Dust Exposure Assessment
Controls & Compliance · Controls & Compliance overview
A dust exposure assessment is the structured evaluation of how much airborne dust workers are exposed to during their normal work, which substances are present, and whether the existing controls are keeping exposure below the relevant Workplace Exposure Limits set out in HSE EH40. It is the technical backbone of COSHH compliance for any workplace with a significant dust risk.
What a dust exposure assessment reviews
A dust exposure assessment looks at the people, tasks, materials, environment and controls together. It identifies the substances and dust fractions present (respirable, inhalable, specific named substances, fibres or PM), characterises how exposure arises during the working day, and quantifies it against the appropriate WEL.
It is a technical document, not a generic risk paragraph. The assessment supports COSHH Regulation 6 (assessment of risk), Regulation 7 (prevention or control of exposure) and Regulation 10 (monitoring exposure where appropriate), and forms the evidence base for decisions about controls, RPE, training and ongoing monitoring.
Risk assessment, exposure monitoring and control review
Three related activities are sometimes confused. A COSHH risk assessment is a qualitative judgement about whether exposure is likely to be adequately controlled, supported by competent reasoning. Exposure monitoring is the quantitative measurement of airborne concentrations against WELs, normally by personal sampling. A control review evaluates whether the engineering, procedural and protective measures in place are working as intended — including LEV TExT reports and RPE programme records.
A robust dust exposure assessment usually combines all three. Pure risk assessment without measurement is hard to defend where exposures could plausibly approach a WEL; measurement without a control review leaves the question of how to improve unanswered.
How tasks, materials and people are considered
The assessment starts by walking the work as it is actually done. It identifies the materials handled and their dust-generating potential, the tasks that generate or disturb dust, the people performing those tasks (with similar exposure groups, or SEGs, used to group workers with comparable exposure profiles), the duration and frequency of each task, the environment in which the work is done, and the controls in place.
It then frames the sampling strategy around the SEGs and tasks most likely to drive exposure. Full-shift personal sampling is the normal default for substance-specific WEL comparison; task-based sampling supports source-tracking and control improvement.
Sampling strategy and methods
UK dust exposure assessment is structured around BS EN 689, which sets out a tiered approach to deciding whether exposure is reliably below the WEL. The reference methodology for gravimetric dust sampling is HSE MDHS 14/4, with substance-specific analytical methods (for example XRD for respirable crystalline silica, GC/MS for some organics, microscopy for fibres) overlaid as required.
Real-time particulate monitoring of PM2.5, PM10 and total respirable mass complements gravimetric sampling by mapping concentrations across the working day and helping identify which specific tasks drive peaks. Real-time data is interpreted alongside, not in place of, substance-specific gravimetric results when comparison against a WEL is required.
Respirable, inhalable, PM and fibre considerations
The relevant dust fraction depends on the substance and its health effects. Respirable dust monitoring is used for substances with deep-lung effects (for example respirable crystalline silica). Inhalable dust monitoring is used for substances acting in the upper airways or systemically (for example wood dust). PM2.5/PM10 mapping is used to characterise fine and coarse particulate in screening or continuous-monitoring scenarios. Airborne fibre assessment by microscopy is used where MMMF, RCF or other fibrous materials are present.
A single dust exposure assessment for a complex workplace may combine several of these measurements, sequenced so that the most exposure-relevant fractions are characterised first.
How findings support proportionate control decisions
Results are most useful when they translate into prioritised action. A defensible assessment reports the 8-hour TWA for each SEG, the comparison to the applicable WEL, the contribution of individual tasks to exposure, the condition of existing controls, and a prioritised set of practical improvements. Improvements are normally framed against the COSHH hierarchy: source elimination first, engineering controls next, administrative measures and RPE thereafter.
Re-monitoring after control changes verifies that the planned exposure reduction has been achieved and closes the assessment loop.
When dust exposure assessment should be reviewed
An assessment should be reviewed whenever the basis for it changes. Typical triggers include a process or material change, the introduction of new equipment, modifications to LEV or workplace layout, exposure monitoring results that approach a WEL, LEV TExT findings that raise concerns, health complaints or symptom reports, and on a defined periodic basis even when nothing else has changed.
Frequently asked questions
Is exposure monitoring always required under COSHH?
COSHH Regulation 10 requires exposure monitoring where it is needed to ensure adequate control or to protect health. For many dust-generating processes this means measurement is the practical way to demonstrate compliance with the WEL, but the requirement is judgement-based rather than a fixed frequency.
How many samples are normally needed?
Sample numbers follow the BS EN 689 strategy and depend on the variability of exposure, the proximity to the WEL and the size of the similar exposure group. A small number of well-chosen samples is often acceptable where exposure is clearly low; more samples are required as results approach the WEL.
What is a similar exposure group?
A similar exposure group (SEG) is a set of workers whose work patterns, tasks, materials and controls are sufficiently similar that their exposures can be characterised together. SEGs are the unit of analysis for COSHH exposure sampling under BS EN 689.
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