Dust is a COSHH substance even when it carries no hazard label at all. Ordinary dust becomes a substance hazardous to health once airborne concentrations reach 10 mg/m³ inhalable or 4 mg/m³ respirable as an 8-hour average — and silica and hardwood dust are far more tightly controlled than that.
This is the part of COSHH that construction and woodworking most often miss. There is no pictogram on a paving slab. But cutting one dry can put a worker over the silica limit in minutes.
Inhalable vs respirable — why two numbers?
Because the size of a particle decides how far into your lungs it gets.
| Inhalable dust | Respirable dust | |
|---|---|---|
| What it is | Everything drawn in through the nose and mouth | The fine fraction that reaches the deep gas-exchange region of the lung |
| Visible? | Often yes | Usually invisible |
| COSHH threshold | 10 mg/m³ (8-hour TWA) | 4 mg/m³ (8-hour TWA) |
The dangerous fraction is the one you cannot see. A workshop that “looks clear” after the visible cloud settles can still be heavily contaminated with respirable particles that stay airborne for hours.
Respirable crystalline silica
Silica is present in most construction materials — concrete, mortar, brick, stone, tile, sandstone and engineered stone worktops. Cutting, grinding, drilling, chasing or polishing releases respirable crystalline silica (RCS).
The workplace exposure limit is 0.1 mg/m³ as an 8-hour time-weighted average (EH40). That is a very small number — a tenth of a milligram averaged across a whole shift.
The health effects build over years and are irreversible:
- Silicosis — permanent scarring of lung tissue
- Chronic obstructive pulmonary disease (COPD)
- Lung cancer — RCS is a recognised carcinogen
- Increased susceptibility to other lung disease
Because RCS is carcinogenic, COSHH requires exposure to be reduced to as low as is reasonably practicable, not simply below 0.1 mg/m³. Being under the limit is not the finish line. See workplace exposure limits explained.
Where it catches people out
- Dry cutting paving, kerbs or blocks with a disc cutter
- Chasing walls for cables or pipes
- Drilling or coring concrete
- Scabbling, grinding or polishing concrete floors
- Fabricating engineered stone worktops — very high silica content
- Sweeping up afterwards, which re-suspends everything that had settled
Wood dust
Wood dust has its own limits in EH40, and hardwood is treated more strictly than softwood:
- Hardwood dust — 3 mg/m³ (8-hour TWA). Hardwood dust is classified as a carcinogen and is associated with sinonasal cancer, a rare cancer of the nose and sinuses that occurs at raised rates among woodworkers.
- Softwood dust — 5 mg/m³ (8-hour TWA).
Wood dust is also a respiratory sensitiser. Once someone develops occupational asthma from it, the sensitisation is usually permanent — any future exposure, even far below the limit, can trigger an attack. That often ends a career in the trade.
Other effects include dermatitis and eye irritation. Where hardwood and softwood are mixed, treat the mixture to the stricter hardwood standard.
Check the current edition of EH40 for any dust you work with — limits are revised between editions.
Other dusts that catch people out
- Flour dust — a well-recognised cause of occupational asthma in bakeries; it has its own workplace exposure limit
- MDF — generates very fine dust and may release formaldehyde when machined
- Cement — alkaline, causing dermatitis and burns as well as respiratory irritation
- Plasterboard and gypsum
- Grain dust in agriculture
Asbestos is not a COSHH dust. It is controlled entirely separately under the Control of Asbestos Regulations 2012 — see asbestos awareness training.
Controlling dust — in the right order
COSHH Regulation 7 sets the sequence. PPE is the last step, not the first.
1. Eliminate
- Order materials cut to size so no cutting happens on site
- Use pre-formed lintels, blocks and kerbs
- Design out chasing by planning service routes
2. Substitute
- Lower-silica materials where the specification allows
- Block splitters instead of disc cutters
- Hand tools instead of powered ones for small jobs
3. Engineering controls — the two that do the real work
Water suppression. Feeding water to the blade or bit stops dust becoming airborne at the point it is created. It must be a proper continuous supply at the right rate — a quick splash from a bottle does nothing, and neither does a tank that runs dry halfway through the cut.
On-tool extraction. A shroud or hood at the cutting point connected to a suitable vacuum. For construction dust that means an M-class extraction unit as a minimum; a domestic or workshop vacuum will simply pass the fine fraction straight through its filter and back into the room.
Also: local exhaust ventilation on fixed woodworking machinery — which must be thoroughly examined and tested at least every 14 months.
4. Ways of working
- Cut outdoors or in a well-ventilated area where possible
- Keep other people out of the immediate area
- Rotate tasks to reduce individual exposure time
- Never dry sweep. Use an M-class vacuum or wet methods — sweeping re-suspends settled dust and undoes the day’s controls in two minutes
- Never use compressed air to blow dust off clothing or surfaces
5. RPE — last, and only done properly
Respiratory protective equipment is a supplement to the controls above, never a substitute. For it to work at all:
- It must be the right assigned protection factor for the exposure
- Tight-fitting masks require face-fit testing for each individual wearer
- A seal cannot be achieved through stubble or a beard — this is not a preference, it is physics; loose-fitting powered hoods are the alternative
- It must be maintained, stored clean, and filters changed on schedule
A dust mask worn over stubble, chosen because it was in the van, protects nobody. See our RPE course.
Health surveillance
Where workers are exposed to RCS or wood dust at levels that could cause disease, COSHH Regulation 11 may require health surveillance — typically respiratory questionnaires and lung function testing, with records kept for 40 years.
Its purpose is early detection. Silicosis and occupational asthma cannot be reversed, but exposure can be stopped before the damage progresses — which only happens if someone is looking.
Further reading
Dust and respiratory training
- Silica Dust Awareness — where RCS comes from, the health effects and how to control it
- Respiratory Protective Equipment (RPE) — selection, fit and maintenance
- Respiratory Diseases Awareness
- COSHH Awareness
Related reading: What is COSHH? · Workplace exposure limits · COSHH employer duties
£9 per course. CPD accredited, 100 % online, verifiable e-certificate on completion. Pay for 2, get 3 — any 3 courses for £18.
Please note: these are CPD-accredited awareness courses and general information, not legal or medical advice. They are not Ofqual-regulated qualifications, and awareness training does not replace face-fit testing, health surveillance or competent occupational hygiene advice. Exposure limits are revised between editions of EH40 — always check the current edition.