Understanding the difference between dynamic and static pass box models is essential when designing an effective contamination control strategy for your cleanroom.
Whether transferring materials between rooms of similar classification or moving goods into higher-grade clean zones, selecting the right type of pass box directly impacts both process efficiency and regulatory compliance.
This article explains the dynamic and static pass box difference, outlines their key structural components, and highlights when each model is most appropriate.
Semi-active, and active pass boxes are also discussed as an intermediate option.
Cleanroom pass box types: static vs. dynamic pass box difference
When comparing cleanroom pass box types, understanding the static vs. dynamic pass box difference is key to selecting the right solution for your facility’s contamination control needs.
- Static pass box – Passive design; provides a physical barrier to enable material transfer between clean zones without active airflow.
- Semi-active pass box – Utilises the facility’s existing HVAC system to supply filtered air through the transfer chamber.
- Active pass box – A simple active unit with HEPA-filtered airflow that draws air from the receiving room to provide a basic clean-air purge. There is no recirculation—the air is exhausted into the cleanroom through a vent.
- Dynamic pass box – actively manages airflow via built-in fans and integrated HEPA filtration, continuously recirculating and purifying the internal air, monitoring differential pressure for consistent performance, and providing DOP/PAO test ports for easy validation.
For most applications requiring advanced contamination control, the choice comes down to a comparison between staticand dynamic models.
1. Static pass box
The static pass box is the simplest form of transfer hatch, designed for moving materials between rooms of equal or similar cleanliness classification.
Its structure typically consists of:
- Outer casing and inner chamber fabricated from 304 stainless steel for chemical resistance, durability, and ease of cleaning. In certain applications, powder-coated steel or 301 stainless steel may be specified.
- Double-door design, with tempered glass windows to provide full visibility during transfers.
- Mechanical or electronic interlock system, ensuring that only one door can be opened at a time. This prevents loss of pressure differential and reduces the risk of contamination ingress.
- Optional UV-C lamp for additional disinfection of transferred materials.
Static pass boxes do not incorporate airflow or filtration systems.
Their performance relies on their sealed construction, making them highly suitable for simple material transfer scenarios where the cleanroom’s HVAC system is sufficient to maintain zone integrity.
They offer several operational advantages:
- Low maintenance requirements
- Minimal noise and vibration
- Long service life
However, they are not suitable for transferring materials between zones with significant differences in cleanliness or where contamination risk is high.
2. Dynamic pass box
In contrast, the dynamic pass box (DPB) is engineered for environments where active contamination control is essential.
Dynamic pass boxes are used to transfer materials from uncontrolled or lower-classified environments into controlled zones, making them essential in industries such as pharmaceutical production, biotechnology, electronics manufacturing, and medical device assembly.
It features recirculated airflow, meaning the air is continuously circulated through the filter so it is constantly being cleaned, which helps maintain the required cleanliness during material transfer.
The structure of a dynamic pass box includes:
- Built-in fan motor, drawing air through a multi-stage filtration system:
- Pre-filter, capturing larger particles and dust.
- HEPA filter (typically H14), ensuring ISO-compliant air cleanliness within the chamber.
- Recirculating airflow system, maintaining controlled, filtered air circulation inside the pass box.
- Electronic interlock system, guaranteeing proper door sequencing.
- Integrated differential pressure gauges to monitor system performance.
- DOP/PAO test ports for HEPA filter validation and compliance testing.
- Optional UV-C lighting to support material disinfection.
Dynamic pass boxes are constructed with polished stainless steel interiors featuring smooth radiused corners to support GMP-compliant cleaning procedures.
They are engineered to operate with low vibration and minimal noise, supporting sensitive environments.
3. Semi-active pass box
The semi-active pass box provides an intermediate solution by leveraging the facility’s existing HVAC system to supply filtered air through the pass box.
This design allows air from the HVAC system to flow through the pass box, typically with the option of adding HEPA filtration to enhance contamination control.
They represent a balance between the simplicity of static pass boxes and the advanced performance of dynamic systems, with lower maintenance requirements than fully dynamic units.
Options such as UV-C lighting, pressure gauges, and interlock timers further expand its capabilities.
4. Active pass box
The active pass box protects clean environments by using built-in HEPA filtration and a fan unit that provides directed airflow. Unlike semi-active designs, these units are fully stand-alone and do not rely on your facility’s HVAC system.
Their interiors are typically constructed from stainless steel with smooth finishes to support GMP-compliant cleaning procedures.
Active pass boxes strike a balance between static and dynamic systems, providing filtered, directed airflow for contamination control without requiring a full recirculation system.
Selecting the appropriate pass box
The choice between static, semi-active, and dynamic pass boxes depends on the specific cleanroom classification, process requirements, and regulatory obligations of the facility.
- Static pass boxes are appropriate for simple material transfers between clean zones of similar classification.
- Active pass boxes provide filtered, directed airflow through built-in HEPA filtration and are suitable for transfers between cleanrooms or between a cleanroom and non-classified space.
- Semi-active pass boxes provide enhanced protection where minor differences in cleanliness levels exist.
- Dynamic pass boxes offer complete, stand-alone contamination control for the most demanding environments.
Understanding the structure and function of each pass box type is essential to achieving optimal performance and compliance.
Conclusion
Cleanroom pass boxes form an integral part of contamination control strategy in regulated environments.
Each element of their structure - from material selection to airflow management - is designed to preserve the integrity of clean zones during material transfer.
KleanLabs offers a full range of static, semi-active, active and dynamic pass box solutions engineered to meet stringent regulatory and operational requirements.
For expert guidance on selecting the right pass box for your application, contact KleanLabs - our team is ready to assist you.
