HSE uses the term respirable crystalline silica (RCS) for the tiny particles of silica that can reach the gas-exchange region of the lungs. Silica is found in concrete, mortar, brick, stone, and many aggregates; cutting and grinding release RCS.

What “respirable” means in practice

Respirable refers to the finest fraction, broadly aligned to the PM4 convention. These particles stay airborne, bypass the upper airways, and settle deep in the lungs where they can cause silicosis and cancer.

Limits and indicators

• HSE Workplace Exposure Limit (WEL) for RCS: 0.1 mg/m³ (8‑hour TWA).
• Visible dust is a strong sign controls are inadequate; re-check your method.
• Use mg/m³ measurements from personal sampling or real-time PM monitors to validate controls.

Controlling RCS on site

• Capture at source: water suppression and tool-mounted extraction with adequate airflow under load.
• Extraction class: M-Class is the minimum for silica-generating tasks; where fine, respirable or carcinogenic dusts are present, use units with H14 final filtration.
• Air cleaning: air scrubbers or negative air units help manage background dust, especially indoors.
• Housekeeping: vacuum surfaces; avoid sweeping and compressed air.

Practical example: pairing a masonry saw with M-Class extraction and a well-placed air scrubber (for example, a MAXVAC unit) often cuts peaks and improves visibility, but always confirm with measurements.

RPE still matters

Use suitable RPE (e.g., P3) when engineering controls cannot reliably keep exposures below the WEL, ensuring face-fit testing and maintenance.

Practical takeaways

• Plan for RCS wherever concrete, stone, or brick are cut or drilled.
• Use at-source extraction plus air cleaning; verify with mg/m³ data.
• Keep filters serviced and assess airflow under load, not free-air ratings.