzle is located. Downstream of the dust feeder is a perforated plate (11) intended to achieve a uniform dust dis-
tribution. In the last third of this duct is the upstream aerosol sampling head. For arrestance tests, this sampling
head shall be blanked off or removed.
To avoid turbulence, the mixing orifice and the perforated plate should be removed during the efficiency test. To
avoid systematic error, removal of these items during pressure drop measurements is recommended.
Section 5 may be used for both efficiency and arrestance measurements and is fitted with a final filter for the ar-
restance test and with the downstream sampling head for the efficiency test. Section 5 could also be duplicated,
allowing one part to be used for arrestance test and the other for the efficiency test.
The test rig can be operated either in both negative or positive pressure. In the case of positive pressure operation
(i.e. the fan upstream the test rig), the test aerosol and loading dust could leak into the laboratory, while at negative
pressure particles could leak into the test system and affect the number of measured particles.
The dimensions of the test rig and the position of the pressure taps are shown in Figure 2.
The pressure drop of the tested filter shall be measured using static pressure taps located as shown in Figure 2.
Pressure taps shall be provided at four points over the periphery of the duct and connected together by a ring line.
Section 6 is fitted with a standardised air flow measuring device. If an alternative air flow measurement device is
used, this section can be shortened.
Key
1 Duct section of the test rig
2 Duct section of the test rig
3 Filter to be tested
4 Duct section including the filter to be tested
5 Duct section of the test rig
6 Duct section of the test rig
7 HEPA filter (at least H13)
8 Inlet point for DEHS particles
9 Dust injection nozzle
10 Mixing orifice
11 Perforated plate
12 Upstream sampling head
13 Downstream sampling head
Figure 1 — Schematic diagram of the test rig
Dimensions in millimetres
Figure 2 — Dimensions of the test rig
Dimensions in millimetres
Key
1 Mixing orifice
2 Perforated plate with Ø 152 mm ± 2 mm
and 40 % open area
3 Pressure tap
4 Transition duct - test filter smaller than
duct
5 Transition duct - test filter larger than duct
Figure 3 — Details of test duct components
7.3 Aerosol generation
7.3.1 DEHS Test Aerosol
The test aerosol described shall consist of untreated or undiluted DEHS. Any other aerosol proven to give equiva-
lent performance may be used. Test aerosol of DEHS (DiEthylHexylSebacate) produced by a Laskin nozzle is
widely used in performance testing of HEPA and ULPA filters.
Figure 4 gives an example of a system for generating the aerosol. It consists of a small container with DEHS liquid
and a Laskin nozzle. The aerosol is generated by feeding compressed particle-free air through the Laskin nozzle.
The atomised droplets are then directly introduced into the test rig. The pressure and air flow to the nozzle are var-
ied according to the test flow and the required aerosol concentration. For a test flow of 0,944 m /s the pressure is
3 3
about 17 kPa, corresponding to an air flow of about 0,39 dm /s (1,4 m /h) through the nozzle.
Any other generator capable of producing droplets in sufficient concentrations in the size range of 0,2 μm to
3,0 μm can be used. One such generator is specified in the French standard NF X 44-060 and consists of two
pressurised containers and a sonic atomiser fed by compressed air.
Before testing, regulate the upstream concentration to reach steady state and to have a concentration below the
coincidence level of the particle counter.
7.3.2 Neutralisation (conditioning) of aerosol
The test aerosol shall be brought to a Boltzmann electrostatic charge distribution by contact with a beta or gamma
radiation generator with an activity of at least 185 MBq (5 mCi), or by a corona discharge ionizer. The corona dis-
charge ionizer shall have a minimum corona current of 3 μA and shall be balanced to provide equal amounts of
positive and negative ions.
Dimensions in millimetres
Key
1 Particle-free air (pressure about 17 kPa)
2 Aerosol to test rig
3 Laskin nozzle
4 Test aerosol (for instance DEHS)
5 Four ˘ 1,0 mm holes 90º apart top edge of holes and just touching the bottom of the collar
6 Four ˘ 2,0 mm holes next to tube in line with radial holes
7 Neutraliser
Figure 4 — DEHS particle generation system
7.4 Aerosol sampling system
Two rigid sample lines of equal length and equivalent geometry (bends and straight lengths) shall connect the up-
stream and downstream sampling heads to the particle counter. The sample tubes shall be electrically conducting
or have a high dielectric constant and have a smooth inside surface (steel, tygon etc).
Tapered sampling probes are placed in the centre of the upstream and downstream measuring sections. The sam-
pling heads shall be centrally located with the inlet tip facing the inlet of the rig parallel to the air flow. The sampling
shall be isokinetic within 10 % at a test flow rate of 0,944 m /s. Isokinetic sampling is also recommended at other
test flows.
Three one-way valves make it possible to sample the aerosol upstream or downstream of the filter under test, or to
have a "blank" suction through a HEPA filter. These valves shall be of a straight-through design. Due to possible
particle losses from the sampling system, the first measurement after a valve is switched should be ignored.
The flow rate can be maintained by the pump in the counter in the case of a particle counter with a high flow rate
(e.g. 0,47 dm /s) or by an auxiliary pump in the case of a counter with smaller sample flow rates. The exhaust line
shall then be fitted with an isokinetic sampling nozzle directly connected to the particle counter to achieve isokinetic
conditions within a tolerance of – 10 %.
Particle losses will occur in the test duct, aerosol transport lines and particle counter. Minimisation of particle losses
is desirable because a smaller number of counted particles will mean larger statistical errors and thus less accurate
results. The influence of particle losses on the result is minimised if the upstream and downstream sampling losses
are made as near equal as possible.
Key
1 Filter
2 HEPA filter (clean air)
3 Valve, upstream
4 Valve, clean air
5 Valve, downstream
6 Computer
7 Particle counter
8Pump
Figure 5 — Schematic diagram of the aerosol sampling system
7.5 Flow measurement
Flow measurement shall be made by standardised flow measuring devices in accordance with EN ISO 5167-1. Ex-
amples are orifice plates, nozzles, Venturi tubes, etc.
The uncertainty of measurement shall not exceed 5 % of the measured value at 95 % confidence level.
7.6 Particle counter
This method requires the use of an optical particle counter (OPC) having a particle size range of at least 0,2 μm to
3,0 μm. The counting efficiency of the OPC shall be ‡ 50 % for 0,2 μm particles. The size range should be divided
into at least five size classes, the boundaries of which should be approximately equidistant on a logarithmic scale.
Clause 8 contains further information and details about the calibration and operation of OPCs, which have to be
used for this test.
7.7 Differential pressure measuring equipment
Measurements of pressure drop shall be taken between measuring points located in the duct wall as shown in Fig-
ure 2. Each measuring point shall comprise four interconnected static taps equally distributed around the periphery
of the duct cross section.
The pressure measuring equipment used shall be capable of measuring pressure differences with an accuracy of
– 2 Pa in the range of 0 Pa to 70 Pa. Above 70 Pa, the accuracy shall be – 3 % of the measured value.
7.8 Dust feeder
Any dust feeder can be chosen as long as it gives the same test result as the dust feeder described below. The
purpose of the dust feeder is to supply the synthetic dust to the filter under test at a constant rate over the test pe-
riod.
...