Why Clean Benches Are Not Required in ISO Class 5 (Class 100) Cleanrooms

Why Clean Benches Are Usually Unnecessary in ISO Class 5 (Class 100) Cleanrooms

Understanding the Core Design Philosophy of ISO Class 5 Cleanrooms

An ISO Class 5 (Class 100) cleanroom is engineered to maintain uniform, high-level cleanliness across the entire controlled space, not just at a single workstation. By definition, ISO Class 5 limits airborne particles ≥0.5 μm to no more than 3,520 particles per cubic meter.

This level of cleanliness is achieved through:

• Unidirectional (laminar) airflow

• Full ceiling coverage with HEPA or ULPA filters

• High air change rates

• Carefully engineered airflow patterns (vertical or horizontal)

Because the entire room already operates as a large laminar flow zone, the functional role of a clean bench becomes largely redundant.

1. Functional Redundancy and Airflow Interference

A clean bench is essentially a local laminar airflow device, designed to create a small ISO Class 5 zone inside a lower-grade cleanroom. However, when placed inside an ISO Class 5 cleanroom, several issues arise:

Airflow Conflict

• ISO Class 5 cleanrooms rely on a stable, unidirectional airflow field to continuously sweep particles away.

• A clean bench introduces its own fan-driven airflow, which can:

  • Disrupt the global airflow pattern

  • Create turbulence or dead zones

  • Reduce the efficiency of particle removal

Instead of improving cleanliness, the clean bench may compromise airflow integrity, especially in precision manufacturing or critical processes.

Violation of Cleanroom Design Principles

The fundamental concept of ISO Class 5 design is:

“Overall environmental control without localized airflow disturbance.”

Adding independent airflow sources runs counter to this principle.

2. Space Utilization and Operational Efficiency

In an ISO Class 5 cleanroom:

• All qualified processes can already be performed directly on open work surfaces

• Clean benches introduce physical barriers that:

  • Reduce usable floor area

  • Complicate material transfer

  • Limit flexibility in equipment layout

  • Restrict personnel movement

Modern ISO Class 5 cleanrooms rely instead on:

• Zoning strategies

• Pressure differentials (core areas maintained at higher positive pressure than adjacent spaces)

• Process segregation by layout, not by equipment enclosure

This approach ensures efficiency without unnecessary structural obstacles.

3. Cost, Energy, and Maintenance Considerations

ISO Class 5 cleanrooms already require:

• Very high air change rates

• Extensive HEPA/ULPA filtration

• Continuous particle monitoring

Adding clean benches results in:

• Higher initial capital costs

• Increased energy consumption (additional fans)

• More frequent filter replacement

• Additional noise and heat load

From an engineering and economic standpoint, clean benches provide no meaningful marginal benefit in an ISO Class 5 environment.

4. Special Exceptions: When Local Enclosures May Be Required

There are limited cases where additional containment is justified, such as:

• Handling highly potent APIs

• Working with toxic or biohazardous materials

• Operator protection requirements

In these scenarios, a biosafety cabinet or isolator—not a clean bench—should be used, as the objective shifts from product protection to personnel and environmental safety.

Conclusion: System-Level Optimization Over Local Add-Ons

ISO Class 5 cleanrooms are designed based on a core engineering principle:

System-level cleanliness control is superior to localized purification.

Clean benches are best suited for:

• Lower-grade cleanrooms (ISO 7–8 / Class 10,000–100,000)

• Targeted process protection upstream of airflow

• Transitional or retrofit environments

In a properly designed ISO Class 5 cleanroom, they are unnecessary, inefficient, and potentially disruptive.