National foreword

This British Standard is the UK implementation of ISO 6868:2026.

The UK participation in its preparation was entrusted to Technical Committee EH/2/2, Work place atmospheres.

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 August 2026.

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).

ISO draws attention to the possibility that the implementation of this document may involve the use of patents. 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 patents 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.

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This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 2, Workplace atmospheres.

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

Exposure to crystalline silica (CS) in the respirable fraction of inhaled airborne dust is a hazard to the health of workers in many industries. For this document, CS refers to the two most common polymorphs, quartz and cristobalite. To assess the exposure of an individual, personal samples of air are taken during a work activity, and then the amount of respirable CS is measured. In addition to the procedures for determining the airborne concentration of respirable CS in a workplace atmosphere, it can be useful, or required, to evaluate the CS content in bulk materials that have a potential risk of being respirable when they are ground or manipulated.

This document is appropriate for the analysis of material selected to be representative of a product, or soil, rock, mineral, waste, depending on the nature of the investigation. Bulk materials are generally in the solid state but can also be made by watery mixtures of insoluble matter (slurries, muds). A variety of origins, compositions, sizes and shapes, such as solid blocks, fragments, slabs, sand, powders and flours, can represent bulk materials.

The knowledge of CS content in natural rocks and soils is useful when, for example, assessing potential exposure by inhalation of airborne dust meeting the respirable convention of ISO 7708^[1^] in work activities that involve excavation, earth moving, and drilling plant operations. Elevated exposures to respirable CS are often found in confined spaces, such as in mining and tunnelling. Knowing the mass fraction of CS in construction materials and natural rocks or soils contributes to the characterization of potential sources of airborne dust and allows planning of risk management measures in order to reduce potential exposures to airborne dust.

The methods in this document can also be used for the analysis of samples, which have been collected for the purpose of classification and labelling of chemicals according to the Globally Harmonized System (GHS), when a CS phase is found as a “substance”, or in “mixtures” and “articles”, as defined in the GHS.

As is necessary in any good routine type analysis, especially where the results can have legal implications, it is useful to establish standard procedures for analysing the specimens. There are several methods mentioned in the literature for the determination of quartz, and many procedures can be developed, but no single procedure is applicable to all situations. Standardizing procedures for X-ray powder diffraction (XRPD) analysis of bulk materials, which are applicable to all materials, is difficult because of the variability of the matrices and their potential interferences. Therefore, the method chosen for the analysis should be carefully tested in the laboratory for the specific conditions.

The problems of processing samples containing either quartz or cristobalite, or both is essentially the same as processing samples of bulk materials in general, and the major problem is preparing a specimen that is representative of the bulk material. The potential accuracy obtainable from a sub-sample or specimen of bulk material is related to the effective number of particles interrogated by the X-ray beam, which is related to the distribution of particles sizes and their absorption coefficients.

1 Scope

This document specifies three methods for quantitative measurement of crystalline silica (CS) major polymorphs (quartz and cristobalite) mass percentage content in bulk samples using X-ray powder diffraction (XRPD). This document also provides general information about the capabilities and limitations of relevance to laboratories working for routine testing.

Only X-ray diffractometers with Bragg-Brentano geometry are considered. XRPD techniques are used to characterize specimens in the form of loose powders, where the median grain size is between 1 μm and 10 μm physical diameter. Block specimens are not considered.

Although a number of methods of analysis are considered in this document, other XRPD methods of analysis can be considered if they are demonstrated to give equivalent results.

2 Normative references

3 Terms and definitions

4 Principle

5 Equipment

5.1 Diffraction system

5.2 Balance

5.3 Reference materials

5.4 Equipment for the preparation of specimens of infinite thickness

5.5 Equipment for the preparation of thin thickness specimens

5.6 Equipment for sample treatment and reagents

6 Sampling

7 Specimen preparation

7.1 General

7.2 Crushing

7.3 Grinding

7.4 Drying

7.5 Pre-concentration and removal of interfering phases

7.6 Weighing and mounting of a specimen of infinite thickness

7.7 Weighing and deposition of thin layer specimen on filter

8 Analysis

8.1 Symbols

8.2 Parameters of a diffraction line profile

8.3 Instrument conditions

8.4 Analytical methods

9 Performance characteristics of the methods

9.1 Limits of detection and quantification

9.2 Uncertainty of measurement

9.3 Equivalency of the methods and between laboratory precision

10 Test report

10.1 Minimum report requirements

10.2 Data to be archived by the laboratory

Bibliography