🔩 Determination of the oxygen index (OI) of plastics at ambient temperature — the minimum volume fraction of oxygen in a mixture with nitrogen flowing upwards through a glass chimney (height 450–500 mm, diameter 75–100 mm) at which a vertical specimen ignited at the top burns longer or over a greater length than the specified limits; self-supporting bars and sheets up to 10,5 mm, solid, laminated and cellular materials with apparent density ≥ 100 kg/m³, films in a frame, short procedure for comparison with a minimum value, PN-EN ISO 4589-2

Materials and NDT PN-EN ISO 4589-2

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 4589-2:2017-06 (English version; scope in Polish on the card), in full (our translation): “This document describes methods for determining the minimum volume fraction of oxygen, in admixture with nitrogen, that will support combustion of small vertical test specimens under specified test conditions. The results are defined as oxygen index (OI) values. These methods are intended for testing materials in the form of self-supporting vertical bars or sheets up to 10,5 mm thick. These methods are suitable for solid, laminated or cellular plastics characterized by an apparent density of 100 kg/m3 or greater. These methods may also be applicable to some cellular plastics with an apparent density of less than 100 kg/m3. A method is also provided for testing plastics in the form of flexible sheets or films supported vertically. For comparative purposes, a procedure is provided for determining whether or not the oxygen index OI of a material lies above some specified minimum value. NOTE For materials that shrink significantly when heated, e.g. highly oriented thin films, it may not be possible to apply the methods satisfactorily.” We read the text of the standard in the preview of ISO 4589-2:2017 from the cover to 5.3 (page 6, gas supplies); we do not have the rest of Clause 5, Clauses 6–11 or Annexes A–E — we only know their titles from the table of contents.

ACCORDING TO THE TEXT OF ISO 4589-2:2017 (foreword, introduction, Clauses 1–5.3, table of contents). The standard was prepared by ISO/TC 61/SC 4 (burning behaviour); the second edition replaces ISO 4589-2:1996 after technical revision and incorporates Amd 1:2005. Introduction: OI results are a sensitive measure of the burning characteristics of materials under controlled laboratory conditions and may be useful for quality control; they depend on the shape, orientation and isolation of the specimen and on the ignition conditions; results from specimens of different thickness or with different ignition procedures may not be comparable; no correlation with burning behaviour under other fire conditions is implied, and the standard is not intended for assessing the fire hazard of a material under actual fire conditions unless as one element of a fire risk assessment; for cellular materials of density below 100 kg/m³ attention is drawn to ISO 3582. Scope (1) — as on the card. References (2): ISO 291:2008, ISO 2859-1, ISO 2859-2, ISO 4589-1, ISO 5725-2, ISO 7823-1, ISO 13943; terms — according to ISO 4589-1 and ISO 13943. Principle (4): a small specimen is supported vertically in a mixture of oxygen and nitrogen flowing upwards through a transparent chimney, its upper end is ignited, and the burning period or the length burned is compared with specified limits; by testing a series of specimens at different oxygen fractions the OI is estimated (8.7); alternatively, for comparison with a specified OI, three specimens are tested at that oxygen fraction and at least two must give an “O” response (8.4). Chimney (5.1): heat-resistant glass tube supported vertically on a base through which the mixture is introduced; recommended height 450–500 mm, inside diameter 75–100 mm; a cap restricting the outlet so that the exhaust velocity is at least 90 mm/s (flow according to A.2; a cap converging to 40 mm at least 10 mm above the chimney has been found satisfactory); chimneys of other dimensions — if shown to give equivalent results; at the bottom a device for even gas distribution (diffuser and mixing chamber with metal foil honeycomb or glass beads), a screen against falling debris, levelling and a dark background are recommended. Holder (5.2): self-supporting specimens are held by a small clamp at least 15 mm from the nearest point that might burn before the extent-of-burning criterion is exceeded; films and flexible sheets — in a frame (Figure 6, tolerances ± 0,25 mm) with marks at 20 mm and 100 mm below the top; smooth holder profile so as not to disturb the flow. Gases (5.3): oxygen and/or nitrogen of not less than 98 % purity (mass fraction) and/or clean air (20,9 % oxygen by volume); moisture of the mixture below 0,1 % (mass fraction), unless the results have been shown to be insensitive to it — the system has a drying device or provision for monitoring moisture. From the table of contents: ignition procedures A (top surface) and B (propagating), marking of specimens for both procedures, selection of successive oxygen fractions and determination of the preliminary one, calculation of OI with determination of k and the standard deviation, precision, short procedure (Clause 10), annexes: calibration (A), calculation of oxygen fraction (B), results sheet (C), interlaboratory results on type VI specimens (D) and precision data from the 1978–1980 trial (E).

STATUS (PKN catalogue cards as of 02.10.2026). The card of PN-EN ISO 4589-2:2017-06 (English version, published 01-06-2017, 40 pages, price group R) has no “Withdrawn” header: Chemistry Sector, KT 141 Plastics, ICS 13.220.40 and 83.080.01, “Introduces: EN ISO 4589-2:2017 [IDT], ISO 4589-2:2017 [IDT]”, “Replaces: PN-EN ISO 4589-2:2006/A1:2006 – English version, PN-EN ISO 4589-2:2006 – Polish version, PN-EN ISO 4589-2:2006/A1:2006 – German version”. The PKN search for “PN-EN ISO 4589-2” (02.10.2026) also shows PN-ISO 4589-2:1999 and the 2006 edition with amendment A1. The EVS catalogue (read 02.10.2026) lists ISO 4589-2:2017 as valid from 12.04.2017.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 4589-2 appears in 8 records at 8 laboratories: AB 005, AB 169, AB 261, AB 304, AB 369, AB 1280, AB 1501, AB 1552. In the current scopes on the PCA website (read 02.10.2026, issues from 04.08.2025 to 01.09.2026): the 2017-06 edition is given by AB 005, AB 169 and AB 1552; the number without a year — by AB 304, AB 369, AB 1280 and AB 1501; AB 261 gives the WITHDRAWN 2006 edition and amendment A1:2006 (next to PN-E-04160-56:1990). The “Laboratories” tab searches for entries STARTING WITH “PN-EN ISO 4589-2” and shows 7 laboratories; AB 304 has an entry without the hyphen (“PN EN ISO 4589-2”) in the database, so it does not appear in this tab — checked with the tab query on the production server labcoda.pl on 02.10.2026.

WHAT THE LABORATORIES TEST (PCA entries). “Oxygen index” of plastics, also of conveyor belts next to PN-93/C-05013 (AB 005); “Flammability by the oxygen index method — procedure A, top ignition”, range up to 99,0 % (AB 169); “Determination of flammability by the oxygen index method” (AB 1552); “Ignitability by the oxygen index method” of plastics and rubber (AB 261), of solid, laminated and cellular plastics, flexible sheets and textile materials (AB 369), of insulating, structural, furnishing and decorative building materials and products (AB 1501) and at AB 1280; “Ignitability” of furnishing and decorative materials used in land construction and rolling stock, next to PN-EN ISO 11925-2 (AB 304).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Comparison: the result depends on shape, thickness and ignition procedure — OI values of specimens of different thickness or ignited by procedure A and B should not be compared, and the OI value does not describe the behaviour of the material in a real fire (introduction). Gas: moisture of the mixture must be below 0,1 % — the standard allows more only if the results have been shown to be insensitive to it — gas purity at least 98 %, and the exhaust velocity from the cap at least 90 mm/s (flow calculated according to A.2). Holder: the clamp must be at least 15 mm from the nearest point that might burn before the extent-of-burning criterion is exceeded (5.2). Material: light cellular materials (below 100 kg/m³) and strongly shrinking films may not be testable by this method. Edition: AB 261 cites the 2006 edition with A1, which the card of the 2017 edition lists as replaced.

WHAT WE DO NOT STATE. We do not have 5.4–5.9 (flow control, oxygen analyser, igniter, timer, fume extraction), Clauses 6–11 or Annexes A–E: dimensions of specimen types I–VI, criteria for “O” and “X” responses (burning time and extent of burning), steps of oxygen fraction change, the OI formula and the values of k, precision data — we therefore give none of these figures.

Method principle

A vertical specimen in a glass chimney through which an oxygen–nitrogen mixture flows upwards is ignited at the top and observed whether burning lasts longer or extends further than the specified limits; by varying the oxygen fraction over a series of specimens the minimum oxygen fraction supporting combustion — the oxygen index OI — is determined.

Applications

• Solid, laminated and cellular plastics (≥ 100 kg/m³), films and flexible sheets — 8 laboratories in PCA scopes
• Furnishing and decorative materials in buildings and rolling stock, building products
• Quality control and comparison with a minimum OI value (short procedure: three specimens, at least two “O”)

Key parameters

Standard

Standard number

PN-EN ISO 4589-2:2017-06 (wersja angielska; EN ISO 4589-2:2017 IDT, ISO 4589-2:2017 IDT)

Title (PL)

Tworzywa sztuczne — Oznaczanie zapalności metodą wskaźnika tlenowego — Część 2: Badanie w temperaturze pokojowej

Title (EN)

Plastics — Determination of burning behaviour by oxygen index — Part 2: Ambient-temperature test

Step-by-step procedure

1. Specimens

   Self-supporting bars or sheets up to 10,5 mm or films in a frame; dimensions, marking and conditioning according to Clause 7 (outside the part we read). PN-EN ISO 4589-2:2017-06 current (PKN cards as of 02.10.2026).

2. Apparatus

   Chimney vertical, oxygen–nitrogen mixture flowing upwards; exhaust velocity ≥ 90 mm/s; specimen in the holder in the centre of the chimney (clamp ≥ 15 mm from the burning zone).

3. Ignition

   The upper end of the specimen is ignited by procedure A (top surface) or B (propagating) — details in 8.3, outside the part we read.

4. Assessment and series

   Compare burning time or extent of burning with the limits (8.4); vary the oxygen fraction for successive specimens (8.5–8.7) and calculate OI (Clause 9).

5. Short procedure

   For comparison with a minimum value: three specimens at the given oxygen fraction, at least two “O” responses (Clause 10).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The test consists of burning plastics in an oxygen-enriched atmosphere — the standard provides for a fume extraction system (5.8, outside the part we read); safety rules are set by the laboratory
• TECHNICAL NOTE: OI does not describe the behaviour of the material in a real fire; results from specimens of different thickness or ignition procedures may not be comparable

Frequently asked questions