A cleanroom airlock is an enclosed transition space between areas with different cleanliness or pressure requirements. It controls how people and materials move between these spaces while helping limit the transfer of contamination. Most airlocks use two doors that should not normally open at the same time. Controlled pressure and filtered ventilation can provide additional protection against contamination.
Why Are Airlocks Used in Cleanrooms?
Airlocks are used to reduce contamination transfer when people, materials, or equipment enter and leave a cleanroom. Opening a door creates a temporary path between two environments. Airborne particles and microorganisms may move through that opening, while people and moving equipment can further disturb the airflow.
An airlock limits this direct exchange by creating a separate space between the two areas. It also supports the pressure relationship the process requires, directing airflow toward or away from the controlled room as needed.
This serves two main purposes. Where product protection is the priority, the pressure strategy helps keep contamination away from the cleaner space. Where containment is required, it helps limit the spread of airborne contaminants to surrounding areas.
Research backs up the need for controlled entry. A full-scale study of an isolation ward found that less than 1% of airborne particles crossed into the higher-pressure zone while the door stayed closed, but that share rose to 2.7% once a person moved through the doorway, and reached as much as 20.7% when particles moved from a higher- to a lower-pressure zone. The setup isn’t identical to a standard cleanroom, but the pattern holds: both door movement and pressure differential shape how much contamination crosses a threshold, which is exactly why cleanroom entry has to be engineered, not left to chance.
How Does a Cleanroom Airlock Work?
A cleanroom airlock works by separating entry into two controlled door movements. You enter through the first door and close it behind you. The second door stays closed while the airlock reaches the required condition or completes a defined delay. Only then do you open the second door and enter the adjoining area.
Interlocks prevent both doors from opening at once during normal operation, while ventilation and pressure differences together control airborne contamination and set the intended airflow direction between spaces.
This kind of control is often formalized in regulation. For sterile medicinal-product manufacturing, EU GMP Annex 1 requires that simultaneous opening of airlock doors leading to Grade A and B areas be prevented, mandates interlocking for these doors, and calls for a time delay where necessary to maintain segregation.
The operating sequence and controls should be selected for the process, not applied the same way to every cleanroom; a facility built for containment and one built for product protection don’t need the same airflow strategy at the door.
What is a Personnel Airlock?
A personnel airlock (PAL) is designed for people entering, leaving, or moving between controlled areas. In some cases, a PAL may also provide space for gowning, hand hygiene, or footwear changes before entry.
The layout should match the number of users and the required entry procedure. This becomes particularly important during shift changes, when frequent door cycles and several operators can increase airflow disturbance.
PAL gives the personnel enough space to follow the correct procedure without unnecessary movement between the cleaner and less-clean zone.
What is a Material Airlock?
A material airlock (MAL) is designed for transferring materials and equipment between controlled areas. These may include components, containers, tools, carts, raw materials, and portable equipment. Passing an item through an MAL does not automatically remove contamination from its surface.
For example, outer packaging from the warehouse may carry dust. The packaging may need to be removed, while exposed surfaces may require cleaning or disinfection before the item moves farther into the controlled area. Processes with greater contamination risks may require validated decontamination methods.
This distinction is important because airborne contamination control and surface decontamination are separate processes.
What Are the Main Types of Cleanroom Airlocks?
Cleanroom airlocks can be classified by their pressure relationship with the rooms on either side. Three common arrangements are cascade, bubble, and sink airlocks.
Cascade Airlocks
A cascade airlock creates a stepwise pressure change:
Lower pressure ← intermediate pressure ← Higher pressure
When a flow path is available, air moves toward the lower-pressure area. This arrangement can maintain directional airflow between areas with different environmental requirements.
Bubble Airlocks
A bubble airlock is maintained at a higher pressure than both adjoining rooms:
Lower pressure ← higher-pressure airlock → low pressure
When a door or leakage path is present, air tends to move outward from the airlock toward the adjoining spaces. This makes the airlock a positive pressure buffer.
Sink Airlocks
A sink airlock is maintained below the pressure of both adjoining rooms:
High-pressure → lower-pressure airlock ← higher pressure
Air tends to move into airlocks from both sides. This arrangement can support containment by limiting the outward movement of airborne contaminants. The right configuration depends on the required airflow direction and the contamination risk. No single arrangement is suitable for every process.
Positive and Negative Pressure Difference
Positive and negative pressure describe how one space is pressurized relative to another. A positive pressure room has higher pressure than the adjacent space. When a flow path opens, air tends to move outward. This arrangement is commonly used when protecting a cleaner product or process from surrounding contamination.
A negative pressure room is maintained at a lower pressure than the surrounding space. Air tends to move inward, which can help contain hazardous or unwanted airborne contaminants. The correct strategy depends on what needs to be protected: the product, personnel and surrounding environment, or both.
What Happens When an Airlock Door Opens?
Opening an airlock door changes the pressure and airflow conditions between the connected spaces. This is why closed-door pressure readings alone cannot describe how an airlock performs during normal use.
A pharmaceutical cleanroom experiment studied personnel entry at initial pressure differentials ranging from 5 to 25 Pa. Researchers found that higher initial pressure differences reduced smoke migration under the tested conditions. The airlock also acted as a buffer between adjoining spaces.
The study does not establish a universal pressure requirement. It shows why airlocks should be evaluated during door operation and personnel movement, not only under static conditions.
How Much Pressure Differential Does a Cleanroom Airlock Need?
The required pressure differential depends on the cleanliness levels of adjoining rooms, contamination risk, airflow direction, process requirements, and applicable standards. For sterile medicinal product manufacturing, EU GMP Annex 1 gives 10 Pa as a minimum guidance value between adjacent rooms of different grades.
Processes involving hazardous materials may require a different pressure arrangement to provide containment. A suitable pressure differential should maintain the intended airflow direction without creating unnecessary operational problems.
The final value should therefore be established for the specific cleanroom and process rather than applied as a fixed setting across all facilities.
How Long Should You Wait Between Airlock Doors?
The delay between airlock doors should allow the space to reach the required condition before the next door opens. The appropriate time is influenced by airlock volume, ventilation rate, pressure conditions, contamination risk, and recovery performance.
In one pharmaceutical cleanroom study, researchers tested door delay from 6 to 36 seconds. Under a specific 5 Pa test condition, a 16-second delay significantly reduced polluted air remaining in the airlock.
The 16-second result applies only to that test condition. In practice, the door delay should be established and verified for the actual airlock rather than copied from another facility.
How Do You Choose the Right Cleanroom Airlock?
Choose the airlock according to what needs protection, what will pass through it, and the environmental conditions on each side. If product protection is the priority, the pressure arrangement should help prevent contamination from reaching the cleaner process. If containment is required, the airflow strategy should help prevent hazardous airborne material from spreading to surrounding areas.
The airlock must also accommodate its intended traffic. Personnel airlocks need enough space for the required entry or gowning procedure, while material airlocks must accommodate the size and movement of carts, equipment, or other transferred items.
Room classifications, pressure requirements, traffic volume, cleaning procedures, available space, and applicable standards then determine the appropriate airlock type, size, ventilation, door controls, and monitoring system.
Conclusion
Airlocks are an important part of keeping a cleanroom controlled as people and materials move in and out. Choosing the right setup comes down to your cleanliness requirements, pressure needs nad how the airlocks will be used each day.
If you’re unsure which airlock is right for your facility, or you’re planning a new cleanroom, Sunnyda Clean Room can help. Get in touch with us to discuss your requirements and find a cleanroom solution that works for your application.
Frequently Asked Questions
What is the main purpose of an airlock in a cleanroom?
A cleanroom airlock provides a controlled space between areas with different cleanliness or pressure conditions. It helps reduce contamination transfer when people, materials, or equipment move from one area to another.
Do all cleanrooms need an airlock?
Not every cleanroom requires the same airlock arrangement. The need for an airlock depends on the cleanroom classification, process, contamination risk, pressure requirements, and applicable industry standards. Pharmaceutical and other highly controlled facilities often use airlocks as part of their contamination-control strategy.
Can both airlock doors be opened at the same time?
During normal operation, airlock doors are generally controlled to avoid opening both at once, since simultaneous opening can weaken the separation between adjoining areas. In sterile pharmaceutical manufacturing, EU GMP Annex 1 requires simultaneous opening of airlock doors leading to Grade A and B areas to be prevented.
What is the difference between a personnel airlock and a material airlock?
A personnel airlock (PAL) is used for people entering or leaving controlled areas and may include space for gowning or other entry procedures. A material airlock (MAL) is used to transfer materials, tools, carts, or equipment. Separating these routes can help facilities manage personnel and material movement more effectively.
Does a material airlock disinfect items entering a cleanroom?
Not by itself. A material airlock controls the transfer of items between areas, but simply passing an item through the airlock does not disinfect its surface. Materials may require cleaning, disinfection, removal of outer packaging, or a validated decontamination process before entering a cleaner area.
What is the difference between an airlock and a pass box?
An airlock is a space that can accommodate people, materials, or equipment, depending on its design. A pass box is a smaller transfer device used primarily to move materials between areas without requiring personnel to pass through. The appropriate option depends on the size of the items, transfer process, and contamination-control requirements.
How often should a cleanroom airlock be tested?
Testing frequency should follow the facility’s qualification, monitoring, maintenance, and regulatory requirements. Checks may include pressure differentials, door interlocks, alarms, airflow behavior, and other performance parameters relevant to the airlock design. Additional testing may also be needed after modifications, repairs, or changes that could affect performance.
What should you consider when designing a cleanroom airlock?
The design should reflect what will pass through the airlock, the cleanliness and pressure requirements on each side, expected traffic, contamination risks, available space, and applicable standards. These requirements determine the appropriate size, pressure arrangement, ventilation, door controls, and monitoring system.
You may also find these blog posts useful
Cleanroom Materials: Composition and Selection Guide
