Dust Exposure FAQ
Resources · Resources overview
Frequently asked questions on workplace dust exposure, respirable and inhalable dust, airborne fibres, PM2.5 and PM10 monitoring, dust extraction, exposure assessment under COSHH and enquiries to Dust Exposure UK. Answers are written for UK health and safety teams and employers managing dust risk in real workplaces.
Dust exposure fundamentals
The questions in this section cover the underlying ideas — what dust exposure means in an occupational context, which fractions are relevant, and how UK regulation frames the problem under the Control of Substances Hazardous to Health Regulations 2002 (COSHH).
Dust monitoring and assessment
Questions about how workplace dust exposure is actually measured: which fractions are sampled, which reference methods are used, how a sampling strategy is built and how results are interpreted against the Workplace Exposure Limits in HSE EH40.
Fibres and fine particles
Airborne fibres, MMMF, ceramic fibre, PM2.5, PM10 and ultrafine particles all need different metrics and different sampling approaches. The questions in this section deal with the most common practical distinctions.
Dust extraction and control
Engineering and procedural controls are how exposure is actually reduced. Questions here cover LEV testing, RPE programmes and the practical relationship between extraction systems and a documented COSHH position.
Working with Dust Exposure UK
Questions about getting in touch, the kinds of enquiries we handle and the typical first steps when a workplace needs to characterise dust exposure or improve its controls.
Frequently asked questions
What is workplace dust exposure?
Workplace dust exposure is the inhalation of airborne solid particulate during normal work. It is assessed under the Control of Substances Hazardous to Health Regulations 2002 (COSHH) against the Workplace Exposure Limits set out in HSE EH40 for specific substances and dust fractions.
What is the difference between respirable and inhalable dust?
Respirable and inhalable describe different size fractions of the same airborne cloud. The inhalable fraction is everything that can be drawn into the nose or mouth (median around 100 µm). The respirable fraction is the smaller subset (50% cut at 4 µm) that can reach the alveolar region of the lung. WELs are set against the fraction relevant to the substance's health effect.
Does COSHH require dust monitoring?
COSHH Regulation 10 requires exposure monitoring where it is needed to ensure adequate control or to protect health. In practice, workplaces with significant dust generation usually need structured personal monitoring to demonstrate that exposure is reliably below the relevant WEL.
What is a Workplace Exposure Limit?
A Workplace Exposure Limit (WEL) is a statutory limit on the concentration of a hazardous substance in workplace air, published by HSE in EH40. WELs are normally expressed as an 8-hour time-weighted average (TWA) and, for some substances, a short-term (15-minute) limit. Exposures must not exceed the WEL and should be reduced as far as reasonably practicable below it.
How is dust exposure actually sampled?
Personal sampling normally draws workplace air at a controlled flow rate through a size-selective sampling head worn in the breathing zone, onto a pre-weighed filter. The filter is weighed and analysed under HSE MDHS 14/4 and substance-specific methods. Results in mg/m³ are compared to the WEL as an 8-hour TWA.
How many dust samples do we need?
Sample numbers follow the BS EN 689 strategy and depend on how variable exposure is, how close it sits to the WEL, and how many workers fall into each similar exposure group. A small number of well-chosen samples is acceptable where exposure is clearly low; more samples are required as results approach the WEL.
Is visible dust a reliable indicator of exposure?
No. The respirable fraction that drives chronic respiratory risk is largely invisible. A workshop that looks clean can still carry exposures above the WEL, and conclusions based on visible dust alone routinely understate respirable risk. Measurement is the reliable basis for judgement.
Is PM2.5 monitoring the same as a COSHH dust assessment?
No. PM2.5 measures total fine-particulate mass without identifying the substance. A COSHH assessment quantifies specific hazardous substances against their own WELs. PM2.5 is useful for mapping and screening; it does not replace substance-specific sampling where a hazardous dust is present.
When are airborne fibres assessed by counting instead of weighing?
Fibre exposure depends on fibre dimensions and biopersistence rather than mass. Fibres meeting the WHO convention (length >5 µm, width <3 µm, aspect ratio ≥3:1) are counted under phase contrast optical microscopy following HSE MDHS 59, with results reported in fibres per millilitre of air.
Are man-made mineral fibres regulated like asbestos?
No. MMMF such as glass wool, rock wool and ceramic fibre are not subject to the Control of Asbestos Regulations 2012. They are assessed under COSHH against their own fibre-specific WELs. Refractory ceramic fibre is additionally classified as a Category 1B inhalation carcinogen under CLP.
What is the WEL for wood dust?
HSE EH40 sets an 8-hour TWA WEL of 3 mg/m³ for hardwood dust and 5 mg/m³ for softwood dust, both against the inhalable fraction. Mixed exposures are assessed against the lower hardwood limit. Hardwood dust is also classified as a Category 1A carcinogen for inhalation.
How often must LEV be tested?
Under COSHH Regulation 9, local exhaust ventilation used to control hazardous substances must receive a thorough examination and test (TExT) at intervals not exceeding 14 months. The TExT report must be kept for at least five years.
Is RPE on its own enough?
No. Under the COSHH hierarchy of control, respiratory protective equipment is the last layer, used in combination with — not instead of — feasible elimination, substitution and engineering controls. Tight-fitting RPE requires individual face-fit testing and a documented programme.
When should a dust exposure assessment be reviewed?
Whenever the basis for it changes. Typical triggers are process or material changes, new equipment, LEV modifications, monitoring results approaching a WEL, LEV TExT findings that flag concerns, reported respiratory symptoms or a planned periodic review cycle.
Do small workshops need formal dust assessment?
COSHH duties apply regardless of business size. Workshops with active sawing, sanding, grinding, powder handling or fibre work will normally need a structured exposure assessment to demonstrate that controls are adequate, even where headcount is small.
How do I get in touch with Dust Exposure UK?
You can contact us by email at info@dustexposure.co.uk or by phone on 0800 433 7914. The contact page also has an enquiry form. We work across the United Kingdom with employers, occupational hygienists and facilities teams managing workplace dust risk.
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