ISO 871:2022

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 2022
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ii
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
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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
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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.
iv
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/
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.
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
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.
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
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.
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
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