Why COSHH Assessments Are Required for Dust
The Control of Substances Hazardous to Health Regulations 2002 (COSHH) require employers to make a suitable and sufficient assessment of the risk to health from hazardous substances before work with those substances begins. Dust is a hazardous substance where it contains or generates harmful materials — and for construction work involving concrete, stone, brick, or contaminated ground, that means hazardous dust is almost always present.
A COSHH assessment for dust is not a theoretical exercise. It should drive real decisions about the controls used for specific activities — and it should be kept up to date as work progresses and activities change.
Step 1: Identify the Hazardous Dusts
Not all construction dust is equally hazardous. The three main categories relevant to construction and demolition are:
- Respirable crystalline silica (RCS) — generated from concrete, stone, brick, sand, mortar, and many other materials. WEL: 0.1 mg/m³. Causes silicosis, lung cancer and other serious conditions.
- Wood dust — generated from cutting, sanding and machining timber. WEL: 3 mg/m³ hardwood, 5 mg/m³ softwood. Causes asthma and nasal cancer.
- General construction dust — WEL: 10 mg/m³ (total inhalable), 4 mg/m³ (respirable). Lower hazard but still a health risk at high levels.
For demolition and construction work, the starting assumption should be that RCS is present. If materials containing silica are being disturbed — and for most demolition, groundworks and masonry work they are — the assessment must address RCS specifically.
Step 2: Assess the Exposure
Assess how much dust each worker is likely to be exposed to, over what period, and in what conditions. Consider:
- The activity (cutting, breaking, sweeping, drilling)
- The duration and frequency of the activity
- The quantity of material involved
- Whether the work is in the open air, partially enclosed, or fully enclosed
- Whether existing ventilation or other controls are in place
For RCS specifically, HSE's COSHH Essentials dust sheets provide exposure estimates for specific activities that can be used to inform your assessment without requiring expensive air monitoring in many cases.
Step 3: Select Controls
Controls must be selected following the COSHH hierarchy: prevention, engineering controls, administrative controls, and PPE. For dust on construction sites:
- Prevention: Can the activity be carried out in a way that doesn't generate the dust? (e.g. using wet methods, pre-formed components)
- Engineering controls: Water suppression at source, on-tool extraction, local exhaust ventilation
- Administrative controls: Reducing exposure duration, rotating workers, using exclusion zones
- PPE: Respiratory protective equipment (RPE) — only as a supplement to, not substitute for, engineering controls
Water suppression is the preferred engineering control for most construction dust-generating activities. The MW Equipment DustBag provides standalone, at-source water mist suppression — no mains required — making it practical for demolition and construction sites where hose infrastructure is impractical. Learn more →
Step 4: Document Your Assessment
The COSHH assessment must be documented where there are 5 or more employees. It should record: the activity and the hazardous substance; the expected exposure level; the controls selected and why; any monitoring or health surveillance required; and when the assessment will be reviewed. The documentation should be accessible on site and updated when activities change.
Step 5: Review and Update
A COSHH assessment is not a one-time document. It must be reviewed when activities change, when new information about the hazard becomes available, or when monitoring suggests controls are not working as intended. On a demolition site where the work front changes daily, this may mean daily updates to reflect the activities planned for that day.