The problem: A pharmaceutical cleanroom holds +15 Pa against the corridor. Every door opening is a contamination event. What door construction, and what door logic, actually protects the classification?

Door construction for cleanrooms

Cleanroom doors differ from ordinary hospital doors in three ways: surface, sealing and integration.

  • Flush steel doors: powder-coated or stainless steel leaves with no ledges, no exposed hinges where avoidable, flush glazing with double-sided vision panels, and welded rather than screwed construction. Anything that traps dust is a cleaning failure waiting to happen.
  • Sealed perimeter: closed-cell gaskets on all four sides; for higher grades, drop-down bottom seals instead of raised thresholds. Air permeability should be verified to EN 12207 (see Chapter 22) where pressure control is critical.
  • Material compatibility: surfaces must withstand the site's disinfection regime — sporicidal agents, hydrogen peroxide vapour (VHP) bio-decontamination cycles in high-grade rooms. Confirm coating and gasket resistance to the actual chemicals used; VHP attacks some elastomers and adhesives.

Interlocks and airlocks

EU GMP Annex 1 defines an airlock as "an enclosed space with interlocked doors, constructed to maintain air pressure control." This is the governing concept:

  • Interlock logic: with two doors A and B forming an airlock, door B cannot open while door A is open. Two-door sequential logic is the baseline for gowning and material entry. Three or more doors may be interlocked for multi-grade passages.
  • Pressure cascade: Annex 1 guidance calls for at least 10 Pa between adjacent rooms of different grades. The airlock sits between them, so each door sees roughly half the differential — practical guidance suggests, for example, a minimum of about 7.5 Pa at each door of a lock on a 15 Pa cascade. Doors and seals must hold their side of this differential continuously, including the leakage that determines how hard the HVAC must work.
  • Active vs passive airlocks: active airlocks connect to HVAC and maintain their own classification and differential; passive ones rely on the cascade. Choose based on grade transition risk — Annex 1 expects justification by risk assessment.
  • Pass-through hatches for materials follow the same interlocked logic at small scale, often with UV or VHP decontamination.

Pressure control and cleanability trade-offs

  • A tighter door reduces HVAC load and stabilises the cascade, but a pressurised room also pushes the door open: closer/operator forces must be selected for the actual differential, and latching must be positive. A door that cannot latch against +15 Pa is a failed barrier.
  • Interlocks conflict with escape requirements. Fire code wins: interlocks must release on fire alarm, and escape-direction doors need emergency override (break-glass or push-to-exit with alarm).
  • Vision panels aid supervision but every frame junction is a potential leak and dirt trap — specify flush double-glazed panels with sealed frames.

Common mistakes

  • Interlocks wired so both doors can be forced open together "for cleaning", and then left that way.
  • Doors hung without accounting for pressure load, leading to slam-close failures or doors held ajar by the differential.
  • Gaskets incompatible with VHP cycles, degrading within a year.
  • No differential pressure monitoring across the airlock — you cannot manage what you do not measure; Annex 1 expects pressure differences to be fitted with indication/monitoring between cleanrooms.

Specification checklist

  • Flush, coved, cleanable surfaces; chemical resistance to site disinfectants and VHP verified
  • EN 12207 air permeability class where pressure-critical
  • Interlock system with fire-alarm release and emergency override
  • Closer/latch rated for the design pressure differential
  • Differential pressure gauges or sensors across each grade boundary
  • Flush vision panels, sealed frames
  • Commissioning: interlock logic test, leakage check, pressure cascade verification