What Is Respirable Crystalline Silica?
Respirable crystalline silica (RCS) is a fine dust generated when materials containing silica — concrete, stone, brick, sand, mortar, and many others — are cut, drilled, ground, crushed or otherwise disturbed. The particles are small enough to penetrate deep into the lungs, where they cause progressive and irreversible scarring (silicosis), lung cancer, and other serious conditions.
Silica is not a niche hazard. It is present in the majority of common construction and demolition materials. Work activities that generate significant silica dust include: cutting concrete with an angle grinder or disc cutter; scabbling or crushing concrete; demolishing masonry structures; crushing aggregate; drilling sandstone or granite; and earthworks on brownfield sites with contaminated soils.
The Legal Position: COSHH and the WEL
The Control of Substances Hazardous to Health Regulations 2002 (COSHH) require employers to prevent or — where prevention is not reasonably practicable — adequately control workers' exposure to hazardous substances, including RCS.
The Workplace Exposure Limit (WEL) for RCS is 0.1 mg/m³ as an 8-hour time-weighted average. This is one of the lowest WELs of any substance on the EH40 list. It was reduced from 0.3 mg/m³ in 2020, following clear evidence that the previous limit was insufficient to prevent disease.
Critically, the COSHH hierarchy of controls requires employers to consider prevention first, then engineering controls, then administrative controls, and only then personal protective equipment (PPE) — and only as a last resort. A worker wearing an RPF20 dust mask is not adequate COSHH compliance if engineering controls (such as water suppression) could have been used instead.
CDM Regulations 2015: The Designer and Principal Contractor Duty
The Construction (Design and Management) Regulations 2015 (CDM) place specific duties on designers and principal contractors in relation to dust. CDM requires principal contractors to ensure that, as far as is reasonably practicable, construction work is carried out in a way that ensures the health and safety of those carrying it out.
For demolition and heavy construction works, this includes ensuring that dust-generating activities are controlled at source — not managed at the boundary.
How Far Uncontrolled Exposure Exceeds the WEL
The gap between the WEL and typical uncontrolled exposures is significant. HSE research and industry monitoring data shows that dry cutting concrete with an angle grinder can generate RCS concentrations 10–50 times the WEL without controls in place. Even lower-intensity activities — such as breaking out concrete or working in enclosed areas with contaminated dust — can exceed the WEL.
This means that without active suppression, most concrete cutting and demolition activities will generate exposures above the legal limit. RPE alone is insufficient — it must be backed by engineering controls.
At-Source Suppression: The Priority Control Method
The HSE's COSHH guidance for construction dust is clear: dust should be controlled at source wherever practicable. The preferred hierarchy is: suppress the dust with water; use on-tool extraction; and use RPE as a supplement, not a substitute.
For demolition and construction sites where mains water is unavailable across the site footprint — which is the majority of sites — this creates a practical challenge. A mains-connected dust cannon requires hose infrastructure from a standpipe to the work area. On an active demolition front, this is impractical.
The MW Equipment DustBag is a standalone mobile dust suppression unit with a 2,000L integrated water tank, 180° oscillating cannon and up to 5 hours of operation without any mains connection. It can be repositioned to follow the demolition front by the site excavator, with no hose infrastructure and no mains supply required. Learn more about the DustBag →
Documentation and Compliance Records
Under COSHH, employers are required to keep records of their hazardous substance risk assessments, control measures in place, and (where relevant) health surveillance. For demolition and construction sites with significant silica exposure, this documentation should include: identification of dust-generating tasks, the controls in place, evidence that controls are being maintained and are effective, and records of any air monitoring carried out.
Principal contractors should also ensure this information is available to H&S managers, inspectors and other parties who may request it on site.
Enforcement
The HSE actively enforces COSHH and CDM requirements for dust on construction sites. Improvement notices, prohibition notices and prosecution are all available to inspectors where they find inadequate dust control. The consequences of non-compliance include enforcement action, financial penalties, reputational damage and — most seriously — preventable disease in workers who will not show symptoms for years or decades.
Given the long latency of silicosis and lung cancer (often 10–30 years between exposure and diagnosis), the full cost of inadequate dust control today will not be visible for a generation.