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Fume Hood Leakage Testing

Created on 03.27
Detailed Introduction to Fume Hood Leakage Testing
Leakage testing is a critical procedure to ensure the safety and containment efficiency of fume hoods. Below is a comprehensive overview based on EU standards (e.g., EN 14175) and global best practices:

1. Purpose of Leakage Testing

Leakage tests verify that a fume hood effectively contains hazardous gases, vapors, or particles, even under dynamic conditions (e.g., user movement or airflow disruptions). Key objectives include:
  • Ensuring
 ≤0.005 ppm leakage rate (EN 14175 requirement for internal/external planes at ≥0.3 m/s face velocity).
  • Validating performance during simulated disturbances (e.g., moving panels or door adjustments).

2. Common Testing Methods

A. Tracer Gas Testing

  • Procedure: Release a tracer gas (e.g., SF₆ or ammonia) inside the hood and measure external leakage using detectors.
    • Internal Plane Test: Gas released inside; leakage measured at the sash opening plane.
    • External Plane Test: Gas released outside; monitor leakage near the user’s breathing zone.
  • Dynamic Testing: Simulate user interference (e.g., moving arms or walking) to assess real-world containment.
B. Pressure Decay Test
  • Seal the hood, pressurize it, and measure pressure drop over time. Rapid decay indicates leaks in the enclosure.

C. Smoke Visualization

  • Use smoke generators (e.g., smoke tubes) to visualize airflow patterns. Ideal containment shows no smoke escaping the hood.

D. Face Velocity Measurement

  • Measure airflow velocity at multiple points across the sash opening.
    • Standard Range: 0.3–0.6 m/s (EU) or 0.4–0.6 m/s (NF X 15-211).
    • Uniformity (±20% variation) is critical to prevent leakage.
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3. Key Standards & Criteria

EN 14175

: Mandates tracer gas testing, face velocity uniformity, and dynamic leakage thresholds.
  • ASHRAE 110-2016: Uses SF₆ tracer gas and quantifies leakage via "containment efficiency."
  • NF X 15-211: Focuses on ductless fume hoods, requiring strict face velocity control (0.4–0.6 m/s).

4. Certification & Validation

  • Type Testing: Conducted in controlled labs to certify hood designs.
  • On-Site Testing: Performed after installation to confirm compliance with local airflow conditions.
  • Regular Maintenance: Annual re-testing is recommended to address wear, filter degradation, or system changes.

5. Critical Factors Affecting Leakage

Sash Position: Improper sash height can disrupt airflow.

  • Room Airflow: Cross-drafts from HVAC systems or foot traffic.
  • Filter Saturation: In ductless hoods, exhausted filters increase leakage risk.
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This testing ensures fume hoods meet safety benchmarks while balancing energy efficiency. Always adhere to regional standards and conduct regular performance checks!
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