Monitoring frequency should match risk, not convenience. The aim is to catch problems early and prove controls work. Use a risk-based schedule that reflects materials, tasks, duration, and proximity to people.

Risk tiers and suggested frequencies

High risk (e.g., concrete cutting, scabbling, dry sweeping, welding fume, enclosed spaces): continuous area monitoring of PM fractions near the task and at receptors; task-based personal sampling as required by COSHH, especially for RCS. Medium risk (e.g., sanding with extraction, controlled demolition): logging area monitors during active periods plus daily spot checks. Low risk (short-duration, well-controlled tasks): start-up and end-of-shift checks, with spot monitoring when tasks change.

Trigger-based escalation

Increase monitoring when weather shifts, containment changes, or new trades begin. If an action level is exceeded, add a second monitor to triangulate, review controls, and consider personal sampling until stability returns.

Placement and logging

Place monitors at breathing height, one near the source and one at a receptor. Use 1-minute or 5-minute logs to capture peaks. Correlate peaks with a site diary so you can assign causes and fix them quickly.

Verification and maintenance

Do daily zero checks and weekly audits of location and configuration. Maintain extraction and air cleaning equipment; verify under-load airflow rather than relying on free-air figures. LEV systems require thorough examination and testing at least every 14 months in the UK.

Practical takeaways

• Match monitoring frequency to risk: continuous for high-risk tasks, logged periods for medium, spot checks for low.
• Escalate when site conditions change or action levels are crossed.
• Use dual locations (source and receptor) and short logging intervals.
• Keep equipment maintained and verify performance under load.
• Document everything: readings, actions, and control changes.

With a risk-based schedule, monitoring becomes a control tool, not a box-tick, and it delivers safer, more predictable work.