Every doorway between two cleanliness grades needs an airlock, but an airlock is not just a box with two doors. Its type, size, and pressure strategy have to match the direction of contamination you are trying to stop — get that choice wrong and the airlock either fails to protect the cleaner room or, worse, leaks the very contamination it was built to contain. This guide covers the airlock types GMP facilities use, the three pressure strategies behind them, and what EU GMP Annex 1 expects from the design.
Key takeaways
- A cleanroom airlock is a small interlocked room that separates two cleanliness grades so people, equipment, or materials can cross the boundary without breaking the pressure cascade.
- The three functional types are the personnel airlock (PAL), the material airlock (MAL), and the air shower, each built for a different kind of crossing.
- Airlocks run one of three pressure strategies — cascade, bubble, or sink — and picking the wrong one for the contamination direction you need to protect defeats the airlock's purpose.
- EU GMP Annex 1 (2022) expects interlocked or alarmed doors so only one door opens at a time, and the airlock's air supply to be sized and qualified as part of the facility's pressure cascade.
- Airlock type and size are layout decisions, not equipment picked after the fact — retrofitting a bubble airlock into ductwork built for a cascade is a construction change, not a settings change.
What is a cleanroom airlock and what does it do?
A cleanroom airlock is a small transition room with two or more interlocked doors that separates areas of different ISO or GMP cleanliness grades. It stops air and contamination moving directly between rooms whenever people, equipment, or materials cross a grade boundary, and it is where personnel gown or materials are wiped down and staged before entering the cleaner side.
The airlock does this by holding its own pressure relative to the two rooms it connects, so air always moves in the direction the design intends when a door opens, and by keeping both doors from opening together so the two rooms are never briefly joined into one airspace.
What are the different types of cleanroom airlocks?
GMP facilities generally use three functional types of airlock, and a single facility usually needs more than one: a personnel airlock for gowning, a material airlock for equipment and components, and, where the class step is large, an air shower to strip loose particles off gowned staff.
| Airlock type | What crosses through | Typical features | Purpose |
|---|---|---|---|
| Personnel airlock (PAL) | Operators | Gowning benches, a "dirty/clean" bench divide, hand sanitising station | Lets staff change into cleanroom garments before entering a higher-grade area |
| Material airlock (MAL) | Equipment, components, raw materials | Pass-through hatch or full room, wipe-down or de-boxing step | Moves materials across a grade boundary without personnel movement |
| Air shower | Gowned personnel | High-velocity HEPA-filtered air jets, interlocked with the airlock doors | Removes loose particles from garments before entry to the core cleanroom |
Separating personnel and material airlocks where space allows keeps gowning traffic away from equipment movement, which is one of the sixteen contamination-control elements a contamination control strategy has to justify.
Cascade, bubble, or sink: which pressure strategy do you need?
An airlock's pressure relative to its two neighbouring rooms is not fixed — it is chosen to match the contamination direction you need to block. GMP designers name three strategies: cascade, bubble, and sink.
| Strategy | Airlock pressure vs. both neighbouring rooms | Contamination direction protected | Typical use case |
|---|---|---|---|
| Cascade | Between the two — steps down from the cleaner room to the less clean one | Protects the cleaner room from the less clean one | A standard one-way step between adjacent GMP grades, e.g. Grade B corridor to Grade C corridor |
| Bubble | Higher than both | Protects each neighbouring room from the other | Between two rooms that must not cross-contaminate each other, such as two independent clean processes sharing a corridor |
| Sink | Lower than both | Contains contamination generated in the airlock, or carried in from one side, so it cannot escape into either room | Transfers involving hazardous, toxic, or biologically active material, where containment matters more than ingress protection |
Our cleanroom HVAC design guide covers the 10–15 Pa per step that EU GMP Annex 1 (2022) gives as a guidance value for the pressure cascade between adjacent grades; the same figure is the usual starting point for sizing a cascade airlock's offset against its two neighbours.
What does EU GMP Annex 1 require for airlock design and operation?
EU GMP Annex 1 (2022) requires airlocks between areas of different cleanliness grades and expects personnel and material airlocks to be separated where the layout allows it, so gowning traffic and equipment movement do not share the same transition space. It also expects an interlocking system, or a visual and/or audible warning system, so that only one door can be opened at a time — the two doors are never open together, which would briefly join the two rooms into one airspace.
Beyond the doors themselves, Annex 1 treats the airlock as part of the facility's air system: its supply airflow, air change rate, and pressure offset have to be sized for the grades it connects and confirmed during qualification, in the same way a room is qualified. A guide to the underlying GMP requirements is maintained by gmp-compliance.org.
How airlock design fits your facility's pressure cascade
An airlock is not designed on its own — its pressure strategy only makes sense in the context of the grades on either side of it. Our primer on GMP zoning and pressure cascades covers how classification decisions set that cascade before any airlock is sized, and the cleanroom HVAC design guide covers how the air change rate and pressure offset are calculated once the cascade is fixed. The airlock is where those two decisions meet a door.
Common cleanroom airlock design mistakes
- Using a cascade airlock where a bubble or sink is actually needed, so the airlock protects the wrong room from the wrong direction of contamination.
- Sharing one airlock for both personnel gowning and material transfer when the layout could have separated them, mixing two very different contamination risks in one space.
- Sizing the airlock as leftover floor space instead of for the gowning steps or equipment it has to hold, which turns it into a bottleneck or a place where doors get propped open.
- Skipping interlock or alarm qualification, so a failed door sensor goes unnoticed until an audit or a contamination event surfaces it.
- Treating the airlock's air change rate as an afterthought rather than sizing it, like the rooms it connects, for the class and recovery time it needs to hold.
An airlock sized and pressurised for the wrong direction of contamination protects nothing — it just adds a door.
Frequently asked questions
What is a cleanroom airlock and what is it for?
A cleanroom airlock is a small transition room with two or more interlocked doors that separates areas of different cleanliness grades. It stops air and contamination from moving directly between rooms when people, equipment, or materials cross a grade boundary, and it is where personnel gown or materials are wiped down before entering the cleaner side.
What are the different types of cleanroom airlocks?
The three common types are the personnel airlock (PAL), where operators gown before entering a cleaner area; the material airlock (MAL), which passes equipment and components through without personnel movement; and the air shower, which blasts gowned personnel with filtered air to remove loose particles before they enter the core cleanroom.
What is the difference between a cascade, bubble, and sink airlock?
A cascade airlock sits at a pressure between its two neighbouring rooms, stepping down from the cleaner side to the less clean one. A bubble airlock is held at higher pressure than both neighbours, protecting each room from the other. A sink airlock is held at lower pressure than both, containing contamination generated inside it or carried in from one side.
What does EU GMP Annex 1 require for airlocks?
EU GMP Annex 1 (2022) requires airlocks between areas of different cleanliness grades, with personnel and material airlocks separated where practical, and an interlocking or warning system so only one door opens at a time. It also expects airlocks to be qualified as part of the pressure cascade, with their air supply sized for the grades they connect.
How do you choose the right airlock type for a design?
Match the airlock's pressure strategy to what you are protecting. Use cascade for a standard one-way step between grades, bubble when both adjoining rooms must be shielded from each other, and sink when the material or process passing through the airlock is the contamination source you need to contain, such as hazardous or biologically active transfers.
What is the difference between an airlock and a pass-through (pass box)?
A pass-through, or pass box, is a small sealed cabinet built into a wall that lets materials cross a grade boundary without opening a room to a corridor; it has no floor space to stand in. An airlock is a full room, sized for personnel or larger equipment, with its own pressure and, usually, interlocked doors.
How PharmaTwin helps
PharmaTwin is a pharmaceutical facility simulator that models airlocks as part of the same pressure cascade as the rooms around them. As you place a personnel or material airlock in the 3D layout, it checks the pressure strategy against the grades on both sides and flags an airlock sized or pressurised for the wrong contamination direction, before the ductwork and doors are built around the wrong assumption.