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A laminar flow hood is a specialized air-cleaning device designed to provide a particle-controlled environment for laboratory, pharmaceutical, and electronic manufacturing applications. Its performance classification depends on the level of cleanliness it can achieve, commonly defined by ISO standards or Federal Standard 209E.

This article explains the cleanroom class of laminar flow hoods, how they are classified, and factors that determine their cleanliness performance.

Laminar flow hoods are typically rated according to:

• 1.1 ISO 14644-1 Standard

  The ISO standard classifies air cleanliness based on particle concentration. Laminar flow hoods usually fall into:

  • ISO Class 5 (most common)
  • Equivalent to Class 100 in the retired Fed Std 209E
  • ISO Class 5 means the hood maintains fewer than 100 particles (≥0.5 μm) per cubic foot, providing a very high level of air purity.
• 1.2 Federal Standard 209E (Retired)

  Still widely referenced in industry:

  • Class 100
  • Equivalent to ISO Class 5
  • Many manufacturers continue to use “Class 100" to describe laminar flow hood performance.

Laminar flow hoods use:

• HEPA filters (H13/H14) removing 99.97–99.995% of 0.3 μm particles
• Unidirectional laminar airflow, typically 0.45 m/s ± 20%
• Enclosed design preventing outside contamination

These features enable the hood to consistently maintain ISO Class 5 cleanliness at the work surface.

• 3.1 Horizontal Laminar Flow Hood
  • Blows clean air horizontally across the workspace
  • Provides ISO Class 5 / Class 100 airflow
• 3.2 Vertical Laminar Flow Hood
  • Clean air flows top-to-bottom
  • Also rated ISO Class 5 / Class 100
• 3.3 Class II Biosafety Cabinets (BSC)
  • Provide product and personnel protection
  • Not cleanroom class, but internal workspace is still ISO Class 5

Several design and operational factors determine if the hood maintains ISO Class 5:

• HEPA/ULPA filter efficiency
• Air velocity and laminarity
• Work surface design and internal airflow
• Frequency of filter replacement and maintenance
• Proper operational practices by users

Even a Class 5 hood can fail if not properly maintained or used.

Therefore, a laminar flow hood is typically classified as ISO Class 5 (Class 100).
This high level of cleanliness makes it suitable for sensitive operations in pharmaceuticals, microelectronics, biotechnology, research laboratories, and sterile manufacturing.