ISO/PRF TS 21911-2

Solid recovered fuels — Determination of self-heating — Part 2: Basket heating tests

Combustibles solides de récupération — Détermination de l'auto-échauffement — Partie 2: Essais utilisant la méthode du point de croisement

General Information

• Status: Not Published
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 300 - Solid recovered materials, including solid recovered fuels
• Drafting Committee: ISO/TC 300 - Solid recovered materials, including solid recovered fuels
• Current Stage: 5060 - Close of voting Proof returned by Secretariat
• Start Date: 02-Jun-2022
• Due Date: 02-Jun-2022
• Completion Date: 02-Jun-2022

RELATIONS

• Consolidates: ISO/TR 22463:2019 - Patient and client eye protectors for use during laser or intense light source (ILS) procedures — Guidance
• Effective Date: 06-Jun-2022

Standards Content (sample)

ISO/DTSPRF TS 21911--2
ISO TC 300/WG 6
Date: 2022-02-21
Secretariat: SIS

Solid recovered fuels — Determination of self-heating — Part 2: Basket heating tests

Combustibles solides de récupération — Détermination de l'autoéchauffement — Partie 2: Essais utilisant

la méthode du point de croisement
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ISO/TS 21911-2:2022(E)
© ISO 20XX 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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2022 – All rights reserved
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ISO/TS 21911-2:2022(E)
Contents

Foreword ............................................................................................................................................................. v

Introduction ...................................................................................................................................................... vi

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

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

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

4 Symbols .................................................................................................................................................. 2

5 Basket heating tests ........................................................................................................................... 5

6 Tests for product classification ...................................................................................................... 5

6.1 UN classification .................................................................................................................................. 5

6.1.1 General ................................................................................................................................................... 5

6.1.2 Test method for self-heating substances – MTC Test N.4 ....................................................... 5

6.1.3 Classification criteria — GHS .......................................................................................................... 6

6.2 Classification criteria — IMO .......................................................................................................... 6

6.3 Applicability of MTC Test N.4 for solid recovered fuels ......................................................... 7

7 Tests for determination of reaction kinetics ............................................................................. 7

7.1 General ................................................................................................................................................... 7

7.2 Isoperibolic test methods ................................................................................................................ 7

7.2.1 General ................................................................................................................................................... 7

7.2.2 Test procedure .................................................................................................................................... 8

7.2.3 Determination of reaction kinetics ............................................................................................... 8

7.2.4 Applicability for solid recovered fuels ........................................................................................ 9

7.3 Crossing-point method ..................................................................................................................... 9

7.3.1 General ................................................................................................................................................... 9

7.3.2 Test procedure ................................................................................................................................. 10

7.3.3 Determination of reaction kinetics ............................................................................................ 10

7.3.4 Applicability for solid recovered fuels ..................................................................................... 11

7.4 Adiabatic hot storage tests ........................................................................................................... 11

7.4.1 General ................................................................................................................................................ 11

7.4.2 Test procedure ................................................................................................................................. 12

7.4.3 Determination of reaction kinetics ............................................................................................ 14

7.4.4 Applicability for solid recovered fuels ..................................................................................... 16

8 Sample handling .............................................................................................................................. 16

8.1 General ................................................................................................................................................ 16

8.2 Sampling ............................................................................................................................................. 16

8.3 Sample transport and storage ..................................................................................................... 16

8.4 Sample preparation ........................................................................................................................ 17

8.5 Sample disposal ............................................................................................................................... 17

9 Test report ......................................................................................................................................... 17

Annex A (informative) Self-ignition behaviour of selected materials suitable to be used as

solid recovered fuels ...................................................................................................................... 19

Annex B (informative) Example of calculating kinetic parameters from crossing point

method tests ...................................................................................................................................... 33

Annex C (normative) Use of data for calculations of critical conditions in storage ................ 41

© ISO 2022 – All rights reserved iii
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ISO/TS 21911-2:2022(E)

Bibliography .................................................................................................................................................... 47

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ISO/TS 21911-2:2022(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 300, Solid recovered materials, including

solid recovered fuels., in collaboration with the European Committee for Standardization (CEN) Technical

Committee CEN/TC 343, Solid recovered fuels, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).
A list of all parts in the ISO 21911 series can be found on the ISO website.

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 v
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ISO/TS 21911-2:2022(E)
Introduction

There is a continuous global growth in trading and use of solid recovered fuels (SRFSRFs). Therefore,

intensive investigations about the risk of fires within SRF -production, handling and storing have been

conducted, see ÖNORM S 2098:2011. Recommendations have beenare given byin ISO 21912.

Depending on the kind of input wastes, the treatment technology applied, the quality of the SRF produced

and the realized storage versions, SRFSRFs can generate heat spontaneously by exothermic biological,

chemical and physical processes. The heat build-up can be significant in large storage volumes if the heat

conduction in the material is low. During some conditions the heat generation can lead to pyrolysis and

spontaneous ignition. The potential for self-heating varies considerably for different types and qualities

of SRF and it is important to be able to identify SRF fractions with high heat generation potential to avoid

fires in stored materials.

Avoiding fires throughout the production and supply chain will have positive consequences on the

acceptance of SRFSRFs and the costs for insurance coverage,

Application of SRF -standards and the use of dedicated standards for the determination of self-heating

will help to reduce the risk of fires and to develop tailor-made recommendations for SRF producers,

logistics providers, SRF users, equipment suppliers/ or manufacturers, consultants, authorities and

insurance providers.

As part of the determination and the assessment of risks for SRF, defined test methods and standards are

established or need to be developed. However, the ageing and degradation due to handling and storage

of SRF in actual environments will affectaffects their characteristics, so safety margins have toshould be

established in relation to actual analysis results.

Two intrinsically different types of teststest methods can be used to estimate the potential of self-heating;

a) In the isothermal calorimetry method described in ISO 21911-1 , the heat flow generated from the

test portion is measured directly.

b) In the basket heating tests described in this document, the temperature of the test portion is being

monitored and the critical ambient temperature (CAT), where the temperature of the test portion

just does not increase significantly due to self-heating, is used for indirect assessment of self-heating.

These two methods are applied at different analysis temperature regimes. The operating temperature for

an isothermal calorimeter is normally in the range 5 °C to 90 °C, whereas basket heating tests are

conducted at higher analysis (oven) temperatures.

NOTE 1 TheThese two types of test methods referred to above do not measure heat production from physical

processes, such as transport of moisture.

NOTE 2 It is likely that oxidation reactions taking place in the low respective high-temperature regimes for solid

recovered fuelsSRFs are of different character and thus have different reaction rates and heat production rates. In

such a casecases, extrapolation of the data from a high-temperature test series can lead to non-conservative results

and mightwill possibly not be applicable without taking the low-temperature reactions into account. In the general

case of two reactions with different activation energies, the high activation energy is “frozen out” at low

[7]

temperatures and the low activation energy reaction is “swamped” at higher temperatures. .

Basket heating tests have been used traditionally for characterisationcharacterization of the tendency for

spontaneous ignition of predominantly coals, but also for other reactive organic materials, such as e.g.

[9]

cottonseed meal, bagasse and milk powder. . The principle used in this typethese types of teststest is to

find the critical ambient temperature (CAT) for a self-heating sample material of specific size and

geometry.
In preparation. Stage at the time of publication: ISO/DIS 21911-1:2022.
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ISO/TS 21911-2:2022(E)

There are several different methods described in the literature with different degreedegrees of

sophistication. The variations span from simple pass and fail tests to more advanced tests from which

[10]
data on reaction rates can be extracted. .

Basket heating tests are useful for assessment of self-heating of solid recovered fuelsSRFs. The test

method selected can be evaluated for its applicability based on the information given in this document.

A compilation of available basket heating test methods is given in this document. Guidance on the

suitability for application of these methods for tests with solid recovered fuelsSRFs is provided.

Basic theory of the use of basket heating test data for calculations of critical conditions in storagesstorage

is provided in Annex C.

The test methods presented require representative samples for the conditions prevailing in the process

(e.g. of SRF -storage). Sample preparation is necessary for this purpose. The methods presented are not

suitable for assessing the fire hazard caused by impurities (disturbing materials),) as they occur mainly

in the input area and the first steps of SRF -production.
© ISO 2022 – All rights reserved vii
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TECHNICAL SPECIFICATION ISO/TS 21911-2:2022(E)
Solid recovered fuels — — Determination of self-heating
— — Part 2: Basket heating tests
1 Scope

This document gives guidance on basket heating tests for characterisationcharacterization of self-heating

properties of solid recovered fuels. (SRFs).
This document includes:
a) a compilation of basket heating test methods,;

b) guidance on the applicability and use of basket heating tests for solid recovered fuels,SRF;

c) information on the application of basket heating test data for calculations of critical conditions in

storagesstorage.

Data on spontaneous heat generation determined using this document is only associated with the specific

quality and age of the sample material.

The information derived using this document is intended for use in quality control and in hazard and risk

assessments related to the procedures given in ISO 21912.
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 21646 , Solid recovered fuels — Sample preparation
ISO 21637:2020, Solid recovered fuels — Vocabulary
ISO 21645, Solid recovered fuels — Methods for sampling
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 21637:2020 and the following

apply.

ISO and IEC maintain terminologicalterminology 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/
In preparation. Stage at the time of publication: ISO/FDIS 21646:2022.
© ISO 2022 – All rights reserved 1
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ISO/TS 21911-2:2022(E)
3.1
analysis temperature
temperature of the analysis environment, i.e. the oven temperature
3.2
Biot number

quotient of the convective heat transfer coefficient (between the sample boundary and the surrounding

air) and the conduction in the sample material normalized by the characteristic dimension of the test

basket
3.3
critical ambient temperature
CAT

ambient temperature (the analysis temperature [(3.1]) or the storage temperature of a storage) where

the internal temperature of the test portion or the stored material increases significantly ([due to self-

heating [(3.4]))]

Note 1 to entry: In EN 15188 the critical ambient temperature is defined as self-ignition temperature, T .

3.4
self-heating

rise in temperature in a material resulting from an exothermic reaction within the material

[SOURCE: ISO 13943:2017, 3.341, modified –— “” has beendomain omitted in the beginning of

thefrom definition.]
3.5
spontaneous ignition
ignition caused by an internal exothermic reaction
[SOURCE: ISO 13943:2017, 3.24, modified — Notes to entry removed.]
3.6
test sample

laboratory sample [(3.7]) after an appropriate preparation made by the laboratory

Note 1 to entry: The test sample is here typically a representative sample from a batch of solid recovered fuel.

[SOURCE: ISO 21637:2020, 3.84, modified –— Note 1 to entry has been added.]
3.7
laboratory sample

combined sample or a sub-sample of a combined sample for use indelivered to a laboratory

[SOURCE: ISO 16559:2014, 4.124] 2022, 3.120, modified — Note 1 to entry removed.]

4 Symbols
Symbol Quantity Typical unit
A pre-exponential factor in Arrhenius expression s
B dimensionless adiabatic temperature rise dimensionless
ℎ·𝐿𝐿
Bi Biot number, (𝐵𝐵𝐵𝐵 = ) dimensionless
𝜆𝜆
2 © ISO 2022 – All rights reserved
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ISO/TS 21911-2:2022(E)
c0 ambient oxygen concentration by volume fraction dimensionless
-1 -1
C specific heat capacity of the reaction products J kg K
-1 -1
C specific heat capacity of the bulk material J kg K
d diameter of body m
2 -1
D diffusion coefficient m s
E activation energy J mol
H Gross calorific value J kg
-2 -1
h heat transfer coefficient W m K
-2 -1
hr radiative amount on heat transfer coefficient; W m K
-2 -1
h convective amount on heat transfer coefficient; W m K
L characteristic length m
n order of reaction dimensionless
P constant dimensionless
𝑞𝑞̇´ heat generation term W m
Q heat of reaction J kg
Q heat of reaction by volume of oxygen J m
-1 -1
R universal gas constant J mol K
Ra Rayleight number dimensionless
S surface m²
t time s
T temperature K
T ambient temperature K
Tp crossing point temperature K
V volume m³
x length coordinate m
δ Frank-Kamenetskii parameter dimensionless
δ critical value of δ dimensionless
𝑅𝑅 𝑇𝑇
ε activation energy parameter, (𝜀𝜀 = ) dimensionless
𝐸𝐸
𝑎𝑎
Ф oxygen diffusion parameter dimensionless
-1 -1
λ thermal conductivity of sample W m K
-1 -1
λair thermal conductivity of air W m K
ρ bulk density kg m
-2 -4
σ Stefan-Boltzmann coefficient W m K
Symbol Quantity Typical unit
A pre-exponential factor in Arrhenius expression s
B dimensionless adiabatic temperature rise dimensionless
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ISO/TS 21911-2:2022(E)
h·L
Biot number, ( Bi= )
Bi dimensionless
c ambient oxygen concentration by volume fraction dimensionless
−1 −1
C specific heat capacity of the reaction products J kg K
−1 −1
C specific heat capacity of the bulk material J kg K
d diameter of body m
2 −1
D diffusion coefficient m s
E activation energy J mol
H gross calorific value J kg
−2 −1
h heat transfer coefficient W m K
−2 −1
h radiative amount on heat transfer coefficient W m K
−2 −1
hc convective amount on heat transfer coefficient W m K
L characteristic length m
n order of reaction dimensionless
P constant dimensionless
q´ heat generation term W m
Q heat of reaction J kg
Q heat of reaction by volume of oxygen J m
−1 −1
R universal gas constant J mol K
Ra Rayleight number dimensionless
S surface m
t time s
T temperature K
T ambient temperature K
T crossing point temperature K
Tsi self-ignition temperature K
V volume m
x length coordinate m
δ Frank-Kamenetskii parameter dimensionless
δ critical value of δ dimensionless
ε RT dimensionless
activation energy parameter,
a
Ф oxygen diffusion parameter dimensionless
−1 −1
λ thermal conductivity of sample W m K
−1 −1
λ thermal conductivity of air W m K
air
ρ bulk density kg m
−2 −4
σ Stefan-Boltzmann coefficient W m K
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ISO/TS 21911-2:2022(E)
5 Basket heating tests

The detailed test procedure varies between different isoperibolic and adiabatic methods. Isoperibolic

methods include that the test portion is put in a wire-mesh basket which is placed in an oven heated to a

fixed elevated temperature. The oven is equipped with a fan to keep the temperature uniform and to give

[9] [10].

a relatively large convective heat transfer coefficient to the test specimen. For adiabatic tests, the

oven temperature is adjusted to the temperature at the centre of the sample, see EN 15188.

Basket heating tests are based on the Frank-Kamenetskii theory of criticality of a self-heating isotropic

slab (see Annex C) and have been developed to determine the reaction kinetics of the global reaction

responsible for heat production in a self-heating material. The large gap volume of pelletized material can

lead to convective heat transport in the bulk if the furnace is equipped with a fan. In this case air flow in

the vicinity of the sample should be kept at a low level and the critical Frank-Kamenetskii parameter

should be corrected (see C.1.3) or the convective transport within the sample should be prevented by

further measures (e.g. finer mesh wire of the basket).

NOTE The critical ambient temperature (CAT) for the test portion in a basket heating teststest is not equal to the

CAT for spontaneous ignition in e.g., for example, large-scale storage. The critical size for spontaneous ignition (if

only heat transfer is considered) is directly related to the surface area-volume ratio of the self-heating specimen

where heat is produced distributed in the volume and heat is dissipated from the surface area only. The test sample

in a laboratory-size basket heating test has a very high surface area-volume ratio and has, consequently, a high CAT

compared to a larger specimen.
6 Tests for product classification
6.1 UN classification
6.1.1 General
[11]

The United Nations Globally Harmonized System of Classification and Labelling of Chemicals (GHS) )

is the international convention for hazard communication and labelling of gaseousgases and vapours,

solid and liquid substances as well asand mixtures. GHS defines limit values, classes and categories and

related measures in relation to the level of hazards during transportation, handling and storage.

[12]

The United Nations Manual of Test and Criteria (MTC) is prescribing) prescribes specific test

procedures in support of GHS.
6.1.2 Test method for self-heating substances – MTC Test N.4
[12]

Test N.4 is described in the United Nations Manual of Tests and Criteria (UN MTC), Part III, 33.3.1.6. ,

sometimes called the basket test.

This basket heating test determines the ability of a substance to undergo oxidative self-heating with

exposure of it to air at temperatures of 100 °C, 120 °C or 140 °C in a 25 mm or 100 mm wire mesh cube.

The N.4 test basket heating test is not intended for determination of self-heating kinetics but rather

prescribed to classify a material (e.g. solid recovered fuelsSRFs) as meeting the criteria for self-heating

[11]
set out by the GHS for hazard communication and labelling purposes.

The test set-up consists of a hot-air circulating oven, cubic sample containers with sides of 25 mm and

100 mm sides made of stainless-steel net with a mesh opening of 0,05 mm, and thermocouples of 0,3 mm

diameter for measurement of the oven temperature and the temperature of the centre of the sample. The

sample container is housed in a cubic container cover made from stainless-steel net with a mesh opening

of 0,60 mm, and slightly larger than the test container. To avoid the effect of air circulation, this cover is

installed in a second steel cage, made from a net with a mesh size of 0,595 mm and 150 mm × × 150 mm

× × 250 mm in size.
© ISO 2022 – All rights reserved 5
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ISO/TS 21911-2:2022(E)

The normal procedure is to start with a test at 140 °C with a 100-mm cube sample cube. The container is

housed in the cover and hung at the centre of the oven. The oven temperature is raised to 140 °C and kept

there for 24 h. A positive result is obtained if spontaneous ignition occurs or if the temperature of the

sample exceeds the oven temperature by 60 °C. If a negative result is obtained, no further test is

necessary.

If a positive result is obtained at 140 °C with a 100-mm cube sample cube, the substance is classified as a

self-heating substance and further testing shall be made to find the correct classification (see 6.1.3).

The bulk density tested can influence the test results. According EN 15188 theThe bulk density of the

sample shall be adjusted according to EN 15188 to the respective practical conditions (if known) and the

tested bulk density shall be recorded. The United Nations Manual of Tests and CriteriaThe MTC contains

no information on the bulk density to be tested.
6.1.3 Classification criteria -— GHS
[11]

The classification criteria are given in chapter 2.11.2 of the GHS. . The criteria are summarized in

Table 1.
Table 1 — Criteria in GHS for self-heating substances and mixtures
Category Criteria
1 A positive result is obtained in a test using 25 mm sample cube at 140 °C

21 A positive result is obtained in a test using 100 a 25-mm sample cube at 140 °C and a Deleted Cells

negative result is obtained in a test using a 25 mm cube sample at 140 °C and the substance

Split Cells
or mixture is to be packed in packages with a volume of more than 3 m ; or

b) a) A positive result is obtained in a test using a 100-mm sample cube at 140 °C and, a

negative result is obtained in a test using a 25-mm cube sample cube at 140 °C, a °C

and the substance or mixture is packed in packages with a volume of more than 3 m ;

b) A positive result is obtained in a test using a 100-mm cube sample cube at 140 °C, a

negative result is obtained in a test using a 25-mm sample cube at 140 °C, a positive

result is obtained in a test using a 100-mm sample cube at 120 °C and the substance or

mixture is to be packed in packages with a volume of more than 450 litres l; or

c) A positive result is obtained in a test using a 100-mm sample cube at 140 °C, a negative

result is obtained in a test using a 25-mm sample cube at 140 °C and a positive result

is obtained in a test using a 100-mm sample cube at 100 °C.

c) A positive result is obtained in a test using 100 mm sample cube at 140 °C and a

negative result is obtained in a test using a 25 mm cube sample at 140 °C and a
positive result is obtained in a test using a 100 mm cube sample at 100 °C.

NOTE Hazard Packing Groupspacking group classification is prescribed depending on flammability

[11]
characteristics of the material, see GHS, Table 32.1..
6.2 Classification criteria -— IMO

Handling guidelines and hazard classifications for all cargoes, including solid recovered fuelsSRFs,

transported onboard ocean vessels are specified by the International Maritime Organization (IMO) in the

[13]

International Maritime Solid Bulk Cargoes (IMSBC) Code. The Code is stipulating UN . This stipulates

the MTC Test N.4 to be used fo
...

TECHNICAL ISO/TS
SPECIFICATION 21911-2
First edition
Solid recovered fuels — Determination
of self-heating —
Part 2:
Basket heating tests
Combustibles solides de récupération — Détermination de l'auto-
échauffement —
Partie 2: Essais utilisant la méthode du point de croisement
PROOF/ÉPREUVE
Reference number
ISO/TS 21911-2:2022(E)
© ISO 2022
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ISO/TS 21911-2:2022(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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE © ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 21911-2:2022(E)
Contents Page

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

Introduction .................................................................................................................................................................................................................................v

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

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

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

4 Symbols .......................................................................................................................................................................................................................... 2

5 Basket heating tests .........................................................................................................................................................................................3

6 Tests for product classification ............................................................................................................................................................ 4

6.1 UN classification.................................................................................................................................................................................... 4

6.1.1 General ........................................................................................................................................................................................ 4

6.1.2 Test method for self-heating substances – MTC Test N.4 ............................................................... 4

6.1.3 Classification criteria — GHS .................................................................................................................................. 4

6.2 Classification criteria — IMO .................................................................................................................................................... 5

6.3 Applicability of MTC Test N.4 for solid recovered fuels ..................................................................................... 5

7 Tests for determination of reaction kinetics ......................................................................................................................... 6

7.1 General ........................................................................................................................................................................................................... 6

7.2 Isoperibolic test methods ............................................................................................................................................................. 6

7.2.1 General ........................................................................................................................................................................................ 6

7.2.2 Test procedure...................................................................................................................................................................... 6

7.2.3 Determination of reaction kinetics .................................................................................................................... 7

7.2.4 Applicability for solid recovered fuels ............................................................................................................ 7

7.3 Crossing-point method .................................................................................................................................................................... 8

7.3.1 General ........................................................................................................................................................................................ 8

7.3.2 Test procedure...................................................................................................................................................................... 8

7.3.3 Determination of reaction kinetics .................................................................................................................... 9

7.3.4 Applicability for solid recovered fuels ............................................................................................................ 9

7.4 Adiabatic hot storage tests ....................................................................................................................................................... 10

7.4.1 General ..................................................................................................................................................................................... 10

7.4.2 Test procedure................................................................................................................................................................... 10

7.4.3 Determination of reaction kinetics ................................................................................................................. 11

7.4.4 Applicability for solid recovered fuels .........................................................................................................12

8 Sample handling ................................................................................................................................................................................................12

8.1 General ........................................................................................................................................................................................................12

8.2 Sampling .................................................................................................................................................................................................... 13

8.3 Sample transport and storage ...............................................................................................................................................13

8.4 Sample preparation ......................................................................................................................................................................... 13

8.5 Sample disposal ..................................................................................................................................................................................13

9 Test report ...............................................................................................................................................................................................................13

Annex A (informative) Self-ignition behaviour of selected materials suitable to be used as

solid recovered fuels .....................................................................................................................................................................................15

Annex B (informative) Example of calculating kinetic parameters from crossing point

method tests ..........................................................................................................................................................................................................22

Annex C (normative) Use of data for calculations of critical conditions in storage .......................................25

Bibliography .............................................................................................................................................................................................................................30

iii
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ISO/TS 21911-2:2022(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 300, Solid recovered materials, including

solid recovered fuels, in collaboration with the European Committee for Standardization (CEN)

Technical Committee CEN/TC 343, Solid recovered fuels, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).
A list of all parts in the ISO 21911 series can be found on the ISO website.

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.
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ISO/TS 21911-2:2022(E)
Introduction

There is continuous global growth in trading and use of solid recovered fuels (SRFs). Therefore,

intensive investigations about the risk of fires within SRF production, handling and storing have been

conducted, see ÖNORM S 2098. Recommendations are given in ISO 21912.

Depending on the kind of input wastes, the treatment technology applied, the quality of the SRF

produced and the realized storage versions, SRFs can generate heat spontaneously by exothermic

biological, chemical and physical processes. The heat build-up can be significant in large storage

volumes if the heat conduction in the material is low. During some conditions the heat generation

can lead to pyrolysis and spontaneous ignition. The potential for self-heating varies considerably for

different types and qualities of SRF and it is important to be able to identify SRF fractions with high

heat generation potential to avoid fires in stored materials.

Avoiding fires throughout the production and supply chain will have positive consequences on the

acceptance of SRFs and the costs for insurance coverage,

Application of SRF standards and the use of dedicated standards for the determination of self-heating

will help to reduce the risk of fires and to develop tailor-made recommendations for SRF producers,

logistics providers, SRF users, equipment suppliers or manufacturers, consultants, authorities and

insurance providers.

As part of the determination and the assessment of risks for SRF, defined test methods and standards

are established or need to be developed. However, ageing and degradation due to handling and storage

of SRF in actual environments affects their characteristics, so safety margins should be established in

relation to actual analysis results.

Two intrinsically different types of test methods can be used to estimate the potential of self-heating;

a) In the isothermal calorimetry method described in ISO 21911-1 , the heat flow generated from the

test portion is measured directly.

b) In the basket heating tests described in this document, the temperature of the test portion is being

monitored and the critical ambient temperature (CAT), where the temperature of the test portion

does not increase significantly due to self-heating, is used for indirect assessment of self-heating.

These two methods are applied at different analysis temperature regimes. The operating temperature

for an isothermal calorimeter is normally in the range 5 °C to 90 °C, whereas basket heating tests are

conducted at higher analysis (oven) temperatures.

NOTE 1 These two types of test methods do not measure heat production from physical processes, such as

transport of moisture.

NOTE 2 It is likely that oxidation reactions taking place in the low respective high-temperature regimes for

SRFs are of different character and thus have different reaction rates and heat production rates. In such cases,

extrapolation of the data from a high-temperature test series can lead to non-conservative results and will

possibly not be applicable without taking the low-temperature reactions into account. In the general case of two

reactions with different activation energies, the high activation energy is “frozen out” at low temperatures and

[7]
the low activation energy reaction is “swamped” at higher temperatures .

Basket heating tests have been used traditionally for characterization of the tendency for spontaneous

ignition of predominantly coals, but also for other reactive organic materials, such as cottonseed meal,

[9]

bagasse and milk powder . The principle used in these types of test is to find the CAT for a self-heating

sample material of specific size and geometry.

There are several different methods described in the literature with different degrees of sophistication.

The variations span from simple pass and fail tests to more advanced tests from which data on reaction

[10]
rates can be extracted .
1) In preparation. Stage at the time of publication: ISO/DIS 21911-1:2022.
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ISO/TS 21911-2:2022(E)

Basket heating tests are useful for assessment of self-heating of SRFs. The test method selected can be

evaluated for its applicability based on the information given in this document.

A compilation of available basket heating test methods is given in this document. Guidance on the

suitability for application of these methods for tests with SRFs is provided.

Basic theory of the use of basket heating test data for calculations of critical conditions in storage is

provided in Annex C.

The test methods presented require representative samples for the conditions prevailing in the process

(e.g. of SRF storage). Sample preparation is necessary for this purpose. The methods presented are not

suitable for assessing the fire hazard caused by impurities (disturbing materials) as they occur mainly

in the input area and the first steps of SRF production.
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TECHNICAL SPECIFICATION ISO/TS 21911-2:2022(E)
Solid recovered fuels — Determination of self-heating —
Part 2:
Basket heating tests
1 Scope

This document gives guidance on basket heating tests for characterization of self-heating properties of

solid recovered fuels (SRFs).
This document includes:
a) a compilation of basket heating test methods;
b) guidance on the applicability and use of basket heating tests for SRF;

c) information on the application of basket heating test data for calculations of critical conditions in

storage.

Data on spontaneous heat generation determined using this document is only associated with the

specific quality and age of the sample material.

The information derived using this document is intended for use in quality control and in hazard and

risk assessments related to the procedures given in ISO 21912.
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 21646 , Solid recovered fuels — Sample preparation
ISO 21637:2020, Solid recovered fuels — Vocabulary
ISO 21645, Solid recovered fuels — Methods for sampling
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 21637 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
analysis temperature
temperature of the analysis environment, i.e. the oven temperature
2) In preparation. Stage at the time of publication: ISO/FDIS 21646:2022.
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ISO/TS 21911-2:2022(E)
3.2
Biot number

quotient of the convective heat transfer coefficient (between the sample boundary and the surrounding

air) and the conduction in the sample material normalized by the characteristic dimension of the test

basket
3.3
critical ambient temperature
CAT

ambient temperature (the analysis temperature (3.1) or the storage temperature) where the internal

temperature of the test portion or the stored material increases significantly [due to self-heating (3.4)]

Note 1 to entry: In EN 15188 the critical ambient temperature is defined as self-ignition temperature, T .

3.4
self-heating

rise in temperature in a material resulting from an exothermic reaction within the material

[SOURCE: ISO 13943:2017, 3.341, modified — “” domain omitted from definition.]

3.5
spontaneous ignition
ignition caused by an internal exothermic reaction
[SOURCE: ISO 13943:2017, 3.24, modified — Notes to entry removed.]
3.6
test sample
laboratory sample (3.7) after an appropriate preparation made by the laboratory

Note 1 to entry: The test sample is here typically a representative sample from a batch of solid recovered fuel.

[SOURCE: ISO 21637:2020, 3.84, modified — Note 1 to entry added.]
3.7
laboratory sample
sample delivered to a laboratory
[SOURCE: ISO 16559:2022, 3.120, modified — Note 1 to entry removed.]
4 Symbols
Symbol Quantity Typical unit
A pre-exponential factor in Arrhenius expression s
B dimensionless adiabatic temperature rise dimensionless
hL·
Bi Biot number, (Bi= ) dimensionless
c ambient oxygen concentration by volume fraction dimensionless
−1 −1
C specific heat capacity of the reaction products J kg K
−1 −1
C specific heat capacity of the bulk material J kg K
d diameter of body m
2 −1
D diffusion coefficient m s
E activation energy J mol
H gross calorific value J kg
−2 −1
h heat transfer coefficient W m K
−2 −1
h radiative amount on heat transfer coefficient W m K
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ISO/TS 21911-2:2022(E)
Symbol Quantity Typical unit
−2 −1
h convective amount on heat transfer coefficient W m K
L characteristic length m
n order of reaction dimensionless
P constant dimensionless
 heat generation term W m
Q heat of reaction J kg
Q heat of reaction by volume of oxygen J m
−1 −1
R universal gas constant J mol K
Ra Rayleight number dimensionless
S surface m
t time s
T temperature K
T ambient temperature K
T crossing point temperature K
T self-ignition temperature K
V volume m
x length coordinate m
δ Frank-Kamenetskii parameter dimensionless
δ critical value of δ dimensionless
ε dimensionless
 RT 
activation energy parameter, ε =
 
 a 
Ф oxygen diffusion parameter dimensionless
−1 −1
λ thermal conductivity of sample W m K
−1 −1
λ thermal conductivity of air W m K
air
ρ bulk density kg m
−2 −4
σ Stefan-Boltzmann coefficient W m K
5 Basket heating tests

The detailed test procedure varies between different isoperibolic and adiabatic methods. Isoperibolic

methods include that the test portion is put in a wire-mesh basket which is placed in an oven heated to

a fixed elevated temperature. The oven is equipped with a fan to keep the temperature uniform and to

[9] [10].

give a relatively large convective heat transfer coefficient to the test specimen For adiabatic tests,

the oven temperature is adjusted to the temperature at the centre of the sample, see EN 15188.

Basket heating tests are based on the Frank-Kamenetskii theory of criticality of a self-heating isotropic

slab (see Annex C) and have been developed to determine the reaction kinetics of the global reaction

responsible for heat production in a self-heating material. The large gap volume of pelletized material

can lead to convective heat transport in the bulk if the furnace is equipped with a fan. In this case

air flow in the vicinity of the sample should be kept at a low level and the critical Frank-Kamenetskii

parameter should be corrected (see C.1.3) or the convective transport within the sample should be

prevented by further measures (e.g. finer mesh wire of the basket).

NOTE The CAT for the test portion in a basket heating test is not equal to the CAT for spontaneous ignition

in, for example, large-scale storage. The critical size for spontaneous ignition (if only heat transfer is considered)

is directly related to the surface area-volume ratio of the self-heating specimen where heat is produced

distributed in the volume and heat is dissipated from the surface area only. The test sample in a laboratory-size

basket heating test has a very high surface area-volume ratio and, consequently, a high CAT compared to a larger

specimen.
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ISO/TS 21911-2:2022(E)
6 Tests for product classification
6.1 UN classification
6.1.1 General
[11]

The United Nations Globally Harmonized System of Classification and Labelling of Chemicals (GHS)

is the international convention for hazard communication and labelling of gases and vapours, solid and

liquid substances and mixtures. GHS defines limit values, classes and categories and related measures

in relation to the level of hazards during transportation, handling and storage.
[12]

The United Nations Manual of Test and Criteria (MTC) prescribes specific test procedures in support

of GHS.
6.1.2 Test method for self-heating substances – MTC Test N.4
[12]

Test N.4 is described in the MTC, Part III, 33.3.1.6, sometimes called the basket test.

This basket heating test determines the ability of a substance to undergo oxidative self-heating with

exposure to air at temperatures of 100 °C, 120 °C or 140 °C in a 25 mm or 100 mm wire mesh cube.

The N.4 test basket heating test is not intended for determination of self-heating kinetics but rather

[11]

prescribed to classify a material (e.g. SRFs) as meeting the criteria for self-heating set out by the GHS

for hazard communication and labelling purposes.

The test set-up consists of a hot-air circulating oven, cubic sample containers with sides of 25 mm and

100 mm made of stainless-steel net with a mesh opening of 0,05 mm, and thermocouples of 0,3 mm

diameter for measurement of the oven temperature and the temperature of the centre of the sample.

The sample container is housed in a cubic container cover made from stainless-steel net with a mesh

opening of 0,60 mm and slightly larger than the test container. To avoid the effect of air circulation,

this cover is installed in a second steel cage, made from a net with a mesh size of 0,595 mm and

150 mm × 150 mm × 250 mm in size.

The normal procedure is to start with a test at 140 °C with a 100-mm sample cube. The container is

housed in the cover and hung at the centre of the oven. The oven temperature is raised to 140 °C and

kept there for 24 h. A positive result is obtained if spontaneous ignition occurs or if the temperature

of the sample exceeds the oven temperature by 60 °C. If a negative result is obtained, no further test is

necessary.

If a positive result is obtained at 140 °C with a 100-mm sample cube, the substance is classified as a self-

heating substance and further testing shall be made to find the correct classification (see 6.1.3).

The bulk density tested can influence the test results. The bulk density of the sample shall be adjusted

according to EN 15188 to the respective practical conditions (if known) and the tested bulk density

shall be recorded. The MTC contains no information on the bulk density to be tested.

6.1.3 Classification criteria — GHS
[11]

The classification criteria are given in chapter 2.11.2 of the GHS . The criteria are summarized in

Table 1.
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ISO/TS 21911-2:2022(E)
Table 1 — Criteria in GHS for self-heating substances and mixtures
Category Criteria
1 A positive result is obtained in a test using a 25-mm sample cube at 140 °C

2 a) A positive result is obtained in a test using a 100-mm sample cube at 140 °C, a negative

result is obtained in a test using a 25-mm sample cube at 140 °C and the substance or

mixture is packed in packages with a volume of more than 3 m ; or

b) A positive result is obtained in a test using a 100-mm sample cube at 140 °C, a negative

result is obtained in a test using a 25-mm sample cube at 140 °C, a positive result is

obtained in a test using a 100-mm sample cube at 120 °C and the substance or mixture is

packed in packages with a volume of more than 450 l; or

c) A positive result is obtained in a test using a 100-mm sample cube at 140 °C, a negative

result is obtained in a test using a 25-mm sample cube at 140 °C and a positive result is

obtained in a test using a 100-mm sample cube at 100 °C.

NOTE Hazard packing group classification is prescribed depending on flammability characteristics of the

[11]
material, see GHS, Table 32.1.
6.2 Classification criteria — IMO

Handling guidelines and hazard classifications for all cargoes, including SRFs, transported onboard

ocean vessels are specified by the International Maritime Organization (IMO) in the International

[13]

Maritime Solid Bulk Cargoes (IMSBC) Code . This stipulates the MTC Test N.4 to be used for testing

but includes additional criteria for solid possessing hazards compared to the GHS criteria in Table 1, as

follows:

a) Does the material undergo dangerous self-heating when tested in accordance with Test N.4 in a

100-mm sample cube at 140 °C?

If yes, class 4.2 applies. Materials in this class are materials, other than pyrophoric materials, which, in

contact with air without energy supply, are liable to self-heating.

b) Does the material show a temperature increase of 10 °C or more when tested in accordance with

Test N.4 in a 100-mm sample cube at 140 °C?

If yes, test in a 100-mm sample cube at 100 °C and if temperature increase is 10 °C or more.

If yes, material hazardous in bulk (MHB) applies.
If no, neither class 4.2 nor MHB applies.
6.3 Applicability of MTC Test N.4 for solid recovered fuels
MTC Test N.4 will possibly be unsuitable for SRFs.

Experience from testing several SRF samples indicates that the CAT for this type of material in 1,0 l

basket heating tests can be lower than 140 °C, especially when various materials, including inert ones,

are present in the mixture, see Annex A and References [14] and [15].

The reasons that this test will possibly be unsuitable as a general test method for SRFs are as follows:

i) th
...