Negative pressure stops dust and fumes migrating to clean areas. Done well, it protects people, speeds clean-up, and supports COSHH compliance, especially for respirable crystalline silica (RCS), wood dust and other fine particulates.

Plan the containment

Define the work area and the clean side. Use rigid panels or polythene sheeting with taped joints to form an airtight enclosure. Create a single entry with a simple two-layer flap or a zipper door. Identify waste and material routes so doors are not propped open.

Equipment and airflow under load

Use a negative air machine or air scrubber with appropriate filtration. For fine or carcinogenic dusts, H14 filtration is recommended. Size by volume and target air changes per hour (ACH). As a rule of thumb, 6–10 ACH is effective for dust control. Always check airflow under load, not free-air figures, because filter loading and ducting reduce performance.

Ducting, placement, and make-up air

Place the machine inside the enclosure and duct the exhaust outside the controlled zone or to atmosphere where safe. Keep duct runs short with minimal bends to reduce pressure drop. Provide intentional make-up air via a small, filtered gap or louvre on the clean side so air consistently flows into the enclosure. Avoid uncontrolled leaks around floors and edges by careful taping.

Verify and maintain

Establish negative pressure before dusty work begins. A simple tissue test at the doorway shows inward airflow; a low-range manometer gives objective confirmation (a few Pascals is typically sufficient for dust work). Monitor particulate with a PM meter where practical. Inspect sheeting, zips and tape daily, and replace clogged pre-filters to maintain airflow and energy efficiency. Keep doors closed and brief all trades on the control strategy.

Integrate with source control and housekeeping

Negative pressure is one layer. Use local exhaust ventilation (LEV) or tool-mounted extraction to capture at source, and maintain strict housekeeping with industrial vacuums (M/H-Class as appropriate) to prevent re-agitation. Avoid sweeping or compressed air. Remember HSE’s WEL for RCS is 0.1 mg/m³—containment helps, but measurement and technique determine outcomes.

Practical takeaways

• Seal the work zone and create a single controlled entry.
• Choose an air scrubber/negative air machine with H14 when dealing with fine hazardous dusts.
• Target 6–10 ACH and verify airflow under load.
• Duct out, keep runs short, and provide deliberate make-up air.
• Prove negative pressure with a manometer or tissue test; maintain filters and seals.

Well-planned negative pressure reduces spread, supports compliance, and keeps neighbouring areas productive while dusty tasks proceed.