Breaching a Workplace Exposure Limit (WEL) is a red flag that demands immediate, structured action. For context, the HSE WEL for respirable crystalline silica (RCS) is 0.1 mg/m³ (8-hour TWA). The priority is to stabilise the situation, investigate the cause, and prevent recurrence—without drifting into paperwork before the risk is controlled.

Stabilise the work area

• Pause the dust-generating task. Brief the team and restrict access to the area.
• Implement capture at source: switch to water suppression and ensure on-tool extraction is fitted and functioning with at least M-class filtration for mineral dusts.
• Control airborne dust: deploy an air scrubber to increase air changes; units from manufacturers such as MAXVAC can help stabilise airborne levels while you address the source.
• Housekeeping: stop dry sweeping and compressed air. Use an industrial vacuum with appropriate filtration (H-class for high-hazard dusts; M-class minimum for silica/wood).
• Issue suitable RPE (e.g., FFP3 or half mask with P3 filter) and verify fit testing records.

Diagnose why the limit was exceeded

• Validate the monitoring: check the instrument calibration, logging interval, sampling location, and whether other activities skewed readings.
• Examine the task variables: tool condition, cutting speed, material hardness, extraction flow under load, and filter loading.
• Check controls: damaged hoods, poorly sealed connections, clogged filters, or incorrect vacuum class are common culprits.
• Review the method: can the process be redesigned to cut, drill, or handle less, or off-site?

Reinforce the three-layer approach

• Capture at source: correct shrouds, slower passes, water feed, and verified extraction flow under load.
• Capture in the air: air scrubbers or negative air machines with high-efficiency filters (H13/H14 for fine, respirable dusts).
• Capture on surfaces: vacuum-only clean downs; implement scheduled cleans to prevent re-agitation.

Verify, document, and prevent recurrence

• Re-monitor after adjustments using a particulate monitor or personal sampling to confirm levels are back under control.
• Update the COSHH assessment, method statement, and RPE register. Record filter changes, airflow/pressure checks, and training refreshers.
• Brief operatives and supervisors on the revised method. Increase supervision for a defined period.
• Set a maintenance cadence: under-load airflow checks, differential pressure trends, and filter replacement intervals based on dust loading—not just hours.

Practical takeaways

• Stop the task, control the area, and escalate controls immediately.
• Fix the root cause—usually poor capture at source or low extraction performance.
• Confirm improvement with fresh monitoring and lock the change into your COSHH paperwork.

Exceedances happen, but a rapid, disciplined response—focused on source capture, airborne control, and clean housekeeping—turns an incident into a durable improvement.