Plastics — Determination of ignition temperature using a hot-air furnace

This document specifies a laboratory method for determining the flash-ignition temperature and spontaneous-ignition temperature of plastics using a hot-air furnace. It is one of a number of methods in use for evaluating the reaction of plastics to the effects of ignition sources. NOTE Information on additional ignition methods can be found in ISO 10093. This method does not give a direct measure of the combustibility or rate of burning of a material or any definition of the safe upper limit of temperature for the plastics in use, and it is inappropriate to use it alone to describe or appraise the fire hazard or fire risk of materials, products or assemblies under actual fire conditions. However, results of this test are suitable for use as elements of a fire hazard or fire risk assessment which takes into account all of the factors pertinent to an assessment of the fire hazard of a particular end use. Tests made under conditions of this method are potentially of considerable value in comparing the relative ignition characteristics of different materials. Values obtained represent the lowest ambient air temperature that has the potential to cause ignition of the material under the conditions of this test. Test values are expected to rank materials according to ignition susceptibility under actual use conditions. The results of this test method are not intended for fire safety engineering calculations.

Plastiques — Détermination de la température d'allumage au moyen d'un four à air chaud

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Status
Published
Publication Date
22-Feb-2022
Current Stage
5060 - Close of voting Proof returned by Secretariat
Completion Date
05-Jan-2022
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INTERNATIONAL ISO
STANDARD 871
Fourth edition
2022-02
Plastics — Determination of ignition
temperature using a hot-air furnace
Plastiques — Détermination de la température d'allumage au moyen
d'un four à air chaud
Reference number
ISO 871:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO 871:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

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
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 871:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus .................................................................................................................................................................................................................... 2

5.1 Option 1 — Setchkin furnace .................................................................................................................................................... 2

5.2 Option 2 – ISO 1182 refractory tube furnace .............................................................................................................. 4

6 Location of thermocouples ........................................................................................................................................... .............................9

7 Test specimens ....................................................................................................................................................................................................... 9

8 Procedure .................................................................................................................................................................................................................10

8.1 Flash-ignition temperature (FIT) ....................................................................................................................................... 10

8.2 Spontaneous-ignition temperature (SIT) .................................................................................................................... 11

9 Precision ....................................................................................................................................................................................................................12

10 Test report ...............................................................................................................................................................................................................12

Annex A (informative) Results obtained by interlaboratory trials using Option 1 (Setchkin

furnace).......................................................................................................................................................................................................................13

Annex B (informative) Typical designs of test apparatus ..........................................................................................................15

Bibliography .............................................................................................................................................................................................................................17

iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 871:2022(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.

This fourth edition cancels and replaces the third edition (ISO 871:2006), which has been technically

revised.
The main changes compared to the previous edition are as follows.

— An option to use a modification of the equipment used for ISO 1182 to assess ignitability has been

added.
— Mandatory information has been provided throughout the document.

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.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 871:2022(E)
Plastics — Determination of ignition temperature using a
hot-air furnace
1 Scope

1.1 This document specifies a laboratory method for determining the flash-ignition temperature and

spontaneous-ignition temperature of plastics using a hot-air furnace. It is one of a number of methods

in use for evaluating the reaction of plastics to the effects of ignition sources.

NOTE Information on additional ignition methods can be found in ISO 10093.

1.2 This method does not give a direct measure of the combustibility or rate of burning of a material

or any definition of the safe upper limit of temperature for the plastics in use, and it is inappropriate

to use it alone to describe or appraise the fire hazard or fire risk of materials, products or assemblies

under actual fire conditions. However, results of this test are suitable for use as elements of a fire hazard

or fire risk assessment which takes into account all of the factors pertinent to an assessment of the fire

hazard of a particular end use.

1.3 Tests made under conditions of this method are potentially of considerable value in comparing

the relative ignition characteristics of different materials. Values obtained represent the lowest ambient

air temperature that has the potential to cause ignition of the material under the conditions of this

test. Test values are expected to rank materials according to ignition susceptibility under actual use

conditions.

1.4 The results of this test method are not intended for fire safety engineering calculations.

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 1182, Reaction to fire tests for products — Non-combustibility test
ISO 13943, Fire safety — Vocabulary
IEC 60584-1, Thermocouples Part 1 EMF Specifications And Tolerances
IEC 60584-2:1982, Thermocouples — Part 2: Tolerances
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 https:// www .electropedia .org/
© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 871:2022(E)
3.1
flash-ignition temperature
FIT

minimum temperature at which, under specified test conditions, sufficient flammable gases are emitted

to ignite momentarily on application of a pilot flame
3.2
spontaneous-ignition temperature
SIT

minimum temperature at which, under specified test conditions, ignition is obtained by heating in the

absence of any additional ignition source
3.3
glowing combustion

combustion of a material in the solid phase without flame but with emission of light from the combustion

zone
4 Principle

A specimen of the material is heated in a hot-air ignition furnace using various temperatures within the

heated chamber, and the flash-ignition temperature is determined with a small pilot flame directed at

the opening in the top of the furnace to ignite evolved gases.

The spontaneous-ignition temperature is determined in the same manner as the flash-ignition

temperature, but without the pilot flame.
NOTE The results from using Option 1 or Option 2 can potentially be different.
5 Apparatus
5.1 Option 1 — Setchkin furnace

5.1.1 Hot-air ignition furnace, similar to that shown in Figure 1, consisting primarily of an electrical

heating unit and a specimen holder.
© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 871:2022(E)
Key
1 thermocouple TC2 10 metal fasteners
2 support rod 11 air-flow meter (not part of furnace)
3 refractory disc cover 12 air flow tangential to cylinder
4 thermocouple TC 13 specimen pan
5 gasket 14 mineral fibre wool
6 thermocouple TC 15 50 turns of No. 16 nichrome wire in heat-resistant cement
7 heater terminals 16 three refractory blocks to space inner tube and support it
8 pilot flame 17 inspection plug (removable)
9 air supply 18 thermal insulation (removable)
Figure 1 — Cross section of hot-air ignition furnace
© ISO 2022 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 871:2022(E)

5.1.2 Furnace tube, with an inside diameter of 100 mm ± 5 mm and a length of 240 mm ± 20 mm,

made of a ceramic that is suitable for use at a temperature of at least 750 °C. The tube shall be positioned

vertically so that it stands on the furnace floor above a plug for the removal of accumulated residue.

5.1.3 Inner ceramic tube, capable of withstanding at least 750 °C, with an inside diameter of

75 mm ± 2 mm, a length of 240 mm ± 20 mm and a thickness of approximately 3 mm, placed centrally

inside the furnace tube and positioned 20 mm ± 2 mm above the furnace floor on three small refractory

spacer blocks. The top shall be covered by a disc of heat-resistant material with a 25 mm ± 2 mm

diameter opening in the centre which is used for observations and allows the passage of smoke and

gases. The pilot flame shall be located immediately above the opening.

5.1.4 Outside air source, to supply clean air near the top of the annular space between the ceramic

tubes through a copper tube at a steady and controllable rate. The air shall be heated and circulated in

the space between the two tubes and enter the inner ceramic tube at the bottom. The air flow shall be

metered by a rotameter or other suitable device.

5.1.5 Electrical heating unit, made of 50 turns of 1,3 mm ± 0,1 mm nichrome wire or equivalent.

The wires, contained within a mineral-fibre sleeve, shall be wound around the furnace tube and shall

be embedded in heat-resistant cement.

5.1.6 Insulation, consisting of a layer of mineral-fibre wool approximately 60 mm thick, and covered

by a sheet- iron jacket.

5.1.7 Pilot igniter, consisting of a copper tube of nominal inside diameter 1,8 ± 0,3 mm attached to

a supply of 94 % minimum purity propane and placed horizontally 5 mm ± 1 mm above the top surface

of the disc cover. The pilot flame shall be adjusted to 20 mm ± 2 mm in length and centred above the

opening in the disc cover.

5.1.8 Specimen support and holder, consisting of a metal specimen pan made of 0,7 mm ± 0,3 mm

thick stainless steel and measuring 40 mm ± 2 mm in diameter by 15 mm ± 2 mm in depth, having a

rounded bottom and held in a ring of approximately 2 mm diameter stainless-steel welding rod. The

ring shall be welded to a length of the same type of rod extending through the cover of the furnace, as

shown in Figure 1. The bottom of the specimen pan shall be located 185 mm ± 2 mm down from the

lower edge of the pilot igniter.

5.1.9 Thermocouples, 0,5 mm in diameter, chromel-alumel (type K) or iron-constantan (type J),

for temperature measurement, connected to a calibrated recording instrument with a tolerance not

exceeding ±2 °C. The thermocouple tolerance shall be in accordance with IEC 60584-2:1982, Table A.1;

class 2 or better. They shall be installed as in Clause 6.

5.1.10 Heating control, consisting of a suitable variable transformer or an automatic controller

connected in series with the heating coils.
5.1.11 Timing device, having an accuracy of 1 s or better.
5.2 Option 2 – ISO 1182 refractory tube furnace

5.2.1 The apparatus shall consist of a refractory tube furnace insulated and surrounded by a

heating coil. The furnace specified in ISO 1182 shall be used. A cone-shaped airflow stabilizer shall be

attached to the base of the furnace and a draft shield to its top. Details are shown in Figure 2.

© ISO 2022 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 871:2022(E)
Dimensions in millimetres
Key
1 stand 11 thermocouple TC
2 insulation 12 one of the two furnace thermocouples
3 magnesium oxide powder 13 external insulating wall
4 furnace tube 14 mineral fibre cement
© ISO 2022 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 871:2022(E)
5 heating coils 15 seal
6 draft shield 16 stabilizer cone
7 heat resisting steel rod for insertion device 17 draft screen (metal sheet)
8 disc cover 18 pilot flame
9 thermocouple TC 19 specimen pan
10 support rod
Figure 2 — Test apparatus for Option 2 (ISO 1182 refractory tube furnace)

5.2.1.1 Two furnace thermocouples shall be provided as specified in ISO 1182 and indicated in 6.3.2.

5.2.1.2 A thermal sensor shall be used to measure the furnace temperature along its central axis.

5.2.1.3 Unless stated otherwise, all dimensions shall have a 5 % tolerance.
5.2.2 Test furnace

5.2.2.1 The furnace tube shall be constructed of a refractory material, as specified in Table 1, of

3 3

density 2 800 kg/m ± 300 kg/m . The furnace tube shall be 150 mm ± 1 mm high with an internal

diameter of 75 mm ± 1 mm and a wall thickness of 10 mm ± 1 mm.

Table 1 — Furnace tube refractory material for apparatus, Option 2 (ISO 1182 refractory tube

furnace)
Material Composition % (kg/kg mass)
Alumina (Al O ) >89
2 3
Silica and alumina (SiO , Al O ) >98
2 2 3
Ferric oxide (Fe O ) <0,45
2 3
Titanium dioxide (TiO ) <0,25
Manganese oxide (Mn O ) <0,1
3 4
Other trace oxides (sodium, potassium, calcium and The balance
magnesium oxides)

5.2.2.2 The top of the draught shield shall be covered by a disc of heat-resistant material with a

25 mm ± 2 mm diameter opening in the centre that is to be used for observation and passage of smoke

and gases. The pilot flame shall be located immediately above the opening.

5.2.2.3 The furnace tube shall be surrounded by an annular space of the following dimensions:

150 mm high and of 10 mm wall thickness.

5.2.2.4 The annular space shall be fitted with top and bottom plates, recessed internally to locate the

ends of the furnace tube.

5.2.2.5 The annular space shall be insulated with a 25 mm layer of an insulating material having a

thermal conductivity of 0,04 W/(m·K) ± 0,01 W/(m·K) at a mean temperature of 20 °C. Magnesium oxide

3 3

powder of a nominal bulk density of 170 kg/m ± 30 kg/m is a suitable material for this use.

5.2.2.6 The furnace tube shall be provided with a single winding of 80/20 nickel/chromium electrical

resistance tape, 3 mm ± 0,1 mm wide and 0,2 mm ± 0,01 mm thick.
© ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 871:2022(E)

5.2.2.7 An open-ended cone-shaped air-flow stabilizer shall be attached to the underside of the

furnace. The air-flow stabilizer shall be 500 mm long and shall be reduced uniformly from an internal

diameter of 75 mm ± 1 mm at the top to an internal diameter of 10,0 mm ± 0,5 mm at the bottom.

The air flow stabilizer shall be manufactured from 1 mm thick sheet steel, with a smooth finish on

the inside. The joint between the air flow stabilizer and the furnace shall have an airtight fit, with an

internal smooth finish. The upper half of the air flow stabilizer shall
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 871
ISO/TC 61/SC 4
Plastics — Determination of ignition
Secretariat: BSI
temperature using a hot-air furnace
Voting begins on:
2021-11-09
Plastiques — Détermination de la température d'allumage au moyen
d'un four à air chaud
Voting terminates on:
2022-01-04
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 871:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 871:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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
© ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 871:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus .................................................................................................................................................................................................................... 2

5.1 Option 1 — Setchkin furnace .................................................................................................................................................... 2

5.2 Option 2 – ISO 1182 refractory tube furnace .............................................................................................................. 4

6 Location of thermocouples ........................................................................................................................................... .............................9

7 Test specimens ....................................................................................................................................................................................................... 9

8 Procedure .................................................................................................................................................................................................................10

8.1 Flash-ignition temperature (FIT) ....................................................................................................................................... 10

8.2 Spontaneous-ignition temperature (SIT) .................................................................................................................... 11

9 Precision ....................................................................................................................................................................................................................12

10 Test report ...............................................................................................................................................................................................................12

Annex A (informative) Results obtained by interlaboratory trials using Option 1 (Setchkin

furnace).......................................................................................................................................................................................................................13

Annex B (informative) Typical designs of test apparatus ..........................................................................................................15

Bibliography .............................................................................................................................................................................................................................17

iii
© ISO 2021 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/FDIS 871:2021(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.

This fourth edition cancels and replaces the third edition (ISO 871:2006), which has been technically

revised.
The main changes compared to the previous edition are as follows.

— An option to use a modification of the equipment used for ISO 1182 to assess ignitability has been

added.
— Mandatory information have been added throughout the document.

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.
© ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 871:2021(E)
Plastics — Determination of ignition temperature using a
hot-air furnace
1 Scope

1.1 This document specifies a laboratory method for determining the flash-ignition temperature and

spontaneous-ignition temperature of plastics using a hot-air furnace. It is one of a number of methods

in use for evaluating the reaction of plastics to the effects of ignition sources.

NOTE Information on additional ignition methods can be found in ISO 10093.

1.2 This method does not give a direct measure of the combustibility or rate of burning of a material

or any definition of the safe upper limit of temperature for the plastics in use, and it is inappropriate

to use it alone to describe or appraise the fire hazard or fire risk of materials, products or assemblies

under actual fire conditions. However, results of this test are suitable for use as elements of a fire hazard

or fire risk assessment which takes into account all of the factors pertinent to an assessment of the fire

hazard of a particular end use.

1.3 Tests made under conditions of this method are potentially of considerable value in comparing

the relative ignition characteristics of different materials. Values obtained represent the lowest ambient

air temperature that has the potential to cause ignition of the material under the conditions of this

test. Test values are expected to rank materials according to ignition susceptibility under actual use

conditions.

1.4 The results of this test method are not intended for fire safety engineering calculations.

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 1182, Reaction to fire tests for products — Non-combustibility test
ISO 13943, Fire safety — Vocabulary
IEC 60584-1, Thermocouples Part 1 EMF Specifications And Tolerances
IEC 60584-2:1982, Thermocouples — Part 2: Tolerances
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 https:// www .electropedia .org/
© ISO 2021 – All rights reserved
---------------------- Page: 5 ----------------------
ISO/FDIS 871:2021(E)
3.1
flash-ignition temperature
FIT

minimum temperature at which, under specified test conditions, sufficient flammable gases are emitted

to ignite momentarily on application of a pilot flame
3.2
spontaneous-ignition temperature
SIT

minimum temperature at which, under specified test conditions, ignition is obtained by heating in the

absence of any additional ignition source
3.3
glowing combustion

combustion of a material in the solid phase without flame but with emission of light from the combustion

zone
4 Principle

A specimen of the material is heated in a hot-air ignition furnace using various temperatures within the

heated chamber, and the flash-ignition temperature is determined with a small pilot flame directed at

the opening in the top of the furnace to ignite evolved gases.

The spontaneous-ignition temperature is determined in the same manner as the flash-ignition

temperature, but without the pilot flame.
NOTE The results from using Option 1 or Option 2 can potentially be different.
5 Apparatus
5.1 Option 1 — Setchkin furnace

5.1.1 Hot-air ignition furnace, similar to that shown in Figure 1, consisting primarily of an electrical

heating unit and a specimen holder.
© ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 871:2021(E)
Key
1 thermocouple TC2 10 metal fasteners
2 support rod 11 air-flow meter (not part of furnace)
3 refractory disc cover 12 air flow tangential to cylinder
4 thermocouple TC 13 specimen pan
5 gasket 14 mineral fibre wool
6 thermocouple TC 15 50 turns of No. 16 nichrome wire in heat-resistant cement
7 heater terminals 16 three refractory blocks to space inner tube and support it
8 pilot flame 17 inspection plug (removable)
9 air supply 18 thermal insulation (removable)
Figure 1 — Cross section of hot-air ignition furnace
© ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/FDIS 871:2021(E)

5.1.2 Furnace tube, with an inside diameter of 100 mm ± 5 mm and a length of 240 mm ± 20 mm,

made of a ceramic that is suitable for use at a temperature of at least 750 °C. The tube shall be positioned

vertically so that it stands on the furnace floor above a plug for the removal of accumulated residue.

5.1.3 Inner ceramic tube, capable of withstanding at least 750 °C, with an inside diameter of

75 mm ± 2 mm, a length of 240 mm ± 20 mm and a thickness of approximately 3 mm, placed centrally

inside the furnace tube and positioned 20 mm ± 2 mm above the furnace floor on three small refractory

spacer blocks. The top shall be covered by a disc of heat-resistant material with a 25 mm ± 2 mm

diameter opening in the centre which is used for observations and allows the passage of smoke and

gases. The pilot flame shall be located immediately above the opening.

5.1.4 Outside air source, to supply clean air near the top of the annular space between the ceramic

tubes through a copper tube at a steady and controllable rate. The air shall be heated and circulated in

the space between the two tubes and enter the inner ceramic tube at the bottom. The air flow shall be

metered by a rotameter or other suitable device.

5.1.5 Electrical heating unit, made of 50 turns of 1,3 mm ± 0,1 mm nichrome wire or equivalent.

The wires, contained within a mineral-fibre sleeve, shall be wound around the furnace tube and shall

be embedded in heat-resistant cement.

5.1.6 Insulation, consisting of a layer of mineral-fibre wool approximately 60 mm thick, and covered

by a sheet- iron jacket.

5.1.7 Pilot igniter, consisting of a copper tube of nominal inside diameter 1,8 ± 0,3 mm attached to

a supply of 94 % minimum purity propane and placed horizontally 5 mm ± 1 mm above the top surface

of the disc cover. The pilot flame shall be adjusted to 20 mm ± 2 mm in length and centred above the

opening in the disc cover.

5.1.8 Specimen support and holder, consisting of a metal specimen pan made of 0,7 mm ± 0,3 mm

thick stainless steel and measuring 40 mm ± 2 mm in diameter by 15 mm ± 2 mm in depth, having a

rounded bottom and held in a ring of approximately 2 mm diameter stainless-steel welding rod. The

ring shall be welded to a length of the same type of rod extending through the cover of the furnace, as

shown in Figure 1. The bottom of the specimen pan shall be located 185 mm ± 2 mm down from the

lower edge of the pilot igniter.

5.1.9 Thermocouples, 0,5 mm in diameter, chromel-alumel (type K) or iron-constantan (type J),

for temperature measurement, connected to a calibrated recording instrument with a tolerance not

exceeding ±2 °C. The thermocouple tolerance shall be in accordance with IEC 60584-2:1982, Table A.1;

class 2 or better. They shall be installed as in Clause 6.

5.1.10 Heating control, consisting of a suitable variable transformer or an automatic controller

connected in series with the heating coils.
5.1.11 Timing device, having an accuracy of 1 s or better.
5.2 Option 2 – ISO 1182 refractory tube furnace

5.2.1 The apparatus shall consist of a refractory tube furnace insulated and surrounded by a

heating coil. The furnace specified in ISO 1182 shall be used. A cone-shaped airflow stabilizer shall be

attached to the base of the furnace and a draft shield to its top. Details are shown in Figure 2.

© ISO 2021 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/FDIS 871:2021(E)
Dimensions in millimetres
Key
1 stand 11 thermocouple TC
2 insulation 12 one of the two furnace thermocouples
3 magnesium oxide powder 13 external insulating wall
4 furnace tube 14 mineral fibre cement
© ISO 2021 – All rights reserved
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ISO/FDIS 871:2021(E)
5 heating coils 15 seal
6 draft shield 16 stabilizer cone
7 heat resisting steel rod for insertion device 17 draft screen (metal sheet)
8 disc cover 18 pilot flame
9 thermocouple TC 19 specimen pan
10 support rod
Figure 2 — Test apparatus for Option 2 (ISO 1182 refractory tube furnace)

5.2.1.1 Two furnace thermocouples shall be provided as specified in ISO 1182 and indicated in 6.3.2.

5.2.1.2 A thermal sensor shall be used to measure the furnace temperature along its central axis.

5.2.1.3 Unless stated otherwise, all dimensions shall have a 5 % tolerance.
5.2.2 Test furnace

5.2.2.1 The furnace tube shall be constructed of a refractory material, as specified in Table 1, of

3 3

density 2 800 kg/m ± 300 kg/m . The furnace tube shall be 150 mm ± 1 mm high with an internal

diameter of 75 mm ± 1 mm and a wall thickness of 10 mm ± 1 mm.

Table 1 — Furnace tube refractory material for apparatus, Option 2 (ISO 1182 refractory tube

furnace)
Material Composition % (kg/kg mass)
Alumina (Al O ) >89
2 3
Silica and alumina (SiO , Al O ) >98
2 2 3
Ferric oxide (Fe O ) <0,45
2 3
Titanium dioxide (TiO ) <0,25
Manganese oxide (Mn O ) <0,1
3 4
Other trace oxides (sodium, potassium, calcium and The balance
magnesium oxides)

5.2.2.2 The top of the draught shield shall be covered by a disk of heat-resistant material with a

25 mm ± 2 mm diameter opening in the centre that is to be used for observation and passage of smoke

and gases. The pilot flame shall be located immediately above the opening.

5.2.2.3 The furnace tube shall be surrounded by an annular space of the following dimensions:

150 mm high and of 10 mm wall thickness.

5.2.2.4 The annular space shall be fitted with top and bottom plates, recessed internally to locate the

ends of the furnace tube.

5.2.2.5 The annular space shall be insulated with a 25 mm layer of an insulating material having a

thermal conductivity of 0,04 W/(m·K) ± 0,01 W/(m·K) at a mean temperature of 20 °C. Magnesium oxide

3 3

powder of a nominal bulk density of 170 kg/m ± 30 kg/m is a suitable material for this use.

5.2.2.6 The furnace tube shall be provided with a single winding of 80/20 nickel/chromium electrical

resistance tape, 3 mm ± 0,1 mm wide and 0,2 mm ± 0,01 mm thick.
© ISO 2021 – All rights reserved
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ISO/FDIS 871:2021(E)

5.2.2.7 An open-ended cone-shaped air-flow stabilizer shall be attached to the underside of the

furnace. The air-flow stabilizer shall be 500 mm long and shall be reduced uniformly from an internal

diameter of 75 mm ± 1 mm at the top to an internal diameter of 10,0 mm ± 0,5 mm at

...

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