EN ISO 16891:2016

SLOVENSKI STANDARD
01-april-2016
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Test methods for evaluating degradation of characteristics of cleanable filter media (ISO
16891:2016)
Prüfmethode zur Ermittlung der Abnahme der Wirksamkeit von abreinigbaren
Filtermedien (ISO 16891:2016)
Méthodes d'essais pour l'évaluation de la dégradation des propriétés des medias filtrants
décolmatables (ISO 16891:2016)
Ta slovenski standard je istoveten z: EN ISO 16891:2016
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.

EN ISO 16891
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2016
EUROPÄISCHE NORM
ICS 91.140.30
English Version
Test methods for evaluating degradation of characteristics
of cleanable filter media (ISO 16891:2016)
Méthodes d'essais pour l'évaluation de la dégradation Prüfmethode zur Ermittlung der Abnahme der
des propriétés des medias filtrants décolmatables (ISO Wirksamkeit von abreinigbaren Filtermedien (ISO
16891:2016) 16891:2016)
This European Standard was approved by CEN on 7 November 2015.

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 16891:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 16891:2016) 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 August 2016, and conflicting national standards shall
be withdrawn at the latest by August 2016.
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.
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 16891:2016 has been approved by CEN as EN ISO 16891:2016 without any modification.
INTERNATIONAL ISO
STANDARD 16891
First edition
2016-01-15
Test methods for evaluating
degradation of characteristics of
cleanable filter media
Méthodes d’essais pour l’évaluation de la dégradation des propriétés
des medias filtrants décolmatables
Reference number
ISO 16891:2016(E)
©
ISO 2016
ISO 16891:2016(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
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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 16891:2016(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 4
5 Principle . 5
6 Test specimen, equipment and test procedure . 6
6.1 General . 6
6.2 Preparation of sheets for gas exposure. 7
6.2.1 Shape and size of tensile specimen . 7
6.2.2 Sample sheet for exposure . 7
6.2.3 Selection of sample sheet through air permeability measurement . 8
6.2.4 Filter media for exposure . 8
6.3 Sample preparation . 9
6.3.1 Exposure system . 9
6.3.2 Heating system .11
6.3.3 Test gas supply system.11
6.3.4 Gas analyzer .11
6.3.5 Gas treatment device .12
6.4 Exposure conditions and procedures .12
6.4.1 Exposure conditions .12
6.4.2 Exposure period and number of exposure .12
6.4.3 Attachment of filter sample sheets in the sample case .13
6.4.4 Implementation of the exposure .13
7 Tensile strength measurement of exposed specimen .14
7.1 Tensile test device .14
7.2 Preparation of a tensile test specimen .14
7.3 Method of tensile test .14
7.4 Characterization of the degradation.15
8 Test report .16
Annex A (informative) Causes and results of degradation of fabrics.17
Annex B (informative) Possible evaluation method for characteristic change of fabrics .18
Annex C (informative) Theoretical consideration of degradation mechanism .19
Annex D (informative) Determination of specimen size .22
Annex E (informative) Experimental setup for gas exposure.26
Annex F (informative) Service temperature of filter materials .30
Annex G (informative) Examples of measured data of fabric at different circumstances .31
Annex H (informative) Example of test report .37
Bibliography .41
ISO 16891:2016(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 WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 142, Cleaning equipment for air and other gases.
iv © ISO 2016 – All rights reserved

ISO 16891:2016(E)
Introduction
The main purpose of using cleanable filter is, of course, to separate dust particles from dirty gases.
They are usually designed to be usable for as long as two years to four years. However, it is very
hard to design and/or select filter media properly, since their important characteristics of collection
performance and residual pressure drop change with operation time. Physical and chemical properties
of filter media, such as degradation in tensile strength, tenacity and so on, also change with time. Those
changes can damage filter media and this can result in the breakage of bag filters and leakage of dust to
the atmosphere. Hence the evaluation of these performances is also important for the rational design
and the selection of appropriate filter media. ISO 11057:2011 has been published to meet the demand
for the evaluation of filtration characteristics.
Changes in physical and chemical properties of filter media are caused by many factors, such as heat,
corrosive gases, and mechanical reasons like clogging weave openings and increasing size of weave
openings, the combination of those factors and so on (see Annex A). These changes are mostly adverse
effects to filter media. Degradation proceeds very slowly, and thus, it takes a long time before recognizable
and/or measurable change appears. Furthermore, the appearance of change depends on the combination
of causes and fibre material. These facts are the main reason why mechanism of property changes has not
.[1]-[13]
been well understood despite its practical importance Hence, the characterization or evaluation
[14][15]
methods for filter media have not been established yet (see Annex B).
Nevertheless, there are demands for the establishment of a guideline for systematic characterization
and evaluation of property change of filter media with respect to their relevant long-time operation
not only from manufacturers of filter media, but also from producers and users of filter installations,
especially the users treating combustion exhaust gases.
To evaluate degradation of filter media in a laboratory, it is important that experiment can be done
in a relatively short time period by using controllable single or a small number of variables, i.e.
causes of change.
Furthermore, it is important that the resulting effects are measureable. From this point of view, heat
intensity is controllable by changing heating temperature and the intensity of corrosive gas is also
controllable by changing gas concentration. Thus, their effect is expected to be accelerated. Of course,
the effects can be evaluated by the degradation of tensile stress.
Evaluation of property change of filter media by corrosive gases can be done by contacting filter media
with those corrosive materials in any phases, i.e. gas, liquid and solid state. Testing by dipping filter
media into a solution of corrosive materials is easy and the resulting effects are expected to be obtained
[16]
in a short period of time. Chinese Standard, GB/T 6719:2009 adopts this method. Solid state testing
can be carried out by hard contact of filter media but it will take a long time and it is very hard to
control the intensity of corrosiveness.
Testing under the gaseous state takes much longer than a liquid type test but the intensity of
corrosiveness is controllable and it is much easier than the test under the solid state. Furthermore, test
temperature and gas conditions except corrosive gas concentrations, are similar to the actual operation
condition of filtration, which is suitable (see Annex B). Hence, in this International Standard, test
methods for evaluating degradation characteristics of cleanable unwoven filter media with synthetic
fibre by heat and corrosive gases are standardized because they are most widely used for bag filtration.
The major objective of this International Standard is to specify the testing method to assess the relative
change of physical performances of new and used cleanable filter media for industrial application, by
[17][18]
exposing it in hot and/or corrosive gas conditions .
INTERNATIONAL STANDARD ISO 16891:2016(E)
Test methods for evaluating degradation of characteristics
of cleanable filter media
1 Scope
This International Standard specifies a standard reference test method useful to assess the relative
degradation characteristics of cleanable filter media for industrial applications under standardized
simulated test conditions. The main purpose of testing is to obtain the information about relative
change of properties of filter media due to exposure to the simulated gas conditions for a long time. The
main target of this International Standard is the property change of nonwoven fabric filters because
they are frequently used under similar circumstances to the test gas conditions described in this
International Standard.
The results obtained from this test method are not intended for predicting the absolute properties of full
scale filter facilities. However, they are helpful for the design of a bag filter and selection and development
of appropriate cleanable filter media, and for the identification of suitable operating parameters.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for the application of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4606, Textile glass — Woven fabrics — Determination of tensile breaking force and elongation at
breaking by strip method
ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and
1)
elongation at maximum force using the strip method
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 29464:2011 and the
following apply.
3.1
aged filter sheet
filter sheet exposed under simulated hot and corrosive gas conditions for a preset period of time to
evaluate the change of filter properties
3.2
air permeability
gas volume flow rate per unit filtration area at pressure drop of 124,5 Pa
3.3
average gas concentration
mean concentration of test gases during the exposure
1) This International Standard replaced ISO 5081, Textiles — Woven fabrics — Determination of breaking strength
and elongation (Strip method).
ISO 16891:2016(E)
3.4
batch type exposure chamber
chamber in which filter sheets are exposed to stationary test gas mixture
3.5
chemical degradation
degradation of chemical properties of filter media by the interaction with test gases
3.6
cleanable filter
filter designed to enable the removal of collected dust by appropriate technique
[SOURCE: ISO 29464:2011; 3.1.77]
3.7
continuous-flow-method
exposing method of filter sheet, which is exposed in a continuous flow of test gas mixture
3.8
corrosive gas
chemicals which react with filter media and change its chemical and physical properties
3.9
degradation
change in physical and chemical performances of filter media by the interaction with corrosive gases
3.10
elongation
incremental change in length of test specimen by tensile test
3.11
elongation at maximum load
incremental change in length of test specimen at maximum load in tensile test
3.12
elongation ratio
ratio of elongation of test specimen to its initial length between holders or its percentage
3.13
elongation ratio at maximum load
ratio of elongation of test specimen at maximum load in tensile test to its initial length between holders
3.14
exposure chamber
chamber to expose test filter sheet to corrosive gases
3.15
filter media
material separating particulate matter from gases and characterized by its separating structure and its
structural and/or textile-technological characteristics
3.16
flow-through type replacement
method to replace test gas in the batch type exposure chamber by introducing test gas continuously
to the chamber
3.17
initial load
initial load applied on the test specimen at the start of tensile test
2 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
3.18
length between holders
length between holders of top and bottom holding chucks positioned at the start of the tensile test
Note 1 to entry: See Figure 3.
3.19
load
tensile strength of test specimen observed in the tensile test
3.20
non-continuous-flow-method
exposing method of filter sheet, which is exposed in still test gas mixture
3.21
nonwoven fabric
filter media using fabric made from long fibres, bonded together with each other by chemical,
mechanical, heat or solvent treatment
3.22
number of replacement
number of test gas replacement for whole heating space volume of the test chamber
3.23
replacement of gas
exchange gas to maintain test gas concentration within certain concentration range
3.24
retention of tensile strength
ratio of tensile strength of the test specimen subjected to thermal and/or acid gas exposure to that of
the test specimen without the exposure
3.25
strip method
method of implementing tensile test with holding whole width of the test specimen with a holding device
3.26
tensile speed
speed to pull a test specimen in tensile test
3.27
tensile strength
value of the maximum load divided by the width of test specimen
3.28
test gas
gas which may cause changes in physical propertied of filter media to be used for tensile test
3.29
vacuum replacement
method to replace test gas in the batch type exposure chamber by the use of vacuum
3.30
thermal exposure
expose filter media at an elevated temperature to accelerate the change of its physical properties
3.31
woven fabric
filter media using a fabric formed by weaving
ISO 16891:2016(E)
4 Symbols and abbreviated terms
A total surface area in a filter media (m )
APA nonwoven fabric with Aromatic Polyamide fibres
−3
C gas concentration (mg•m )
−1
F(A) constant related to total surface area of filter media (N•mm )
Glass fabric with Glass fibres
−1
K effective reaction constant (s )
3 −1 −1
k reaction constant (m •mg •s )
L length of specimen (mm)
L length between holders (mm)
L length of holder (mm)
MD machine direction
P load (N)
P maximum load (N)
max
p pressure (Pa)
PI nonwoven fabric with Polyimide
PPS nonwoven fabric with Polyphenylene Sulfide
PTFE nonwoven fabric with Polytetrafluoroethylene
−1
Q flow rate of test gas (l•min )
3 −1 −2
q air permeability of filter [(cm •s ) •cm ]
−1
S tensile speed (mm•min )
T temperature (°C)
TD transverse direction
t exposure time (s),(h)
V volume of the exposure chamber (l)
w width of holder (mm)
δ elongation (mm)
δ elongation at maximum load (mm)
max
ε elongation ratio (%)
ε maximum elongation ratio (%)
max
−1
τ tensile strength (N•mm )
4 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
−1
τ tensile strength of the filter media without exposure (N•mm )
−1
Δτ tensile strength difference between after and before (N•mm )
exposure
5 Principle
Physical performance of filter media mostly degrades with time because of long time exposure under
severe gas conditions, such as hot and/or corrosive gas conditions. When filter media is exposed to hot
and/or corrosive gas atmospheres such as NOx, SOx, HCl and moisture etc., those gases are considered to
interact with materials in fibres and thus affect crystallinity and/or other bonding of molecules in fibres,
i.e., they decompose fibre in the media to some extent. Hence, these conditions result in irreversible
damage to media and weaken physical performances like tensile strength, elongation and so on.
Details of the above mentioned process have not been understood well yet, but tensile strength after
filter media is exposed to corrosive gases and/or high temperature is expressible by the following
formula with the assumption that degradation reaction between corrosive gas and some reactive
component in a fibre is pseudo linear.
 
ττ0=− tFΔτ =1AK−exp − t (1)
() () () ()
 
 
where
Τ(t) tensile strength of filter media;
F(A) unknown constant related to total surface area of filter media;
K effective reaction constant and is related to the degradation of media.
The first derivative of Formula (1) becomes,
dΔττd
=- =eKF AKxp − t (2)
() ()
dt dt
Similar formula can be obtained applying Hooke’s law between tensile strength and elongation as:
dΔδ
∝KF AKexp − t (3)
() ()
dt
Formula (2) and Formula (3) suggest that a straight line is obtained when the logarithm of first
derivative of tensile strength of filter media and elongation is plotted against exposure time t in a semi-
log paper, as shown in Figure 1. The slope of the line in Figure 1 gives K [see the details of the derivation
of Formula (2) and Formula (3) in Annex C].
ISO 16891:2016(E)
Key
t exposure time (h)
y lg(-dτ/dt)
Figure 1 — Relation between gradient of tensile strength of filter media and exposure time to
corrosive gas
The degradation process is usually very slow, and thus, measurable changes in the physical properties
(like tensile strength and elongation) usually appear after filter media has been exposed for a very long
time period. Hence, it shall be accelerated by some means to evaluate the effect through an experiment.
In this International Standard, degradation is accelerated by exposing filter media to a higher corrosive
gas concentration and higher gas temperature.
6 Test specimen, equipment and test procedure
6.1 General
The test specimen, equipment and procedure at each step shall be chosen so as to ensure good
reproducibility and repeatability of the test. The equipment to prepare the samples for the measurement
generally consists of the following main components: gas supply system; exposure chamber and
heating system; exhaust gas treatment unit; vacuum pump; and gas analysing system. Figure 2 shows a
schematic diagram of the equipment.
The test shall be carried out using the following three steps:
Step 1: Preparation of filter sample sheets for gas exposure
Air permeability of filter sample sheets for gas exposure shall be similar, so as to obtain reliable data
(described in 6.2). Air permeability of filter media with a size defined in 6.2.3 shall be measured
and suitable sheets selected based upon the measured air permeability.
Step 2: Exposure of sheets
Sheets selected at Step 1 shall be exposed to thermal and/or corrosive gas conditions (described in
6.3 and 6.4).
Step 3: Tensile test
Tensile specimens of machine direction (MD) and transverse direction (TD) shall be cut from
exposed sheets. Then tensile strength and elongation of specimens shall be measured by the
scheme described in Clause 7.
6 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
Key
1 gas supply
2 exposure chamber
3 heating system
4 gas treatment
5 vacuum pump
6 gas analysis
Figure 2 — Schematic diagram of equipment to prepare sample for physical performance test
6.2 Preparation of sheets for gas exposure
6.2.1 Shape and size of tensile specimen
A rectangular shape without shoulders between holders shall be adopted in tensile tests as shown in
Figure 3, since filter media is soft and porous. Hence the size of the sheet of filter media to expose shall
be large enough for the tensile test to obtain reliable and reproducible data. According to the results
shown in Annex D, the measured tensile strength of nonwoven filter media with a rectangular test
sheet does not depend on the width of holder w, in the range from 20 mm to 50 mm and length between
holders L , from 80 mm to 120 mm (see Annex D). Hence, in this International Standard, a rectangular
shape with w = 25 mm width and L = 100 mm in length between holders shall be adopted and other
dimensions are determined as L = 50 mm, L = 200 mm.
3 1
Key
L length of specimen
L length between holders
L length of holder
w width of holder
Figure 3 — Shape of tensile specimen
6.2.2 Sample sheet for exposure
To deteriorate every filter sheet equally, test gases shall have contact with all fibres in the filter for the
whole exposure period. Therefore, a continuous-flow-through type of test gas flow shall be adopted.
Here, in the continuous-flow-method, the test gas flow through sheets during whole the exposure
period is the same as during actual bag filter operation. Test gases used for the exposure are corrosive
except O , and, thus, it is important to minimize gas consumption not only because of the cost of gas but
also for safety reasons. The sample sheet holder and flow rate for the exposure is specified in 6.3.
ISO 16891:2016(E)
Based on these considerations, the size of the sheet to be exposed to test gases was determined as
105 mm × 250 mm, in which test gas flows through the central part with an area of 65 mm × 210 mm,
which shall be large enough to cut two tensile test specimens of 25 mm × 210 mm, as shown in Figure 4.
Sample sheets shall be cut with the size of 105 mm × 250 mm in the central part of the filter media roll
with at least four sheets for each direction.
Dimension in mm
Key
1 MD
2 TD
3 filter media
Figure 4 — Preparation of sample sheet for test gas exposure
6.2.3 Selection of sample sheet through air permeability measurement
The tensile strength of a specimen strongly depends on the structure of the specimen. Nonwoven
filter media is composed of bonded entangling fibres. They distribute uniformly macroscopically but
not microscopically because of manufacturing mechanism and it results in the unevenness of packing
density or mass of fibres. Unevenness of fibre distribution in the filter, i.e. filter structure, can change
physical properties such as tensile strength and/or elongation, air permeability and so on. In this sense,
it is essential to eliminate filter media with different structures from the test to avoid the fluctuation
of measured data due to the unevenness of filter structure. Hence, by sample sheets with similar
structure shall be selected before they are exposed to test gases structure. However, it is difficult to
select from the product information about the media given by manufacturer, i.e. it is usually limited to
mean value of air permeability and mass of fibres per unit area of the filter. However, air permeability of
filter media is the same when the filter structure is the same. This means that filter media with similar
structures show a similar air permeability so that air permeability can be used for the selection of filter
media with a similar structure. Hence at least four sample sheets for gas exposure shall be selected
according to the air permeability of each sheet. Air permeability of each sheet shall be within ±10 %
from the mean air permeability of the filter media specified by the manufacturer.
6.2.4 Filter media for exposure
In the range of this International Standard, any nonwoven filter media made of synthetic fibres can
be used for the test, since degradation is evaluated by the change of tensile strength and elongation
of the media.
8 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
6.3 Sample preparation
6.3.1 Exposure system
In the practical bag filtration, hot and/or corrosive gases, of course, flow through filter media and thus,
every fibre in the filter is exposed to corrosive gas at the same concentration so that degradation takes
place evenly regardless of the location in the filter, i.e. not only its surface but also its inside.
The purpose of exposing filter media to hot and/or corrosive gas conditions is to accelerate the change
of physical performances of the media by satisfying certain contact between every fibre in the filter
media and corrosive gas, i.e. to prepare an aged filter sample. To meet these requirements, a gas
temperature and through type chamber shall be adopted for the sample sheet exposing method. This
is a continuous-flow-through method and the test gas flows continuously in and out the chamber. The
sample sheets are placed in the chamber like a barrier to block the test gas flow rate. Hence, the test gas
flows through the inner space of the media and thus contacts with all fibres during its passage through
the sheets. Since contact time between fibres and the test gas is short even at a very slow gas stream,
the consumption of test gas by the interaction with fibres is considered to be small because of the low
reaction rate. Therefore, the test gas concentration change from inlet concentration is considered to be
small. Outlet test gas shall be exhausted directly to the atmosphere after an appropriate de-toxifying
treatment, i.e. a circulating-gas type exposure system shall not be adopted, since some unknown gas
components, which have some side effects, can be produced by the interaction between test gas and
filter media.
Figure 5 shows an example of a continuous flow through system. It is composed of a gas supply unit,
heating and exposure unit, gas concentration monitoring unit and exhaust gas cleaning unit. Test gases
and balance gas are fed from gas cylinders. Moisture is generated by heating. Their flow rates, especially
test gases with small flow rates, shall be precisely controlled by mass-flow-controllers to maintain test
gas concentration constant. After they are mixed well at the mixing box, they are introduced to the
exposure chamber in a heating system. Inlet concentration of the test gas shall be measured before and
during the exposure.
NOTE Test gases are a potential hazard. If test gases leak, corrosion of material occurs and thus special
care is needed.
Key
1 test gas 7 heating system
2 balance gas 8 gas analyzer
3 mass flow controller 9 gas treatment device
4 mixing box 10 pump
5 moisture generator 11 gas line for inlet gas concentration measurement
6 expose chamber with filter sample sheets 12 gas line for gas concentration measurement for exhaust gas
Figure 5 — Example of continuous flow through type setup for exposure test
Figure 6 shows an example of an exposure chamber which is placed in the heating system. The chamber
to install the sample case (shown in Figure 7) shall be an airtight box with inlet and outlet pipes and
temperature sensors. The sample case is composed of a case and a frame plate, and shall have the
ISO 16891:2016(E)
capacity to hold a maximum of eight filter sample sheets and separators. The sample sheets with MD
and TD shall be piled up as described in 6.3.1. A separator sheet shall be inserted between each pair
of adjacent sample sheets to prevent direct interaction between fibres in different sample sheets. The
frame plate shall be placed on the top of the pile. Then, they shall be slid into the case and pressed to the
case by screws to prevent the leakage of test gas from the periphery and the entanglement of fibres in
different sheet (as shown in Figure 7). Then, the sample case shall be fixed to the chamber by pressing
down the lid of the chamber. Materials used for the chamber and the sample case shall have an excellent
corrosion and adsorption resistance against the test gases. Furthermore, separator sheets shall be non-
cohesive with the test sample sheet material and of a suitable thickness, such as a PTFE sheet with
1 mm thickness.
Figure 6 — Exposure chamber
10 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
Key
1 frame plate
2 separator
3 sample filter sheets
4 sample case
Figure 7 — Details of sample case
A chamber other than the flow-through-type chamber can be used for the sample preparation if it is an
equivalent type of apparatus by comparison with the standard reference apparatus (see Annex E).
A comparison shall be performed with the standard reference apparatus according to the procedure
specified in this International Standard: three filter media shall be tested on both apparatus
simultaneously (same location and same time) under the same test conditions.
6.3.2 Heating system
The heating system, inside which the exposure chamber is placed, is used for heating the chamber. It
shall be capable of heating up to the higher temperature than the maximum exposure temperature.
The temperature of the system shall be controlled within test temperatures ±1 %. However, control
accuracy of ±5 % can be adoptable through the negotiation between stakeholders when the suitable
temperature measuring device with required accuracy is not commercially available.
6.3.3 Test gas supply system
Any type of gas supply system may be used as far as specified gas composition and flow rate are
maintained during the exposure test. Examples of gas supply system are shown in Figure E.4.
6.3.4 Gas analyzer
Outlet concentration of the test gas shall be measured by an appropriate instrument, either continuously
or intermittently, to keep the concentration constant during the exposure and also to determine the
accurate gas concentration.
ISO 16891:2016(E)
6.3.5 Gas treatment device
Gases used in this test are corrosive and are harmful even at low concentration. Therefore, appropriate
gas treatment such as absorption or neutralization shall be performed before they are released to the
atmosphere. Gas concentration after treatment shall be monitored occasionally for safety.
6.4 Exposure conditions and procedures
6.4.1 Exposure conditions
6.4.1.1 Composition of test gas
Exposure of corrosive gas shall be chosen so as to be appropriate for the usage of the filter media from
Table 1. However, test gas and its concentration (other than listed in Table 1) may be chosen after
negotiation between stakeholders.
Table 1 — Gas composition for exposure
Exposing gas Gas composition
N N : 100 % (only for thermal exposure)
2 2
NO NO : 0,1 %; O : 10 %; N : balance
x 2 2 2
SO : 0,1 %; N : balance
2 2
SO
x
SO : 0,1 %; moisture: 20 %; N : balance
2 2
HCl: 0,2 %; N : balance
HCl
HCl 0,2 %; moisture 20 %; N : balance
Mixed gas 1 NO : 0,1 %; SO : 0,1 %; HCl: 0,2 %; O : 10 %; N : balance
2 2 2 2
Mixed gas 2 NO : 0,1 %; SO : 0,1 %; HCl: 0,2 %; O : 10 %; moisture: 20 %;
2 2 2
N : balance
6.4.1.2 Gas temperature
Temperature of exposure gas shall be determined about 10 % higher than the service temperature of
filter material in the practical filtration operation but it shall be lower than its softening temperature.
However, the test temperature may change after negotiation between stakeholders.
The service temperature and the recommended test temperature of filter materials are summarized in
Annex F.
6.4.2 Exposure period and number of exposure
According to Formula (1), tensile strength changes exponentially with exposure time (shown as solid
line in Figure 8); but it is empirically known that tensile strength often has a short maximum as the
exposure starts and then decreases with time (shown as dotted line in Figure 8).
Hence, the exposure period and number of exposures shall be specified as three exposures with periods
such as 50 h and 200 h and one exposure with a period of time less than 50 h or between 50 h to 200 h.
However, the number of exposures and length of exposing period may be changed after negotiation
between stakeholders.
12 © ISO 2016 – All rights reserved

ISO 16891:2016(E)
Key
required measuring point
selective measuring point
t exposure time (h)
y τ(t) or δ (t)
max
Figure 8 — Trend of experimental degradation
6.4.3 Attachment of filter sample sheets in the sample case
At first, four sample sheets with similar permeability are selected for each direction of filter media MD
and TD, i.e. eight sample sheets in total, according to the procedures described in 6.2. Then, selected
sample sheets and separators shall be piled up alternately and among sample sheets, MD and TD shall
also be alternated. The frame plate shall be placed on the top of the pile. Then, they shall be slid in the
sample case and pressed to the case by screws to prevent the leakage of test gas from the periphery
but not screwed too firmly to avoid the entanglement of fibres in neighbouring sheets. The sample case
shall be fixed to the chamber by pressing down the lid of the chamber. Materials used for the chamber
and sample case shall have an excellent corrosion and adsorption resistance against test gases.
6.4.4 Implementation
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