HVAC and Cleanroom Qualification, From Classification to PQ
A short, practical walkthrough of qualifying classified areas — airflow, pressure cascades, HEPA integrity and particle classification — and where these projects most often fall short.
What does qualifying a cleanroom actually involve?
HVAC and cleanroom qualification proves a classified area consistently controls particles, pressure, temperature, humidity and airflow within the limits its intended use requires. That means testing under both "at rest" and "in operation" conditions, because particle counts and pressure behavior change once personnel and equipment are active — a room that classifies perfectly empty can still fail once people start working in it.
Defining Classification Before Testing Begins
The room's intended grade or ISO class should drive the qualification plan, not the other way around.
The URS should define the required grade (A/B/C/D or ISO 5/7/8) for each room, the pressure cascade between adjacent areas, temperature and humidity ranges, and which zones are critical enough to need continuous monitoring versus periodic testing. HVAC design review should confirm duct routing, HEPA filter placement and airflow pattern support that classification before installation locks it in.
Because Annex 1's 2022 revision moved away from fixed air-change recommendations, the design and qualification must instead demonstrate — through airflow visualization and recovery data — that the air supply is genuinely sufficient, rather than relying on an inherited rule-of-thumb figure from an older facility.
IQ and OQ: What Gets Verified
IQ confirms the installed system matches design; OQ proves it performs across both room states.
| Phase | What to Verify | Typical Evidence |
|---|---|---|
| IQ | Duct routing, filter placement and room finishes match approved drawings | Drawings, installation checks |
| IQ | HEPA filter certificates and mounting frame seal | Filter certificates, visual inspection |
| OQ | HEPA integrity scan, airflow velocity and uniformity | DOP/PAO scan results, velocity readings |
| OQ | Pressure cascade, including during door-open events | Differential pressure logs |
| OQ | Airflow visualization (smoke study), recovery time | Video recordings, particle recovery data |
PQ: Proving the Room Holds Classification in Use
Performance qualification runs the room through realistic conditions, not just an idle snapshot.
Nonviable particle counts and viable (microbial) monitoring should be captured across a representative operating period, both at rest and in operation, at locations that reflect actual risk to the product — not wherever is most convenient to sample. For aseptic Grade A/B areas, PQ data should correlate with personnel gowning qualification and, where applicable, support the facility's media fill program.
Recovery time — how long the room takes to return to its classified state after a defined worst-case disturbance, such as a door held open — should be measured and documented, since this is one of the clearest indicators of whether the airflow design actually works under real conditions rather than only on paper.
Where HVAC and Cleanroom Qualification Goes Wrong
A handful of recurring gaps account for most classification-related audit findings.
The most frequent gap is classifying only "at rest" and skipping "in operation" testing, leaving the room unproven under the conditions it actually runs in. A close second is omitting airflow visualization studies that Annex 1's 2022 revision now expects for critical zones. Teams also run HEPA integrity testing before ductwork balancing is finalized, which invalidates the scan once airflow is rebalanced afterward. And recovery time testing is frequently skipped entirely, even though it's one of the more telling indicators of a genuinely robust airflow design.
HVAC & Cleanroom Qualification FAQs
What is the difference between 'at rest' and 'in operation' classification?
'At rest' means the room is complete with equipment installed but not running and no personnel present. 'In operation' means the facility is functioning with people and equipment active. Both states must be qualified.
What air change rate is required for a Grade C cleanroom?
EU GMP Annex 1 (2022) no longer prescribes a fixed number. The required air supply must be justified and demonstrated through airflow visualization and particle recovery data, not an inherited rule-of-thumb figure.
How is HEPA filter integrity tested?
A DOP or PAO aerosol challenge scan test is performed across the entire filter face and frame seal, with leakage required below 0.01% of the upstream challenge concentration at any scanned point.
What pressure differential is required between cleanroom grades?
A commonly used reference is 10–15 Pascals between adjacent areas of different classification, sustained even during door openings. The value should be justified by risk assessment, not assumed.
Are airflow visualization (smoke) studies mandatory?
Yes, for critical zones under EU GMP Annex 1 (2022), performed both at rest and in operation and video recorded. Results should directly inform the environmental monitoring program design.
How long should cleanroom recovery time testing take?
No fixed number is mandated. Qualification should establish a justified recovery time from a defined worst-case disturbance, with roughly 15–20 minutes commonly used as an industry reference.
Key References
- EU GMP Annex 1 (2022) — Manufacture of Sterile Medicinal Products
- ISO 14644-1 — Classification of Air Cleanliness by Particle Concentration
- ISO 14644-2 — Monitoring to Provide Evidence of Cleanroom Performance
- FDA — Sterile Drug Products Produced by Aseptic Processing: Current GMP