EN ISO 16890-2:2016

SLOVENSKI STANDARD
01-marec-2017
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SIST EN 779:2012
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Air filters for general ventilation - Part 2: Measurement of fractional efficiency and air flow
resistance (ISO 16890-2:2016)
Luftfilter für die allgemeine Raumlufttechnik - Teil 2: Ermittlung des
Franktionsabscheidegrades und des Durchflusswiderstandes (ISO 16890-2:2016)
Filtres à air pour ventilation générale - Partie 2: Mesurage du rendement fractionnaire et
de la résistance à l'écoulement de l'air (ISO 16890-2:2016)
Ta slovenski standard je istoveten z: EN ISO 16890-2:2016
ICS:
91.140.30 3UH]UDþHYDOQLLQNOLPDWVNL Ventilation and air-
VLVWHPL conditioning systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 16890-2
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2016
EUROPÄISCHE NORM
ICS 91.140.30 Supersedes EN 779:2012
English Version
Air filters for general ventilation - Part 2: Measurement of
fractional efficiency and air flow resistance (ISO 16890-
2:2016)
Filtres à air de ventilation générale - Partie 2: Luftfilter für die allgemeine Raumlufttechnik - Teil 2:
Mesurage de l'efficacité spectrale et de la résistance à Ermittlung des Franktionsabscheidegrades und des
l'écoulement de l'air (ISO 16890-2:2016) Durchflusswiderstandes (ISO 16890-2:2016)
This European Standard was approved by CEN on 19 September 2016.

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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 16890-2:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 16890-2:2016) has been prepared by Technical Committee ISO/TC 142
"Cleaning equipment for air and other gases" in collaboration with Technical Committee CEN/TC 195
“Air filters for general air cleaning” the secretariat of which is held by UNI.
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 June 2017, and conflicting national standards shall be
withdrawn at the latest by June 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document supersedes EN 779:2012.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 16890-2:2016 has been approved by CEN as EN ISO 16890-2:2016 without any
modification.
INTERNATIONAL ISO
STANDARD 16890-2
First edition
2016-12-01
Air filters for general ventilation —
Part 2:
Measurement of fractional efficiency
and air flow resistance
Filtres à air de ventilation générale —
Partie 2: Mesurage de l’efficacité spectrale et de la résistance à
l’écoulement de l’air
Reference number
ISO 16890-2:2016(E)
©
ISO 2016
ISO 16890-2:2016(E)
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved

ISO 16890-2:2016(E)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 4
4.1 Symbols . 4
4.2 Abbreviated terms . 6
5 General test requirements . 6
5.1 Test device requirements . 6
5.2 Test device installation . 6
5.3 Test rig requirements . 6
6 Test materials . 7
6.1 Liquid phase aerosol . 7
6.1.1 DEHS test aerosol . 7
6.1.2 DEHS/DES/DOS - formula . 7
6.1.3 DEHS properties . 7
6.1.4 Liquid phase aerosol generation . 7
6.2 Solid phase aerosol . 8
6.2.1 Potassium chloride (KCl) test aerosol . 8
6.2.2 KCl - formula . 8
6.2.3 KCl properties . 8
6.2.4 Solid phase aerosol generation . 9
6.3 Reference aerosols .10
6.3.1 Reference aerosol for 0,3 µm to 1,0 µm .10
6.3.2 Reference aerosol for 1,0 µm to 10,0 µm .10
6.3.3 Other reference aerosols .10
6.3.4 Matching criteria .11
6.4 Aerosol loading .11
7 Test equipment.11
7.1 Test rig .11
7.1.1 Dimensions .11
7.1.2 Construction materials .12
7.1.3 Test rig shape .12
7.1.4 Test rig air supply .13
7.1.5 Test rig isolation .13
7.1.6 D/S mixing orifice .13
7.1.7 Aerosol sampling .14
7.1.8 Test rig air flow rate measurement . .16
7.1.9 Resistance to air flow measurement .16
7.1.10 Non 610 mm × 610 mm (24,0 inch × 24,0 inch) test devices .17
7.1.11 Dust injection testing .18
7.2 Aerosol particle counter .18
7.2.1 General.18
7.2.2 OPC sampled size range .18
7.2.3 OPC particle size ranges .18
7.2.4 Sizing resolution.19
7.2.5 Calibration .19
7.2.6 Air flow rate .19
7.2.7 Zero counting .19
7.2.8 Dual OPC(s) .19
7.3 Temperature, relative humidity.20
ISO 16890-2:2016(E)
8 Qualification of test rig and apparatus .20
8.1 Schedule of qualification testing requirements .20
8.1.1 General.20
8.1.2 Qualification testing .20
8.1.3 Qualification documentation .20
8.2 Qualification testing .21
8.2.1 Test rig — Pressure system testing .21
8.2.2 OPC — Air flow rate stability test .22
8.2.3 OPC — Zero test . . .22
8.2.4 OPC — Sizing accuracy .23
8.2.5 OPC — Overload test .23
8.2.6 Aerosol generator — Response time .24
8.2.7 Aerosol generator — Neutralizer .24
8.2.8 Test rig — Air leakage test.25
8.2.9 Test rig — Air velocity uniformity .26
8.2.10 Test rig — Aerosol uniformity .27
8.2.11 Test rig — Downstream mixing .28
8.2.12 Test rig — Empty test device section pressure .29
8.2.13 Test rig — 100 % efficiency test and purge time .30
8.2.14 Test rig — Correlation ratio .30
8.3 Maintenance .30
8.3.1 General.30
8.3.2 Test rig — Background counts .31
8.3.3 Test rig — Reference filter test .32
8.3.4 Test rig — Pressure reference test .33
8.3.5 Test rig — Final filter resistance .33
9 Test methods .33
9.1 Air flow rate .33
9.2 Measurement of resistance to air flow .33
9.3 Measurement of fractional efficiency .33
9.3.1 Aerosol sampling protocol .33
9.3.2 Background sampling .33
9.3.3 Testing sequence for a single OPC.34
9.3.4 Testing sequence for dual OPC testing .36
10 Data reduction and calculations .38
10.1 Correlation ratio .38
10.1.1 Correlation ratio general.38
10.1.2 Correlation ratio data reduction .38
10.2 Penetration and fractional efficiency .40
10.2.1 Penetration and fractional efficiency general .40
10.2.2 Penetration data reduction .40
10.3 Data quality requirements .43
10.3.1 Correlation background counts .43
10.3.2 Efficiency background counts .43
10.3.3 Correlation ratio .43
10.3.4 Penetration .44
10.4 Fractional efficiency calculation .44
11 Reporting results .45
11.1 General .45
11.2 Required reporting elements .45
11.2.1 Report general .45
11.2.2 Report values .45
11.2.3 Report summary .45
11.2.4 Report details .47
Annex A (informative) Example .50
Annex B (informative) Resistance to air flow calculation.57
iv © ISO 2016 – All rights reserved

ISO 16890-2:2016(E)
Bibliography .59
ISO 16890-2:2016(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 142, Cleaning equipment for air and other gases.
This first edition of ISO 16890-2, together with ISO 16890-1, ISO 16890-3 and ISO 16890-4, cancels and
replaces ISO/TS 21220:2009, which has been technically revised.
ISO 16890 consists of the following parts, under the general title Air filters for general ventilation:
— Part 1: Technical specifications, requirements and classification system based upon particulate matter
efficiency (ePM)
— Part 2: Measurement of fractional efficiency and air flow resistance
— Part 3: Determination of the gravimetric efficiency and the air flow resistance versus the mass of test
dust captured
— Part 4: Conditioning method to determine the minimum fractional test efficiency
vi © ISO 2016 – All rights reserved

ISO 16890-2:2016(E)
Introduction
The effects of particulate matter (PM) on human health have been extensively studied in the past
decades. The results are that fine dust can be a serious health hazard, contributing to or even causing
respiratory and cardiovascular diseases. Different classes of particulate matter can be defined according
to the particle size range. The most important ones are PM , PM and PM . The U.S. Environmental
10 2,5 1
Protection Agency (EPA), the World Health Organization (WHO) and the European Union define
PM as particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off
at 10 µm aerodynamic diameter. PM and PM are similarly defined. However, this definition is not
2,5 1
precise if there is no further characterization of the sampling method and the sampling inlet with a
clearly defined separation curve. In Europe, the reference method for the sampling and measurement
of PM is described in EN 12341. The measurement principle is based on the collection on a filter of the
PM fraction of ambient particulate matter and the gravimetric mass determination (see EU Council
Directive 1999/30/EC of 22 April 1999).
As the precise definition of PM , PM and PM is quite complex and not simple to measure, public
10 2,5 1
authorities, like the U.S. EPA or the German Federal Environmental Agency (Umweltbundesamt),
increasingly use in their publications the more simple denotation of PM as being the particle size
fraction less or equal to 10 µm. Since this deviation to the above mentioned complex “official” definition
does not have a significant impact on a filter element’s particle removal efficiency, the ISO 16890 series
refers to this simplified definition of PM , PM and PM .
10 2,5 1
Particulate matter in the context of the ISO 16890 series describes a size fraction of the natural aerosol
(liquid and solid particles) suspended in ambient air. The symbol ePM describes the efficiency of an air
x
cleaning device to particles with an optical diameter between 0,3 µm and x µm. The following particle
size ranges are used in the ISO 16890 series for the listed efficiency values.
Table 1 — Optical particle diameter size ranges for the definition of the efficiencies, ePM
x
Efficiency Size range, µm
ePM 0,3 ≤ × ≤10
ePM 0,3 ≤ × ≤2,5
2,5
ePM 0,3 ≤ × ≤1
Air filters for general ventilation are widely used in heating, ventilation and air-conditioning applications
of buildings. In this application, air filters significantly influence the indoor air quality and, hence, the
health of people, by reducing the concentration of particulate matter. To enable design engineers and
maintenance personnel to choose the correct filter types, there is an interest from international trade
and manufacturing for a well-defined, common method of testing and classifying air filters according
to their particle efficiencies, especially with respect to the removal of particulate matter. Current
regional standards are applying totally different testing and classification methods which do not allow
any comparison with each other, and thus hinder global trade with common products. Additionally,
the current industry standards have known limitations by generating results which often are far away
from filter performance in service, i.e. overstating the particle removal efficiency of many products.
With this new ISO 16890 series, a completely new approach for a classification system is adopted, which
gives better and more meaningful results compared to the existing standards.
The ISO 16890 series describes the equipment, materials, technical specifications, requirements,
qualifications and procedures to produce the laboratory performance data and efficiency classification
based upon the measured fractional efficiency converted into a particulate matter efficiency (ePM)
reporting system.
Air filter elements according to the ISO 16890 series are evaluated in the laboratory by their ability to
remove aerosol particulate expressed as the efficiency values ePM , ePM and ePM . The air filter
1 2,5 10
elements can then be classified according to the procedures defined in ISO 16890-1. The particulate
removal efficiency of the filter element is measured as a function of the particle size in the range of
0,3 µm to 10 µm of the unloaded and unconditioned filter element as per the procedures defined in
this part of ISO 16890. After the initial particulate removal efficiency testing, the air filter element is
ISO 16890-2:2016(E)
conditioned according to the procedures defined in ISO 16890-4 and the particulate removal efficiency
is repeated on the conditioned filter element. This is done to provide information about the intensity of
any electrostatic removal mechanism which may or may not be present with the filter element for test.
The average efficiency of the filter is determined by calculating the mean between the initial efficiency
and the conditioned efficiency for each size range. The average efficiency is used to calculate the ePM
x
efficiencies by weighting these values to the standardized and normalized particle size distribution of
the related ambient aerosol fraction. When comparing filters tested in accordance with the ISO 16890
series, the fractional efficiency values shall always be compared among the same ePM class (ex. ePM
x 1
of filter A with ePM of filter B). The test dust capacity and the initial arrestance of a filter element are
determined as per the test procedures defined in ISO 16890-3.
viii © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 16890-2:2016(E)
Air filters for general ventilation —
Part 2:
Measurement of fractional efficiency and air flow
resistance
1 Scope
This part of ISO 16890 specifies the aerosol production, the test equipment and the test methods used
for measuring fractional efficiency and air flow resistance of air filters for general ventilation.
It is intended for use in conjunction with ISO 16890-1, ISO 16890-3 and ISO 16890-4.
The test method described in this part of ISO 16890 is applicable for air flow rates between 0,25 m /s
3 3 3 3 3
(900 m /h, 530 ft /min) and 1,5 m /s (5 400 m /h, 3 178 ft /min), referring to a test rig with a nominal
face area of 610 mm × 610 mm (24,0 inch × 24,0 inch).
ISO 16890 (all parts) refers to particulate air filter elements for general ventilation having an ePM
efficiency less than or equal to 99 % and an ePM efficiency greater than 20 % when tested as per the
procedures defined within ISO 16890 (all parts).
NOTE The lower limit for this test procedure is set at a minimum ePM efficiency of 20 % since it will be very
difficult for a test filter element below this level to meet the statistical validity requirements of this procedure.
Air filter elements outside of this aerosol fraction are evaluated by other applicable test methods, (see
ISO 29463 (all parts)).
Filter elements used in portable room-air cleaners are excluded from the scope.
The performance results obtained in accordance with ISO 16890 (all parts) cannot by themselves be
quantitatively applied to predict performance in service with regard to efficiency and lifetime.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 16890-1, Air filters for general ventilation — Part 1: Technical specifications, requirements and
efficiency classification system based upon Particulate Matter (PM)
ISO 16890-3, Air filters for general ventilation — Part 3: Determination of the gravimetric efficiency and
the air flow resistance versus the mass of test dust captured
ISO 16890-4, Air filters for general ventilation — Part 4: Conditioning method to determine the minimum
fractional test efficiency
ISO 5167-1, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-
section conduits running full — Part 1: General principles and requirements
ISO 21501-1, Determination of particle size distribution — Single particle light interaction methods —
Part 1: Light scattering aerosol spectrometer
ISO 21501-4, Determination of particle size distribution — Single particle light-interaction methods —
Part 4: Light scattering airborne particle counter for clean spaces
ISO 16890-2:2016(E)
ISO 29463, High-efficiency filters and filter media for removing particles in air
ISO 29464:2011, Cleaning equipment for air and other gases — Terminology
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 29464 and the following apply.
3.1 Air flow and resistance
3.1.1
air flow rate
volume of air passing through the filter per unit time
[SOURCE: ISO 29464:2011, 3.2.38]
3.1.2
nominal air flow rate
air flow rate (3.1.1) specified by the manufacturer
3.1.3
resistance to airflow
difference in pressure between two points in an airflow system at specified conditions, especially when
measured across the filter element (3.2.2)
3.2 Test device
3.2.1
test device
filter element (3.2.2) to be tested
3.2.2
filter element
structure made of the filtering material, its supports and its interfaces with the filter housing
3.2.3
upstream
U/S
region in a process system traversed by a flowing fluid before it enters that part of the test device (3.2.1)
3.2.4
downstream
D/S
area or region into which fluid flows on leaving the test device (3.2.1)
3.3 Aerosol
3.3.1
liquid phase aerosol
liquid particles suspended in a gas
3.3.2
solid phase aerosol
solid particles suspended in a gas
3.3.3
reference aerosol
defined approved aerosol for test measurement within a specific size range
2 © ISO 2016 – All rights reserved

ISO 16890-2:2016(E)
3.3.4
neutralization
action of bringing the aerosol to a Boltzmann charge equilibrium distribution with bipolar ions
3.4 Particle counter
3.4.1
particle counter
device for detecting and counting numbers of discrete airborne particles present in a sample of air
[SOURCE: ISO 29464:2011, 3.1.27]
3.4.2
optical particle counter
OPC
particle counter (3.4.1) which functions by illuminating airborne particles in a sample flow of air,
converting the scattered light impulses to electrical impulse data capable of analysis to provide data on
particle population and size distribution
[SOURCE: ISO 29464:2011, 3.29]
3.4.3
sampling air flow
volumetric flow rate through the instrument
3.4.4
particle size
ps
geometric diameter (equivalent spherical, optical or aerodynamic, depending on context) of the
particles of an aerosol
[SOURCE: ISO 29464:2011, 3.1.126]
3.4.5
particle size distribution
presentation, in the form of tables, numbers or graphs, of the experimental results obtained using a
method or an apparatus capable of measuring the equivalent diameter of particles in a sample or capable
of giving the proportion of particles for which the equivalent diameter lies between defined limits
[SOURCE: ISO 29464:2011, 3.1.128]
3.4.6
isokinetic sampling
technique for air sampling such that the probe inlet air velocity is the same as the velocity of the air
surrounding the sampling point
[SOURCE: ISO 29464:2011, 3.1.144]
3.5 Efficiency
3.5.1
efficiency
fraction or percentage of a challenge contaminant that is removed by a test device (3.2.1)
3.5.2
fractional efficiency
ability of an air cleaning device to remove particles of a specific size or size range
Note 1 to entry: The efficiency plotted as a function of particle size gives the particle size efficiency spectrum.
[SOURCE: ISO 29464:2011, 3.1.61]
ISO 16890-2:2016(E)
3.5.3
penetration
P
ratio of particle count detected downstream versus the particle count upstream
[SOURCE: ISO 29464:2011, 3.1.130]
3.5.4
correlation ratio
R
calculation of any potential bias between the upstream and downstream sampling systems
3.6 Other terms
3.6.1
HEPA filter
filters with performance complying with requirements of filter class ISO 35 to ISO 45 as per ISO 29463-1
[SOURCE: ISO 29464:2011, 3.1.88]
3.6.2
reference filter
primary device possessing accurately known parameters used as a standard for calibrating
secondary devices
[SOURCE: ISO 29464:2011, 3.39]
4 Symbols and abbreviated terms
4.1 Symbols
DEHS (DiEthylHexylSebacate)
KCl potassium chloride solid phase aerosol
Ra current radioactivity of the source
Ra radioactivity of the source at date of manufacturer
t time (years)
t half-life time (years)
0,5
CV coefficient of variation
δ standard deviation of the data points
mean mean value of the data points
U upstream correlation count for sample i, and particle size, ps
c,i,ps
D downstream correlation count for sample i, and particle size, ps
c,i,ps
U , U upstream beginning or final background average count at a specific particle size, ps
B,b,ps B,f,ps
D , D downstream beginning or final background average count at a specific particle size, ps
B,b,ps B,f,ps
D downstream background average count for efficiency sample, i, and for particle size, ps
B,ps
4 © ISO 2016 – All rights reserved

ISO 16890-2:2016(E)
D downstream background average count for correlation sample, i, and for particle size, ps
B,c,ps
B , B measured beginning or final upstream background count for sample, i, and particle size, ps
b,i,ps f,i,ps
d , d measured beginning or final downstream background count for particle size, ps
b,ps f,ps
U , U upstream background average count for efficiency or correlation at a specific particle
B,ps B,c,ps
size, ps
N measured upstream efficiency count for sample, i, and particle size, ps
i,ps
U upstream efficiency average for sample, i, and for particle size, ps
i,ps
U sum of the upstream particle counts for particle size, ps
tot,ps
D downstream efficiency average for sample, i, and for particle size, ps
i,ps
R correlation ratio for sample, i, and for particle size, ps
i,ps
correlation ratio at a specific particle size, ps
R
ps
n number of samples
e 95 % uncertainty of the correlation value at a specific particle size, ps
c,ps
st student’s t distribution variable
v number of degrees of freedom for student’s t distribution variable
lower confidence limit of the correlation ratio at a specific particle size, ps
R
lcl,ps
upper confidence limit of the correlation ratio at a specific particle size, ps
R
ucl,ps
δ standard deviation of the correlation value at a specific particle size, ps
c,ps
U sum of the upstream particles sampled during correlation at a specific particle size, ps
c,tot,ps
U correlation particles sampled for sample, i, and for particle size, ps
c,i,ps
P penetration or the fraction of particulate that penetrates the test device
observed penetration at a specific particle size, ps
P
o,ps
final penetration at a specific particle size, ps
P
ps
lower confidence limit o
...