ISO 13909-4:2016

Hard coal and coke - Mechanical sampling - Part 4: Coal - Preparation of test samples

ISO 13909-4:2016 describes the preparation of samples of coal from the combination of primary increments to the preparation of samples for specific tests.

Houille et coke — Échantillonnage mécanique — Partie 4: Charbon — Préparation des échantillons pour essai

General Information

• Status: Published
• Publication Date: 22-Jun-2016
• ICS: 73.040 - Coals
• Technical Committee: ISO/TC 27/SC 4 - Sampling
• Drafting Committee: ISO/TC 27/SC 4 - Sampling
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 22-Jul-2025
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 13909-4:2025 - Coal and coke - Mechanical sampling - Part 4: Preparation of test samples of coal
• Effective Date: 27-May-2023
• Revises: ISO 13909-4:2001 - Hard coal and coke - Mechanical sampling - Part 4: Coal - Preparation of test samples
• Effective Date: 04-May-2013

Overview

ISO 13909-4:2016, "Hard coal and coke - Mechanical sampling - Part 4: Coal - Preparation of test samples", specifies procedures for preparing coal test samples from primary increments through to samples ready for specific laboratory tests. This part of the ISO 13909 series focuses on the constitution, reduction, division, mixing and drying of coal samples and provides guidance on equipment design, precision checks and bias testing. It is the 2016, corrected edition and forms part of a comprehensive set of standards for mechanical sampling of coal and coke.

Key Topics and Requirements

• Scope of sample preparation: Procedures from combining primary increments to producing test-specific samples (e.g., moisture, size analysis, general analysis).
• Precision objectives: Guidance on estimating overall precision and target preparation/testing variance (V_PT), with recommended V_PT levels of 0.2 or less for ash and moisture testing.
• Constitution of samples: Rules for combining increments by time- or mass-basis and for weighted combination of prepared samples.
• Division methods: Detailed mechanical and manual division techniques, including:
  • Mechanical dividers and falling-stream cutters (design, cutter velocity, mass of cut, cut interval)
  • Manual methods such as riffle, flattened-heap, and strip-mixing and splitting.
• Reduction and mixing: Use of reduction mills, mixing procedures and recommendations for obtaining representative subsamples.
• Sample drying and storage: Air-drying guidance and considerations for moisture-sensitive samples, including when to remove samples off-line to avoid moisture loss.
• Preparation for specific tests: Procedures for extracting moisture samples, preparing size-analysis samples, and making common samples for multiple tests.
• Equipment design and quality checks: Guidance on divider design, preparation systems, and provisions for checking precision and testing for bias.

Practical Applications

• Ensures representative, reproducible coal and coke test samples for quality control, commercial trading, regulatory compliance and research.
• Supports laboratory analysts preparing samples for moisture determination, ash analysis, size distribution and other routine tests.
• Useful for plant sampling engineers, QA/QC managers, coal traders and inspectors who must demonstrate defensible sampling and sample-preparation practices.

Who Uses This Standard

• Coal and coke producers and processors
• Analytical laboratories and testing facilities
• Power plants and industrial end-users requiring guaranteed fuel specifications
• Regulatory agencies, certification bodies and auditors
• Equipment manufacturers (dividers, reduction mills) designing preparation systems

Related Standards (applicable)

• ISO 13909 series: Part 1, Part 2, Part 3, Part 5, Part 6, Part 7, Part 8
• ISO 589 (Total moisture), ISO 3310-1 (Test sieves)

Keywords: ISO 13909-4, coal sample preparation, mechanical sampling, sample reduction, riffle divider, flattened-heap, moisture sample, sample precision, coal testing standards.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13909-4
Second edition
2016-07-01
Hard coal and coke — Mechanical
sampling —
Part 4:
Coal — Preparation of test samples
Houille et coke — Échantillonnage mécanique —
Partie 4: Charbon — Préparation des échantillons pour essai
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2016 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precision of sample preparation . 1
5 Constitution of a sample . 2
5.1 Introduction . 2
5.2 Combination of increments . 2
5.2.1 Time-basis sampling . . 2
5.2.2 Mass-basis sampling . 2
5.3 Combination of samples . 3
6 Division . 3
6.1 General . 3
6.2 Mechanical methods .10
6.2.1 General.10
6.2.2 Mass of cut .10
6.2.3 Interval between cuts .10
6.2.4 Division of individual increments .10
6.2.5 Division of samples .13
6.3 Manual methods .14
6.3.1 Riffle method .14
6.3.2 Flattened-heap method .15
6.3.3 Strip-mixing and splitting method .17
7 Reduction .19
7.1 General .19
7.2 Reduction mills .19
8 Mixing.19
9 Air-drying .19
10 Preparation of samples for specific tests .20
10.1 Types of test samples .20
10.2 Preparation of samples for determination of total moisture only .20
10.2.1 General.20
10.2.2 Storage .22
10.2.3 Sample reduction.22
10.2.4 Sample division .23
10.3 Preparation of samples for general analysis only .23
10.3.1 General.23
10.3.2 Air-drying .23
10.3.3 Reduction and division .23
10.4 Common samples .24
10.4.1 General.24
10.4.2 Extraction of moisture sample by mechanical division.25
10.4.3 Extraction of moisture sample by manual method .25
10.5 Preparation of size-analysis sample .26
10.6 Preparation of samples for other tests .27
11 Reserve sample .28
12 Design of equipment for preparation .28
12.1 Dividers .28
12.2 Design of cutters for falling-stream dividers .28
12.2.1 General.28
12.2.2 Cutter velocity .29
12.3 Preparation systems .29
12.3.1 General.29
12.3.2 Design criteria .29
12.3.3 Abnormal operation .30
12.4 Provision for checking for precision .30
12.5 Provision for testing for bias .30
Bibliography .31
iv © ISO 2016 – All rights reserved

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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 4,
Sampling.
This second edition cancels and replaces the first edition (ISO 13909-4:2001), which has been
technically revised.
ISO 13909 consists of the following parts, under the general title Hard coal and coke — Mechanical
sampling:
— Part 1: General introduction
— Part 2: Coal — Sampling from moving streams
— Part 3: Coal — Sampling from stationary lots
— Part 4: Coal — Preparation of test samples
— Part 5: Coke — Sampling from moving streams
— Part 6: Coke — Preparation of test samples
— Part 7: Methods for determining the precision of sampling, sample preparation and testing
— Part 8: Methods of testing for bias
Introduction
The objective of sample preparation is to prepare one or more test samples from the primary increments
for subsequent analysis. The requisite mass and particle size of the test sample depend on the test to be
carried out.
The process of sample preparation may involve constitution of samples, reduction, division, mixing and
drying, or all or a combination of these.
Primary increments may be prepared individually as test samples or combined to constitute samples
either as taken or after having been prepared by reduction and/or division. Samples may either be
prepared individually as test samples or combined on a weighted basis to constitute a further sample.
When difficulty in handling the coal or coals being sampled is expected at a particular stage in sample
preparation, or if there is a likelihood of losing moisture by evaporation, it is necessary to withdraw the
sample or increment from the on-line system at the stage immediately prior to the point of difficulty
and proceed off-line.
vi © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 13909-4:2016(E)
Hard coal and coke — Mechanical sampling —
Part 4:
Coal — Preparation of test samples
1 Scope
This part of ISO 13909 describes the preparation of samples of coal from the combination of primary
increments to the preparation of samples for specific tests.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 589, Hard coal — Determination of total moisture
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 13909-1, Hard coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-2, Hard coal and coke — Mechanical sampling — Part 2: Coal — Sampling from moving streams
ISO 13909-3, Hard coal and coke — Mechanical sampling — Part 3: Coal — Sampling from stationary lots
ISO 13909-7, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision
of sampling, sample preparation and testing
ISO 13909-8, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 apply.
4 Precision of sample preparation
From the equations given in ISO 13909-7, the estimated absolute value of the precision of the result
obtained for the lot at the 95 % confidence level, P , for sampling is given by Formula (1):
L
V
I
+V
PT
n
P = 2 (1)
L
m
where
P is the estimated overall precision of sampling, sample preparation and testing for the lot at
L
a 95 % confidence level, expressed as a percentage absolute;
V is the primary increment variance;
I
V is the preparation and testing variance for both off-line and on-line systems;
PT
n is the number of increments to be taken from a sub-lot;
m is the number of sub-lots in the lot.
The procedures given in this part of ISO 13909 are designed to achieve levels of V of 0,2 or less for
PT
both ash and moisture tests. Better levels are expected when using mechanical dividers.
For some preparation schemes, however, practical restrictions may prevent the preparation and testing
variance being as low as this. Under these circumstances, the user should decide whether to achieve
the desired overall precision by improving the preparation scheme or by dividing the lot into a greater
number of sub-lots.
The errors occurring in the various stages of preparation and analysis, expressed in terms of variance,
may be checked by the method given in ISO 13909-7.
5 Constitution of a sample
5.1 Introduction
Primary increments shall be taken in accordance with the procedures specified in ISO 13909-2 and
ISO 13909-3.
Individual increments are usually combined to form a sample. A single sample may be constituted
by combination of increments taken from a complete sub-lot or by combining increments taken from
individual parts of a sub-lot. Under some circumstances, e.g. size analysis or bias testing, the sample
consists of a single increment which is prepared and tested. Examples of the constitution of samples are
shown in Figure 1.
The procedures for increment combination (5.2) may vary according to whether the primary increments
were taken using a time-basis (5.2.1) or a mass-basis (5.2.2) sampling scheme.
Samples may also be prepared by the combination of other samples (see 5.3).
5.2 Combination of increments
5.2.1 Time-basis sampling
The mass of the primary increments shall be proportional to the flow rate at the time of sampling.
The primary increments may be combined into a sample either directly as taken or after having been
prepared individually to an appropriate stage by fixed-ratio division (see Clause 6).
5.2.2 Mass-basis sampling
If the primary increments are of almost uniform mass (see note), they may be combined into a sample,
either directly as taken or after having been prepared individually to an appropriate stage by fixed-
ratio division (see Clause 6).
NOTE Almost uniform mass has been achieved if the coefficient of variation of the increment masses is less
than 20 % and there is no significant correlation between the flow rate at the time of taking the increment and
the mass of the increment (see ISO 13909-2:2016, Annex A).
2 © ISO 2016 – All rights reserved

If the primary increments are not of almost uniform mass, they may only be combined into samples
after having been divided individually by fixed-mass division (see Clause 6).
a) Example 1
b) Example 2
Figure 1 — Examples of the constitution of samples
5.3 Combination of samples
When combining samples, the mass of the individual samples shall be directly proportional to the mass
of the coal from which they were taken in order to obtain a weighted mean of the quality characteristic
for the sub-lot. Prior to combination, division shall be by fixed-ratio division (see Clause 6).
6 Division
6.1 General
Division can be
— on-line mechanically, or
— off-line mechanically or manually.
Whenever possible, mechanical methods are preferred to manual methods to minimize human error.
Examples of dividers are shown in Figure 2.
Mechanical dividers are designed to extract one or more parts of the coal in a number of cuts of relatively
small mass. When the smallest mass of the divided sample that can be obtained in one pass through the
divider is greater than that required further passes through the same divider or subsequent passes
through further dividers may be necessary.
If coal does not run freely through a sample divider it may be necessary to air-dry the sample as
described in Clause 10 before sample division is undertaken.
Manual division is normally applied when mechanical methods would result in loss of integrity, e.g. loss
of moisture or size degradation. Manual methods may themselves result in bias, particularly if the mass
of coal to be divided is large.
a)  Rotating disc type b)  Rotating cone type

Key Key
1 feed 1 feed
2 reject 2 rotating cone
3 divided sample 3 adjustable slot
4 divided sample
5 reject
The material from a mixing container is fed by scrapers A stream of coal is allowed to fall onto a rotating cone;
to the centre of the dividing disc. From there it is the adjustable slot with lips in the cone allows the stream
discharged over the range of the disc through special to fall directly onto the sample receiver for part of each
clearing arms. The sample falls through adjustable revolution.
slots into chutes; the reject is carried away through a
cleaning conduit. The whole interior space is cleaned
by scrapers.
Figure 2 — Examples of dividers
4 © ISO 2016 – All rights reserved

c)  Container type
Key
1 feed
2 divided sample in rotating receivers
The coal stream flows to the hopper and this flow is intercepted by the top edge of a number of sector-shaped
containers dividing the flow into equal parts. Either the hopper or the containers may rotate. The machine can be
controlled for the following operations:
1)  for dividing;
2)  for collecting duplicates;
3)  for collecting replicates.
Figure 2 — Examples of dividers (continued)
d)  Chain bucket type
Key
1 feed
2 reject
3 divided sample
A chain mechanism as shown is equipped with buckets spread at equal pitch. The buckets travel in a single direction
or change direction at preset time periods. The bucket intercepts the free-falling coal stream to extract cuts which
discharge to sample as the bucket inverts.
Figure 2 — Examples of dividers (continued)
6 © ISO 2016 – All rights reserved

e)  Slotted-belt type
Key
1 slotted belt
2 feed
3 inclined chute
4 divided sample
5 reject
An endless belt as shown having slots spaced at equal pitch with lips that act as cutting edges passing below a feed
chute. The coal stream is fed to the chute and, as each slot passes through the stream, a cut is taken. The stream
which falls onto the plain part of the belt is carried to rejects.
Figure 2 — Examples of dividers (continued)
f)  Rotating plate type g)  Rotating chute type

Key Key
1 feed 1 feed
2 reject 2 reject
3 divided sample 3 divided sample
A flat plate with lipped slots spaced at equal pitch A hollow shaft with a rotating conical hopper and chute
rotates beneath a feed chute. Coal is fed into the which distributes the coal to one or more stationary
feed chute, then, falls onto the rotating plate to form cutters within a housing as shown. Each cutter is designed
a ribbon bed which is carried to the plough and to take cuts from the coal stream and the rejects are
discharged to rejects. As a slot passes through the discharged through the hollow shaft.
stream, a cut is taken.
Figure 2 — Examples of dividers (continued)
8 © ISO 2016 – All rights reserved

h)  Rotating cutter type i)  Cutter-chute type

Key Key
1 feed 1 feed
2 divided sample 2 divided sample
3 reject 3 reject
One or more rotating cutters take cuts from the coal The cutter-chute traverses the full coal stream and diverts a
stream as it is fed into the housing through a feed chute portion from the stream. When the coal stream is not being
as shown. Coal not collected by the rotating cutters is cut by the chute, it is deflected by the angle plate to reject.
directed to reject at the bottom of the housing.
Figure 2 — Examples of dividers (continued)
6.2 Mechanical methods
6.2.1 General
Mechanical sample division may be carried out on an individual increment or a sample which has been
crushed, if necessary, to an appropriate nominal top size. Division shall be either by fixed-mass division
or by fixed-ratio division subject to the conditions set out in 6.2.3.
NOTE The procedures described for fixed-ratio division are the simplest to implement. However, other
procedures can be used, provided that the mass of the divided sample is proportional to the mass of the feed, e.g.
the number of cuts could be kept constant by making the feed rate of each division proportional to the mass of
coal to be divided.
6.2.2 Mass of cut
The cuts shall be of uniform mass throughout the division of an increment. In order to achieve this, the
flow of coal to the divider shall be uniform and the cutting aperture shall be constant. The method of
feeding the divider shall be designed to minimize any segregation caused by the divider.
The cutting aperture shall be at least three times the nominal top size of the coal to be divided.
6.2.3 Interval between cuts
In order to minimize bias, the first cut for each mass to be divided shall be made at random within the
first cutting interval. For secondary and tertiary dividers, the cycle time shall not be evenly divisible
into the cycle time of the cutter which precedes it.
For fixed-mass division, the interval between taking cuts shall be varied proportionally to the mass of
coal to be divided so that divided samples having almost uniform mass are obtained.
For fixed-ratio division, the interval between taking cuts shall be constant, irrespective of the variations
of masses of coal to be divided, so that the divided-sample masses are proportional to the mass of the feed.
6.2.4 Division of individual increments
6.2.4.1 Number of cuts
The number of cuts for dividing an increment shall be determined as follows.
a) For fixed-mass division, the minimum number of cuts for dividing primary increments shall be
four. An equal number of cuts shall be taken from each primary increment in the sub-lot.
b) For fixed-ratio division, the minimum number of cuts for dividing a primary increment of mean
mass shall be four.
c) For subsequent division of individual divided primary increments, a minimum of one cut shall be
taken from each cut from the preceding division.
An example of a procedure for division of individual increments and subsequent sample division is
shown in Figure 3 a).
10 © ISO 2016 – All rights reserved

a) Example of division of individual increments (minimum number of cuts)
Figure 3 — Examples of procedures for division of increments and samples
b)  Example of two-stage division of individual increments
Figure 3 — Examples of procedures for division of increments and samples (continued)
6.2.4.2 Minimum mass of divided increment
The minimum mass of a divided increment shall be such that the combined masses of all the divided
increments in the sub-lot shall, at each stage, be greater than the mass given in Table 1 corresponding
to the purpose for which the sample has been taken and the nominal top size. If the increment masses
are too low to satisfy this requirement, the divided increment shall be crushed prior to further division
(e.g. as shown in Figure 3 b).
12 © ISO 2016 – All rights reserved

6.2.5 Division of samples
6.2.5.1 Number of cuts
The sample constituted from all increments, or divided increments, shall be divided by taking a
minimum of 60 cuts.
NOTE If, during preparation, the sample is thoroughly mixed and it can be established that the required
precision can be achieved, the number can be reduced to 20.
If the mass is too low, an alternative manual method of division should be used.
6.2.5.2 Minimum mass of divided samples
For most parameters, particularly size analysis and those that are particle-size related, the precision
of the result is limited by the ability of the sample to represent all the particle sizes in the mass of coal
being sampled.
The minimum mass of divided samples is dependent on the nominal top size of the coal, the precision
required for the parameter concerned and the relationship of that parameter to particle size. The
attainment of the required minimum mass after division will not, in itself, guarantee the required
precision, because division precision is also dependent on the number of cuts taken during division
(see 6.2.4.1 and 6.2.5.1).
Values for the minimum mass of divided samples for general analysis to reduce the variance due to
the particulate nature of the coal to 0,01, corresponding to a precision of 0,2 % with regard to ash, are
[1]
given in Table 1 (see CSIRO report ). Table 1 gives the corresponding minimum masses of divided
samples for total moisture analysis, which are approximately 20 % of the minimum masses for general
analysis, subject to an absolute minimum of 0,65 kg. Values for the minimum mass of divided samples
for size analysis are given in Table 1 for division precisions of 1 % and 2 % respectively. These masses
have been calculated on the basis of the precision of the determination of oversize, i.e. the coal above
the normal top size. The precision for other size fractions will normally be better than this. Note that,
in each case, the overall division precision is determined by the sum of the division variances for each
sample-division stage.
The minimum mass of divided samples, m , for other desired levels of precision may be calculated from
S
Formula (2):
 
P
mm=   (2)
SS,0
 
P
 R 
where
m is the minimum mass of sample after division specified in Table 1 for a given nominal top size;
S,0
P is the precision for a given di
...

INTERNATIONAL ISO
STANDARD 13909-4
Second edition
2016-07-01
Corrected version
2016-11-01
Hard coal and coke — Mechanical
sampling —
Part 4:
Coal — Preparation of test samples
Houille et coke — Échantillonnage mécanique —
Partie 4: Charbon — Préparation des échantillons pour essai
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2016 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precision of sample preparation . 1
5 Constitution of a sample . 2
5.1 Introduction . 2
5.2 Combination of increments . 2
5.2.1 Time-basis sampling . . 2
5.2.2 Mass-basis sampling . 2
5.3 Combination of samples . 3
6 Division . 3
6.1 General . 3
6.2 Mechanical methods .10
6.2.1 General.10
6.2.2 Mass of cut .10
6.2.3 Interval between cuts .10
6.2.4 Division of individual increments .10
6.2.5 Division of samples .13
6.3 Manual methods .14
6.3.1 Riffle method .14
6.3.2 Flattened-heap method .15
6.3.3 Strip-mixing and splitting method .17
7 Reduction .18
7.1 General .18
7.2 Reduction mills .18
8 Mixing.18
9 Air-drying .18
10 Preparation of samples for specific tests .19
10.1 Types of test samples .19
10.2 Preparation of samples for determination of total moisture only .19
10.2.1 General.19
10.2.2 Storage .21
10.2.3 Sample reduction.21
10.2.4 Sample division .22
10.3 Preparation of samples for general analysis only .22
10.3.1 General.22
10.3.2 Air-drying .22
10.3.3 Reduction and division .22
10.4 Common samples .23
10.4.1 General.23
10.4.2 Extraction of moisture sample by mechanical division.24
10.4.3 Extraction of moisture sample by manual method .24
10.5 Preparation of size-analysis sample .25
10.6 Preparation of samples for other tests .26
11 Reserve sample .27
12 Design of equipment for preparation .27
12.1 Dividers .27
12.2 Design of cutters for falling-stream dividers .27
12.2.1 General.27
12.2.2 Cutter velocity .28
12.3 Preparation systems .28
12.3.1 General.28
12.3.2 Design criteria .28
12.3.3 Abnormal operation .29
12.4 Provision for checking for precision .29
12.5 Provision for testing for bias .29
Bibliography .30
iv © ISO 2016 – All rights reserved

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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 27, Solid mineral fuels, Subcommittee SC 4,
Sampling.
This second edition cancels and replaces the first edition (ISO 13909-4:2001), which has been
technically revised.
ISO 13909 consists of the following parts, under the general title Hard coal and coke — Mechanical
sampling:
— Part 1: General introduction
— Part 2: Coal — Sampling from moving streams
— Part 3: Coal — Sampling from stationary lots
— Part 4: Coal — Preparation of test samples
— Part 5: Coke — Sampling from moving streams
— Part 6: Coke — Preparation of test samples
— Part 7: Methods for determining the precision of sampling, sample preparation and testing
— Part 8: Methods of testing for bias
This corrected version of ISO 13909-4:2016 incorporates the following correction:
— the wrong Figure 6 has been replaced by the correct one.
Introduction
The objective of sample preparation is to prepare one or more test samples from the primary increments
for subsequent analysis. The requisite mass and particle size of the test sample depend on the test to be
carried out.
The process of sample preparation may involve constitution of samples, reduction, division, mixing and
drying, or all or a combination of these.
Primary increments may be prepared individually as test samples or combined to constitute samples
either as taken or after having been prepared by reduction and/or division. Samples may either be
prepared individually as test samples or combined on a weighted basis to constitute a further sample.
When difficulty in handling the coal or coals being sampled is expected at a particular stage in sample
preparation, or if there is a likelihood of losing moisture by evaporation, it is necessary to withdraw the
sample or increment from the on-line system at the stage immediately prior to the point of difficulty
and proceed off-line.
vi © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 13909-4:2016(E)
Hard coal and coke — Mechanical sampling —
Part 4:
Coal — Preparation of test samples
1 Scope
This part of ISO 13909 describes the preparation of samples of coal from the combination of primary
increments to the preparation of samples for specific tests.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 589, Hard coal — Determination of total moisture
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 13909-1, Hard coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-2, Hard coal and coke — Mechanical sampling — Part 2: Coal — Sampling from moving streams
ISO 13909-3, Hard coal and coke — Mechanical sampling — Part 3: Coal — Sampling from stationary lots
ISO 13909-7, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision
of sampling, sample preparation and testing
ISO 13909-8, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 apply.
4 Precision of sample preparation
From the equations given in ISO 13909-7, the estimated absolute value of the precision of the result
obtained for the lot at the 95 % confidence level, P , for sampling is given by Formula (1):
L
V
I
+V
PT
n
P = 2 (1)
L
m
where
P is the estimated overall precision of sampling, sample preparation and testing for the lot at
L
a 95 % confidence level, expressed as a percentage absolute;
V is the primary increment variance;
I
V is the preparation and testing variance for both off-line and on-line systems;
PT
n is the number of increments to be taken from a sub-lot;
m is the number of sub-lots in the lot.
The procedures given in this part of ISO 13909 are designed to achieve levels of V of 0,2 or less for
PT
both ash and moisture tests. Better levels are expected when using mechanical dividers.
For some preparation schemes, however, practical restrictions may prevent the preparation and testing
variance being as low as this. Under these circumstances, the user should decide whether to achieve
the desired overall precision by improving the preparation scheme or by dividing the lot into a greater
number of sub-lots.
The errors occurring in the various stages of preparation and analysis, expressed in terms of variance,
may be checked by the method given in ISO 13909-7.
5 Constitution of a sample
5.1 Introduction
Primary increments shall be taken in accordance with the procedures specified in ISO 13909-2 and
ISO 13909-3.
Individual increments are usually combined to form a sample. A single sample may be constituted
by combination of increments taken from a complete sub-lot or by combining increments taken from
individual parts of a sub-lot. Under some circumstances, e.g. size analysis or bias testing, the sample
consists of a single increment which is prepared and tested. Examples of the constitution of samples are
shown in Figure 1.
The procedures for increment combination (5.2) may vary according to whether the primary increments
were taken using a time-basis (5.2.1) or a mass-basis (5.2.2) sampling scheme.
Samples may also be prepared by the combination of other samples (see 5.3).
5.2 Combination of increments
5.2.1 Time-basis sampling
The mass of the primary increments shall be proportional to the flow rate at the time of sampling.
The primary increments may be combined into a sample either directly as taken or after having been
prepared individually to an appropriate stage by fixed-ratio division (see Clause 6).
5.2.2 Mass-basis sampling
If the primary increments are of almost uniform mass (see note), they may be combined into a sample,
either directly as taken or after having been prepared individually to an appropriate stage by fixed-
ratio division (see Clause 6).
NOTE Almost uniform mass has been achieved if the coefficient of variation of the increment masses is less
than 20 % and there is no significant correlation between the flow rate at the time of taking the increment and
the mass of the increment (see ISO 13909-2:2016, Annex A).
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If the primary increments are not of almost uniform mass, they may only be combined into samples
after having been divided individually by fixed-mass division (see Clause 6).
a) Example 1
b) Example 2
Figure 1 — Examples of the constitution of samples
5.3 Combination of samples
When combining samples, the mass of the individual samples shall be directly proportional to the mass
of the coal from which they were taken in order to obtain a weighted mean of the quality characteristic
for the sub-lot. Prior to combination, division shall be by fixed-ratio division (see Clause 6).
6 Division
6.1 General
Division can be
— on-line mechanically, or
— off-line mechanically or manually.
Whenever possible, mechanical methods are preferred to manual methods to minimize human error.
Examples of dividers are shown in Figure 2.
Mechanical dividers are designed to extract one or more parts of the coal in a number of cuts of relatively
small mass. When the smallest mass of the divided sample that can be obtained in one pass through the
divider is greater than that required further passes through the same divider or subsequent passes
through further dividers may be necessary.
If coal does not run freely through a sample divider it may be necessary to air-dry the sample as
described in Clause 10 before sample division is undertaken.
Manual division is normally applied when mechanical methods would result in loss of integrity, e.g. loss
of moisture or size degradation. Manual methods may themselves result in bias, particularly if the mass
of coal to be divided is large.
a)  Rotating disc type b)  Rotating cone type

Key Key
1 feed 1 feed
2 reject 2 rotating cone
3 divided sample 3 adjustable slot
4 divided sample
5 reject
The material from a mixing container is fed by scrapers A stream of coal is allowed to fall onto a rotating cone;
to the centre of the dividing disc. From there it is the adjustable slot with lips in the cone allows the stream
discharged over the range of the disc through special to fall directly onto the sample receiver for part of each
clearing arms. The sample falls through adjustable revolution.
slots into chutes; the reject is carried away through a
cleaning conduit. The whole interior space is cleaned
by scrapers.
Figure 2 — Examples of dividers
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c)  Container type
Key
1 feed
2 divided sample in rotating receivers
The coal stream flows to the hopper and this flow is intercepted by the top edge of a number of sector-shaped
containers dividing the flow into equal parts. Either the hopper or the containers may rotate. The machine can be
controlled for the following operations:
1)  for dividing;
2)  for collecting duplicates;
3)  for collecting replicates.
Figure 2 — Examples of dividers (continued)
d)  Chain bucket type
Key
1 feed
2 reject
3 divided sample
A chain mechanism as shown is equipped with buckets spread at equal pitch. The buckets travel in a single direction
or change direction at preset time periods. The bucket intercepts the free-falling coal stream to extract cuts which
discharge to sample as the bucket inverts.
Figure 2 — Examples of dividers (continued)
6 © ISO 2016 – All rights reserved

e)  Slotted-belt type
Key
1 slotted belt
2 feed
3 inclined chute
4 divided sample
5 reject
An endless belt as shown having slots spaced at equal pitch with lips that act as cutting edges passing below a feed
chute. The coal stream is fed to the chute and, as each slot passes through the stream, a cut is taken. The stream
which falls onto the plain part of the belt is carried to rejects.
Figure 2 — Examples of dividers (continued)
f)  Rotating plate type g)  Rotating chute type

Key Key
1 feed 1 feed
2 reject 2 reject
3 divided sample 3 divided sample
A flat plate with lipped slots spaced at equal pitch A hollow shaft with a rotating conical hopper and chute
rotates beneath a feed chute. Coal is fed into the which distributes the coal to one or more stationary
feed chute, then, falls onto the rotating plate to form cutters within a housing as shown. Each cutter is designed
a ribbon bed which is carried to the plough and to take cuts from the coal stream and the rejects are
discharged to rejects. As a slot passes through the discharged through the hollow shaft.
stream, a cut is taken.
Figure 2 — Examples of dividers (continued)
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h)  Rotating cutter type i)  Cutter-chute type

Key Key
1 feed 1 feed
2 divided sample 2 divided sample
3 reject 3 reject
One or more rotating cutters take cuts from the coal The cutter-chute traverses the full coal stream and diverts a
stream as it is fed into the housing through a feed chute portion from the stream. When the coal stream is not being
as shown. Coal not collected by the rotating cutters is cut by the chute, it is deflected by the angle plate to reject.
directed to reject at the bottom of the housing.
Figure 2 — Examples of dividers (continued)
6.2 Mechanical methods
6.2.1 General
Mechanical sample division may be carried out on an individual increment or a sample which has been
crushed, if necessary, to an appropriate nominal top size. Division shall be either by fixed-mass division
or by fixed-ratio division subject to the conditions set out in 6.2.3.
NOTE The procedures described for fixed-ratio division are the simplest to implement. However, other
procedures can be used, provided that the mass of the divided sample is proportional to the mass of the feed, e.g.
the number of cuts could be kept constant by making the feed rate of each division proportional to the mass of
coal to be divided.
6.2.2 Mass of cut
The cuts shall be of uniform mass throughout the division of an increment. In order to achieve this, the
flow of coal to the divider shall be uniform and the cutting aperture shall be constant. The method of
feeding the divider shall be designed to minimize any segregation caused by the divider.
The cutting aperture shall be at least three times the nominal top size of the coal to be divided.
6.2.3 Interval between cuts
In order to minimize bias, the first cut for each mass to be divided shall be made at random within the
first cutting interval. For secondary and tertiary dividers, the cycle time shall not be evenly divisible
into the cycle time of the cutter which precedes it.
For fixed-mass division, the interval between taking cuts shall be varied proportionally to the mass of
coal to be divided so that divided samples having almost uniform mass are obtained.
For fixed-ratio division, the interval between taking cuts shall be constant, irrespective of the variations
of masses of coal to be divided, so that the divided-sample masses are proportional to the mass of the feed.
6.2.4 Division of individual increments
6.2.4.1 Number of cuts
The number of cuts for dividing an increment shall be determined as follows.
a) For fixed-mass division, the minimum number of cuts for dividing primary increments shall be
four. An equal number of cuts shall be taken from each primary increment in the sub-lot.
b) For fixed-ratio division, the minimum number of cuts for dividing a primary increment of mean
mass shall be four.
c) For subsequent division of individual divided primary increments, a minimum of one cut shall be
taken from each cut from the preceding division.
An example of a procedure for division of individual increments and subsequent sample division is
shown in Figure 3 a).
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a) Example of division of individual increments (minimum number of cuts)
Figure 3 — Examples of procedures for division of increments and samples
b)  Example of two-stage division of individual increments
Figure 3 — Examples of procedures for division of increments and samples (continued)
6.2.4.2 Minimum mass of divided increment
The minimum mass of a divided increment shall be such that the combined masses of all the divided
increments in the sub-lot shall, at each stage, be greater than the mass given in Table 1 corresponding
to the purpose for which the sample has been taken and the nominal top size. If the increment masses
are too low to satisfy this requirement, the divided increment shall be crushed prior to further division
(e.g. as shown in Figure 3 b).
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6.2.5 Division of samples
6.2.5.1 Number of cuts
The sample constituted from all increments, or divided increments, shall be divided by taking a
minimum of 60 cuts.
NOTE If, during preparation, the sample is thoroughly mixed and it can be established that the required
precision can be achieved, the number can be reduced to 20.
If the mass is too low, an alternative manual method of division should be used.
6.2.5.2 Minimum mass of divided samples
For most parameters, particularly size analysis and those that are particle-size related, the precision
of the result is limited by the ability of the sample to represent all the particle sizes in the mass of coal
being sampled.
The minimum mass of divided samples is dependent on the nominal top size of the coal, the precision
required for the parameter concerned and the relationship of that parameter to particle size. The
attainment of the required minimum mass after division will not, in itself, guarantee the required
precision, because division precision is also dependent on the number of cuts taken during division
(see 6.2.4.1 and 6.2.5.1).
Values for the minimum mass of divided samples for general analysis to reduce the variance due to
the particulate nature of the coal to 0,01, corresponding to a precision of 0,2 % with regard to ash, are
[1]
given in Table 1 (see CSIRO report ). Table 1 gives the corresponding minimum masses of divided
samples for total moisture analysis, which are approximately 20 % of the minimum masses for general
analysis, subject to an absolute minimum of 0,65 kg. Values for the minimum mass of divided samples
for size analysis are given in Table 1 for division precisions of 1 % and 2 % respectively. These masses
have been calculated on the basis of the precision of the determination of oversize, i.e. the coal above
the normal top size. The precision for other size fractions will normally be better than this. Note that,
in each case, the overall division precision is determined by the sum of the division variances for each
sample-division stage.
The minimum mass of divided samples, m , for other desired levels of precision may be calculated from
S
Formula (2):
 
P
mm=   (2)
SS,0
 
P
 R 
...