ISO 16258-2:2015 - Workplace air: RCS analysis by X‑ray diffraction (Indirect method)

Overview

ISO 16258-2:2015 specifies a laboratory indirect X‑ray diffraction (XRD) method for measuring respirable crystalline silica (RCS) in workplace air. The method covers analysis when dust is recovered from a collection substrate (filters or foams), treated and redeposited onto an analysis filter prior to XRD. The scope includes the common polymorphs quartz and cristobalite; less common polymorphs (e.g., tridymite) are excluded due to lack of reference material.

Key SEO keywords: ISO 16258-2:2015, respirable crystalline silica, RCS, X-ray diffraction, workplace air, indirect analysis, filters, occupational hygiene.

Key topics and requirements

• Analytical principle: Recover dust from sampling substrates, treat to remove interferences, redeposit on an analysis filter, then quantify RCS by XRD.
• Sampling substrates: Guidance for a range of collection substrates (PVC, MCE, cellulose nitrate filters, polyurethane foams) and compatible samplers.
• Instrumental parameters: Recommended XRD instrumental and scan parameters, calibration curve development, and drift correction practices.
• Gravimetric analysis: Concurrent gravimetric determination of respirable dust where required.
• Sample treatment: Procedures to remove interfering materials and prepare redeposition (e.g., furnace, plasma asher options).
• Absorption correction: Methods to correct for X‑ray absorption effects introduced by redeposited matrices.
• Performance characteristics: Discussion of limit of detection, minimum detectable values, limits of quantification and uncertainty considerations.
• Limitations: Under low dust loads or low silica content, the indirect approach may not meet expanded uncertainty requirements of EN 482; ISO 24095 gives uncertainty guidance.

Practical applications and users

Who uses this standard:

• Industrial hygienists and occupational safety professionals measuring worker exposure to RCS.
• Analytical laboratories performing workplace air monitoring and XRD analysis.
• Employers, health and safety managers, and regulators verifying control measures and compliance with occupational exposure limits. Practical uses:
• Assessing individual exposure and effectiveness of engineering controls or respiratory protection.
• Laboratory method selection when direct-on-filter analysis is not feasible or when samples originate from varied samplers/filters.
• Ensuring consistent, traceable RCS data for exposure assessment and risk management.

Related standards

• ISO 16258-1 (Direct-on-filter method)
• ISO 24095 (Guidance for measurement of RCS; uncertainty)
• EN 482 (general criteria for workplace exposure measurement - expanded uncertainty)
• ISO 7708, ISO 13137, ISO 15767 (sampling definitions, pumps, weighing/uncertainty)

This standard helps laboratories and occupational hygiene practitioners implement a validated, traceable indirect XRD workflow for RCS measurement in workplace air, while highlighting method limitations and supporting quality assurance.