Gowning and contamination control

A cleanroom at rest and a cleanroom in operation are different physical systems, and the difference is people. The room’s filtration removes what enters from outside; the operator is a source inside the barrier, generating particles continuously and unavoidably, at a rate no air-change number can be designed against without also accounting for the garment.

The human as an emitter

Skin renews itself by shedding corneocytes — flattened, keratinised cell fragments roughly 30 µm across — at a rate of the order of hundreds of millions per person per day. A minority carry viable organisms with them, which is the point: a skin squame is not merely a particle, it is a vehicle. Emission is strongly activity-dependent. Commonly cited cleanroom figures put an operator standing nearly still at the order of 10^5 particles ≥0.5 µm per minute and a walking operator one to two orders of magnitude higher, and the same ratio applies to viable release. This is why aseptic technique is largely a discipline of slow, deliberate movement, and why interventions — the moments when a person reaches into a critical zone — are the events that environmental monitoring is designed to catch.

Speech, coughing and skin friction against clothing all raise the rate. So does the act of gowning itself, which is why the gowning room is classified one grade below the room it serves and is itself a controlled sequence rather than a changing area.

What the garment does, and where it fails

A cleanroom coverall is made from continuous-filament fabric — usually polyester, often with a conductive grid — that sheds essentially nothing itself and filters particles carried outward by body-driven airflow. The fabric is rarely the limiting element. Every time a person moves, the garment acts as a bellows, pumping air out through whatever openings exist, so the barrier’s real performance is set at the interfaces: cuff to glove, hood to mask, mask to goggle, zip closure, and the overlap of boot cover and leg. A correctly specified garment gowned so that a wrist is briefly exposed is not a partly effective barrier at that point; it is an aperture with a pump behind it.

Sterile garments for grade A and B use are terminally sterilised, normally by gamma irradiation, and are single-use or re-processed under a validated laundering and sterilisation regime with a defined maximum number of cycles, because filtration efficiency degrades with laundering.

Qualification measures the operator

Because the barrier is made at the interfaces, the competence being certified is the sequence: gowning in a strict order that never lets a gowned surface contact an ungowned one, using mirrors and a defined step-over line to separate zones. EU GMP Annex 1 requires that personnel entering grade A and B areas be qualified for gowning and periodically requalified, with the assessment supported by contact-plate and glove-print sampling of the gowned operator, and with aseptic process simulation used to test technique under realistic conditions.

The limitation is worth stating plainly. This is a test of a person on a day, sampled at a few surfaces. It cannot demonstrate that no viable particle was released, only that none was recovered where sampled — which is why gowning qualification is treated as one control among several rather than as evidence of sterility.