Particle counts are usually measured inside the room. The contamination that matters often arrives through the door: a carton that was stored in a loading bay, a bag that was handled with a bare hand, a sleeve that brushed the frame. The airlock is the one place where the room can still be protected, and it is the place most often treated as a corridor.
Material flow is a design decision
Every item that enters should have a defined route: what is wiped, where it is opened, what leaves the wrapper behind. If that route is not written down, it is invented at the door by whoever is carrying the box, and it changes with the shift.
The basic rule is that the outer surface never enters the clean side. A carton stays in the transfer zone; the inner bag is wiped and carried in; the inner bag is opened at the point of use. A triple-bagged sterile product is a sequence, not a guarantee.
Wipe-down is a step, not a gesture
A wipe-down has to cover the whole outer surface, including the bottom and the seams, with a wet cloth and a defined motion. A dry wipe moves dust; a damp wipe lifts it. The cloth should be changed between items, or at least turned, and the wipe-down surface should be cleaned at the end of the transfer.
The most common failure is the bottom of the bag, which is never wiped because the bag is held by the top. Put it down on a clean surface, wipe the bottom, then lift it.
Airflow and pressure
Airlocks are designed with a pressure cascade so that air moves from the cleaner side to the less clean side. That only works if the doors are interlocked or disciplined: both doors open at once turns the airlock into a pass-through for whatever is in the corridor.
Check the pressure differential at the start of each shift and after any door fault. A gauge that reads zero is not a maintenance issue; it is a contamination event that has already happened.
| Transfer step | Control | Record |
|---|---|---|
| Carton at the door | Outer wrapper removed | Time, operator |
| Inner bag | Wiped on all faces | Wipe lot, if critical |
| Air lock | One door at a time | Pressure check |
| Point of use | Inner bag opened | Open time |
What to record
Not every transfer needs a document, but critical ones do: sterile consumables, items entering a Grade A zone and anything that has been in a non-controlled area. Record the item, the lot, the time and the person. If a monitoring result moves, the record is the only way to reconstruct the day.
For routine consumables, a log at the airlock with the time and the item is enough. The point is not bureaucracy; it is the ability to answer a question three weeks later.
A weekly check
Once a week, stand at the airlock for ten minutes and watch. Count how many people open both doors, how many put a carton on the clean-side floor, how many wipe the top of a bag and not the bottom. Write the numbers down.
The observation is more useful than a procedure review because it shows what the shift actually does. Fix the layout before retraining; most transfer failures are caused by a bench that is in the wrong place.
Should the outer bag be wiped or removed?
Both, in that order. Wipe the outer bag in the transfer zone, then remove it and leave it behind. Carrying the outer bag in defeats the purpose of the wipe.
Can a pass-through hatch replace an airlock?
For small items it can, if the hatch is interlocked and the airflow is correct. It still needs a wipe-down step and a rule about which side the packaging stays on.
How often should the airlock be cleaned?
At least at the end of each shift, and immediately after a spill or a damaged carton. The walls, the floor and the door seals are the surfaces that matter.
