In cleanroom environments where airborne contamination control is critical, even the smallest material transfer process must follow strict protocols. One commonly used solution is the pass box—a compact chamber that allows items to move between rooms without compromising cleanliness. But not all pass boxes are created equal. In this article, we break down the two main types: static pass boxes and dynamic pass boxes, explaining how they work, where they’re used, and why choosing the right one matters.
What Is a Pass Box?
A pass box, also known as a pass-through chamber or cleanroom transfer hatch, is a closed enclosure installed between two controlled areas. It allows materials to pass through while minimizing the risk of cross-contamination.
The core feature of any pass box is the interlocking door mechanism—only one door can be opened at a time. This prevents direct airflow between rooms, significantly reducing the chance of particle migration.
For a broader understanding of air cleanliness classifications, refer to ISO 14644 standards, the global benchmark for cleanroom design and operation.
Two Types: Static vs Dynamic Pass Boxes
There are two main types of pass boxes. Though similar in appearance, they operate on different principles and are suited for different scenarios.
🔹 Static Pass Box: Simplicity for Equal Environments
Definition:
A static pass box is a non-ventilated chamber with no built-in airflow system. It simply relies on the physical barrier and interlocking doors to prevent contamination.
Working Principle:
No HEPA/ULPA filters or internal airflow
Air inside the chamber is static (unchanged)
Relies solely on interlocked access to block airflow
Use Case:
Ideal for transferring non-critical items between two cleanrooms of the same ISO classification (e.g., ISO 7 to ISO 7).
It is not suitable for use between clean and non-clean environments.
Typical Applications:
Electronics assembly
Non-sterile packaging
Clean area to clean area transfer
🔸 Dynamic Pass Box: Active Air Purification for Critical Transfers
Definition:
A dynamic pass box integrates a HEPA or ULPA filtration system and a blower fan to actively flush the chamber with clean air before allowing the second door to open.
Working Principle:
HEPA-filtered air flows through the chamber during transfer
Blower ensures particle removal by positive pressure
Often includes UV light and control systems for validation
This design mimics the concept of an airlock and is especially effective in air cleanliness-sensitive environments. For reference on HEPA filter efficiency, see the U.S. EPA guide on air filters.
Use Case:
Used for transferring materials from uncontrolled or lower-classified areas into cleaner zones (e.g., warehouse to ISO 7 cleanroom).
Typical Applications:
Pharmaceutical production (sterile rooms)
Biotech labs
Hospitals and medical device plants
Cleanroom entrances from raw material areas
Quick Comparison Table
| Feature | Static Pass Box | Dynamic Pass Box |
|---|---|---|
| Internal Airflow | None | Active airflow with HEPA filter |
| Particle Control | Basic (via door interlock) | High (filtration + positive pressure) |
| Cleanroom Level | Equal class only | Uncontrolled to classified zones |
| Cost | Lower | Higher (due to motor & filters) |
| Applications | Packaging, electronics | Pharma, hospital, food-grade |
Why Choosing the Right Type Matters
Choosing the wrong pass box can compromise your cleanroom’s integrity. For instance, using a static pass box between a general area and a cleanroom can introduce particles into the sterile zone, defeating the purpose of contamination control.
If your process involves sterile, pharmaceutical, or biologically sensitive materials, the dynamic version is not just recommended—it’s a regulatory expectation. Refer to FDA’s cleanroom validation guidelines for more details on air contamination control.
Conclusion
In summary, static pass boxes are best suited for cleanroom-to-cleanroom transfers where both areas maintain the same cleanliness classification. They are simple, cost-effective, and ideal for non-critical applications like packaging or electronics assembly. On the other hand, dynamic pass boxes are essential for transferring materials from less controlled or uncontrolled environments into cleaner zones. With built-in HEPA filtration and active air circulation, they provide a much higher level of particle control and are widely used in pharmaceutical, biotech, and sterile manufacturing. Choosing the right type depends not only on cleanliness requirements but also on regulatory expectations and operational risks. For any environment where contamination risk matters, understanding this difference is not optional—it’s essential.
Need Help Selecting the Right Pass Box?
Whether you’re building a new cleanroom or upgrading an existing one, we offer both standard and custom pass box solutions. Our engineers can help you determine the best configuration based on airflow, door type, filter class, and validation needs.
Frequently Asked Questions
1. What is the main difference between a static and a dynamic pass box?
The key difference lies in airflow. A static pass box has no internal air circulation system and is used between cleanrooms of the same cleanliness level. In contrast, a dynamic pass box uses a HEPA-filtered airflow system to actively remove contaminants, making it suitable for transfers from uncontrolled or lower-classified areas into clean zones.
2. When should I use a dynamic pass box instead of a static one?
Use a dynamic pass box when transferring materials from non-cleanroom areas or lower ISO zones into cleaner environments, especially in pharmaceutical, biotech, or sterile production. Static pass boxes should only be used between two cleanrooms of equal classification.
3. Is a dynamic pass box required by cleanroom standards?
While standards like ISO 14644 and FDA guidance don’t mandate dynamic pass boxes explicitly, they require air cleanliness levels to be maintained at all times. In critical applications, dynamic boxes are typically used to ensure compliance with these expectations.
4. Do dynamic pass boxes require regular maintenance?
Yes. Dynamic pass boxes have filters, fans, and sometimes UV lights that require regular maintenance. HEPA filters should be inspected and replaced every 6–12 months depending on usage and particle load.
