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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.

1. Cleanroom Classification Standards for Laminar Flow Hoods

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.

2. Why Laminar Flow Hoods Are Classified as ISO Class 5 / Class 100

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. Examples of Laminar Flow Hood Types and Their Classification

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

4. Factors Affecting Laminar Flow Hood Cleanliness Class

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.

5. Summary

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.