ISO 18283:2022

Coal and coke - Manual sampling

This document provides the basic terms used in manual sampling of coal and coke and describes the general principles of sampling. It provides procedures and requirements for establishing a manual sampling scheme, methods of manual sampling, sampling equipment, handling and storage of samples, sample preparation and a sampling report, and applies to manual sampling during the transfer of coal or coke. Guidelines for manual sampling in stationary situations are given in Annex B, but this method of sampling does not provide a representative test sample and the sampling report shall state this. This document covers sampling of brown coals and lignites, but does not include sampling from coal seams, for which guidance is given in ISO 14180. Mechanical sampling of coal and coke is covered in ISO 13909.

Houille et coke — Échantillonnage manuel

General Information

• Status: Published
• Publication Date: 20-Mar-2022
• ICS: 73.040 - Coals
• ICS: 75.160.10 - Solid fuels
• Technical Committee: ISO/TC 27/SC 4 - Sampling
• Drafting Committee: ISO/TC 27/SC 4/WG 7 - Manual sampling
• Current Stage: 6060 - International Standard published
• Start Date: 21-Mar-2022
• Due Date: 14-Nov-2021
• Completion Date: 21-Mar-2022

Relations

• Revises: ISO 18283:2006 - Hard coal and coke - Manual sampling
• Effective Date: 23-Apr-2020

Overview

ISO 18283:2022 - "Coal and coke - Manual sampling" is the international standard that defines terms, principles and practical procedures for manual sampling of coal and coke during transfer operations. The document sets out how to design a sampling scheme, select sampling methods and equipment, handle and store samples, prepare test portions and report results. It covers brown coals and lignites, and explicitly excludes sampling from coal seams (see ISO 14180). Mechanical sampling is covered separately in ISO 13909.

Key Topics and Requirements

The standard provides detailed guidance on the technical and quality requirements needed to obtain representative manual samples:

• Establishing a sampling scheme: definitions, parameters, division of lots, precision and bias considerations, requirements for test samples.
• Precision and variance: how to calculate overall precision, primary increment variance, sub-lot variance, and determination of acquired precision through replicate sampling.
• Sampling methods: time-basis (interval) sampling, mass-basis sampling, stratified random sampling, and rules for random selection of increments.
• Scenarios for coal in motion: practical procedures for stopped belts, falling streams, moving belts, stockpiles (building/reclaiming), grabs, front-end loaders, barges, trucks, railcars and wagons.
• Sampling equipment: recommended manual tools (ladles, shovels, scoops, probes, manual cutters), and stopped-belt sampling frames.
• Sample handling and storage: sample size, container selection, labelling/identification, moisture loss control, and reserve samples.
• Sample preparation: constitution, division (mechanical and manual), reduction (reduction mills), mixing, air-drying, and preparation for total moisture, general analysis, size analysis and special tests.
• Reporting and traceability: content and format of the sampling report and packing/marking requirements.
• Annex B: guidance for stationary-lot sampling (informative) - this method does not provide a representative test sample unless stated in the report.

Practical Applications and Users

ISO 18283 is intended for organizations and professionals involved in coal and coke quality control and material transfer:

• Coal and coke producers, traders and port operators
• Power plants, steelworks and coke oven operators
• QA/QC laboratories and testing facilities
• Inspectors, auditors and contractual quality verifiers
• Material handling engineers and sampling technicians

Using ISO 18283 supports more reliable coal quality measurement, reduces sampling bias, ensures sample integrity (moisture and size), and improves contractual clarity for deliveries.

Related Standards

• ISO 13909 - Mechanical sampling of coal and coke
• ISO 14180 - Guidance for sampling from coal seams

Keywords: ISO 18283, coal sampling, manual sampling, coke sampling, sampling scheme, sampling equipment, sample preparation, moisture determination, coal quality, sampling precision.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18283
Second edition
2022-03
Coal and coke — Manual sampling
Houille et coke — Échantillonnage manuel
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Establishing a sampling scheme.4
4.1 General . 4
4.1.1 Sampling . 4
4.1.2 Sampling scheme . 5
4.1.3 Parameters . 5
4.1.4 Sampling methods. 5
4.2 Design of the sampling scheme . 6
4.2.1 General . 6
4.2.2 Coal or coke to be sampled and considerations for sampling . 6
4.2.3 Division of lots . 6
4.2.4 Precision of results . 7
4.2.5 Bias of results . 7
4.2.6 Requirements for test samples . 7
4.3 Precision of sampling . 8
4.3.1 General . 8
4.3.2 Precision and total variance . 8
4.3.3 Primary increment variance . 9
4.3.4 Sub-lot variance . 10
4.3.5 Preparation and testing variance . 10
4.3.6 Number of sub-lots and number of increments per sub-lot . 11
4.3.7 Minimum mass of samples for general analysis and determination of total
moisture content .12
4.4 Checking the overall precision for the lot by calculation and selection of sampling
scheme. 15
4.5 Determination of acquired precision by replicate sampling . 15
4.5.1 General .15
4.5.2 Method and calculation .15
4.5.3 Precision obtained using normal sampling scheme . 16
4.6 Size analysis . 16
5 Methods of sampling .17
5.1 General . 17
5.2 Sampling by time interval (time-basis sampling) . 17
5.3 Sampling by mass interval (mass-basis sampling) . 18
5.4 Stratified random sampling . 18
5.4.1 General . 18
5.4.2 Stratified random sampling by time interval . 18
5.4.3 Stratified random sampling by mass interval . 18
5.5 Extracting the increment . 18
5.6 Coal or coke in motion . 19
5.6.1 General . 19
5.6.2 Stopped belt . 19
5.6.3 Falling stream .20
5.6.4 Moving belt .20
5.6.5 Stockpiles (building/reclaiming) . 21
5.6.6 Grabs/front-end loaders . 21
5.6.7 Barges/trucks/railcars/wagons (loading/unloading) .22
5.7 Moisture/common sample .22
iii
5.8 Different coals or cokes . 23
5.9 Random selection of increments . 23
6 Sampling equipment .24
6.1 General . 24
6.2 Examples . 25
6.2.1 Ladles. 25
6.2.2 Shovels . 25
6.2.3 Scoops . 25
6.2.4 Probes . 25
6.2.5 Manual cutter . 26
6.2.6 Stopped-belt sampling frame . 26
7 Handling and storage of samples .28
7.1 Sample size . 28
7.2 Time.28
7.3 Divided sample .29
7.4 Containers . .29
7.5 Moisture loss/breakage or degradation .30
7.6 Identification/labelling . 31
8 Sample preparation .31
8.1 General . 31
8.2 Constitution of a sample . 31
8.3 Division . 32
8.3.1 General . 32
8.3.2 Mechanical methods .33
8.3.3 Manual methods . 36
8.4 Reduction .40
8.4.1 General .40
8.4.2 Reduction mills .40
8.5 Mixing . 41
8.6 Air-drying of coal . 41
8.7 Coal — Preparation of test samples . 42
8.7.1 Types of test samples. 42
8.7.2 Preparation of samples for determination of total moisture content . 42
8.7.3 Preparation of samples for general analysis . 43
8.7.4 Common samples . 45
8.7.5 Preparation of size-analysis sample . 47
8.7.6 Preparation of samples for other tests .48
8.7.7 Reserve sample .49
8.8 Coke — Preparation of test samples .49
8.8.1 Types of test samples.49
8.8.2 Preparation of coke samples for determination of total moisture content .50
8.8.3 Preparation of samples for general analysis . 52
8.8.4 Storage .53
8.8.5 Physical test sample . 53
8.8.6 Samples for special properties . 53
8.8.7 Reserve sample . 53
9 Packing and marking of samples .53
10 Sampling report .54
Annex A (informative) Example of calculation of precision, mass of increments,number of
sub-lots and number of increments per sub-lot .55
Annex B (informative) Methods of sampling coal and coke from stationary lots .58
Bibliography .60
iv
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 27, Coal and Coke, Subcommittee SC 4,
Sampling.
This second edition cancels and replaces the first edition (ISO 18283:2006), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 18283:2006/Cor.1:2006.
The main changes are as follows:
— Removal of any reference to intermittent sampling. Only continuous sampling is permitted.
— Discussion of the need to eliminate bias prior to discussing precision.
— Deletion of the separate tables on calculated numbers of increments.
— Deletion of the table on reference increment mass.
— Separation of tables for minimum sample masses for coal and coke.
— Removal of the table for reduced minimum sample mass for large sizes of coal and coke.
— Inclusion of manual sampling from a moving conveyor, provided a risk assessment is conducted
at the outset and that this type of sampling is only permitted on a slow-moving belt or at low flow
rates. Furthermore, at higher flow rates, mechanical assistance is necessary to ensure that primary
increments can be collected safely.
— Restriction of the type of probes that can be used.
— Deletion of augers for manual sampling.
— Inclusion of a photograph of a gated riffle.
— Exclusion of sampling of large fuels in excess of the nominal top sizes in Tables 1, 2 and 4, because it
is not practical.
v
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.
vi
Introduction
Mechanical sampling from moving streams is the preferred method for sampling coal and coke.
However, often mechanical facilities are not available. Moreover, for sized coal or coke, mechanical
sampling may be a problem because of (size) degradation by the sampling system.
The fundamental requirements of sampling are that all particles of the coal or coke in the lot are
accessible to the sampling instrument and thus have a non-zero chance of being selected, and that each
individual particle of equal mass has an equal probability of being selected and included in the sample.
When sampling manually, conditions are often far from ideal. The methods described in this document
are intended to obtain the most representative sample that can be safely achieved. Manual sampling
should only be applied if no possibility for mechanical sampling exists.
The purpose of taking and preparing a sample of coal or coke is to provide a test sample that, when
analysed, provides test results representative of the lot or sub-lot sampled.
The first stage of sampling, known as primary sampling, is the taking from positions distributed
over the entire lot of an adequate number of coal or coke portions known as primary increments. The
primary increments are then combined into a sample. From this sample, the required number and types
of test samples are prepared by a series of processes jointly known as sample preparation.
In devising a sampling procedure, it is also essential to guard against bias in the taking of increments.
Bias can arise from:
a) incorrect location/timing of increments,
b) incorrect delimitation and extraction of increments,
c) particle size segregation at the point of sampling,
d) loss of integrity of increments after extraction.
Methods for measuring bias are described in ISO 13909-8.
vii
INTERNATIONAL STANDARD ISO 18283:2022(E)
Coal and coke — Manual sampling
WARNING — This document can involve hazardous materials, operations and equipment, and
does not purport to address all the safety issues associated with its use. It is the responsibility of
the user of this document to establish appropriate health and safety practices.
1 Scope
This document provides the basic terms used in manual sampling of coal and coke and describes the
general principles of sampling. It provides procedures and requirements for establishing a manual
sampling scheme, methods of manual sampling, sampling equipment, handling and storage of samples,
sample preparation and a sampling report, and applies to manual sampling during the transfer of coal
or coke. Guidelines for manual sampling in stationary situations are given in Annex B, but this method
of sampling does not provide a representative test sample and the sampling report shall state this.
This document covers sampling of brown coals and lignites, but does not include sampling from coal
seams, for which guidance is given in ISO 14180. Mechanical sampling of coal and coke is covered in
ISO 13909.
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 579, Coke — Determination of total moisture
ISO 589, Hard coal — Determination of total moisture
ISO 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
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 following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
air-drying
process of bringing the moisture content of the sample near to equilibrium with the atmosphere in the
area in which further reduction and division of the sample are to take place
Note 1 to entry: Air-drying to equilibrium with the atmosphere applies to coal. Drying of coke is generally to
facilitate sample preparation.
3.2
bias
systematic error that leads to the average value of a series of results being persistently higher or
persistently lower than those that are obtained using a reference sampling method
3.3
common sample
sample collected for more than one intended use
3.4
continuous sampling
taking of a sample from every consecutive sub-lot (3.30) so that increments (3.10) are taken at uniform
intervals over the entire lot (3.11) being handled
3.5
cut
see increment (3.10)
3.6
divided increment
part obtained from the division of the increment (3.10) in order to decrease its mass
Note 1 to entry: Such division can be done with or without prior size reduction.
3.7
fixed-mass division
method of sample division in which the mass retained is predetermined and independent of the mass of
the feed
3.8
fixed-ratio division
method of sample division in which the division ratio is predetermined, i.e. the mass of sample retained
is a fixed proportion of the mass of the feed
3.9
general analysis test sample
sample prepared to pass a sieve of nominal size of openings of 212 µm used for the determination of
most chemical and some physical characteristics
3.10
increment
portion of coal or coke extracted in a single operation of the sampling device
Note 1 to entry: Cut is an equivalent term.
3.11
lot
defined quantity of coal or coke for which the quality is to be determined
Note 1 to entry: A lot can be divided into sub-lots.
3.12
manual sampling
extraction of increments (3.10) by human effort
3.13
mass-basis sampling
taking of increments (3.10) whereby the position of each increment (3.10) to be extracted from the
stream of coal or coke is measured by a mass interval of stream flow and the increment (3.10) mass is
fixed
3.14
mechanical sampling
extraction of increments (3.10) by mechanical means
3.15
moisture sample
sample taken specifically for the purpose of determining total moisture
Note 1 to entry: For coke, this sample can also be used for general analysis.
3.16
nominal top size
aperture size of the smallest sieve in the range included in the R 20 Series on which not more than 5 %
of the mass of the sample is retained
Note 1 to entry: See ISO 565, square hole.
3.17
physical sample
sample taken specifically for the determination of physical characteristics, e.g. physical strength
indices or size distribution
3.18
precision
closeness of agreement between independent test results obtained under stipulated conditions
Note 1 to entry: This is often defined using an index of precision, such as 2 standard deviations.
Note 2 to entry: A determination might be made with great precision and the standard deviation of a number of
determinations on the same sub-lot might, therefore, be low; but such results are accurate only if they are free
from bias.
3.19
primary increment
increment (3.10) extracted at the first stage of sampling, prior to any sample division and/or sample
reduction
3.20
random sampling
extracting of increments (3.10) at random mass or time intervals
3.21
replicate sampling
extracting, at intervals, of increments (3.10) that are combined in rotation into different containers to
give two or more samples of approximately equal mass
3.22
representative sample
sample collected in such a manner that the analyses, size distribution and moisture content represent
that of the lot (3.11)
3.23
sample
quantity of coal or coke, representative of a larger mass for which the quality is to be determined
3.24
sample division
process in sample preparation whereby the sample is divided into representative, separate portions
3.25
sample preparation
process of bringing samples to the condition required for analysis or testing
Note 1 to entry: Sample preparation covers mixing, particle size reduction, sample division and sometimes air-
drying (3.1) of the sample and may be performed in several stages
3.26
sample reduction
process in sample preparation whereby the particle size of the sample is reduced by crushing or
grinding
3.27
size analysis sample
sample taken specifically for particle size analysis
3.28
standard deviation
square root of the variance
3.29
stratified random sampling
extracting of an increment at random within the mass interval or time interval determined for mass-
basis sampling or time-basis sampling respectively
3.30
sub-lot
part of a lot (3.11) for which a test result is required
3.31
systematic sampling
extracting of increments (3.11) at uniform time intervals according to a predetermined plan
3.32
test sample
sample which is prepared to meet the requirements of a specific test
3.33
time-basis sampling
extracting of increments whereby the position of each increment to be collected from the stream of coal
or coke is measured by a time interval and the increment mass is proportional to the flow rate at the
time the increment is taken
3.34
variance
measure of dispersion, which is the sum of the squared deviations of observations from their average
divided by one less than the number of observations
4 Establishing a sampling scheme
4.1 General
4.1.1 Sampling
Mechanical sampling of coal and coke in accordance with ISO 13909-2, ISO 13909-3 and ISO 13909-5
is the preferred method. However, where this is not possible, manual sampling may be conducted.
The recommended method for manual sampling of coal and coke is while it is being transferred, e.g.
loading or unloading of ships, barges, wagons, rail cars and trucks, transferring coal or coke using
fixed/moveable conveyors and/or stackers, or during the formation of or reclaiming from stockpiles.
For safety and practical reasons, manual sampling of coal or coke being transferred is sometimes not
possible.
NOTE Manual sampling in stationary situations (see Annex B) refers to static lots, where no formation of or
reclaiming from piles/heaps takes place.
Increments should be collected by trained sampling personnel. Instructions should be as complete
and as simple as possible, in particular, the position of sampling and the times at which increments
are taken should be specified and not left to the personal judgement of the sampling personnel. These
instructions, which should preferably be set out in writing, should be prepared by the sampling
supervisor from the information given in this document.
4.1.2 Sampling scheme
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) select or assume the required overall precision for the lot (see 4.3.2);
d) determine or assume the variability of the coal or coke (see 4.3.3 and, if relevant, 4.3.4) and the
variance of preparation and testing (see 4.3.5);
e) ascertain the nominal top size of the coal or coke for the purpose of determining the mass of
increment and sample (see 4.3.6.3 and 4.3.7);
f) the nominal top size should initially be ascertained by consulting the consignment details or by
visual estimation and should be verified by preliminary test work;
g) select the sampling device (see Clause 6);
h) establish the number of sub-lots and the number of increments per sub-lot required to attain the
desired precision (see 4.3.6);
i) determine the method of combining the increments into samples and the method of sample
preparation (see Clause 8);
j) define the sampling interval in terms of time or mass (see Clause 5);
k) determine where to collect the increments (see Clause 5).
4.1.3 Parameters
In order to ensure that the result obtained is to the required precision, the following parameters are
considered:
a) variability of the coal or coke;
b) number of increments to be taken from the lot;
c) number of sub-lot samples to be constituted for the lot;
d) number of increments comprising each sub-lot sample;
e) mass of sample relative to nominal top size.
4.1.4 Sampling methods
In this document, only continuous sampling methods are considered.
4.2 Design of the sampling scheme
4.2.1 General
The basic first step in the design of a sampling scheme is a review of the requirements for operations in
order to draw up instructions for the sampling operator(s). The instructions should cover all sampling
problems likely to be encountered.
It is important that the sampling operator receive instructions that are simple, easily understood and
capable of only one interpretation. These instructions, which should be set out in writing, should be
prepared by the sampling supervisor after inspecting the sampling site and referring to the information
given in this document. The following items in the following list and described in 4.2.2 to 4.2.6 should
be considered by the supervisor when compiling instructions:
a) coal or coke to be sampled and considerations for sampling;
b) lot size and number of sub-lots;
c) method of sampling;
d) requirements for test samples;
e) number of increments per lot or sub-lot;
f) mass of sample;
g) precision of results;
h) bias of results.
4.2.2 Coal or coke to be sampled and considerations for sampling
The first stage in the design of the scheme is to identify the coal or coke to be sampled. Samples may be
required for technical evaluation, process control, quality control and for commercial reasons by both
the producer and/or seller and the customer. It is essential to ascertain exactly at what stage in the
handling process the sample is required and, as far as practicable, to design the scheme accordingly.
In some instances, however, it can prove impracticable to obtain samples at the point preferred and, in
such cases, a more practicable alternative is required, provided a representative sample can be taken.
The following identifications are indispensable for the design of a manual sampling scheme:
a) coal or coke properties, e.g. fines, lump and, more specifically, the nominal top size; furthermore,
whether dry, wet or free flowing;
b) location and the handling system;
c) transport means/carriers;
d) where to sample in the handling process, taking into account contract terms and the practicability
for sampling;
e) human safety risks.
4.2.3 Division of lots
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. The size of each sub-lot should be selected for convenience of sampling,
e.g. coal or coke despatched or delivered over a period of time, a train load, a wagon load, or coal or
coke produced during a certain period, e.g. a shift. For large lots, such as ocean-going vessels, it is
recommended to sample in multiple sub-lots for the reasons below. It is common industry practice to
limit sub-lot sizes to a maximum of 10 000 t. However, when the loading or discharge rate is less than
1 000 t/h, it is recommended that sub-lot sizes be limited to 5 000 t to avoid moisture bias due to long
periods of sample collection.
Such division into a number of sub-lots may be necessary to achieve the following:
a) the required precision (calculated by the procedure in 4.5);
b) maintain the integrity of the sample, e.g. avoiding bias that can result from changes of moisture due
to standing or oxidation;
c) create convenience when sampling lots over a long period, e.g. on a shift basis;
d) keep sample masses manageable, taking into account the maximum lifting capacity of operators;
e) distinguish different components of a mixture of coal or coke, e.g. different coal types within one
lot.
4.2.4 Precision of results
After the overall precision of the lot has been decided, the number of sub-lots and the number of
increments per sub-lot collected shall then be determined as described in 4.3.6 and the mass of the
primary increments shall be determined as described in 4.3.6.3.
For single lots, the quality variation shall be assumed as the worst case (see 4.3.3). The precision of
sampling achieved may be measured using the procedure of replicate sampling (see 4.5).
At the start of regular sampling of unknown coal or coke, the worst-case quality variation shall be
assumed in accordance with 4.3.3 and 4.3.4.
If any subsequent change in precision is required, the number of sub-lots and of increments shall
be changed as determined in 4.3.6 and the precision attained rechecked. The precision shall also be
checked if there is any reason to suppose that the variability of the coal or coke being sampled has
increased. The number of increments determined in 4.3.6 applies to the precision of the result when the
sampling errors are large relative to the sample preparation and testing errors, e.g. moisture. However,
in some tests, the testing errors are themselves large. In this case, it can be necessary to prepare two or
more test portions from the sample and use the mean of the determinations to give a better precision.
4.2.5 Bias of results
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 mass of the primary increment, the divided
sample and the test sample to maintain integrity (see 4.3.6.3 and 4.3.7).
It may be necessary, when collecting samples for moisture determination from lots over an extended
period, to limit the standing time of samples by dividing the lot into a number of sub-lots. For
establishing the loss of integrity of the sample, a bias test can be carried out to compare a series of
reference samples immediately after extraction with samples after standing for the normal time to
establish moisture or calorific value loss due to standing (see ISO 13909-8).
Bias testing for manual sampling can be performed according to the same principles as for mechanical
sampling using a reference method to judge a manual sampling practice (see ISO 13909-8).
4.2.6 Requirements for test samples
In the sampling scheme and in the scheme of preparation of samples, attention shall be paid to
requirements on the samples for testing.
A number of tests are carried out on crushed or pulverized samples of prepared top sizes as mentioned
in the relevant testing standards, e.g. ash on a − 0,212 mm sample. However, some tests require
samples either in the original state or prepared to a particle size somewhere between original state and
0,212 mm.
Examples of physical tests on samples in their original state are size-distribution tests, float and sink
tests, coking tests, etc.
Examples of tests on partly crushed and prepared samples are total moisture, Hardgrove grindability
index and dilatation.
In view of the above, consideration of the sampling and preparation schemes should foresee either
whether all required samples can be taken and prepared from a common sample or whether it is
necessary to take a number of separate samples. In all cases, the masses of the common sample and the
required test samples should be maintained in accordance with the minimum masses as prescribed in
this document and in the standard specifying the test method. In case of differences between standards,
the greater mass should be maintained.
In case the mass of the sample as calculated in accordance with this document is insufficient for the
masses of the required test samples, the number of increments taken from each lot or sub-lot shall be
increased by increasing the sampling frequency to provide the required mass
4.3 Precision of sampling
4.3.1 General
In all methods of sampling, sampling preparation and analysis, errors are incurred, and the
experimental results obtained from such methods for any given parameter deviate from the true value
of that parameter. As the true value cannot be known exactly, it is not possible to assess the accuracy
of the experimental results, i.e. the closeness with which they agree with the true value. However, it is
possible to make an estimate of the precision of the experimental results, i.e. the closeness with which
the results of a series of experiments made on the same coal or coke
...