The Unremarkable Case Needs Its Evidence Too
The clean-up test under EU GMP Annex 1 demonstrates that a cleanroom returns to the required state in time after activity ends. It comprises three blocks of measurements: the measurements before the activity, the measurements during the decay phase, and the measurements taken once the at-rest limit has been reached. The measurements before the activity verify the initial state, those afterwards the regained at-rest state. Between them lie the measurements during the decay phase: they start when the activity ends and record the course of the particle concentration until the cleanliness class limit is met again – the clean-up time is derived from them. The number of measurements before and afterwards is held per measurement method in the master data.
Until now the post-measurements were only triggered if the cleanliness class limit had been exceeded during the preceding measurements. If the room remained unremarkable, the test ended without a post-measurement – and therefore without any values documenting the at-rest state afterwards.
Why Post-Measurements Were Previously Limited to Excursions
The previous logic was not an oversight; it followed directly from the definition of the clean-up time: it is the time the room needs to return from a limit excursion to the required state. If the limit was never exceeded, that time is 0 by definition – there is no recovery that could be measured, and a post-measurement would not have changed the result. That is precisely why the post-measurements were not carried out in this case. This evaluation is still correct and remains valid: what has been extended is not the calculation of the clean-up time, but solely the scope of the evidence.
What Changes
The post-measurements now take place in every case, regardless of whether a limit excursion occurred. Where the limit was never exceeded, the clean-up time determined remains 0 – so nothing changes in the evaluation. What changes is the evidence: every clean-up test performed now has measured values documenting the regained at-rest state.
Why This Is More Than a Formality
A report that shows no post-measurement in the unremarkable case raises the same question at every review: was nothing measured because there was nothing to measure – or because the measurement was omitted? That distinction can no longer be made after the fact, and explaining it in an audit regularly costs more time than the measurement itself would have taken. With post-measurements throughout, the question disappears: every test has the same structure and delivers the same kind of evidence, regardless of the outcome.
Effect on the Measurement Workflow
Nothing changes inside the cleanroom. As soon as the activity has ended, the sequence of decay and post-measurements runs automatically on the instrument. The number of measurements before and afterwards continues to be maintained per measurement method in the master data and does not have to be adjusted for this.
Comparability Over Time
One side effect only becomes visible across several campaigns: because every test has the same scope, the results are comparable with one another. A gradually lengthening recovery – caused for instance by clogging filters or altered air routing – becomes apparent earlier, because the unremarkable tests now contribute data points instead of gaps.
Evidence that only comes into existence when something goes wrong is no evidence at all!