ISO 4589-4:2021

INTERNATIONAL ISO
STANDARD 4589-4
First edition
2021-04
Plastics — Determination of burning
behaviour by oxygen index —
Part 4:
High gas velocity test
Plastiques — Détermination du comportement au feu au moyen de
l'indice d'oxygène —
Partie 4: Essai à vitesse élevée de gaz
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

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
Foreword
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 4, Burning
behaviour.
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iv © ISO 2021 – All rights reserved

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].
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.
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
...