Retro-commissioning a decade-old cleanroom

We started with the paper trail before touching a single filter: as-built drawings against what was actually installed, the filter change log against the maintenance contract's stated schedule, and eighteen months of pressure and particle trend data. Two changes had happened that were never documented — a partition wall moved during a line reconfiguration three years earlier, and a return grille had been partially blocked by a since-removed piece of equipment's mounting frame.

Nothing had alarmed and nothing had broken — on a facility this age, that is usually the tell that something has drifted, not the sign that nothing has.

The walkthrough tests told the rest of the story: recovery time in the affected room had crept from 14 minutes at original qualification to just over 22, still inside most alarm bands individually but compounding with a filter bank that was six months past its scheduled change date on paper — a date the maintenance log showed had actually been skipped twice. Door interlock testing found one airlock door that could be forced open against its interlock with moderate effort, a seal issue rather than an electrical fault, but one that had been letting a leak path exist unnoticed on every shift change.

Remediation was mechanical rather than dramatic: replace the loaded filter bank, reseal and adjust the airlock door, restore the return grille to its original free area, and rebalance the room against the original commissioning setpoints rather than whatever the drifted current state suggested. We requalified with a fresh recovery time test and a short particle count campaign, and it passed comfortably — the room had never needed new equipment, only its original condition restored and documented.

The client is now on a structured maintenance agreement with us rather than an ad hoc one, specifically so the next undocumented change gets caught in a quarterly review rather than by an inspector.