ISO 4589-4:2021

INTERNATIONAL ISO
STANDARD 4589-4
First edition
Plastics — Determination of burning
behaviour by oxygen index —
Part 4:
High gas velocity test
PROOF/ÉPREUVE
Reference number
ISO 4589-4:2021(E)
©
ISO 2021

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ISO 4589-4:2021(E)

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ISO 4589-4:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles for determination of HOI . 2
5 Apparatus . 2
6 Calibration of equipment. 7
7 Preparation of test specimens . 7
7.1 Test specimen form . 7
7.2 Sampling . 8
7.3 Test specimen dimensions and preparation . 8
7.4 Marking of test specimen . 8
7.5 Conditioning . 8
8 Procedure for determination of HOI . 8
8.1 Setting up the apparatus. 8
8.2 Setting volume fraction of oxygen and gas flow velocity . 9
8.3 Procedure for ignition of the test specimen . 9
8.4 Assessing the burning behaviour of test specimen .10
8.5 Selecting successive volume fraction of oxygen .10
8.6 Determining the preliminary volume fraction of oxygen .10
8.7 Volume fraction of oxygen changes .10
9 Calculation and expression of results .11
9.1 Calculation of the HOI .11
9.2 Determination of k .12
9.3 Standard deviation of oxygen volume fraction measurements .13
10 Precision of test results .13
11 Test report .13
Annex A (normative) Calibration of equipment .14
Annex B (informative) Example of test results sheet for HOI .15
Annex C (informative) Interlaboratory test data on HOI measurement .18
Annex D (informative) Blow-off behaviour at high gas velocity — How to predict
the flammability of materials .20
Bibliography .29
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ISO 4589-4:2021(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 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 61, Plastics, Subcommittee SC 4, Burning
behaviour.
A list of all parts in the ISO 4589 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.
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ISO 4589-4:2021(E)

Introduction
This document has been prepared to extend the test methods available for the determination of
flammability by oxygen index to higher gas velocity of oxygen/nitrogen mixture to which plastic
materials can be exposed in a service situation where the gas velocity is higher than that specified in
ISO 4589-2. The gas velocity at the position of the test specimen is measured prior to the test.
The output of the test described in this document can be used, for example, in the evaluation of the
burning behaviour of plastics materials used in circumstances where forced ventilation air flow
governs the supply of oxygen to the fire. See References [10] to [16].
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INTERNATIONAL STANDARD ISO 4589-4:2021(E)
Plastics — Determination of burning behaviour by
oxygen index —
Part 4:
High gas velocity test
1 Scope
This document specifies a test method for determining the minimum volume fraction of oxygen, in
admixture with nitrogen, at ambient temperature, that supports combustion of small vertical sheet test
specimen under a specified gas velocity that is higher than that specified in ISO 4589-2.
NOTE The result is expressed as a high gas velocity oxygen index (HOI).
In addition, this document specifies the testing apparatus for determining the HOI.
The test method is applicable to materials in the form of sheets up to 2 mm thick. It is also applicable to
flexible sheet materials that are supported vertically by a specified specimen holder.
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 291:2008, Plastics — Standard atmospheres for conditioning and testing
ISO 2859-1, Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by
acceptance quality limit (AQL) for lot-by-lot inspection
ISO 2859-2, Sampling procedures for inspection by attributes — Part 2: Sampling plans indexed by limiting
quality (LQ) for isolated lot inspection
ISO 13943, Fire safety — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
high gas velocity oxygen index
HOI
minimum volume fraction of oxygen, in a mixture of oxygen and nitrogen, at a specified gas velocity
that supports flaming combustion of a material under specified test conditions
Note 1 to entry: The specified gas velocity is greater than 40 mm/s and is typically between 600 mm/s and
1 000 mm/s.
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Note 2 to entry: The HOI is usually expressed as a percentage, at the gas velocity used (e.g. HOI = 34,6 %,
800 mm/s).
4 Principles for determination of HOI
A small test specimen is supported vertically in a mixture of oxygen and nitrogen that flows upwards
through a transparent chimney. The volume fraction of oxygen in the gas mixture is pre-determined,
controlled and measured. The vertical velocity of the gas mixture gas is pre-determined, controlled and
measured. The upper end of the specimen is ignited, and its subsequent burning behaviour is observed
in order to compare the burnt length of the specimen, with respect to the limits specified. The HOI is
determined from a series of tests using different volume fractions of oxygen (see 8.7).
5 Apparatus
5.1 Test chimney, which shall consist of a heat-resistant glass tube supported vertically on a base
through which the oxygen/nitrogen gas mixture can be introduced (see Figure 1).
The recommended dimensions of the chimney are 450 mm to 500 mm in height and an inside diameter
of 75 mm to 100 mm. The upper outlet shall be open without any restriction.
NOTE It has been found that the outlet cup defined in ISO 4589-2:2017, 5.1 creates flow turbulence in the
chimney at a high gas velocity.
A chimney having a height more than 500 mm or less than 450 mm can be used, if it is shown to give the
specified gas velocity within the permitted limit of variance.
The lower end of the chimney, or the base upon which the chimney is supported, shall incorporate a
device for evenly distributing the gas mixture entering the chimney as shown in Figure 1. The mounting
of a porous screen below the level of the specimen holder is helpful to prevent falling combustion debris
from fouling the gas entry and distribution paths. One option is to construct the chimney in such a way
that it can be divided in half, so as to make the setting of samples and cleaning easier.
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ISO 4589-4:2021(E)

Dimension in millimetres
Key
1 chimney glass tube
2 gas flow controlling chamber
3 inlet of oxygen/nitrogen gas mixture
Figure 1 — Typical chimney arrangement
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ISO 4589-4:2021(E)

5.2 Specimen holder, which shall be suitable for supporting a specimen vertically in the centre of the
chimney.
The specimen holder can be hanged from the upper edge of the chimney (see Figure 2) or supported by
a vertical rod raised from the base of the chimney (see Figure 3). The specimen shall be supported by
the vertical edges of the frames of the specimen holder. The vertical frames of the specimen holder shall
have reference marks at 20 mm, 100 mm and 140 mm as shown in Figure 2 and Figure 3. The surfaces
of the specimen holder and its support shall be smooth in order to minimize the turbulence of the gas
flow in the chimney.
Dimensions in millimetres
with tolerances ± 0,25 mm
Key
1 upper reference mark
2 lower reference mark
3 positioning mark for the top edge of the test specimen
NOTE The test specimen is held securely along both upright edges between forks made of stainless steel.
Figure 2 — Suspended specimen holder
(Option A hanging specimen holder)
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ISO 4589-4:2021(E)

Dimensions in millimetres
with tolerances ± 0,25 mm
Key
1 upper reference mark
2 lower reference mark
3 positioning mark for the bottom edge of the test specimen
NOTE The test specimen is held securely along both upright edges between forks made of stainless steel.
Figure 3 — Supported specimen holder
(Option B: Specimen holder supported from the bottom)
5.3 Gas supplies, which shall be suitable for supporting an oxygen/nitrogen gas mixture with a gas
velocity of up to 1 000 mm/s in the chimney. The gas velocity shall be within 50 mm/s of the desired value.
The supply rate of oxygen/nitrogen gas mixture in this document is greater than that specified in
ISO 4589-2 and it is necessary to have higher gas supply capability than that for ISO 4589-2.
5.4 Gas control system, which shall be suitable for setting and adjusting the volume fraction of oxygen
in a gas mixture entering into the chimney with a resolution of 0,1 % and an accuracy of ±0,2 % when the
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ISO 4589-4:2021(E)

gas velocity of the mixture within the chimney is 800 mm/s ± 50 mm/s at 23 °C ± 2 °C. The gas velocity
shall be controllable within the range of 600 mm/s to 1 000 mm/s.
The gas control system shall also be capable of supplying the oxygen/nitrogen gas mixture at the gas
velocity of 100 mm/s or less for the ignition stage of the test (see 8.3).
Means shall be provided for ensuring that the temperature of the gas mixture entering into the chimney
is 23 °C ± 2 °C. If such means involves an internal probe, its position and profile shall be designed to
minimize the turbulence within the chimney.
NOTE It has been found that the temperature measurement can be done by a device specified in 5.9 and/
or 5.10.
An example of the suitable gas control system is given in Figure 4.
Key
1 N supply port 11 gas flow controlling chamber
2
2 O supply port 12 bypass outlet
2
3 pressure regulator 13 flow rate control valve
4 N supply valve 14 open/shut valve
2
5 O supply valve 15 mixed gas sampling port
2
6 pressure gauge 16 flow rate control valve
7 digital mass flow controller [for N ] 17 coupler (plug)
2
8 digital mass flow controller [for O ] 18 coupler (socket)
2
9 bypass flow rate control valve 19 test chimney glass tube
10 open/shut valve 20 igniter
Figure 4 — Example of diagram of gas control system
5.5 Oxygen analyser, which shall be suitable for measuring the volume fraction of oxygen in the gas
mixture entering the chimney with a resolution of 0,1 % and an accuracy of ±0,1 % of the mixture.
NOTE 1 It has been found that paramagnetic oxygen analysers meet the accuracy requirements.
NOTE 2 In case the volume fraction of oxygen around the position of the specimen differs from that controlled
at the air supply line, troubleshooting will be necessary.
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ISO 4589-4:2021(E)

5.6 Flame igniter, which shall comprise a tube that can be inserted into the chimney to apply to the
test specimen a flame issuing from an outlet of 2 mm ± 1 mm diameter at the end of the tube.
The flame fuel shall be propane, without premixed air. The purity of the propane gas shall be at least
98 %. The fuel supply shall be adjusted so that, for the set volume fraction of oxygen, the total flame
height is 16 mm ± 4 mm when the tube is vertical within the chimney.
Use of a flame height gauge is recommended.
5.7 Timing device, which shall be capable of measuring periods up to 5 min with an accuracy of ±0,5 s.
5.8 Fume extraction system, which shall be capable of providing sufficient ventilation or exhaust to
remove fumes or soot expelled from the chimney without disrupting the gas flow rate or temperatures in
the chimney.
5.9 Gas velocity measurement device, i.e. anemometer, which shall be capable of measuring vertical
gas velocity at the specimen position in the test chimney and have a resolution of 0,01 m/s.
NOTE A hot-wire anemometer has been found suitable for this purpose. It has been found that this device
usually can also measure gas temperature as specified in 5.10.
5.10 Gas temperature device. The temperature measurement device for measuring the gas
temperature in the chimney shall have an accuracy and a resolution of 0,5 K.
6 Calibration of equipment
For conformance with this method, calibrate the equipment periodically in accordance with the
instructions given in Annex A so that the maximum interval between recalibration and the use
conforms to the periods stated in Table 1.
Table 1 — Equipment calibration frequencies
Item Maximum period between calibrations
Leak tests for gas system joints (as required by A.1)
a) For joints disturbed during use or cleaning of the apparatus Immediately
b) For undisturbed equipment 6 months
Gas flow rate (as required by A.2) 6 months
Gas velocity measurement device (as required by A.3) 1 year
Oxygen analyser (as required by A.4) 1 week
Mass flow controller (as required by A.5) 1 year
Gas temperature measurement device (as required by A.6) 1 year
7 Preparation of test specimens
7.1 Test specimen form
Of the six specimen forms listed in ISO 4589-2:2017, Table 2, only one form “V” is used in this test
+0
method. Test specimen form “V” is flexible film or sheet and shall have the length of (140 ) mm and
−5
width of (52 + 0,5) mm. The thickness of twat specimen shall be up to 2 mm.
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ISO 4589-4:2021(E)

7.2 Sampling
Obtain a sample sufficient for preparation of at least 15 test specimens for tests in a gas velocity. The
sample shall be taken in accordance with the material specification. Otherwise, it shall be taken in
accordance with ISO 2859-1 or ISO 2859-2, as applicable.
7.3 Test specimen dimensions and preparation
The test specimen shall be made by any applicable procedures that comply with the appropriate
material specification (see NOTE 1) or ISO methods (see NOTE 2) for preparing specimens, mould or cut
test specimens.
NOTE 1 Some material specifications can require selection and identification of the “state of the test specimen”
used (e.g. in a “defined state” or “basic state” for a styrene-based polymer or copolymer).
NOTE 2 In the absence of a relevant specification, one or more procedures in ISO 293, ISO 294, ISO 295,
ISO 2818 or ISO 3167 can be used.
Ensure that the surfaces of specimens are clean and free from flaws that could affect burning behaviour
(e.g. peripheral moulding flash or burrs from machining).
Note the position and orientation of test specimens with respect to any asymmetry in the sample
material (see NOTE 3).
NOTE 3 HOI can be significantly affected by differences in the ease of ignition or burning behaviour, due to
material inhomogeneity (e.g. different levels of shrinkage when heated for specimens cut in different directions
from asymmetrically oriented thermoplastics film).
7.4 Marking of test specimen
The test specimens shall be marked at 20 mm and 100 mm from the end at which the specimen is to be
ignited.
7.5 Conditioning
The test specimens shall be conditioned for 24 h at 23 °C ± 2 °C and (50 ± 5) % relative humidity. After
24 h conditioning, if the stability of the mass of the test specimen reaches to 0,1 % or less changes, then
allow to conduct test. Otherwise, follow ISO 291:2008, 8.1, to keep specimen in conditioning chamber
for at least 88 h (maximum duration is 88 h).
Test specimens of cellular materials that may contain volatile flammable material should preferably
be purged of such volatile material prior to conditioning at 23 °C and 50 % relative humidity. Test
specimens may be purged satisfactorily by pre-conditioning at 60 °C in suitable ventilated ovens for
168 h. Larger blocks of such materials may require longer pre-treatment. It is important that facilities
for cutting test specimens from cellular material that may contain volatile flammable material are
suitable for the hazards involved.
8 Procedure for determination of HOI
8.1 Setting up the apparatus
8.1.1 Maintain ambient temperature for the test apparatus at 23 °C ± 2 °C. If necessary, keep the test
specimens in an enclosure at 23 °C ± 2 °C and relative humidity (50 % ± 5 %) from which each test
specimen can be taken when required.
8.1.2 Recalibrate equipment components, if necessary (see Clause 6 and Annex A). Before conducting
a test, clean the glass chimney to maintain good visibility. If necessary, clean the gas inlets or inlet screen,
and the temperature sensor (if fitted).
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8.1.3 Ensure that the test chimney is set in vertical (see Figure 1).
8.2 Setting volume fraction of oxygen and gas flow velocity
8.2.1 Select an initial volume fraction of oxygen to be used. When possible, base this volume fraction on
past results for similar materials. Alternatively, try to ignite a test specimen in air, and note the burning
behaviour. If the test specimen burns rapidly, select an initial volume fraction of about 18 % oxygen; if
the specimen burns gently or unsteadily, select an initial oxygen volume fraction of about 21 %; if the
specimen does not continue to burn in air, select an initial volume fraction of at least 25 %, depending on
the difficulty of ignition or the period of burning before extinguishing in air.
8.2.2 Select a gas velocity between 600 mm/s to 1 000 mm/s to which HOI is to be determined.
NOTE It is found suitable to conduct the tests with gas velocity of 600, 800 and 1 000 mm/s for determining
blow-off behaviour in terms of volume fraction of oxygen. See Annex D.
8.2.3 Shut the bypass valve (device 10 in Figure 4). Set the gas mixing and flow controls for nitrogen
and oxygen supply (devices 3 to 8 in Figure 4) so that an oxygen/nitrogen mixture at 23 °C ± 2 °C
containing the pre-determined volume fraction of oxygen is flowing at the selected gas velocity within
the chimney.
8.2.4 Measure the volume fraction of the oxygen using oxygen analyser (see 5.5) which samples the
mixture gas at the gas sampling port (device 15 of Figure 3). Record the volume fraction of oxygen.
8.2.5 The gas velocity in the test chimney at the level of top of the specimen and 20 mm horizontally
from the centre of the chimney shall be measured by the gas flow velocity measurement device as
specified in 5.9. The gas velocity shall be within 50 mm/s of the desired value. The gas velocity can be
controlled by the flow rate control valve (device 16 in Figure 3).
8.2.6 Once the pre-determined volume fraction of oxygen and gas velocity are obtained, keep left the
mass flow controller of oxygen and nitrogen untouched (device 7 and 8 in Figure 3). For shutting the flow
of oxygen and nitrogen, use supply valves of these gases (device 4 and 5 in Figure 3).
8.3 Procedure for ignition of the test specimen
8.3.1 Mount a test specimen vertically in the centre of the chimney so that the top of the test specimen
is at least 30 mm below the open top of the chimney, and the lowest exposed part of the test specimen is
at least 100 mm above the top of the gas distribution device at the base of the chimney.
8.3.2 Open the bypass valve (device 10 in Figure 3) and set the gas velocity to 100 mm/s or less (see 5.4).
8.3.3 Supply oxygen and nitrogen to the chimney by opening the gas supply valves (device 4 and 5
in Figure 3). Let the gas flow to purge the test chimney for at least 20 s prior to the ignition of the test
specimen and maintain the flow without change during the ignition.
8.3.4 After the purge, ignite the test specimen using flame ignitor (see 5.6) to burn only on the top
surface of the test specimen by sweeping the ignitor flame along the top surface of the test specimen.
This ignition process shall not be continued for more than 30 s.
8.3.5 After ignition of the test specimen, shut the bypass valve (device 10 in Figure 3) so that the gas
velocity in the chimney becomes the selected velocity.
8.3.6 Consider the specimen to be ignited, for the purpose of measuring the extent of burning, as soon
as any part of the visible burning portion reaches the level of the upper reference mark.
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8.3.7 Observe the burning behaviour of the test specimen and record if the limit of burning was or
was not exceeded (see 8.4) at the pre-determined volume fraction of oxygen and the pre-determined gas
velocity.
8.4 Assessing the burning behaviour of test specimen
When the combustion continues and exceed the lower reference level, note the burning behaviour
accordingly, and extinguish the flame. This is recorded as an “X” response.
When the combustion does not exceed the lower reference level, note the burning behaviour accordingly.
This is recorded as an “O” response.
NOTE The lower reference level is 40 mm above the bottom edge of the test specimen.
8.5 Selecting successive volume fraction of oxygen
The procedure described in 8.6 and 8.7 is based upon Reference [17] using the specific case where
N − N = 5 (see 8.7.2 and 8.7.3), with an arbitrary step size for certain changes to be made in the oxygen
T L
volume fra
...