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ISO/TR 27628:2010 — Workplace Atmospheres — Ultrafine, Nanoparticle and Nano-Structured Aerosols — Inhalation Exposure Characterization
Advanced Methodologies for Measuring and Characterizing Occupational Exposure to Airborne Nanomaterials
Occupational exposure to airborne nanoparticles represents one of the most significant challenges in contemporary industrial hygiene. Unlike conventional dusts and fumes, nanoparticle aerosols exhibit unique behaviours: they remain airborne for extended periods, penetrate conventional respiratory protective equipment more readily, deposit efficiently in the alveolar region of the lungs, and can translocate from the respiratory tract to other organs including the brain. ISO/TR 27628:2010 provides the methodological framework for characterising inhalation exposure to ultrafine, nanoparticle, and nano-structured aerosols in workplace atmospheres, establishing a scientific basis for exposure assessment and risk management.
Exposure Metrics and Sampling Strategies
ISO/TR 27628 establishes that nanoparticle exposure cannot be adequately described by mass concentration alone — the traditional metric for workplace airborne contaminants. At the nanoscale, number concentration and surface area concentration are more relevant metrics for health effects, as many nanomaterial toxicity mechanisms (oxidative stress, inflammation, protein binding) correlate more strongly with particle number and surface area than with mass. The standard therefore recommends a multi-metric approach: number concentration (particles/cm³) using condensation particle counters (CPCs) or scanning mobility particle sizers (SMPS), surface area concentration (μm²/cm³) using diffusion charging or BET-equivalent methods, active surface area using epiphaniometry, and mass concentration (μg/m³) using filter-based gravimetric analysis or TEOM (tapered element oscillating microbalance) for specific size fractions.
The standard details two complementary sampling strategies: personal sampling and area (static) sampling. Personal sampling uses battery-powered pumps worn by workers with size-selective samplers that match the inhalable, thoracic, and respirable conventions defined in ISO 7708 and EN 481. For nanomaterials, the respirable fraction is of primary interest as nanoparticles deposit predominantly in the alveolar region. Area sampling, using stationary instruments, provides time-resolved data on spatial and temporal variations in nanoparticle concentrations, identifying emission sources and peak exposure events. The standard recommends combining both approaches: personal samplers for compliance assessment against occupational exposure limits (OELs), and area monitoring for source identification and control verification.
| Metric | Instrument / Method | Size Range | Application | Advantages | Limitations |
|---|---|---|---|---|---|
| Number concentration | CPC, SMPS | 1 nm – 1 μm | Real-time monitoring | High sensitivity | No chemical information |
| Surface area concentration | Diffusion charger, NSAM | 10 nm – 1 μm | Alveolar dose estimate | Health-relevant metric | Calibration dependent |
| Active surface area | Epiphaniometer | 1 nm – 10 μm | Surface reactivity | Direct measurement | Not widely available |
| Mass concentration | Filter gravimetric, TEOM | 10 nm – 10 μm | Regulatory compliance | Standard method | Low sensitivity for nano |
| Size distribution | SMPS, ELPI, FMPS | 1 nm – 10 μm | Source apportionment | Detailed information | Complex, expensive |
Sampling and Analysis Protocols
ISO/TR 27628 provides detailed protocols for sampling and analysis of nanoparticle aerosols. For filter-based sampling, the choice of filter substrate is critical: polycarbonate track-etched (PCTE) filters are recommended for subsequent electron microscopy analysis due to their flat surface and well-defined pore structure, while Teflon (PTFE) filters are preferred for gravimetric and chemical analysis due to their low hygroscopicity and high purity. Sampling flow rates and durations must be optimised to collect sufficient material for analysis without overloading the filter, as particle-particle interactions on overloaded filters can alter morphology and bias size distribution measurements.
The standard places particular emphasis on electron microscopy analysis of collected nanoparticles, recognising that particle morphology, agglomeration state, and elemental composition are critical parameters for exposure characterisation. TEM analysis at magnifications of 20,000× to 200,000× enables visualisation of individual nanoparticles and their agglomerates, while EDX (energy-dispersive X-ray spectroscopy) provides elemental identification. The standard recommends counting a minimum of 500 particles per sample for statistically robust size distributions, with automated image analysis software to increase throughput and reduce operator bias. For crystalline nanoparticles, SAED (selected area electron diffraction) patterns provide crystallographic information that can distinguish polymorphs with different toxicological profiles.
When characterising workplace nanoparticle exposures, always perform background measurements in the same location during non-production periods. Urban background aerosol number concentrations typically range from 10,000 to 50,000 particles/cm³, and industrial activities can elevate concentrations to 10⁶–10⁷ particles/cm³. Subtracting background contributions is essential for isolating process-specific emissions.
Risk Assessment and Control Implications
ISO/TR 27628 provides guidance on interpreting exposure measurements for risk assessment purposes. In the absence of established occupational exposure limits (OELs) for most engineered nanomaterials — only a handful of substances (e.g., TiO₂, carbon black, welding fumes) have formal OELs that explicitly consider the nanoscale fraction — the standard recommends using the “control banding” approach adapted for nanomaterials. This approach assigns exposure scenarios to risk bands based on a combination of hazard potential (derived from physicochemical properties and toxicological data) and exposure potential (from workplace measurements). Each risk band prescribes a set of control measures, ranging from good industrial hygiene practice for the lowest band to full containment with HEPA filtration and personal protective equipment for the highest.
From an engineering control perspective, the standard emphasises that conventional LEV (local exhaust ventilation) systems designed for micron-sized particles may be ineffective for nanoparticles due to their different aerodynamic behaviour. Nanoparticles follow gas streamlines and may not be captured by hood designs that rely on particle inertia for collection. High-velocity, low-volume (HVLV) systems with close-capture hoods, HEPA-filtered exhaust, and complete enclosure of nanoparticle-handling processes are recommended as primary engineering controls. The effectiveness of these controls should be verified using real-time nanoparticle monitoring instruments both inside and outside the controlled area.
Never rely on traditional dust masks (FFP1/FFP2 or N95) for nanoparticle protection without verification. While these respirators provide some protection against nanoparticles, the most penetrating particle size (MPPS) for mechanical filters is typically in the range of 50–200 nm, where filtration efficiency can drop below 95% for electrostatic filter media. For high-exposure scenarios, powered air-purifying respirators (PAPR) with HEPA filters or supplied-air respirators (SAR) provide more reliable protection.
Frequently Asked Questions
Q: What is the difference between ultrafine particles and engineered nanoparticles in workplace monitoring?
Ultrafine particles (UFPs) are incidental nanoparticles generated by processes such as combustion, welding, and engine exhaust. Engineered nanomaterials are intentionally produced. Both fall within the same size range (<100 nm), and ISO/TR 27628 applies to both, but engineered nanomaterials often require additional chemical-specific analysis to distinguish them from background UFPs.
Ultrafine particles (UFPs) are incidental nanoparticles generated by processes such as combustion, welding, and engine exhaust. Engineered nanomaterials are intentionally produced. Both fall within the same size range (<100 nm), and ISO/TR 27628 applies to both, but engineered nanomaterials often require additional chemical-specific analysis to distinguish them from background UFPs.
Q: What is the most penetrating particle size (MPPS) for respirators?
The MPPS for most mechanical filter media is approximately 50–200 nm, where diffusion and interception collection mechanisms are least efficient. At this size range, some respirators may allow up to 5–10% penetration. For reliable protection against nanoparticles, HEPA (H13/H14) filters with certified efficiency ≥99.95% are recommended.
The MPPS for most mechanical filter media is approximately 50–200 nm, where diffusion and interception collection mechanisms are least efficient. At this size range, some respirators may allow up to 5–10% penetration. For reliable protection against nanoparticles, HEPA (H13/H14) filters with certified efficiency ≥99.95% are recommended.
Q: How do I determine if workplace nanoparticle levels are acceptable?
In the absence of formal OELs, the control banding approach in ISO/TR 27628 can be used. Compare measured concentrations to available benchmark OELs (e.g., NIOSH REL for TiO₂: 0.3 mg/m³ for ultrafine fraction), or use the nano-reference values (NRV) proposed by the Dutch social partners: 40,000 particles/cm³ for biopersistent granular nanomaterials.
In the absence of formal OELs, the control banding approach in ISO/TR 27628 can be used. Compare measured concentrations to available benchmark OELs (e.g., NIOSH REL for TiO₂: 0.3 mg/m³ for ultrafine fraction), or use the nano-reference values (NRV) proposed by the Dutch social partners: 40,000 particles/cm³ for biopersistent granular nanomaterials.
Q: Can real-time nanoparticle monitors replace filter-based sampling?
Real-time monitors provide invaluable temporal resolution but cannot replace filter-based sampling for chemical identification and gravimetric analysis. The standard recommends using both approaches in parallel: real-time instruments for identifying peak exposures and source contributions, and filter samples for chemical characterisation and regulatory compliance.
Real-time monitors provide invaluable temporal resolution but cannot replace filter-based sampling for chemical identification and gravimetric analysis. The standard recommends using both approaches in parallel: real-time instruments for identifying peak exposures and source contributions, and filter samples for chemical characterisation and regulatory compliance.
