ISO 13909-3:2025

International
Standard
ISO 13909-3
Third edition
Coal and coke — Mechanical
2025-07
sampling —
Part 3:
Sampling of coal from stationary lots
Charbon et coke — Échantillonnage mécanique —
Partie 3: Échantillonnage du charbon sur lots statiques
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Establishing a sampling scheme. 2
4.1 General .2
4.2 Design of the sampling scheme .2
4.2.1 Material to be sampled .2
4.2.2 Division of lots .2
4.2.3 Precision of sampling .2
4.2.4 Bias of sampling .3
4.3 Precision of results .3
4.3.1 Precision and total variance .3
4.3.2 Primary increment variance .4
4.3.3 Preparation and testing variance .4
4.3.4 Number of sub-lots and number of increments per sub-lot .4
4.4 Minimum mass of sample .6
4.5 Mass of primary increment .8
4.6 Size analysis .8
5 Methods of sampling from wagons, barges and ships . 9
5.1 General .9
5.2 Number of increments and sub-lots .9
5.2.1 General analysis and moisture samples .9
5.2.2 Common sample .9
5.3 Taking the increments .9
5.4 Distribution of increments.10
5.4.1 Wagons .10
5.4.2 Barges.10
5.4.3 Ships .10
5.4.4 Random selection of increments .10
6 Methods of sampling from stockpiles .11
7 Sampling equipment — mechanical auger .11
8 Handling and storage of samples .13
9 Sample preparation . 14
10 Minimization of bias . . 14
10.1 Causes of bias .14
10.2 Checking for precision and bias .14
11 Verification .15
Bibliography .16

iii
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
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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this may not represent the latest information, which may be obtained from the patent database available at
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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 27, Coal and coke, Subcommittee SC 4, Sampling.
This third edition cancels and replaces the second edition (ISO 13909-3:2016), which has been technically
revised.
The main changes are as follows:
— the title was updated to align with the ISO 13909 series;
— the scope was updated;
— several aspects of the sampling were updated to state of the art.
A list of all parts in the ISO 13909 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.

iv
International Standard ISO 13909-3:2025(en)
Coal and coke — Mechanical sampling —
Part 3:
Sampling of coal from stationary lots
1 Scope
This document specifies procedures for the mechanical sampling of coal from stationary lots, for example,
from wagons, barges, ships and stockpiles. These procedures are to be used when it is not possible to sample
the lots during loading or discharge according to ISO 13909-2. Procedures for sample preparation are given
in ISO 13909-4.
This document is applicable to mechanical sampling from stationary coal lots, to obtain samples from which
test samples for the determination of moisture, and for general analysis including physical and chemical
tests, can be prepared in accordance with the requirements and recommendations set out in ISO 13909-4.
In this document, the principles and procedures for designing a sampling scheme are given, together with
typical examples of applications; in addition, practices for the execution of sampling in different sampling
situations are described. The methods described are limited to those on which it is possible to conduct a test
for bias.
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 13909-1, Coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-2, Coal and coke — Mechanical sampling — Part 2: Sampling of coal from moving streams
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 13909-7:2025, Coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of
sampling, sample preparation and testing
ISO 13909-8, 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.
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/

4 Establishing a sampling scheme
4.1 General
The general procedure for establishing a sampling scheme is as follows.
a) Define the quality parameters to be determined and the types of samples required.
b) Define the lot.
c) Define or assume the precision required (see 4.3.1).
d) Determine the method of combining the increments into samples and the method of sample preparation
(see ISO 13909-4).
e) Determine or assume the variability of the coal (see 4.3.2) and the variance of preparation and testing
(see 4.3.3). Methods for determining variability and variance of preparation and testing are given in
ISO 13909-7.
f) Establish the number of sub-lots and the number of increments per sub-lot required to attain the desired
precision (see 4.3.4).
g) Decide upon the sampling interval, in tonnes.
h) Ascertain the nominal top size of coal for the purpose of determining the minimum mass of sample (see
4.4 and Table 1).
The nominal top size may initially be ascertained by consulting the consignment details, or by visual
estimation, and may be verified, if necessary, by preliminary test work.
i) Determine the minimum average increment mass (see 4.5).
4.2 Design of the sampling scheme
4.2.1 Material to be sampled
The first stage in the design of the scheme is to identify the coal to be sampled. Samples may be required
for technical evaluation, process control, quality control and for commercial reasons by both the producer
and the customer. It is essential to ascertain exactly at what stage in the coal-handling process the sample
is required and, as far as practicable, to design the scheme accordingly. In some instances, however, it
may prove impracticable to obtain samples at the preferred points and, in such cases, a more practicable
alternative is required.
4.2.2 Division of lots
A lot may be sampled as a whole or as a series of sub-lots, e.g. coal despatched or delivered over a period of
time, a ship load, a train load, a wagon load or coal produced in a certain period (e.g. a shift).
It can be necessary to divide a lot into a number of sub-lots in order to improve the precision of the results.
For lots sampled over long periods, it can be expedient to divide the lot into a series of sub-lots, obtaining a
sample for each.
4.2.3 Precision of sampling
After the desired sample precision has been selected, the number of sub-lots and the minimum number
of increments per sub-lot collected shall be determined as described in 4.3.4, and the average mass of the
primary increments shall be determined as described in 4.5.
For single lots, the quality variation shall be assumed as the worst case (see 4.3.2 and 4.3.3). The precision of
sampling achieved may be measured using the procedure of replicate sampling (see ISO 13909-7).

At the start of regular sampling of unknown coals, the worst-case quality variation shall be assumed, in
accordance with 4.3.2, 4.3.3 and 4.3.4. When sampling is in operation, a check may be carried out to confirm
that the desired precision has been achieved, using the procedures described in ISO 13909-7.
If any subsequent change in precision is required, the number of sub-lots and of increments shall be changed
as determined in 4.3.4 and the precision attained shall be rechecked. The precision shall also be checked
if there is any reason to suppose that the variability of the coal being sampled has increased. The number
of increments determined in 4.3.4 applies to the precision of the result when the sampling errors are large
relative to the testing errors, e.g. for moisture content.
4.2.4 Bias of sampling
It is of particular importance in sampling to ensure, as far as possible, that the parameter to be measured is
not altered by the sampling and sample preparation process or by subsequent storage prior to testing. This
can require, in some circumstances, a limit on the minimum mass of primary increment (see 4.5).
When collecting samples for moisture determination from lots over an extended period, it can be necessary
to limit the standing time of samples by dividing the lot into a number of sub-lots (see 4.3.4.1).
When a coal sampling scheme is implemented, it shall be checked for bias in accordance with the methods
given in ISO 13909-8.
4.3 Precision of results
4.3.1 Precision and total variance
In all methods of sampling, sample preparation and analysis, errors are incurred and the experimental
results obtained from such methods for any given parameter will deviate from the true value of that
parameter. While the absolute deviation of a single result from the “true” value cannot be determined, it is
possible to make an estimate of the precision of the experimental results. This is the closeness with which
the results of a series of measurements made on the same coal agree among themselves.
It is possible to design a sampling scheme by which, in principle, an arbitrary level of precision can be
achieved.
The required overall precision for a lot is normally agreed between the parties concerned. In the absence of
such agreement, a value of one tenth of the ash may be assumed up to 10 % ash, subject to a maximum of 1 %
absolute for ash above 10 %.
The theory of the estimation of precision is discussed in ISO 13909-7. The following formula is derived:
V
I
+V
PT
n
P =2 (1)
L
m
where
P is the estimated index of overall precision of sampling, sample preparation and testing for
L
the lot at a 95 % confidence level, expressed as percentage absolute;
V is the primary increment variance;
I
n is the number of increments taken per sub-lot;
m is the number of sub-lots in the lot;
V is the preparation and testing variance.
PT
If the quality of a coal of a type not previously sampled is required, then in order to devise a sampling
scheme, assumptions have to be made about the variability (see 4.3.2). The precision actually achieved for a
particular lot by the scheme devised can be measured by the procedures given in ISO 13909-7.

4.3.2 Primary increment variance
The primary increment variance, V , depends upon the type and nominal top size of coal, the degree of pre-
I
treatment and mixing, the absolute value of the parameter to be determined and the mass of increment taken.
The number of increments required for the general-analysis sample and the moisture sample shall be
calculated separately using the relevant values of increment variance and the desired precision. If a common
sample is required, the number of increments required for that sample shall be the greater of the numbers
calculated for the general analysis sample and the moisture sample respectively.
NOTE For many coals, the increment variance for ash is higher than that for moisture and hence, for the same
precision, the number of increments required for the general analysis sample is adequate for the moisture sample and
for the common sample.
The value of the primary increment variance, V , required for the calculation of the precision using
I
Formula (1) can be obtained by either:
a) direct determination on the coal to be sampled using one of the methods described in ISO 13909-7; or
b) assuming a value determined for a similar coal from a similar coal handling and sampling system.
If neither of these values is available, a value of V = 5 for ash of unwashed and blended coals and V = 3 for
I I
the ash of washed coals can be assumed initially and checked, after the sampling has been carried out, using
one of the methods described in ISO 13909-7.
4.3.3 Preparation and testing variance
The value of the preparation and testing variance, V , required for the calculation of the precision using
PT
Formula (1) can be obtained by either:
a) direct determination on the coal to be sampled using one of the methods described in ISO 13909-7; or
b) assuming a value determined for a similar coal from a similar sample preparation scheme.
If neither of these values is available, a value of 0,2 with regard to ash can be assumed initially and checked,
after the preparation and testing has been carried out, using one of the methods described in ISO 13909-7.
4.3.4 Number of sub-lots and number of increments per sub-lot
4.3.4.1 General
The number of increments taken from a lot in order to achieve a particular precision is a function of the
variability of the quality of the coal in the lot, irrespective of the mass of the lot. The lot may be sampled as
a whole, resulting in one sample, or divided into a number of sub-lots resulting in a sample from each. Such
division may be necessary in order to achieve the required precision, and the necessary number of sub-lots
shall be calculated using the procedure given in 4.3.4.2.
Another important reason for dividing the lot is to maintain the integrity of the sample, i.e. to avoid bias
after taking the increment, particularly in order to minimize loss of moisture due to standing. The need to
do this division is dependent on factors such as the time taken to collect samples, ambient temperature and
humidity conditions, the ease of keeping the sample in sealed containers during collection and the particle
size of the coal. It is recommended that, if moisture loss is suspected, a bias test be carried out to compare
the quality of a reference sample immediately after extraction with the sample after standing for the normal
time. If bias is found, the sample standing time shall be reduced by collecting samples more frequently, i.e.
increasing the number of sub-lots.
There can be other practical reasons for dividing the lot, such as:
a) for convenience when sampling over a long period;
b) to keep sample masses manageable.

The designer of a sampling scheme shall cater for the worst case anticipated and will then tend to use a higher
value for V than may actually occur when the scheme is in operation. On implementing a new sampling
I
scheme, a check on the actual precision being achieved shall be carried out using the methods described in
ISO 13909-7. This may be necessary to achieve the required precision, in which case, the number of sub-lots
and increments shall be recalculated using the procedures given in 4.3.4.2.
4.3.4.2 Calculation
...