National foreword

This British Standard is the UK implementation of ISO 13909‑7:2025. It supersedes BS ISO 13909‑7:2016, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee W/-, Miscellaneous Standards.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2025.

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 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) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

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 third edition cancels and replaces the second edition (ISO 13909‑7:2016), which has been technically revised.

The main changes are as follows:

references have been updated;
the results discussed in Clause B.4 have been clarified.

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.

Introduction

Two different situations are considered when a measure of precision is required. In the first, an estimate is made of the precision that can be expected from an existing sampling scheme and, if this is different from that desired, adjustments are made to correct it. In the second, the precision that is achieved on a particular lot is estimated from the experimental results actually obtained using a specifically designed sampling scheme.

The formulae developed in this document are based on the assumption that the quality of the fuel varies in a random manner throughout the mass being sampled and that the observations will follow a normal distribution. Neither of these assumptions are strictly correct. Although the assumption that observations will follow a normal distribution is not strictly correct for some fuel parameters, this deviation from assumed conditions will not materially affect the validity of the formulae developed for precision checking since the statistics used are not very sensitive to non-normality. Strictly speaking, however, confidence limits will not always be symmetrically distributed about the mean. For most practical uses of precision, however, the errors are not significant.

In this document, the term “fuel” is used where the method is applicable to both coal and coke and either “coal” or “coke” where the method is exclusively applicable to that commodity.

1 Scope

This document defines methods for estimating overall precision and for deriving values for primary increment variance which can be used to modify the sampling scheme to change the precision. Methods for checking the variance of sample preparation and testing are also described.

In this document, formulae are developed which link the variables that contribute to overall sampling precision.

2 Normative references

3 Terms and definitions

4 General

5 Formulae relating to factors affecting precision

5.1 General

5.2 Sampling

6 Estimation of primary increment variance

6.1 Direct determination of individual primary increments

6.2 Determination using the estimate of precision

7 Methods for estimating precision

7.1 General

7.2 Duplicate sampling with twice the number of increments

7.3 Duplicate sampling during routine sampling

7.4 Alternatives to duplicate sampling

7.5 Precision adjustment procedure

8 Calculation of precision

8.1 Replicate sampling

8.2 Normal sampling scheme

9 Methods of checking sample preparation and testing errors

9.1 General

9.2 Target value for variance of sample preparation and analysis

9.3 Checking procedure as a whole

9.4 Checking stages separately

9.5 Procedure for obtaining two samples at each stage

9.6 Example

Bibliography

BS ISO 13909-7:2025

Coal and coke. Mechanical sampling - Methods for determining the precision of sampling, sample preparation and testing

Current

Published:

31 Jul 2025