SIST EN ISO 5659:2026

SLOVENSKI STANDARD
01-april-2026
Polimerni materiali - Nastajanje dima - Določanje optične gostote s preskusom v
enojni preskusni komori (ISO 5659:2026)
Plastics - Smoke generation - Determination of optical density by a single-chamber test
(ISO 5659:2026)
Kunststoffe -Rauchentwicklung -Bestimmung der optischen Dichte durch
Einkammerprüfung (ISO 5659:2026)
Plastiques - Production de fumée - Détermination de la densité optique par un essai en
enceinte unique (ISO 5659:2026)
Ta slovenski standard je istoveten z: EN ISO 5659:2026
ICS:
13.220.40 Sposobnost vžiga in Ignitability and burning
obnašanje materialov in behaviour of materials and
proizvodov pri gorenju products
83.080.01 Polimerni materiali na Plastics in general
splošno
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 5659
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2026
EUROPÄISCHE NORM
ICS 13.220.40; 83.080.01 Supersedes EN ISO 5659-2:2017
English Version
Plastics - Smoke generation - Determination of optical
density by a single-chamber test (ISO 5659:2026)
Plastiques - Production de fumée - Détermination de la Kunststoffe - Rauchentwicklung - Bestimmung der
densité optique par un essai en enceinte unique (ISO optischen Dichte durch Einkammerprüfung (ISO
5659:2026) 5659:2026)
This European Standard was approved by CEN on 13 January 2026.

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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 5659:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 5659:2026) has been prepared by Technical Committee ISO/TC 61 "Plastics" in
collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by SIS.
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 2026, and conflicting national standards shall
be withdrawn at the latest by August 2026.
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.
This document supersedes EN ISO 5659-2:2017.
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 5659:2026 has been approved by CEN as EN ISO 5659:2026 without any modification.

International
Standard
ISO 5659
First edition
Plastics — Smoke generation —
2026-01
Determination of optical density by
a single-chamber test
Plastiques — Production de fumée — Détermination de la densité
optique par un essai en enceinte unique
Reference number
ISO 5659:2026(en) © ISO 2026
ISO 5659:2026(en)
© ISO 2026
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
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 5659:2026(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles of the test . 3
5 Suitability of a material or product for testing . 3
5.1 Material or product geometry .3
5.2 Surface characteristics .3
5.3 Asymmetrical products .3
6 Specimen construction and preparation . 4
6.1 Number of specimens .4
6.2 Size of specimens .4
6.3 Specimen preparation .4
6.4 Conditioning.5
6.5 Wrapping of specimens.5
6.6 Dimensionally unstable materials .5
7 Apparatus and ancillary equipment . 6
7.1 General .6
7.2 Test chamber .6
7.2.1 Construction.6
7.2.2 Chamber pressure control facilities .7
7.2.3 Chamber wall temperature .10
7.3 Specimen support and heating arrangements .11
7.3.1 Radiator cone.11
7.3.2 Framework for support of the radiator cone, specimen holder and heat flux
meter .11
7.3.3 Radiation shield .14
7.3.4 Heat flux meter .14
7.3.5 Specimen holder .14
7.3.6 Pilot burner . 15
7.4 Gas supply . 15
7.5 Photometric system .16
7.5.1 General .16
7.5.2 Light source .16
7.5.3 Photo detector .16
7.5.4 Additional equipment .18
7.6 Chamber leakage .18
7.7 Cleaning materials .19
7.8 Ancillary equipment .19
7.8.1 Balance (optional) .19
7.8.2 Timing device .19
7.8.3 Linear measuring devices .19
7.8.4 Auxiliary heater .19
7.8.5 Protective equipment . .19
7.8.6 Recorder .19
7.8.7 Water-circulating device .19
7.8.8 Oxygen meter (optional) .19
8 Test environment .20
9 Setting-up and calibration procedures .20
9.1 General . 20

iii
ISO 5659:2026(en)
9.2 Alignment of photometric system . 20
9.2.1 General . 20
9.2.2 Beam collimation . 20
9.2.3 Beam focusing. 20
9.3 Selection of compensating filter(s) .21
9.4 Linearity check .21
9.5 Calibration of range-extension filter .21
9.6 Chamber leakage rate test . 22
9.7 Burner calibration . 22
9.8 Radiator cone calibration . 22
9.9 Cleaning . 23
9.10 Frequency of checking and calibrating procedure . 23
10 Test procedure .24
10.1 General .24
10.2 Preparation of test chamber.24
10.3 Tests with pilot flame .24
10.4 Preparation of the photometric system .24
10.5 Loading the specimen . 25
10.6 Recording of light transmission . 25
10.7 Observations . 25
10.8 Termination of test. 25
10.9 Testing in different modes . 26
11 Expression of results .26
11.1 Specific optical density, D . 26
s
11.2 Clear-beam correction factor, D .27
c
12 Precision .27
13 Test report .27
Annex A (normative) Calibration of heat flux meter .29
Annex B (informative) Variability in the specific optical density of smoke measured in the
single-chamber test .30
Annex C (informative) Determination of mass optical density .32
Annex D (informative) Precision data from tests on intumescent materials.37
Annex E (informative) Guidance on optical density testing .39
Annex F (informative) Specific sample preparation .46
Annex G (informative) Background to standard reference materials .49
Bibliography .50

iv
ISO 5659:2026(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 61, Plastics, Subcommittee SC 4, Burning
behaviour, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This first edition of ISO 5659 cancels and replaces ISO 5659-2:2017, which has been technically revised.
The main changes are as follows:
— Annex G has been added as background information.
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 5659:2026(en)
Introduction
Fire is a complex phenomenon; its development and effects depend upon a number of interrelated factors.
The behaviour of materials and products depends upon the characteristics of the fire, the method of use of
[1]
the materials and the environment in which they are exposed to (see also ISO/TS 3814 and ISO 13943).
A test such as is specified in this document deals only with a simple representation of a particular aspect of
the potential fire situation, typified by a radiant heat source, and it cannot alone provide any direct guidance
on behaviour or safety in fire. A test of this type may, however, be used for comparative purposes or to
ensure the existence of a certain quality of performance (in this case, smoke production) considered to have
a bearing on fire behaviour generally. It would be wrong to attach any other meaning to results from this
test.
The term “smoke” is defined in ISO 13943 as a visible suspension of solid and/or liquid particles in gases
resulting from incomplete combustion. It is one of the first response characteristics to be manifested and
should almost always be taken into account in any assessment of fire hazard as it represents one of the
greatest threats to occupants of a building or other enclosure, such as a ship or train, on fire.
The responsibility for the preparation of ISO 5659 was transferred during 1987 from ISO/TC 92 to ISO/TC 61
on the understanding that the scope and applicability of the standard for the testing of materials should not
be restricted to plastics but should also be relevant to other materials where possible, including building
materials. See Annex G for further information.

vi
International Standard ISO 5659:2026(en)
Plastics — Smoke generation — Determination of optical
density by a single-chamber test
1 Scope
This document specifies a method of measuring smoke production from the exposed surface of specimens
of materials or composites. It is applicable to specimens that have an essentially flat surface and do not
exceed 25 mm in thickness when placed in a horizontal orientation and subjected to specified levels of
thermal irradiance in a closed cabinet with or without the application of a pilot flame. This method of test is
applicable to all plastics.
It is intended that the values of optical density determined by this test be taken as specific to the specimen
or assembly material in the form and thickness tested and are not to be considered inherent, fundamental
properties.
The test is intended primarily for use in research and development and fire safety engineering in buildings,
trains, ships, etc. and not as a basis for ratings for building codes or other purposes. No basis is provided
for predicting the density of smoke that can be generated by the materials upon exposure to heat and flame
under other (actual) exposure conditions. This test procedure excludes the effect of irritants on the eye.
NOTE This test procedure addresses the loss of visibility due to smoke density, which generally is not related to
irritancy potency (see Annex E).
It is emphasized that smoke production from a material varies according to the irradiance level to which the
specimen is exposed. The results yielded from the method specified in this document are based on exposure
2 2
to the specific irradiance levels of 25 kW/m and 50 kW/m .
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, Plastics — Standard atmospheres for conditioning and testing
ISO 13943, Fire safety — Vocabulary
ISO 14934-3, Fire tests — Calibration and use of heat flux meters — Part 3: Secondary calibration method
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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
assembly
fabrication of materials (3.6) and/or composites (3.2)
Note 1 to entry: Sandwich panels are an example of an assembly.

ISO 5659:2026(en)
Note 2 to entry: The assembly can include an air gap.
3.2
composite
combination of materials (3.6) which are generally recognized in building construction as discrete entities
Note 1 to entry: Coated or laminated materials are examples of composites.
3.3
essentially flat surface
surface which does not deviate from a plane by more than 1 mm
3.4
exposed surface
surface of the product (3.9) subjected to the heating conditions of the test
3.5
irradiance
radiant flux incident on an infinitesimal element of the surface containing the point divided by the area of
that element
3.6
material
basic single substance or uniformly dispersed mixture
Note 1 to entry: Metal, stone, timber, concrete, mineral fibre and polymers are examples.
3.7
mass optical density
MOD
measure of the degree of opacity of smoke in terms of the mass loss of the material (3.6)
3.8
optical density of smoke
D
measure of the degree of opacity of smoke, taken as the negative common logarithm of the relative
transmission of light
3.9
product
material (3.6), composite (3.2) or assembly (3.1) about which information is required
3.10
specific optical density
D
s
optical density multiplied by a factor which is calculated by dividing the volume of the test chamber by the
product (3.9) of the exposed area of the specimen (3.11) and the path length of the light beam
Note 1 to entry: See 11.1.1.
3.11
specimen
representative piece of the product to be tested together with any substrate or surface coating
Note 1 to entry: The specimen can include an air gap.
3.12
intumescent material
material (3.6), that expands in excess of normal thermal expansion under the action of heat normally
generated by the fire
Note 1 to entry: Generally, a material developing an expanded structure of thickness >10 mm during the test, with the
cone heater 25 mm from the specimen, is considered as intumescent material.

ISO 5659:2026(en)
[2]
Note 2 to entry: Definition adapted from ISO 10294-5 .
4 Principles of the test
Specimens of the product are mounted horizontally within a chamber and exposed to thermal radiation on
their upper surfaces at selected levels of constant irradiance up to 50 kW/m .
The smoke evolved is collected in the chamber, which also contains photometric equipment. The attenuation
of a light beam passing through the smoke is measured. The results are reported in terms of specific optical
density.
5 Suitability of a material or product for testing
5.1 Material or product geometry
5.1.1 The method is applicable to essentially flat materials, products, composites or assemblies not
exceeding 25 mm in thickness.
5.1.2 The method is sensitive to small variations in geometry, surface orientation, thickness (either overall
or of the individual layers), mass and composition of the material, and so the results obtained by this method
only apply to the thickness of the material or product as tested.
5.1.3 It is not possible to calculate the specific optical density of one thickness of a material or product
from the specific optical density of another thickness of the material or product.
5.2 Surface characteristics
A material or product having one of the following properties is suitable for testing:
a) an essentially flat exposed surface;
b) a surface irregularity which is evenly distributed over the exposed surface provided that
1) at least 50 % of the surface of a representative 100 mm area lies within a depth of 10 mm from a
plane taken across the highest points on the exposed surface, or
2) for surfaces containing cracks, fissures, or holes not exceeding 8 mm in width or 10 mm in depth, the
total area of such cracks, fissures, or holes at the surface does not exceed 30 % of a representative
100 mm area of the exposed surface.
When an exposed surface does not meet the requirements of either 5.2 a) or 5.2 b), the material or product
shall be tested in a modified form complying as close as possible with the requirements given in 5.2. The test
report shall state that the material or product has been tested in a modified form and clearly describe the
modification.
5.3 Asymmetrical products
It is possible that a product submitted to this test will have faces which differ or contain laminations of
different materials arranged in a different order in relation to the two faces. If either of the faces can be
exposed in use within a room, cavity, or void, both faces shall be tested.

ISO 5659:2026(en)
6 Specimen construction and preparation
6.1 Number of specimens
6.1.1 The test sample shall comprise a minimum of 12 specimens if all four modes are to be tested: six
specimens shall be tested at 25 kW/m (three specimens with a pilot flame and three specimens without
a pilot flame) and six specimens shall be tested at 50 kW/m (three specimens with a pilot flame and three
specimens without a pilot flame).
If fewer than four modes are to be tested, a minimum of three specimens per mode shall be tested.
6.1.2 An additional number of specimens as specified in 6.1.1 shall be used for each face, in accordance
with the requirements of 5.2.
6.1.3 An additional 12 specimens (i.e. three specimens per test mode) shall be held in reserve if required
by the modes specified in 10.9.
6.1.4 In case of dimensionally unstable materials (see 6.6), it is necessary to make a preliminary test with
the cone heater at 50 mm from the specimen, so at least two additional specimens are required.
6.2 Size of specimens
6.2.1 The specimens shall be square, with sides measuring 75 mm ± 1 mm.
6.2.2 Materials of 25 mm nominal thickness or less shall be evaluated at their full thickness. For
comparative testing, materials shall be evaluated at a thickness of 1,0 mm ± 0,1 mm. All materials consume
oxygen when they burn in the chamber, and the smoke generation of some materials (especially rapid-
burning or thick specimens) is influenced by the reduced oxygen concentration in the chamber. As far as
possible, materials shall be tested in their end-use thickness.
6.2.3 Materials with a thickness greater than 25 mm shall be cut to give a specimen thickness of
25 mm ± 0,1 mm, in such a way that the original (uncut) face can be evaluated.
6.2.4 Specimens of multi-layer materials with a thickness greater than 25 mm, consisting of core
material(s) with facings of different materials, shall be prepared as specified in 6.2.3 (see also 6.3.2).
6.3 Specimen preparation
6.3.1 The specimen shall be representative of the material and shall be prepared in accordance with
the procedures described in 6.3.2 and 6.3.3. The specimens shall be cut, sawn, moulded or stamped from
identical sample areas of the material, and records shall be kept of their thicknesses and, if required, their
masses.
6.3.2 If flat sections of the same thickness and composition are tested in place of curved, moulded or
speciality parts, this shall be stated in the test report. Any substrate or core materials for the specimens
shall be the same as those used in practice.
6.3.3 When coating materials, including paints and adhesives, are tested with the substrate or core as
used in practice, specimens shall be prepared following normal practice, and in such cases the method of
application of the coating, the number of coats and the type of substrate shall be included in the test report.
6.3.4 This test method has been found suitable for applications outside the field of plastics, or to
transformed products in their end-use shape. Such specific sampling conditions are proposed in Annex F.

ISO 5659:2026(en)
6.4 Conditioning
6.4.1 Before the test, specimens shall be conditioned to constant mass at a temperature of (23 ± 2) °C and
a relative humidity of (50 ± 5) % in accordance with ISO 291.
Constant mass is considered to be reached when two successive weighing operations, carried out at an
interval of 24 h, do not differ by more than 0,1 % of the mass of the test piece or 0,1 g, whichever is the greater.
Materials, such as polyamides, which require more than one week of conditioning to reach equilibrium, shall
be tested after conditioning for a period specified by the applicant. This period shall not be less than one
week and shall be described in the test report.
6.4.2 While in the conditioning chamber, specimens shall be supported in racks so that air has access to all
surfaces.
Forced air movement in the conditioning chamber may be used to assist in accelerating the conditioning
process.
The results obtained from this method are sensitive to small differences in specimen conditioning. It is
important therefore to ensure that the requirements of 6.5 are followed carefully.
6.5 Wrapping of specimens
6.5.1 All specimens shall be covered across the back, along the edges and over the front surface periphery,
leaving a central exposed specimen area of 65 mm × 65 mm, using a single sheet of aluminium foil
(approximately 0,04 mm thick) with the dull side in contact with the specimen. Care shall be taken not to
puncture the foil or to introduce unnecessary wrinkles during the wrapping operation. The foil shall be
folded in such a way as to minimize losses of any melted specimen material at the bottom of the specimen
holder. After mounting the specimen in its holder, any excess foil along the front edges shall be trimmed off.
6.5.2 Wrapped specimens of thickness up to 12,5 mm shall be backed with a sheet of non-combustible
3 3
insulating board of oven-dry density 850 kg/m ± 100 kg/m and nominal thickness 12,5 mm and a layer of
low-density (nominal 65 kg/m ) refractory fibre blanket under the non-combustible board.
Wrapped specimens of thickness greater than 12,5 mm but less than 25 mm shall be backed with a layer of
low-density (nominal 65 kg/m ) refractory fibre blanket.
Wrapped specimens of a thickness of 25 mm shall be tested without any backing board or refractory fibre
blanket.
6.5.3 For resilient materials, each specimen in its aluminium foil wrapper shall be installed in the holder
in such a way that the exposed surface lies flush with the inside face of the opening of the specimen holder.
Materials with uneven exposed surfaces shall not protrude beyond the plane of the opening in the specimen
holder.
6.5.4 When thin impermeable specimens, such as thermoplastic films, become inflated during the test
owing to gases trapped between the film and backing, they shall be maintained essentially flat by making
two or three cuts (20 mm to 40 mm long) in the film to act as vents.
6.6 Dimensionally unstable materials
Samples that intumesce or deform so that they contact the pilot, or reach the level of the heater base plate,
shall be tested with a separation of 50 mm between the base plate of the cone heater and the upper surface
of the specimen. In this case, the heater calibration (see 9.8) shall be performed with the heat flux meter
positioned 50 mm below the cone heater base plate. It shall be stressed that the time to ignition measured
with this separation is not comparable to that measured with the separation of 25 mm. If, when tested
with a separation of 50 mm between the cone heater base plate and the upper surface of the specimen, the

ISO 5659:2026(en)
specimen still intumesces or deforms such that it contacts the pilot flame, or the upper specimen surface
reaches the level of the cone heater baseplate, the specimen is not suitable for the testing to this document.
Other dimensionally unstable products, for example products that warp or shrink during testing, shall be
restrained against excessive movement.
These materials should be tested using the fine wire grid made of (0,8 ± 0,1) mm with wire spacing of
(20 ± 2) mm, as illustrated in Figure 1.
Figure 1 — Grid for materials that distort
Materials that intumesce in a fluid phase such that molten materials overflow the edge frame or seep
between the edge frame and the specimen holder invalidate the test. Therefore, such materials should be
tested without the edge frame and should be housed in 0,1 mm thick aluminium tray wrappings which
extend 10 mm above the top edge of the test specimen.
7 Apparatus and ancillary equipment
7.1 General
The apparatus (see Figure 2) shall consist of an air-tight test chamber with provision for containing a
specimen holder, radiator cone, pilot burner, light transmission and measuring system and other, ancillary
facilities for controlling the conditions of operation during a test.
7.2 Test chamber
7.2.1 Construction
7.2.1.1 The test chamber (see Figure 2 and Figure 3) shall be fabricated from laminated panels, the
inner surfaces of which shall consist of either a porcelain enamelled metal not more than 1 mm thick or an
equivalent coated metal which is resistant to chemical attack and corrosion and capable of easy cleaning. The
...