Understanding why dust settles or lingers in the air is essential for safety, compliance, and productivity on UK sites. The smaller the particle, the longer it can remain airborne, driving exposure to respirable hazards and nuisance contamination that slows work and triggers rework.

Why some dust never seems to settle

Particles behave according to size, shape, and density. PM10 is inhalable, PM4 is the respirable fraction relevant to lung deposition, PM2.5 and PM1 behave like smoke. Larger chips drop quickly under gravity. Fine particles are dominated by turbulence, thermal plumes from people and equipment, and electrostatic forces. PM1 can remain suspended for hours, continually re-entrained by foot traffic or ventilation. Humidity can increase agglomeration, making dust settle faster, while dry air promotes persistence.

Airflow patterns matter as much as generation rate. Supply diffusers, open doors, and even warm surfaces create eddies that keep dust airborne. This is why air scrubber placement, extraction capture velocity, and room pressure strategy are critical.

Compliance and exposure risk

Under COSHH and HSE EH40, the UK Workplace Exposure Limit for respirable crystalline silica is 0.1 mg/m³ as an 8-hour TWA. That is a tiny mass in a large volume of air, roughly a pinch of dust dispersed through a small room. OSHA standards also emphasise respirable fractions. The implication is clear: if you can see dust, your PM2.5 and PM1 are already elevated.

The three-layer framework

1) Capture at source

Prevent dust from escaping with water suppression, tool-mounted local exhaust ventilation, slower cutting speeds, and process redesign. Correctly matched shrouds and hoses maintain capture velocity at the point of generation.

2) Capture in the air

Use air scrubbers, LEV, or negative air machines to manage airborne particulate. Specify multi-stage filtration: pre-filter to protect the main filter, then main filter, then an H13 or H14 HEPA final stage for fine or carcinogenic dusts. H14 should be used for respirable silica, asbestos, or similar high-risk dusts. Size units by airflow under load, not free-air ratings, and account for filter loading over time.

3) Capture on surfaces

Prevent re-agitation by avoiding sweeping and compressed air. Use industrial vacuums with M-Class or H-Class performance and high-efficiency filtration. Keep hoses antistatic where possible and service machines regularly to hold performance as filters load.

Monitoring and verification

Use a particulate monitor or laser particle counter to trend PM10, PM4, PM2.5, and ideally PM1. Adjust workflows, airflow, and housekeeping frequency based on data. Differential pressure readings in Pa across filters help schedule timely changes before performance drops.

Practical takeaways

• Design out dust first, then engineer controls, then housekeeping.
• Specify H14 as the final stage for respirable or carcinogenic dusts.
• Measure airflow under load and re-check after filter changes.
• Verify with a PM meter and keep records for COSHH compliance.
• Never sweep or use compressed air; vacuum with suitable filtration.

Dust settles only when physics allows it. By shaping those conditions with source capture, controlled airflow, and disciplined housekeeping, you cut exposure, stay within WELs, and keep projects moving.