ISO 22262-1 Test Method: SEM/EDXA Determination of Man-Made Mineral Fibres in Air and Dust

ISO 22262-1 is an internationally recognized test method for the identification and quantification of man-made mineral fibres (MMMF) in air and dust samples using scanning electron microscopy combined with energy-dispersive X-ray analysis. This technical article explains the scope of the ISO 22262-1 test method, the types of samples that can be analyzed, the key measurement parameters, and its practical applications in occupational hygiene, indoor air quality assessment, and product compliance testing.

Technical Overview

ISO/TS 22262-1 belongs to the ISO 22262 series of technical specifications in the field of air quality and establishes a standardized method for evaluating man-made mineral fibres (MMMF), also known as man-made vitreous fibres (MMVF) or synthetic mineral fibres. The method relies on scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDXA) to detect, count, size, and chemically classify fibrous particles collected on membrane filters.

Optical microscopy alone is often insufficient for this task because many man-made mineral fibres, such as fine glass wool or micro-fibres, have diameters below the practical resolution limit of phase-contrast light microscopy. Scanning electron microscopy provides high-resolution imaging of fibre morphology, while EDXA supplies the elemental composition needed to distinguish man-made mineral fibres from asbestos fibres, gypsum needles, and organic fibres such as cellulose or textile filaments.

The ISO 22262-1 test method is conceptually related to other fibre-measurement standards, including ISO 14966 for inorganic fibres in ambient air, ISO 10312 for fibre counting by phase-contrast optical microscopy, and ISO 13794 for fibres in settled dust. It complements these methods by focusing specifically on the electron-optical and chemical characterization of man-made mineral fibres.

• Applicable fibre geometry is typically defined by the WHO counting criteria: length greater than 5 µm, width less than 3 µm, and an aspect ratio of at least 3:1.
• Results are expressed as fibre number concentrations, commonly in fibres per cubic centimetre or fibres per cubic metre of air.
• Chemical classification allows differentiation among glass wool, rock and slag wool, refractory ceramic fibres, and naturally occurring asbestos varieties.
• The method is suitable for personal exposure monitoring, stationary area sampling, and the analysis of settled or suspended dust.

Testing Samples

Airborne Fibre Samples

Air samples are collected by drawing a measured volume of air through membrane filters mounted in open-face filter cassettes. Mixed cellulose ester membrane filters or track-etched polycarbonate filters with suitable pore sizes are commonly used. Sampling can be performed with battery-powered personal pumps worn by workers or with stationary pumps positioned at fixed locations, using calibrated low flow rates over extended sampling periods to achieve adequate sensitivity.

Settled Dust Samples

Dust deposited on building surfaces, inside ventilation ducts, or retained on HVAC filters can be analyzed to evaluate historical or ongoing fibre release. The dust is recovered using adhesive film, micro-vacuum cassettes, or wipe techniques, and is subsequently transferred onto a filter for electron-optical examination.

Bulk Materials and Products

Raw insulation wools, refractory ceramic fibre products, ceiling tiles, and other fibre-containing materials can be characterized by preparing a suspension of the material and depositing a representative aliquot onto a filter. This allows the fibre type, dimensions, and elemental fingerprint of the product to be documented for comparison with airborne findings.

Testing Items

Depending on the client's objective, the ISO 22262-1 test method supports the following measurement and reporting items:

• Fibre number concentration in air, reported in fibres/cm³ or fibres/m³ with blank correction.
• Counts of respirable fibres meeting the WHO geometry criteria.
• Fibre length, diameter, and aspect-ratio distributions for exposure characterization.
• Elemental classification of individual fibres by EDXA, distinguishing alkali-rich glass fibres, calcium-magnesium-silicate rock and slag wools, high-alumina refractory ceramic fibres, and amphibole or serpentine asbestos.
• Relative abundance of man-made mineral fibres versus other particle populations in dust samples.
• Estimated limit of detection and measurement uncertainty associated with the reported concentration.

Testing Methods

The analytical workflow under ISO 22262-1 follows a clearly defined sequence to ensure reproducible and defensible results:

• Sample collection: air or dust is captured on membrane filters under calibrated, documented flow conditions, and field blanks are taken alongside the samples.
• Filter preparation: a defined portion of the filter is mounted for microscopy; organic filter media are commonly ashed at low temperature and the inorganic residue is redeposited onto a smooth substrate, which is then sputter-coated with a conductive layer such as gold.
• Electron-optical examination: the specimen is scanned in the SEM at an established magnification along a systematic traverse pattern, and fibres are located using defined counting rules for particles crossing the edges of the viewing field.
• Morphological evaluation: each candidate fibre is measured to determine whether it satisfies the length, width, and aspect-ratio criteria for counting.
• Chemical analysis: an EDXA spectrum is acquired from each counted fibre, and the normalized element intensities are compared with classification criteria to assign the fibre to a chemical group.
• Calculation and reporting: the fibre concentration is calculated from the number of counted fibres, the fraction of filter area examined, the air volume sampled, and the blank value, and the final report includes size distributions and chemical classification summaries.
• Quality assurance: laboratory blanks, replicate counting, instrument calibration, and participation in interlaboratory comparison programs support the validity of the results.

Applications

The ISO 22262-1 test method is used across a wide range of industrial, regulatory, and investigative contexts:

• Occupational exposure assessment in the manufacture, installation, removal, and demolition of mineral wool and refractory ceramic fibre products.
• Indoor air quality investigations in offices, schools, and public buildings where fibrous dust complaints or visible fibre release has occurred.
• Product stewardship and regulatory compliance programmes for fibre producers, including evaluation against classification requirements for respirable fibres.
• Clearance verification after remediation or abatement work involving fibrous insulation materials.
• Environmental and emission studies that quantify fibre release from building components, appliances, or industrial equipment.
• Research and development supporting the design of low-biodurability, low-emission fibre products.

FAQ

What counts as a fibre under ISO 22262-1?

A particle is generally counted as a fibre when it is longer than 5 µm, thinner than 3 µm, and has a length-to-width ratio of at least 3:1, consistent with the widely applied WHO convention for respirable fibres. Particles that meet the geometry criteria but fail the chemical classification for man-made mineral fibres are reported separately.

How does ISO 22262-1 differ from phase-contrast microscopy methods?

Phase-contrast optical microscopy methods, such as ISO 8672 and ISO 10312, count fibres but cannot reliably resolve the finest fibres or determine their composition. ISO 22262-1 uses SEM/EDXA to provide both superior morphological resolution and elemental identification, enabling fibre-type-specific reporting rather than a total fibre count alone.

What detection limit can be achieved?

The detection limit depends on the volume of air sampled, the fraction of the filter surface examined, and the blank levels. Increasing the sampled air volume or extending the counting effort lowers the achievable detection limit, and the laboratory reports an estimate specific to each measurement.

Can settled dust and bulk materials be tested?

Yes. In addition to airborne fibre measurements, the method supports the analysis of settled surface dust, duct deposits, and bulk products, which is useful for source identification and for corroborating air monitoring results.

Why is chemical classification important?

Health-based criteria and occupational exposure limits differ among fibre types, for example between refractory ceramic fibres and conventional insulation wools. EDXA-based classification ensures that reported concentrations are attributed to the correct fibre category, which is essential for meaningful regulatory and risk assessment decisions.