Pass Box: Definition, Specifications & Working Principle

Have you ever wondered how industries maintain sterile environments while transferring materials? In cleanrooms—spaces critical for pharmaceuticals, electronics, and healthcare—the answer lies in a seemingly simple yet highly engineered solution: the pass box. This unassuming unit acts as a gateway for material transfer, ensuring contamination control without compromising airflow or cleanliness. But what exactly is a pass box, and why is it indispensable for modern industries? Let’s dive into its definition, specifications, working principles, and real-world applications.

What is a Pass Box? (Definition & Purpose)

A pass box is a specialized enclosure installed in cleanroom partition walls, designed to transfer materials between two areas—whether they’re both cleanrooms, or a cleanroom and a non-clean environment. Its primary role is to act as a buffer zone, minimizing disruptions to the cleanroom’s controlled environment. Here’s why it’s critical:

Primary Purpose

1. Prevent Contamination: By limiting direct door openings between areas, pass boxes reduce airflow disturbances that could introduce dust, microbes, or other contaminants.

2. Minimize Personnel Movement: Fewer trips in and out of cleanrooms mean less risk of human-borne contamination.

3. Sterilization & Safety: Equipped with UV lights for disinfection and interlock systems to prevent cross-contamination, pass boxes ensure materials are safe before entry.

Key Features

• Interlocked Doors: Two doors that cannot open simultaneously (mechanical or electronic interlocks).

• UV Disinfection: Built-in UV lamps kill bacteria on transferred items.

• Modular Design: Available in static or dynamic configurations to suit different cleanliness needs.

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Types of Pass Boxes

Pass boxes are categorized by their functionality, with two main types dominating industrial use: static and dynamic. A third, specialized type—air shower pass boxes—adds an extra layer of decontamination.

1. Static Pass Box

Definition & Use Case

• Purpose: Transfers materials between cleanrooms of the same cleanliness level (e.g., ISO 7 to ISO 7).

• Ideal For: Low-risk environments like electronics assembly or food processing, where cross-contamination risks are minimal.

• Industries: Pharmaceuticals (non-aseptic areas), electronics, and general manufacturing.

Key Components

• Interlock System: Mechanical (physical latches) or electronic (sensors and electromagnetic locks).

• UV Sterilization Lamp: Activates when doors close, typically for 15–30 minutes.

• Construction: Stainless steel (SUS304) interior for easy cleaning; exterior may be powder-coated steel or stainless steel.

Working Principle

1. Open one door and place materials inside.

2. Close the door; UV light activates to disinfect items.

3. Once the cycle completes, the opposite door unlocks for material retrieval.

2. Dynamic (Self-Cleaning) Pass Box

Definition & Use Case

• Purpose: Transfers materials between areas of different cleanliness levels (e.g., non-cleanroom to ISO 5 cleanroom).

• Ideal For: High-sterility environments like pharmaceutical aseptic zones, hospitals, and research labs.

• Key Features

• HEPA Filters: H13 or H14 filters remove 99.995% of particles ≥0.3 microns.

• Differential Pressure Gauge: Monitors filter integrity (0–250 Pa range).

• Motorized Blower: Generates airflow to remove dust from materials.

Working Principle

1. Air is sucked through a pre-filter (G4) to trap large particles.

2. A centrifugal fan pushes air through HEPA filters, creating ultra-clean airflow.

3. Filtered air circulates in the chamber, neutralizing contaminants before the opposite door opens.

4. Optional nozzles can blast high-velocity air (20–33 m/s) to dislodge dust from item surfaces.

3. Air Shower Pass Box (Specialized Dynamic Type)

• Design: Features high-speed air jets (laminar or turbulent flow) to “shower” materials with clean air.

• Use Case: Critical environments like aerospace component handling or biopharmaceutical labs, where even 微量 (trace) contaminants are unacceptable.

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Pass Box Structure & Components

Understanding a pass box’s anatomy helps clarify its efficiency. Let’s break down the key components:

1. Casing & Body

• Materials:

• Exterior: Powder-coated steel (cost-effective) or SUS304/201 stainless steel (corrosion-resistant, ideal for humid environments).

• Interior: Always SUS304 stainless steel for smooth surfaces and easy sanitization.

• Dimensions:

• Static: Smaller footprints (e.g., 620×560×580 mm external, 500×500×500 mm working space).

• Dynamic: Larger due to filters and blowers (e.g., 770×680×1100 mm external, 600×600×600 mm working space).

2. Doors & Interlock System

• Doors:

• Tempered glass windows for visibility, sealed with rubber gaskets to prevent particle ingress.

• Handles vary by interlock type (mechanical latches vs. electronic touchpads).

• Interlocks:

• Mechanical: Simple, reliable, the best choice for low-tech environments.

• Electronic: Features LED indicators, audible alerts, and remote monitoring (e.g., “Door A open” warnings).

3. Filtration & Sterilization Systems

• UV Lights:

• Lifespan: ~4,000 hours; must be replaced promptly if dim or non-functional.

• Activation: Automatically turns on when both doors close, off when any door opens.

• HEPA Filters:

• Efficiency: H13 (99.97%) or H14 (99.995%) at 0.3 microns.

• Replacement: Pre-filters (G4) every 6 months; HEPA filters every 6–12 months (depending on usage).

4. Additional Features

• Differential Pressure Gauge: Found in dynamic pass boxes, it signals when filters need replacement (e.g., pressure drop >25 Pa).

• DOP/PAO Test Port: Allows leak testing of HEPA filters using aerosol particles.

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How Does a Pass Box Work? (Working Principle)

Static Pass Box Operation

1. Loading: Open the outer door, place materials inside, and close it.

2. Disinfection: UV light activates for 15–30 minutes, killing bacteria on item surfaces.

3. Unloading: Once the cycle finishes, the inner door unlocks for material retrieval.

Dynamic Pass Box Operation

1. Air Filtration: The fan pulls ambient air through the pre-filter and HEPA filter, creating Class 100 (ISO 5) air quality.

2. Pressurization: The chamber equalizes pressure with the target cleanroom to prevent airflow surges.

3. Dust Removal: High-velocity air from nozzles (if equipped) blows off loose particles from materials.

4. Safety Check: The differential pressure gauge must show normal readings before the inner door opens.

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Pass Box Specifications & Dimensions

Standard Models

Model	Type	External Size (L×D×H, mm)	Working Size (L×D×H, mm)	Power	Interlock
VCR500SP	Static	620×560×580	500×500×500	220V/50Hz	Mechanical/Electronic
VCR600DP	Dynamic	770×680×1100	600×600×600	220V/50Hz	Electronic
VCR700SP	Static	820×860×780	700×700×700	220V/50Hz	Mechanical/Electronic
VCR800DP	Dynamic	970×880×1300	800×800×800	220V/50Hz	Electronic

Customization Options

• Size: Non-standard dimensions for odd-shaped materials (e.g., large equipment parts).

• Features: Intercom systems, multiple UV lamps, or roller conveyors for heavy items.

• Mounting: Wall-mounted (standard) or floor-mounted for stability with heavy loads.

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Applications of Pass Boxes

Pass boxes are vital across industries where contamination control is non-negotiable:

1. Pharmaceuticals

• Use Case: Transferring sterile vials, packaging materials, or lab samples between aseptic zones and non-aseptic areas.

• Key Requirement: Dynamic pass boxes with HEPA filtration to meet GMP standards.

2. Electronics

• Use Case: Moving microchips, circuit boards, or sensitive components into dust-free assembly rooms.

• Key Requirement: Static pass boxes to prevent electrostatic discharge (ESD) via stainless steel surfaces.

3. Food & Beverage

• Use Case: Transferring raw ingredients, packaged foods, or equipment into sanitized production areas.

• Key Requirement: Stainless steel construction for easy cleaning and resistance to moisture.

4. Healthcare & Labs

• Use Case: Transporting surgical instruments, culture samples, or pharmaceuticals into operating rooms or biohazard labs.

• Key Requirement: Dynamic pass boxes with UV and HEPA for high-level disinfection.

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Precautions & Maintenance Tips

Daily Usage Best Practices

1. Never Open Both Doors: Violating the interlock system can compromise cleanroom integrity.

2. Sanitize Regularly: Wipe interior surfaces with 70% isopropyl alcohol (IPA) to remove residue.

3. Monitor UV Functionality: Check that lights activate promptly when doors close.

Maintenance Schedule

Component	Maintenance Task	Frequency
UV Lamp	Replace when lifespan (4,000 hours) is reached	Every 4,000 hours
Pre-Filter (G4)	Clean or replace to remove large particles	Every 6 months
HEPA Filter	Replace to maintain filtration efficiency	Every 6–12 months
Differential Gauge	Check pressure readings for filter clogs	Weekly

Pro Tip: Keep a maintenance log to track filter replacements and UV lamp usage, ensuring compliance with audit requirements.

Choosing the Right Pass Box

Key Factors to Consider

1. Cleanroom Classification:

• Static for same-level transfers (e.g., ISO 8 to ISO 8).

• Dynamic for cross-level transfers (e.g., ISO 6 to ISO 5).

2. Material Size & Weight:

• Choose larger working dimensions for bulky items; add conveyors for heavy loads.

3. Regulatory Compliance:

• Ensure the pass box meets ISO 14644, GMP, or FDA standards for your industry.

Supplier Considerations

• Reputation: Look for suppliers with proven expertise in cleanroom equipment.

• After-Sales Support: Prioritize providers offering installation, training, and maintenance services.

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FAQ Module

Q1: Can a static pass box be used for transferring items from a non-cleanroom to a cleanroom?
A: No. Static pass boxes lack HEPA filtration, making them unsuitable for cross-level transfers. Use a dynamic pass box instead to ensure contaminants are filtered out.
Q2: How often should I replace HEPA filters in a dynamic pass box?
A: Typically every 6–12 months, but this depends on usage frequency and particle load. Monitor the differential pressure gauge—if readings exceed the recommended range, replace filters immediately.
Q3: What’s the difference between mechanical and electronic interlocks?
A: Mechanical interlocks use physical latches (simple, low-cost), while electronic interlocks use sensors and electromagnetic locks (more reliable, with status indicators). Electronic systems are preferred for high-risk environments.
Q4: Can pass boxes be used in negative-pressure cleanrooms?
A: Yes, but ensure the pass box is designed for negative pressure. Dynamic pass boxes with pressure equalization features work best in such setups.
Q5: How long does UV disinfection take in a pass box?
A: Most protocols require 15–30 minutes of UV exposure. Some industries (e.g., healthcare) may extend this to 60 minutes for high-risk items.

Conclusion

Pass boxes are the unsung heroes of cleanroom operations, enabling safe material transfer while preserving strict contamination control. Whether you need a basic static unit for same-level transfers or a high-tech dynamic pass box with HEPA filtration, understanding their design, specs, and maintenance is key to optimizing cleanroom efficiency. By choosing the right pass box and adhering to best practices, industries can safeguard product quality, comply with regulations, and ensure seamless workflows in even the most demanding environments.
Ready to enhance your cleanroom’s material transfer process? Explore trusted suppliers and request a quote tailored to your needs.