A grade C suite is handed over with every qualification test passed. After a few cycles of the rotating disinfection programme the sealant at the wall-to-floor junction loses adhesion where the trolleys run, the glass of an observation window goes hazy, and the plate of an electrical penetration, sealed by a contractor other than the one that erected the walls, leaks air whenever the airlock door opens. None is an HVAC failure, and none would have been caught by the qualification tests.
The construction detail had never been written as a verifiable performance requirement: it was left to supplier habit and site sequence. Finishes and openings are not picked from a catalogue. They are decided by keeping apart three levels that collapse into one on site: GMP expectation, cleanability principle and engineering choice. This article is part of the Cleanrooms & HVAC Systems cluster.
Why the construction detail drives tender, qualification and operation
A specification that points to an "equivalent system" produces bids that cannot be compared: every supplier prices its own standard detail, and the difference surfaces when changing it is costly. The test list in Annex 1 §4.25 does not measure the cleanability of a junction, while a leaky envelope shows up indirectly as unaccounted airflow and as instability of the pressure cascade. In operation, every discontinuity that retains residue lengthens cleaning time, and every change to the structure triggers requalification under §4.32, which sets maximum intervals of 6 months for grade A and B and 12 months for C and D [REQUIREMENT].
What actually binds
The first filter to apply to any supplier statement about finishes.
| Source | Status / Date | What it actually binds |
|---|---|---|
| Annex 1, EudraLex Vol. 4 | C(2022) 5938 final, applicable since 25 August 2023 | Surfaces and materials (§4.5–4.9), transfers (§4.10–4.11), separate PAL and MAL (§4.12), interlocking for A/B (§4.13), differentials (§4.14–4.16), qualification (§4.23–4.32) |
| Chapters 3 and 5, EudraLex Vol. 4 | Operational since 1 March 2015 | Design against cross-contamination (3.6), effective ventilation (3.12), technical measures including airlocks and cascade (5.21). No figures |
| Annex 15, EudraLex Vol. 4 | Operational since 1 October 2015 | Methodology: URS, DQ, FAT/SAT, IQ/OQ/PQ, requalification at a justified frequency, change control |
| 21 CFR 211.42(c)(10)(i) and 211.46 | Current eCFR | Smooth, hard, easily cleanable surfaces; ventilation and filtration. No figures |
| ISO 14644-4, -5, -13; EN 17141:2020 | Voluntary; ISO 14698-1/-2 withdrawn on 16 March 2026 | Design and start-up, operations, surface cleaning, biocontamination. Method, not obligation |
Three levels that must not be merged
- GMP expectation: what the text asks in words, without quantification. The only level you can defend by citing a clause.
- Cleanability principle: the physical reason a solution meets that expectation — continuity, no traps, nothing the cleaning agent cannot reach, inspectability, chemical and mechanical resistance.
- Engineering choice: the specific solution, from the wall system to the gasket material, defended with a documented justification and field evidence.
The envelope: walls, ceilings, floors
Surface continuity
Every interruption — a joint, a corner, a screw head, a trim — has less cleaning-agent contact time and a higher chance of retaining residue. Two variables can be governed at design stage: interruptions per unit of surface and their position relative to the activities. Modular panel systems, continuous coatings and welded sheet differ precisely on this.
Junctions and coving: fix the performance, not the geometry
No primary source prescribes a coving geometry. What goes into the URS is performance: no internal corner that traps residue, a junction inspectable and repairable without dismantling the envelope, sealant integrity under the intended disinfection cycle. Verification comes before the technical voids close, and again after the first complete cycle.
Floors, traffic and impact resistance
The requirement is not a catalogue class but a description of real traffic: wheels and weight of the equipment moved, transit frequency, turning and parking points. From there follow the covering, the junctions, the coving and the protections. Every protection must itself be cleanable: a bumper integrated and sealed into the finish is a solution, one screwed on top of it is a problem.
Compatibility with the disinfection programme as a design requirement
Annex 1 §4.33–4.36 covers cleaning and disinfection, validation of disinfection, sterile disinfectants in grade A and B and validated fumigation. The programme — agents, in-use concentrations, contact times, rotation, any vaporised agent — must therefore be formalised before materials are ordered. If it changes in operation, compatibility is reassessed as a change.
The requirement reads: every exposed material — finishes, sealants, gaskets, glazing, hardware, airlock and pass box interiors — must retain its functional characteristics after repeated exposure to the actual agents. Verification stands on three legs: a supplier declaration per material and per agent; testing on coupons that include the junctions and not only the flat sheet, because the weak point is almost always the interface between dissimilar materials; periodic review of the most heavily worked surfaces. Acceptance criteria are performance-based — no change against the reference coupon, no loss of adhesion, no change in appearance that impairs visual inspection — because no primary source gives universal thresholds.
Openings in the envelope: doors, windows, airlocks, pass boxes
Doors and windows
The expectation is explicit: airlock and pass-box doors must not open simultaneously and interlocking is required for grade A/B (§4.13) [REQUIREMENT]; production in A/B must be observable from outside (§4.17). The principle adds flush frames, glazing sealed on both faces, no rebate that collects residue. The choice covers swing direction, perimeter sealing and behaviour on opening, a cascade transient to design rather than endure; interlock logic is defined in the URS and verified in OQ.
Airlocks: PAL and MAL
§4.12 requires airlocks that separate different grades, flushed with filtered air, with personnel (PAL) and material (MAL) airlocks kept separate [REQUIREMENT]; §4.10 treats material transfer as a major risk and §4.11 requires unidirectional processes towards A/B. Between adjacent rooms of different grade Annex 1 states a minimum differential of 10 Pa, explicitly qualified as a guidance value (§4.14) [GUIDANCE]. The taxonomy that sorts airlocks into cascade, sink and bubble does not appear in Annex 1: in a GMP document it must be declared as engineering terminology. The airlock is also the room with the highest density of surfaces — benches, hooks, containers — each a finish subject to the same requirements as the walls, and placed without obstructing gowning or the flow assumed by the zoning.
Pass boxes and transfer hatches
A pass box is at once equipment and a wall penetration, and must be qualified in both natures. As equipment it needs interlocking, continuous inspectable interior surfaces, removable shelves and gaskets compatible with the agents in use. As a penetration it needs a declared frame-sealing detail, executed by an identified party and verified before the walls close. Passive or ventilated is a risk-based decision.
Penetrations and seals: where room integrity is lost
An envelope is defined more by its holes than by its surfaces. Every cable, pipe, duct, sprinkler head, light fitting and sensor is a discontinuity somebody has to close again, to an approved detail and at a precise point in the sequence. Integrity is lost for organisational reasons: whoever makes the penetration answers to a different contract from whoever supplied the envelope. The countermeasures are contractual: each type assigned to a single contractor for execution and reinstatement; an approved detail per type; no ceiling or riser closed before joint inspection of the hidden work, with photographic records; a leakage check with method and criterion agreed beforehand. The result is read with the air balance during TAB and turnover, while correction is still possible.
Lighting, utilities and maintainability
§6.1–6.6 asks that pipework and ducting avoid recesses and surfaces difficult to clean. The design decision is which components must be maintainable from outside the classified area: light fittings served from the technical space, terminal filters replaceable from the plenum, instruments accessible without entering grade A or B. Every component serviceable only from inside must be declared, because it generates a procedure, a re-clean and an impact on qualification. Drains and water points are excluded from the higher grade areas on principle, and justified in the CCS where they remain.
Construction matrix: expectation, principle, choice
| Element | GMP expectation | Cleanability principle | Engineering choice to justify |
|---|---|---|---|
| Walls and ceilings | Cleanable surfaces, suitable materials (§4.5–4.9) | Fewer interruptions; no unintended air path from the plenum | Wall system, joints, panel access |
| Floors and coving | Cleanable surface, resistant to the intended use | Continuity between orthogonal planes, no traps | Covering, junctions, coving up the wall |
| Doors and windows | Interlocking for A/B (§4.13), observability (§4.17) | Flush surfaces, inspectable hardware | Swing, perimeter sealing, interlock logic |
| Airlocks | Grade separation, filtered air, separate PAL and MAL (§4.12) | Cleanable fittings, no route carrying contamination back | Number, fixed fittings, air regime |
| Pass boxes | Interlocking; transfer as a major risk (§4.10) | Continuous interior, no blind corner | Passive or ventilated, gaskets, frame sealing |
| Penetrations | Air regime maintained in all operating conditions (§4.14) | Discontinuity closed continuously, and inspectable | Detail per type, single accountability |
| Lighting and utilities | No recess or hard-to-clean surface (§6.1–6.6) | Inspectable routes, no undrainable point | Service from outside, drains |
Justifying the choices with QRM
ICH Q9(R1) applies QRM to facilities, equipment and utilities in Annex II.4. Formality is a continuum (§5.1): a detail already in use and verified on site does not call for the apparatus a new material or an unused agent demands. Subjectivity has to be acknowledged (§5.3): "we have always done it this way" is the most frequent bias here, because a supplier's standard detail is perceived as the state of the art. The tools in Annex I are there to produce one useful output: the critical details to verify in the field before the closures.
Worked example: Site Vega
Site Vega is a realistic but fictitious example. The site is building a grade B suite with grade C background, with a rotating disinfection programme including a sporicidal agent and, for the material airlock, periodic decontamination with a vaporised agent. At DQ the team requires the material specification to state, for every exposed surface, compatibility with the actual agents. Two items are not covered: the gasket of the observation windows and the sealant chosen by the electrical contractor for the panel penetrations. The first is resolved before ordering, with a qualified gasket and a repeat test on a coupon covering the glass-to-frame interface. The second is organisational: the penetrations move by contract to the envelope contractor, with joint inspection before the ceilings are closed.
Levels of prescriptiveness
| Statement | Level | Source or basis |
|---|---|---|
| Airlocks separating different grades, with separate PAL and MAL and interlocking for A/B | [REQUIREMENT] | Annex 1 §4.12, §4.13 |
| Minimum differential of 10 Pa between adjacent rooms of different grade | [GUIDANCE] | Annex 1 §4.14, guidance value |
| Requalification within 6 months for A and B and 12 months for C and D, and after changes | [REQUIREMENT] | Annex 1 §4.32 |
| Design and start-up to ISO 14644-4; operation and cleaning to -5 and -13 | [STANDARD] | Voluntary standards |
| Impact resistance derived from documented real traffic | [GEP] | Good engineering practice |
| Number and detailing of penetrations justified by risk | [QRM] | ICH Q9(R1), Annex II.4 |
| Material-to-disinfectant compatibility testing on coupons that include the junction | [GUIDEGXP] | GuideGxP operational recommendation |
Operational checklist
- Freeze the disinfection programme before issuing the material specification, and require declared compatibility with the actual agents for every exposed material.
- Put coupon testing with junctions and gaskets into the tender.
- Write finish requirements as performance and map surface interruptions to compare bids.
- Assign each penetration to a single contractor for execution and reinstatement, with an approved detail per type.
- Set hold points before every ceiling or riser closure.
- Define the interlock logic in the URS and verify it in OQ, deriving protections from real traffic.
- List the components serviceable only from inside and assess their impact on qualification.
- Agree method and criterion of the leakage check before performing it.
- Re-inspect the most heavily worked junctions after the first disinfection cycle.
- Handle every change of finish, material or agent as change control.
Recurring mistakes and red flags
- Specifying finishes from a catalogue, then finding the material does not withstand the sporicides.
- Defining the disinfection programme after handover, making compatibility a retrospective check.
- Presenting a coving geometry or resistance class as a regulatory requirement.
- Treating fixed airlock fittings as a minor supply rather than a surface to be cleaned.
- Closing ceilings and risers without joint inspection of hidden work.
- Using cascade, sink and bubble as if it were Annex 1 terminology.
- Handling a change in a classified area without requalification.
If this way of separating expectation, principle and choice is useful in daily work, The Pragmatic GMP is the newsletter where we publish technical analysis of this kind on cleanrooms, HVAC and qualification, with no promotional content.
Key takeaways
- Primary sources ask for cleanable surfaces, separate airlocks and interlocks, not geometries, thicknesses or resistance classes.
- Every decision splits into GMP expectation, cleanability principle and engineering choice: only the first is defended with a clause.
- Material compatibility with the disinfection programme is a design requirement, closed before ordering.
- Penetrations are where room integrity is lost, for organisational reasons before technical ones.
- The useful checks are those scheduled before the closures: afterwards, correcting means reopening a released envelope.
References
- Annex 1, C(2022) 5938 final, applicable since 25 August 2023.
- Annex 15, since 1 October 2015; ICH Q9(R1), Step 4 on 18 January 2023.
- WHO TRS 1010, Annex 8, 2018, HVAC for non-sterile products.
- ISO 14644-4:2022 and ISO 14644-5:2025.
- 21 CFR Part 211, 211.42 and 211.46.
- EudraLex Volume 4 and ISPE guidance documents, the latter non-regulatory.
