NPU Calculator

Include the size of any Decontamination Units, Air-locks or Bag-locks in your calculation.

Negative Pressure in Asbestos Removal Enclosures

In New Zealand, maintaining negative pressure in asbestos removal enclosures is essential for safety and regulatory compliance under Health and Safety at Work (Asbestos) Regulations 2016 and WorkSafe New Zealand guidelines - ACOP. By keeping the air pressure inside the enclosure lower than outside, any leaks draw contaminated air inward, preventing asbestos fibres from escaping into adjacent areas.

Key Points:

  • Containment: Negative pressure ensures asbestos fibres remain contained within the removal area.

  • Safety: Protects workers and the public, meeting strict NZ health and safety standards.

  • Regulatory Compliance: Approved guidelines require at least 8 air changes per hour (ACH) for effective ventilation.

  • Calculation:
    Determine your enclosure's volume (in m³) and multiply by 8 ACH.

Our SQN NPU Calculator simplifies this process, whether you input the volume directly or derive it from enclosure dimensions, ensuring your asbestos removal project meets New Zealand’s safety and compliance standards.

Further Considerations

Adequate Airflow Intake

  • Makeup Air Supply: Ensure that sufficient clean air is introduced into the removal enclosure to replace contaminated air, this is crucial for maintaining the required negative pressure.

  • Proper Positioning: Air inlets should be well positioned to avoid drawing in recirculated or contaminated air, correctly located air intakes are key to achieving consistent air movement.

Impact of Roving Heads and Additional Openings

  • Loss of Pressure: When using roving heads or other equipment that temporarily opens the enclosure, be aware that these gaps can lead to a loss of negative pressure. This should be accounted for in your calculations.

  • Control of Voids: As additional voids open(such as those created during the dropping of ceilings), their impact must be mitigated by sealing off above the void or allowing for the additional volume in your calculation.

Strategic Positioning of Equipment

  • Airflow Management: The Negative Pressure Unit (NPU) and Decontamination Unit (DCU) should be placed so that they optimise airflow throughout the enclosure, ensuring a uniform negative pressure environment. i.e. at opposite ends.

  • Avoiding Stagnant Zones: The overall system should be designed to promote even air movement. Uniform distribution prevents the creation of “dead spots” where contaminated air could accumulate.