Overview
ISO 8672:2014 - Air quality - Determination of the number concentration of airborne inorganic fibres by phase contrast optical microscopy - Membrane filter method - specifies a standardized laboratory and sampling procedure to measure the number concentration of optically visible airborne inorganic fibres in workplace atmospheres. The method uses phase contrast optical microscopy (PCM) on specimens prepared from membrane filters and defines counting criteria, sample preparation, quality assurance and reporting procedures.
Key technical topics and requirements
- Scope and applicability: Intended for workplace air monitoring where inorganic fibres predominate; not suitable for identifying fibre composition.
- Countable fibre definition: Objects with maximum width < 3 µm, overall length > 5 µm, and length:width ratio > 3:1.
- Sampling: Personal and static sampling using battery-powered pumps drawing a known volume of air through membrane filters (25 mm diameter preferred; pore size ~0.8–1.2 µm commonly used).
- Specimen preparation: Opaque membrane filters are cleared and mounted (e.g., acetone‑triacetin or dimethyl formamide‑Euparal procedures described in annexes) to produce optically transparent slides for PCM.
- Microscopy and counting: Phase contrast microscope adjustment, eyepiece graticule calibration, counting fields and sizing are specified (see clauses on microscope performance and counting rules).
- Detection limits and limitations: Theoretical lower detection limit for a 480 L sample is about 0.007 fibres/cm3, but practical detection is often ~0.1 fibres/cm3 due to background artefacts and blank counts. Very thin fibres below PCM visibility or fibres with refractive index similar to mounting media may be undercounted; electron microscopy may be needed for finer analysis.
- Quality assurance: Reference slides, blanks, inter-laboratory comparisons, and procedural controls are required to reduce operator dependence and uncertainty.
- Reporting: Standardized test report elements, uncertainty assessment and recommended sampling records are defined.
Practical applications and users
ISO 8672:2014 is used for:
- Occupational exposure monitoring (personal and static) to inorganic fibres (including asbestos surveillance contexts where PCM is appropriate)
- Workplace compliance and risk assessment, control-measure verification and clearance screening (noting the need for larger sample volumes in very clean atmospheres)
- Industrial hygiene and environmental labs performing routine fibre counting
Primary users include occupational hygienists, analytical laboratories, regulators, asbestos removal contractors, and safety managers.
Related standards
- Normative reference: ISO 13137 (pumps for personal sampling).
- The document cross-references established counting and terminology sources (e.g., ASTM and EN documents noted in the standard).
Keywords: ISO 8672:2014, air quality, airborne inorganic fibres, phase contrast optical microscopy, membrane filter method, fibre counting, workplace atmospheres, occupational exposure.