Most site dust monitors use optical particle counting. A laser shines through the sample stream; particles scatter light, which a sensor detects. The signal’s intensity and shape are used to estimate particle size and count, then algorithms convert counts into mass (PM10, PM2.5, PM1). This gives real-time trends to manage dust at source, in the air, and during clean-up.

The key components

• Sampling: a fan or pump draws air at a controlled flow so readings are stable.
• Optical engine: laser, lens, and detector register each particle’s scattered light.
• Electronics and firmware: bin counts by size and estimate mass concentration.
• Enclosure and inlets: protect from rain and large debris; some add cyclone inlets.

Strengths and limitations

• Strengths: immediate feedback for task control, alarms for exceedances, data logging for COSHH records.
• Limitations: humidity, particle composition, and shape affect light scattering. Optical PM can drift from gravimetric mass if not checked.

Practical set-up on site

• Place at breathing height near the workface but out of direct jet streams from tools or scrubbers.
• Warm up for a few minutes; zero-check if the device supports a filter cap or zero attachment.
• Log baseline before work starts, then track during task changes.
• Use action levels that trigger controls: switch on LEV, increase air changes, or pause and damp down.
• Protect the sensor: shrouds outdoors, away from water spray; keep intakes clean.

Maintenance that keeps data trusted

• Weekly: wipe inlets, inspect filters, and review drift against a reference area.
• Monthly: flow check, firmware updates, and a zero/span verification where available.
• Periodically: validate against a gravimetric sample for your dust type.

Using the readings

Align monitors with the three-layer framework: prove source capture is working, verify air scrubber positioning by watching PM fall across the area, and confirm that vacuum-only housekeeping is preventing re‑suspension. If readings plateau, inspect filters and airflow under load, not just rated figures.