EN ISO 29461-4:2025

SLOVENSKI STANDARD
01-julij-2025
Zračni filtrski sistemi rotacijskih strojev - 4. del: Preskusne metode za statične
filtrirne sisteme v obalnih in priobalnih okoljih (ISO 29461-4:2025)
Air intake filter systems for rotary machinery - Part 4: Test methods for static filter
systems in coastal and offshore environments (ISO 29461-4:2025)
Ansaugfiltersysteme von Rotationsmaschinen - Prüfverfahren - Teil 4: Prüfverfahren für
statische Filtersysteme in Meeres- und Offshore-Umgebungen (ISO 29461-4:2025)
Systèmes de filtration d'air d'admission pour machines tournantes - Partie 4: Méthodes
d'essai des systèmes de filtration statique en milieu côtier et offshore (ISO 29461-
4:2025)
Ta slovenski standard je istoveten z: EN ISO 29461-4:2025
ICS:
29.160.99 Drugi standardi v zvezi z Other standards related to
rotacijskimi stroji rotating machinery
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 29461-4
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2025
EUROPÄISCHE NORM
ICS 29.160.99
English Version
Air intake filter systems for rotary machinery - Part 4: Test
methods for static filter systems in coastal and offshore
environments (ISO 29461-4:2025)
Systèmes de filtration d'air d'admission pour machines Ansaugfiltersysteme von Rotationsmaschinen -
tournantes - Partie 4: Méthodes d'essai des systèmes Prüfverfahren - Teil 4: Prüfverfahren für statische
de filtration statique en milieu côtier et offshore (ISO Filtersysteme in Meeres- und Offshore-Umgebungen
29461-4:2025) (ISO 29461-4:2025)
This European Standard was approved by CEN on 28 March 2025.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 29461-4:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 29461-4:2025) has been prepared by Technical Committee ISO/TC 142
"Cleaning equipment for air and other gases" in collaboration with Technical Committee CEN/TC 195
“Cleaning equipment for air and other gases” 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 October 2025, and conflicting national standards shall
be withdrawn at the latest by October 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 29461-4:2025 has been approved by CEN as EN ISO 29461-4:2025 without any
modification.
International
Standard
ISO 29461-4
First edition
Air intake filter systems for rotary
2025-04
machinery —
Part 4:
Test methods for static filter
systems in coastal and offshore
environments
Systèmes de filtration d'air d'admission pour machines
tournantes —
Partie 4: Méthodes d'essai des systèmes de filtration statique en
milieu côtier et offshore
Reference number
ISO 29461-4:2025(en) © ISO 2025

ISO 29461-4:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
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or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 29461-4:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Air flows .2
3.2 Efficiencies .2
4 Symbols and abbreviated terms. 2
5 Principle . 3
6 Test rig and equipment . 3
6.1 Test rig .3
6.2 Test duct .4
6.2.1 Test rig layout .4
6.2.2 Test air conditioning .5
6.2.3 Measurement of the air flow rate .5
6.2.4 Measurement of pressure drop .5
6.2.5 Solid salt aerosol mixing section .5
6.2.6 Measurement of temperature and relative humidity .5
6.3 Measurement equipment.5
6.3.1 Test rig instrumentation .5
6.3.2 Sodium flame photometer .6
6.4 Solid salt aerosol sampling .7
6.4.1 Sample probes.7
6.4.2 Sampling air flow .7
6.5 Solid salt aerosol generation .7
6.5.1 Salt generation.7
6.5.2 Aerosol injection .7
6.6 Water spray device .7
6.7 Water collection device .7
7 Qualification of test rig and apparatus . 8
7.1 Pressure system testing .8
7.2 Solid salt aerosol uniformity .8
7.2.1 Aerosol uniformity parameters .8
7.2.2 Aerosol uniformity protocol .8
7.2.3 Aerosol uniformity results .8
7.2.4 Water droplet size distributions .9
7.2.5 Water fog sedimentation check .9
7.2.6 Schedule of qualification .9
8 Test conditions . 9
8.1 Test air .9
8.2 Test water . .10
9 Test method . 10
9.1 Stop criteria .10
9.2 Adjustment of the test air flow rate .10
9.3 Preparatory checks .10
9.3.1 Operational readiness of the measuring instruments .10
9.3.2 Zero level check measurement of the sodium flame photometer (SFP) .10
9.3.3 Absolute pressure, temperature and relative humidity of the test air .10
9.3.4 Starting up the salt generator .11
9.3.5 Installation of the test filter .11
9.3.6 Flushing the test filter .11

iii
ISO 29461-4:2025(en)
9.4 Measurements .11
9.4.1 Measurement of pressure drop .11
9.4.2 Measurement of the salt removal efficiency .11
9.4.3 Measurement of the water removal efficiency . 12
9.4.4 Cumulative salt loading . 12
9.4.5 Cumulative salt penetration . 13
10 Test procedure .13
10.1 Preparation of test rig (no test object installed) . 13
10.2 Cleaning of test rig . 13
10.3 Primary weighing of the test object . 13
10.4 Installation of the test object .14
10.5 Primary water deluge challenge .14
10.6 Salt loading . .14
10.7 Water deluge challenge .14
10.8 Relative humidity cycles . 15
10.9 End of test . 15
10.10 Secondary weighing of the test object . 15
11 Reporting results . 16
11.1 General .16
11.2 Observations .16
11.3 Report template .18
Annex A (informative) Ultrafine dry solid salt generator .21
Bibliography .28

iv
ISO 29461-4:2025(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 142 Cleaning equipment for air and other gases,
in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
195, Cleaning equipment for air and other gases, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
A list of all parts in the ISO 29461 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO 29461-4:2025(en)
Introduction
The use of gas turbines in the oil and gas industry represents one of the most challenging applications for
this engine technology. The major constraint of the oil and gas industry is to run 24/7 at full load with
minimum downtime. In oil and gas activity, the installation must be run as close as possible to 100 % of the
time with the highest level of efficiency (current production compared to nominal production).
An additional challenge for oil and gas applications lies in the absence of a back-up turbine on site, especially
for mechanical-drive gas turbine configurations.
The coastal and offshore environment probably represents the harshest conditions for gas turbines. Humidity,
rainfall and seasonal dust are the most obvious visible conditions that operators face on site. Hidden in the
combustion air, alkali such as potassium, sodium or magnesium, as well as sulfur, soot, volatile hydrocarbons,
oily vapours, and particles all generate gas turbine issues including compressor fouling, air-cooling passage
fouling, vane and blade erosion, and compressor corrosion. Combined with sulfur in fuels, these alkali in
combustion air create hot corrosion. Finally, heavy rainfall can induce filter washings that release filtered
particles into the compressor. All these phenomena impact the gas turbine availability on site.
The role of a highly efficient air filtration system is to maintain the engine cleanliness by preventing the
introduction of contaminants into the gas turbine air intake. Achieving a high level of engine cleanliness
helps maintain engine integrity and efficiency and reduces the need for water washes which generate
avoidable downtime.
Currently, high efficiency filter elements are characterized by a limited number of parameters, namely filter
efficiency and most penetrating particle size (MPPS). These parameters, related to a single filter element, are
measured in laboratory conditions close to favourable inland conditions with synthetic dust. Consequently,
these conditions are far from the reality observed on site, offshore or near coast, where filter elements are
usually part of a system. The test results do not therefore provide a basis for predicting either operational
filter performance or service life.
The objective of this document is to consider how the effect of water spray, humidity and salt affects the
performance of an air filter. The tested air flow passing through the filter element is close to the air flow rate
operated on site for the three different concepts: low, medium or high velocity filter elements.
Soot, volatile hydrocarbons, oily vapours and particles also have impact on filter characterization and
performance. The separate parts of ISO 29461 cover particles, while soot, volatile hydrocarbons and oily
vapours are yet to be addressed. Current test methods are not mature enough for the inclusion of soot,
volatile hydrocarbons and oily vapours.
The ageing of a filter element installed offshore and near the coast is addressed to allow the prediction of
operational filter performance and its associated service life. It must be understood how filter elements
perform during different cycles representing typical site conditions such as heavy rainfall, low and high
humidity, filter element unloaded and loaded.
Depending on the gas turbine applications, the service life of the filter element is also a criterion to take into
consideration. In this case, the robustness, loading capacity and pressure drop characteristics of the filter
elements become key parameters for design and testing.

vi
International Standard ISO 29461-4:2025(en)
Air intake filter systems for rotary machinery —
Part 4:
Test methods for static filter systems in coastal and offshore
environments
1 Scope
This document defines test methods for performance testing of individual filter elements and of the complete
1)
filtration system.
This procedure is intended for filter elements and filter systems which operate at flow rated up to 8 000 m /h
per filter element.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 2813, Paints and varnishes - Determination of gloss value at 20°, 60° and 85°
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 16890-2:2022, Air filters for general ventilation — Part 2: Measurement of fractional efficiency and air flow
resistance
ISO 29461-2:2022, Air intake filter systems for rotary machinery – Test methods – Part 2: Filter element
endurance test in fog and mist environments
ISO 29463-1, High efficiency filters and filter media for removing particles from air — Part 1: Classification,
performance, testing and marking
ISO 29464, Cleaning of air and other gases — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 29464 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www. iso. org/o bp
— IEC Electropedia: available at https:// www.e lectropedia. org/
1) The filters will be loaded with ultra-fine salt particles of a size mostly sub micron during variable humidity to simulate
real offshore and coastal conditions hence filters with an initial conditioned efficiency lower than 50 % for the ePM
particles (filter class T7) are likely to underperform and would not be suited as a single stage filter.

ISO 29461-4:2025(en)
3.1 Air flows
3.1.1
air flow rate
volume of air flowing through the filter per unit time
[SOURCE: ISO 29464:2024, 3.1.29]
3.1.2
test air flow rate
rate of air flow used for testing
Note 1 to entry: The flow rate is usually expressed in volumetric units [m /h (cfm)].
Note 2 to entry: Test flow rate may differ from the manufacturer’s specified flow through the air cleaner.
[SOURCE: ISO 29464:2024, 3.1.32]
3.1.3
design air flow rate
air flow rate specified by the manufacturer
[SOURCE: ISO 29464:2024, 3.1.30]
3.2 Efficiencies
3.2.1
salt removal efficiency
measure of the ability of a filter to remove salt from the air passing through it
3.2.2
water removal efficiency
measure of the ability of a filter to remove water from the air passing through it
3.3
test device
air filter or device to be tested
4 Symbols and abbreviated terms
CV coefficient of variation
c
water fog mass concentration, g/m
wm
d
saturated wet air moisture content, g/kg
d
ambient air moisture content, g/kg
dP pressure drop, Pa
E salt removal efficiency
salt
E water removal efficiency
w
m
water mass penetrated through tested filter at the end of the test, kg
p
m
total water fog generation amount, kg
tot
Na sodium
ISO 29461-4:2025(en)
NaCl sodium chloride
RH relative humidity
SFP sodium flame photometer
5 Principle
The test method is designed to challenge the air intake test object (the test object can be a complete system,
a single filter or a multi-stage filter system) with sub-micron salt in order to ensure that the fibre structure
is challenged deep within the filter and not only on the surface. This allows simulation of salt loading, and
the cycling of relative humidity allows simulation of aging because the salt particulates will transform from
dry to liquid phase. In field operating conditions, the filters are exposed to both sub-micron and larger salt
particles and water droplets.
The main “failure” modes or weaknesses to be detected by using this test method are:
a) bypass of salt and water through not properly sealed construction;
EXAMPLE Too little glue between frame parts causing leakage.
b) penetration of salt and water through the filter media;
EXAMPLE Construction is sealed well, but the filter media has poor water repellence, causing leaks
through media.
c) adverse pressure reaction to either moisture or salt loading, or both.
6 Test rig and equipment
6.1 Test rig
The test rig can be configured in multiple different ways depending on the object being tested, this document
defines testing individual filter elements.
NOTE To perform a multi-stage test, an appropriate test procedure is under preparation for a later revision of this
document.
In case of circular cartridge filters, the test setup (mounting of the filters in the test duct) shall be as close
to the real application as possible. This shall however be analysed specifically for each construction, taking
into consideration the possible jetting effect that can affect the velocity and aerosol concentration in the test
duct cross section (see ISO 29461-1:2021, Clause 5). The intended orientation (horizontal or vertical) should
be noted in the report.
ISO 29461-4:2025(en)
Dimensions in millimetres
Key
nd
1 injection of solid salt aerosol and water spray device 5 2 downstream drain
rd
2 upstream drain 6 3 downstream drain
st
3 1 downstream drain 7 ISO 25E filter
4 test device
Figure 1 — Test duct measurement section of single filter element
6.2 Test duct
6.2.1 Test rig layout
The test rig (see Figure 1) should consist of several duct sections with 650 mm × 650 mm (25,6” × 25,6”)
nominal inner dimensions. If the cross-section dimensions deviates from this, it shall be stated in the report.
The section where the test filter is installed shall be representative of the cross-sectional area and geometry
for a filter arrangement within the proposed inlet system.
Each rig module shall have central drain installed in the bottom wall of the test duct in order to collect any
water upstream or downstream of the filter, to further aid collection of water the floor shall slope towards
the drain with a slope angle of 1° to 3°.
The bottom wall of the test duct downstream of the test device shall be black (gloss level 20 % at 60° in
accordance with ISO 2813) to aid detection of any salt bypass. A minimum of two walls per module shall be
transparent or include windows. Additionally, cameras can be used to aid detection of water by-pass.
The test rig shall be operated in a negative pressure air flow arrangement, which represents the typical air
flow condition for a gas turbine. A positive pressure arrangement is not typically encountered in gas turbine
air inlet systems.
ISO 29461-4:2025(en)
6.2.2 Test air conditioning
A filter with an efficiency of ISO 25 E in accordance with ISO 29463-1 shall be placed in the loop to ensure
high quality air is entering in the measurement section. If a non-recirculating rig is used, the inlet air shall
instead be pre-filtered with an efficiency of ISO 25 E.
Depending on numerus external factors such as the ambient relative humidity of the test lab etc. additional
equipment can potentially be installed in the test rig in order to adjust the conditions of the test air to within
specification as described in 8.1
6.2.3 Measurement of the air flow rate
Flow measurement shall be made by standardized flow measuring devices in accordance with ISO 5167-1.
The uncertainty of measurement shall not exceed ±100 m /h of the measured value. The equipment shall be
calibrated at regular intervals to ensure the required accuracy.
6.2.4 Measurement of pressure drop
The measuring points for pressure drop, dP, shall be arranged so that the mean value of the static pressure in
the flow upstream and downstream of the filter can be measured. The planes of the pressure measurements
upstream and downstream shall be positioned in regions of an even flow with a uniform flow profile, at a
minimum distance of 350 mm from the forward and rearward most protruding part of the test object.
Smooth holes with a diameter of 2 mm ± 0,5 mm for the pressure measurements shall be drilled in three of
the test duct walls, the hole in the floor shall be left out as there is a high risk of that hole clogging with either
water or salt, or both. The holes shall be drilled perpendicular to the direction of flow. The three holes shall
be interconnected with a circular pipe or tube.
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. The equipment shall be calibrated at regular intervals to ensure the required accuracy.
6.2.5 Solid salt aerosol mixing section
The solid salt aerosol input and the mixing section shall be constructed so that the aerosol uniformity meets
the requirements set out in 7.2.2.
6.2.6 Measurement of temperature and relative humidity
The temperature measuring instrument used shall be capable of measuring temperature with an accuracy of
±1 °C. The relative humidity measuring instrument used shall be capable of measuring the relative humidity
with an accuracy of ±2 %. The equipment shall be calibrated at regular intervals to ensure the required
accuracy.
6.3 Measurement equipment
6.3.1 Test rig instrumentation
The test rig shall be equipped with:
— pressure transducers for measuring atmospheric pressure as well as pressure drop over filters, flow
devices etc.;
— humidity sensors;
— temperature sensors.
ISO 29461-4:2025(en)
6.3.2 Sodium flame photometer
A sodium flame photometer (SFP) works by analysing the light emitted from sodium atoms when they are
excited in a flame, see Figure 2.
When a solution of metallic salt is sprayed as fine droplets into a flame, due to the heat of the flame, the
droplets dry leaving a fine residue of salt. This fine residue converts into neutral atoms.
Due to the thermal energy of the flame, the atoms get excited and, after that, return to ground state. In this
process of return to ground state, excited atoms emit radiation of specific wavelength. This wavelength of
radiation emitted is specific for every element.
This specificity of the wavelength of light emitted makes it a qualitative aspect, while the intensity of
radiation depends on the concentration of element. This makes it a quantitative aspect.
The radiation emitted in the process is of a specific wavelength dependent on the element. For sodium (Na)
this wavelength is in the range of 589 nm, for potassium (K) it is around 767 nm.
The sensitivity of the SFP shall be ≤ 10 ng/m .
Depending on the model of SFP, the output can either be of measured sodium content or a converted sodium
chloride value. If the output is sodium content only, this shall be converted into sodium chloride as follows:
c
Na
c =( )
NaCl
0,3935
Since the test duct is operated in negative pressure, the pressure condition at the sample inlet of the SFP can
affect the measurement depending on the design.
The SFP shall be operated according to the manufacturer’s specification and be of suitable design for the test
setup in this document.
The SFP shall be suitable for sampling airborne salt.
Key
1 burner 4 detector
2 concave mirror 5 display and recorder
3 optical filter
Figure 2 — Flame photometry — Schematic diagram

ISO 29461-4:2025(en)
6.4 Solid salt aerosol sampling
6.4.1 Sample probes
Tapered sharp-edged sampling probes are placed in the centre of the upstream and downstream measuring
sections. The sampling heads shall be centrally located on the line with the inlet tip facing the inlet of the
test rig parallel to the air flow. The sampling probe tip diameter shall be sized to provide isokinetic sampling
within 10 % in the test rig for a test air flow rate of 4 250 m /h. The sampling probe tip diameter shall be
sized to provide isokinetic sampling within 10 % in the test rig for either all three default test flow rates or
the actual test air flow rate, or both. The probe diameter shall be 6 mm or larger.
6.4.2 Sampling air flow
The air flow rate of the sampling pump used (onboard or external) shall be sufficient to provide isokinetic
sampling while meeting the requirements of 6.4.1. The sampling air flow rate shall be within the tolerances
of the instrument specification (range) during aerosol measurement.
6.5 Solid salt aerosol generation
6.5.1 Salt generation
The SSA shall be generated using a salt generator. An example of the technical specification is included in
Annex A. The salt used for tests according to this document is sodium chloride (NaCl).
The saline solution used in the salt generator is made by mixing NaCl and water (concentration 30 g NaCl/100 g
water). This solution is used in the salt generator (Annex A) to produce an aerosol with a concentration of
4 mg NaCl per cubic meter of test air (tolerance +0,2/-0 mg). The output concentration of the salt generator
is adjusted by regulating the air pressure to the Laskin nozzles. If the test is interrupted, the Laskin nozzles
shall be checked and, if needed, cleaned to ensure the correct output once the test is restarted. The saline
solution level in the salt generator shall be 50 mm +30/-0 above the holes in the Laskin nozzle.
An auxiliary heater is connected to the salt generator to dry the aerosol, the heater shall be adjustable for
air flow and temperature and set to an air flow of 200 l/min ±10 %, the air temperature in the salt generator
shall be 35 °C ± 5 °C in the centre of part 11 in the generator, see Figure A.6.
6.5.2 Aerosol injection
The aerosol shall be injected into the airstream from one injection point located in the centre of the cross-
section of the test duct, the injection point shall be facing against the airstream and have a diameter of 100 mm.
6.6 Water spray device
A water spray device is used to generate a uniform water fog. The device shall fulfil the requirements
specified in ISO 29461-2:2022, 7.2.
6.7 Water collection device
The collection basins connected to the drains shall be built and configured in such a way that they can be
closed off from the rig and removed while keeping the rig free from leaks (i.e. by using ball valves), the
volume of each basin shall be 10 l. To ensure free flow of water into the basins and to make sure that there
is no pressure difference between the basin and the rig the basin shall be fitted with a ventilation that is
connected back to the same test duct section as the drain.

ISO 29461-4:2025(en)
7 Qualification of test rig and apparatus
7.1 Pressure system testing
Pressure system testing shall meet the requirements specified in ISO 16890-2:2022, 8.2.1
7.2 Solid salt aerosol uniformity
7.2.1 Aerosol uniformity parameters
The uniformity of the challenge aerosol concentration across the test rig cross section shall be determined
by a nine-point traverse in the 650 mm × 650 mm (25,6“× 25,6”) test rig immediately upstream of the test
device location using the grid points as shown in Figure 3.
3 3 3
The traverse measurements shall be performed at air flow rates of 4 250 m /h, 6 000 m /h and 8 000 m /h
(or the maximum design flow rate for the test rig). The traverse shall be made by repositioning a single
probe to maintain the same sample line configuration for each of the nine grid points. The inlet nozzle of the
sample probe shall be a tapered sharp-edged sample probe
...