An open cleanroom door is a contamination event. Particles and air travel with every transfer, and room pressure can shift. That is why cleanrooms use a pass box ( also called passed through chamber, pass-through box, or transfer hatch).
The real question is whether you need a static or a dynamic pass box. Dynamic is not automatically better. The right choice depends on what you transfer, the cleanliness level on each side, and the contamination risk. This guide helps you decide.
What Is a Pass Box?
A pass box is an enclosed chamber built into a wall or partition. It lets you move materials between two areas without anyone walking through the boundary. Think of it as a controlled transfer point.
Most designs have a door on each side, and an interlock prevents both doors from opening at the same time. That small feature matters. If both doors opened together, air could flow directly between the rooms and upset the pressure relationship between them.
You will find pass boxes in pharmaceutical plants, biotechnology facilities, laboratories, medical device factories, electronics manufacturing, and other controlled environments. Not every transfer carries the same risk, which is where static and dynamic designs differ.
What Is a Static Pass Box?
A static pass box is the simpler design. It forms a physical barrier between two controlled spaces but normally has no fan-driven, HEPA-filtered airflow of its own.
The transfer sequence is:
Load the material → close the first door → complete the required cleaning or waiting step → open the opposite door → remove the material.
The interlocks stop someone on the other side from opening their door while the first one is open.
When a static pass box makes sense: when materials move between areas with compatible contamination-control requirements, and your risk assessment shows active filtered airflow is not needed. It has no blower to maintain, uses little energy, is generally simpler to maintain, and usually costs less up front.
Its limitation is that it does not actively purge airborne particles from the chamber. You depend more on room conditions, packaging procedures, cleaning routines, the interlock, and your operating procedures.
How to Use a Static Pass Box Well (UV and Disinfection Steps)
Many buyers choose a static pass box, so the procedure around it matters as much as the hardware. A static unit does no air cleaning of its own: your SOP does the contamination control.
A typical routine looks like this:
1. Prepare the Chamber
Wipe the empty chamber with your approved disinfectant before each shift or batch, and respect the disinfectant’s contact time.
2. Strip Outer Packaging First
Remove shipping cartons before the item reaches the pass box, not inside it.
3. Disinfect the Item Before Loading
Wipe the outer surface of the item or its inner pack with an approved agent and let it dry.
4. Load and Close
Space items so every face is exposed, close the door, and check the interlock indicator.
5. Hold for the Defined Time
Your SOP should state the minimum dwell time and the reason for it.
6. UV Step
If the unit has a UV lamp, use a timer and turn items so more surfaces are exposed. UV reaches only line-of-sight surfaces, loses output as the lamp ages, and does not remove particles.
Common mistakes: treating UV as a sterilizer, stacking items so they shadow each other, skipping the interlock check, forcing or overriding the interlock, and never replacing aging UV lamps.
When a static box stops being enough: consider a dynamic pass box if you see repeated particle excursions, items that shed fibers, a widening grade gap between the rooms, or open product exposed nearby.
What Is a Dynamic Pass Box?
A dynamic pass box adds controlled airflow and filtration to the transfer chamber. A typical design uses a fan or blower to move air through a HEPA filter and through the chamber. Depending on the design, air is circulated or handled through another engineered arrangement.
Why does that matter? When the door to the less clean side opens, airborne particles can enter while you load. After that door closes, filtered airflow can reduce the airborne particle concentration before the opposite door is released. This makes dynamic pass boxes useful when your process needs tighter control of airborne contamination.
Dynamic Does Not Mean Sterile
A HEPA filter removes airborne particles at its rated performance level. It does not automatically sterilize the surfaces of materials inside the chamber. Filtered air, surface disinfection, microbial decontamination and sterilization are different processes.
Be cautious if a supplier says only, It has HEPA filtration, so your materials will be clean. Ask what has actually been tested.
Static vs Dynamic Pass Box
Both types use interlocked doors between two rooms. Only the dynamic type adds a fan and HEPA filter to the chamber.
Airflow and Airborne Contamination Control
A static pass box has no independent airflow, so it relies on the surrounding rooms and your procedures. A dynamic pass box circulates air through a HEPA filter and can actively reduce airborne particles in the chamber. For reference, an H13 filter captures at least 99.95% and an H14 filter at least 99.995% of the most penetrating particle size (EN 1822; ISO 29463 gives equivalent classes). Neither type sterilizes surfaces.
Recovery Time and Load Sensitivity
When you open the less clean side door, chamber conditions change. A dynamic pass box needs time after the door closes to restore the required conditions. This is often called recovery or purge time.
There is no universal answer, such as always wait five minutes. Recovery depends on the chamber, airflow rate, starting condition, filtration, load arrangement, and acceptance criteria. Where your application requires it, testing can establish a suitable period, and the interlock sequence can be built around that verified result. That is far stronger than picking an arbitrary timer.
Example acceptance criterion: after a door open challenge, the chamber returns to ISO Class 5 limits (3,520 particles per m3 at 0.5 μm and larger, per ISO 14644-1) within a time you specify and verify by testing.
A dynamic pass box may perform well during empty-chamber testing, but its performance can change once materials are placed inside. A larger container in the airflow path can change how air moves, restrict circulation, or create weak spots. This is why representative loading conditions matter during qualification, and why airflow visualization is useful. It shows the actual air path under defined test conditions.
Cost, Energy and Maintenance
Static units cost less to buy, use less energy, and need simple maintenance. Dynamic units cost more and use more energy. They also need fan maintenance, HEPA filter replacement, and filter integrity testing.
What the Pressure Gauge Measures
A differential pressure gauge on a dynamic pass box usually monitors the pressure drop across its filter, which changes as the filter loads. That is not the same as the pressure difference between the two cleanrooms. The room pressure cascade is part of the wider HVAC design.
Testing and Qualification Scope
A static unit has fewer items to test, mainly the door, interlock seals, and cleanability. A dynamic unit adds HEPA integrity testing, airflow and velocity checks, particle counts, alarms, and recovery testing.
Static vs Dynamic Pass Box Comparison Table
| Feature | Static Pass Box | Dynamic Pass Box |
| Independent airflow | Normally no | Yes |
| HEPA filtration | Normally no | Yes |
| Fan/blower | No | Yes |
| Door interlock | Yes | Yes |
| Active chamber purge | No | Yes, depending on design |
| Initial cost | Lower | Higher |
| Energy consumption | Lower | Higher |
| Maintenance | Simpler | More involved (fan, filter) |
| Filter testing | Not applicable without HEPA | Required as specified |
| Best suited to | Lower-risk controlled transfers | Transfers needing active airborne contamination control |
Typical Specifications and Cost Ranges
Use these reference points when you write your URS. Exact values vary by manufacturer and design, so confirm each one on the datasheet.
| Item | Static pass box | Dynamic pass box |
| HEPA filter | None | H13 (at least 99.95%) or H14 (at least 99.995%) at the most penetrating particle size, per EN 1822 / ISO 29463 |
| Chamber airflow | None | Often around 0.3 to 0.5 m/s, depending on design |
| Nozzle air speed (air shower type) | Not applicable | Commonly 20 m/s or more |
| Chamber material | SUS304 stainless steel, or a powder-coated steel shell with a SUS304 chamber | SUS304 or SUS316L stainless steel |
| Interlock | Mechanical or electronic | Usually electronic |
| UV lamp | Optional | Optional |
| Indicative price, small unit (about 500 mm cube) | Roughly USD 400 to 1,500 | Roughly USD 1,500 to 5,000 |
Prices are indicative only and vary with size, material, controls, documentation and region. A dynamic unit costs more mainly because of its fan, HEPA filter and controls, and it adds ongoing filter replacement and testing. SUS316L, electronic alarms, custom dimensions and validation documents (FAT, IQ, OQ) push the price higher.
Which Pass Box for Which Job?
Use this table as a starting point. Your own risk assessment has the final say.
| Material or process | Typical starting point | Why |
| Documents, labels, small tools between similar lower-grade areas | Static | Low particle risk, compatible room conditions |
| Pre-cleaned, packaged components moving between neighboring grades | Static or dynamic, based on risk assessment | Depends on packaging and grade difference |
| Components moving from a lower grade into a higher grade | Dynamic | Active particle reduction before the second door opens |
| Items going to aseptic or high-grade processing areas | Dynamic, often combined with validated surface decontamination | HEPA air alone does not decontaminate surfaces |
| Loose-particle-prone items (cartons, fibrous materials) | Dynamic with air shower function, plus unpacking step | Air jets help remove loose particles; outer packaging should still be removed first |
| Hazardous or potent materials | Containment-rated equipment | Standard pass boxes are designed for product protection, not containment |
| Items needing validated microbial decontamination | VHP or other validated decontamination transfer system | Neither static nor standard dynamic units provide this on their own |
GMP Grade, ISO 14644 and Pass Box Selection
Cleanrooms are classified by airborne particle limits. ISO 14644-1 defines ISO classes, while EU GMP Annex 1 defines Grades A to D for sterile medicinal products manufacturing. As a rough guide, Grade A corresponds to ISO 5, Grade B to ISO 5 at rest and ISO 7 in operation, Grade C to ISO 7 at rest and ISO 8 in operation, and Grade D to ISO 8 at rest.
Why this matters for pass boxes: the bigger the cleanliness gap between the two sides, the more your transfer step needs to control. Common examples:
- D → C: a small step, where a well-designed static pass box with good cleaning procedures may be considered.
- C → B: a larger step into a more critical area, where a dynamic pass box is commonly evaluated.
- Into or near Grade A/B aseptic areas: expect stricter requirements, and often validated decontamination such as VHP, with your quality unit and the applicable regulations deciding the final requirement.
These pairings are examples, not rules. Always follow your site’s contamination control strategy and the regulations that apply to your product and market.
Common Pass Box Features Buyer Ask About
Interlock Type
Mechanical interlocks use physical linkages and need no power. Electronic (electromagnetic) interlocks use locks and control logic, and can add indicator lights, alarms and an emergency-release function. Ask what happens during a power failure.
UV Lamps
Many pass boxes include a UV lamp. It can reduce microorganisms on exposed surfaces, but only where UV light reaches, and effectiveness depends on lamp output, distance, exposure time and lamp age. Shadowed areas get little or no exposure. Treat UV as a supporting feature, not a replacement for validated disinfection.
Construction Material
Stainless steel is the usual choice for cleanrooms. SUS304 is common, while SUS316 or 316L may be chosen where harsher cleaning agents are used. Look for smooth, crevice-free surfaces, rounded internal corners and chemical compatibility with your disinfectants.
Air Shower Pass Box
This is a dynamic variant that blows HEPA-filtered air through nozzles onto the items inside, helping remove loose particles from surfaces. It does not remove the need for sensible unpacking and cleaning steps.
Other Options
Viewing windows, differential-pressure gauges, interlock indicators, alarms, and a controller for timing the cycle.
How to Select a Pass Box
Start With the Transfer Process
Map the journey of your material. Where does it start? How is it packaged? Where is outer packaging removed? Does it need wiping down? Which room does it enter next?
For example, putting a cardboard shipping carton in a dynamic pass box does not make its exterior suitable for a highly controlled area. Your procedure may require removing the shipping packaging first, then cleaning the inner packaging. The pass box is one part of your contamination-control system, not the entire system.
Product Protection or Containment?
Most pass boxes protect a cleaner room or product from outside contamination. If the material itself is hazardous, your priority may be keeping contamination in. That affects pressure direction, filtration, seals and equipment design, and you may need containment-specific equipment.
Sizing
Bigger is not automatically better. Start with the largest item you expect to transfer, add clearance to load and unload it, and for dynamic units consider how the load affects airflow. Also check operator comfort, can someone wearing gloves load it easily, is the mounting height practical, and is the door easy to operate? Over hundreds of transfers, these details matter.
Write a URS Before Requesting Quotes
Prepare a User Requirements Specification (URS) that defines:
- room conditions and classifications on both sides
- material types and maximum load dimensions
- direction and frequency of transfer
- required airflow and filtration
- construction material and surface finish
- door and interlock requirements
- alarms and controls
- cleaning and disinfectant compatibility
- recovery requirements
- qualification requirements and documentation
- utilities and maintenance access
Without a URS, you may receive three quotes for three very different machines that are all called a dynamic pass box.
Questions to Ask Your Manufacturer
- What does dynamic mean in this particular design?
- Where does air enter and return?
- What filter specification is used?
- What does the pressure gauge measure?
- How was recovery time established?
- What happens if power fails?
- How is the HEPA filter replaced and tested?
- What qualification documents are supplied?
- Can you show the test evidence behind the performance claim?
A drawing and a brochure are useful. Test data is better.
Qualification
A specification tells you what equipment is designed to do. Qualification helps demonstrate what the installed equipment actually does. Depending on the application, your program may include Factory Acceptance Testing (FAT), Site Acceptance Testing (SAT), Installation Qualification (IQ), Operational Qualification (OQ) and Performance Qualification (PQ).
Tests can include door-interlock challenges, HEPA integrity testing, airflow measurements, particle counts, alarms, pressure monitoring, airflow visualization and recovery testing. Not every test applies to every pass box. Your plan should reflect the URS, the design, the intended use and your quality requirements.
Wrapping Up
Choosing between a static and a dynamic pass box is about controlling risk during material transfer. A static unit is a simple interlocked barrier. A dynamic unit adds filtered airflow to control airborne particles. The better pass box is the one that solves your actual transfer problem, not the cheaper or the more advanced one.
Not sure which fits your facility? Send Sunnyda Clean Room your room grades, the materials you transfer and the size of your largest item. We will recommend the right solution and send a quotation with the qualification documents you need. Contact us today for a free consultation.
Frequently Asked Questions
What is the main difference between a static and a dynamic pass box?
A static pass box is an interlocked transfer chamber without its own fan or HEPA filter. A dynamic pass box adds a fan and HEPA-filtered airflow to reduce airborne particles inside the chamber.
Is a dynamic pass box always better than a static pass box?
No. A dynamic unit gives you more active contamination control, but it costs more and needs more maintenance. If your risk assessment shows active filtered airflow is unnecessary, a static pass box can be the right choice.
Does a dynamic pass box sterilize materials?
No. HEPA filtration removes airborne particles but does not automatically sterilize surfaces. If you need validated microbial decontamination, consider a VHP or other validated decontamination transfer system.
Why do pass boxes have interlocks?
The interlock prevents both doors from being open at once, which protects the pressure relationship and limits air exchange between the two rooms.
How long should the recovery or purge time be?
There is no universal figure. It depends on chamber design, airflow rate, load, filtration and your acceptance criteria. Testing can establish a suitable time for your application.
Which pass box suits a D to C or C to B transfer?
A D to C transfer with good procedures may be suited to a static unit. A C to B transfer is commonly evaluated for a dynamic unit. The final choice depends on your risk assessment, contamination control strategy and regulations.
Do I need a UV lamp in my pass box?
Not necessarily. UV can support surface microbial reduction where light reaches, but it does not replace validated disinfection. Decide based on your risk assessment.
What material should a cleanroom pass box be made of?
Stainless steel is the usual choice. SUS304 is common, and SUS316 or 316L may suit harsher cleaning agents. Choose smooth, crevice-free construction compatible with your disinfectants.
What is an air shower pass box?
It is a dynamic pass box with nozzles that blow HEPA-filtered air onto the items inside to help remove loose particles from surfaces.
Which tests should a dynamic pass box go through?
Common tests include interlock checks, HEPA integrity testing, airflow measurements, particle counts, alarm checks, pressure monitoring, airflow visualization and recovery testing, depending on your URS and quality requirements.
