Particulate Monitoring
Core Dust · Core Dust overview
Particulate monitoring is the measurement of solid (and sometimes liquid) airborne particles in workplace and indoor air. In an occupational context it covers gravimetric size-selective sampling against EH40 Workplace Exposure Limits and real-time optical monitoring of task and area concentrations.
What particulate monitoring covers
Particulate monitoring is the set of methods used to characterise airborne particulate exposure. In UK workplaces it encompasses personal gravimetric sampling for the respirable and inhalable fractions, fibre counting under phase-contrast microscopy, and real-time optical measurement of size-resolved particle mass or number concentration.
Each method answers a different question. Gravimetric sampling produces a defensible 8-hour TWA mass concentration comparable to an EH40 Workplace Exposure Limit. Real-time optical monitoring shows how that exposure builds across tasks and identifies the high-emission moments to target. Fibre counting addresses exposures (for example to MMMF or ceramic fibres) that mass measurement does not adequately describe.
Workplace particulate monitoring vs general air quality
Occupational particulate monitoring and ambient or indoor-air-quality monitoring are related but not interchangeable. Ambient air quality work typically uses PM2.5 and PM10 mass concentrations measured by reference or equivalent methods against air quality standards expressed as 24-hour or annual means.
Workplace particulate monitoring uses the respirable, thoracic and inhalable size conventions defined for occupational exposure, sampled in the breathing zone of the worker, and compared against 8-hour TWA and short-term WELs in EH40. Reporting and instrument requirements differ accordingly. Where indoor-air-quality and occupational questions overlap (for example in offices, schools and commercial premises), both perspectives may be relevant and should be reported clearly.
Respirable, inhalable and PM fractions
The respirable and inhalable conventions describe deposition probabilities in different regions of the respiratory tract and are sampled with size-selective heads (cyclones for respirable, IOM-style heads for inhalable). The thoracic convention sits between them and is used for substances with effects in the conducting airways.
PM2.5 and PM10 are alternative size cuts used widely in air quality work, defined by 50% sampling efficiency at 2.5 µm and 10 µm aerodynamic diameter respectively. They are not direct substitutes for the occupational conventions, but real-time optical monitors that report PM fractions can be valuable for task-level mapping when interpreted alongside gravimetric reference samples.
How a monitoring strategy is selected
A defensible monitoring strategy follows BS EN 689 and starts from the substances present, the relevant EH40 limits and the questions the assessment must answer. Similar exposure groups are defined; the number and timing of personal samples are chosen to characterise variability; and instruments are selected to match the size convention required by each substance.
Where the priority is compliance demonstration, gravimetric personal sampling dominates and BS EN 689 statistics drive interpretation. Where the priority is investigation or control optimisation, real-time monitors are used to identify and rank task contributions. Most well-designed assessments combine the two.
- Identify substances and the size fraction(s) required by each EH40 entry.
- Define similar exposure groups by task, area and shift pattern.
- Plan enough personal samples across representative conditions to support BS EN 689 interpretation.
- Use real-time optical monitoring to map task contribution where useful.
- Document sampling conditions thoroughly so results can be re-interpreted later.
Interpreting findings cautiously
Particulate monitoring results are condition-dependent. A single shift sample showing exposure below a WEL does not by itself demonstrate that long-term exposure is controlled — it shows that exposure was below the WEL on that day, in those conditions, for that worker. BS EN 689 provides a structured way to combine multiple samples into a robust conclusion.
Equally, a single elevated result does not by itself indicate a chronic exposure problem. It indicates that on that day the WEL was approached or exceeded, and that further monitoring or control review is warranted. Interpretation should always describe the conditions, controls and tasks during sampling.
Practical improvement planning
Particulate monitoring is most useful when it leads to a clear improvement plan. The strongest reports tie each elevated result to a specific task or source, rank tasks by contribution to total exposure, and recommend control improvements that target the largest contributors first under the COSHH hierarchy.
Re-monitoring after changes is essential. Engineering controls that look effective in commissioning often perform differently in routine operation, and the only way to confirm sustained control is repeat measurement.
Frequently asked questions
Is PM2.5 monitoring equivalent to respirable dust monitoring?
Not directly. PM2.5 and the respirable convention have different size cuts and different sampling curves. Real-time PM2.5 instruments can complement respirable gravimetric sampling for task mapping, but comparison against the respirable EH40 WELs requires a sampler that implements the respirable convention under MDHS 14/4.
What is BS EN 689 and why does it matter?
BS EN 689 is the European standard for workplace exposure assessment by measurement. It sets out how to define similar exposure groups, how many samples to take, and how to interpret results statistically against a Workplace Exposure Limit. UK assessments aiming for a defensible compliance position generally follow it.
When should real-time particulate monitors be used?
Real-time monitors are valuable for identifying which tasks contribute most to exposure, for evaluating control improvements in real time, and for screening before more formal gravimetric sampling. They do not replace gravimetric measurement against a WEL.
How often should particulate monitoring be repeated?
Frequency depends on substance, prior results and process stability. Where prior results have approached the WEL, periodic re-monitoring is expected. Re-monitoring is also expected after a material, process or control change. BS EN 689 sets out the criteria for whether further measurement is required.
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