PM2.5 and PM4 represent the fine fraction that penetrates deep into the lungs. PM4 aligns closely with the “respirable” fraction used in occupational hygiene, which includes respirable crystalline silica. Understanding these sizes helps you choose effective controls and verify performance with air monitoring systems.

What PM tells you—and what it doesn’t

PM10 indicates coarse dust from movement and handling. PM2.5–PM4 often rises with cutting, sanding, or thermal processes. Size alone does not identify composition, so treat rises in fine PM as a cue to check tasks that generate respirable dust and verify RPE and engineering controls.

Design controls around the fine fraction

At source: keep shrouds sealed, use water suppression where suitable, and run tool extraction before contact. In the air: use LEV or air scrubbers with high-efficiency filters; specify H14 where respirable or carcinogenic dusts are present. On surfaces: vacuum only with M-Class or H-Class units and avoid sweeping or compressed air.

Measure to manage

Track PM2.5/PM4 trends by zone and shift to see if controls hold up under load. Spikes during bag changes or clean-up suggest sequence issues; background rises may mean filter loading or bypass. For silica, remember the HSE WEL of 0.1 mg/m³ (8-hr TWA) as context—peaks are prompts to recheck exposure and fit testing.

From data to improvement

When fine PM stays elevated, intensify source capture, reduce drop heights, and add temporary air scrubbing near the task. Portable units such as the MAXVAC Dustblocker range can stabilise ambient levels while permanent fixes are implemented.

Practical takeaways

• Watch PM2.5/PM4 to understand respirable risk.
• Tighten source control and maintain LEV performance.
• Use H14 filtration for fine or carcinogenic dusts.
• Vacuum only with rated industrial units; never sweep.
• Verify improvements with trend data under real load.

Fine particles drive long-term harm and short-term complaints. By centring controls and measurement on PM2.5 and PM4, you make each improvement count where it matters most.