Controlling Silica Dust on Construction Sites

Respirable crystalline silica (RCS) is one of the most serious occupational health hazards on UK construction sites. Cutting, grinding, drilling or breaking materials such as concrete, sandstone, brick and mortar releases fine particles that penetrate deep into the lungs. Prolonged exposure causes silicosis — an irreversible and potentially fatal scarring of lung tissue — as well as lung cancer and chronic obstructive pulmonary disease (COPD). Controlling silica dust on construction sites is therefore a legal duty, not an optional precaution.

The Legal Basis

The Control of Substances Hazardous to Health Regulations 2002 (COSHH) require employers to:

1. Assess the risk from RCS exposure (supported by the broader duty under reg 3 of the Management of Health and Safety at Work Regulations 1999).
2. Prevent exposure where reasonably practicable; where prevention is not practicable, adequately control it.
3. Apply controls in the correct hierarchy — not simply reach for a dust mask.

The Workplace Exposure Limit (WEL) for RCS is 0.1 mg/m³ (8-hour TWA). This is not a safe threshold — it is a legal ceiling. COSHH requires employers to reduce exposure to as low as reasonably practicable (ALARP) below that limit. Where CDM 2015 applies, the principal contractor must also coordinate dust control across trades on site.

Understanding Where RCS Comes From

Common silica-containing materials include:

High-energy, dry operations produce the most dust: angle grinding concrete, dry cutting kerbs with a disc cutter, and jackhammering are among the worst. Even short-duration tasks matter — 15 minutes of dry angle grinding concrete can generate RCS well above the WEL.

The Correct Control Hierarchy Under COSHH

1. Elimination

Ask whether the task is necessary at all. Can a pre-cast or pre-cut component remove the need to cut on site? Re-specifying materials or methods at the design stage (a CDM 2015 designer duty) can eliminate the hazard entirely.

2. Substitution

Use lower-silica materials where the specification allows — for example, substituting high-silica sandstone for a lower-silica alternative in landscaping work.

3. Engineering Controls

These are the most effective and reliable controls for most site tasks:

• On-tool extraction (OTE): Shrouded angle grinders, disc cutters and hammer drills connected to an industrial vacuum unit rated to at least M-class (for RCS, H-class is often preferable). OTE must be compatible with the specific tool — check manufacturer guidance.
• Water suppression: A continuous, controlled water feed at the cutting or drilling point suppresses dust at source. Effective for disc cutting, core drilling and some grinding operations. Requires proper water management to avoid slip hazards and runoff issues.
• Local exhaust ventilation (LEV): For fixed or semi-fixed operations (cutting tables, masonry saws), a hooded LEV system connected to an H-class vacuum or industrial dust extractor provides consistent capture.
• Enclosure and segregation: Isolate dusty operations from other workers. Establish exclusion zones and use physical barriers or sheeting where practicable.

4. Administrative Controls

• Limit the duration of high-dust tasks; rotate workers to reduce individual exposure time.
• Schedule dusty work when fewer workers are present in the area.
• Never use compressed air to blow dust off clothing or surfaces.
• Ensure workers are trained to understand what RCS is, why it matters, and how to use and maintain controls correctly.
• Carry out face-fit testing and maintain records — RPE that does not seal correctly provides no meaningful protection.

5. Respiratory Protective Equipment (RPE) — Last Resort, Not First Line

RPE is the last control, not a substitute for engineering measures. For RCS:

• A minimum of FFP3 disposable mask or a half-face respirator with a P3 filter is required.
• FFP2 masks are not sufficient for RCS.
• RPE must be compatible with the wearer's face — a face-fit test is mandatory where tight-fitting RPE is used.
• Consider powered air-purifying respirators (PAPRs) for longer-duration tasks or where wearers have facial hair that prevents a tight seal.

Monitoring and Health Surveillance

Where significant RCS exposure cannot be ruled out, employers should consider air monitoring to verify that controls are working and that exposure remains below the WEL. HSE provides MDHS101 guidance on dust measurement methods.

Health surveillance — including periodic lung function testing — is required under COSHH where there is a reasonable likelihood of ongoing exposure. Records must be retained for 40 years.

Putting It into Your RAMS

A COSHH assessment for silica-generating tasks must identify the specific materials and operations involved, evaluate the likely exposure, and specify each control measure with the person responsible for checking it. The method statement in your RAMS should describe the exact sequence of work: which tool, which dust-suppression method, what class of vacuum, the exclusion zone dimensions, and the RPE required as a backup. Vague entries such as "dust mask to be worn" are insufficient and will not satisfy a site inspection or an HSE investigation.

Good dust control is not complicated — but it does require the right equipment, properly maintained, used consistently on every task, every day.