A pharmaceutical cleanroom passed its ISO 14644 particle classification at rest — then failed operational pressure mapping. The cause was not the HVAC: two doorsets leaked enough at 15 Pa that the cascade between Grade C and Grade D zones collapsed whenever a door cycled. The doors were "cleanroom doors" by catalogue description, but no leakage class had ever been specified, so no measurable requirement existed to fail against. Airtightness is a number, not an adjective.

Where a doorset leaks

Leakage paths, in rough order of typical contribution:

  1. Bottom gap — usually the largest single path. Solutions: automatic drop seal (a seal bar that lowers as the door closes and lifts as it opens), or threshold seals where a raised threshold is acceptable. In hospitals, drop seals dominate because thresholds obstruct beds and trolleys.
  2. Perimeter gaps at jambs and head — compression gaskets (silicone, EPDM) in the frame or on the leaf edge. Silicone tolerates disinfectants and temperature better; EPDM is cheaper.
  3. Frame-to-wall interface — the most neglected path. A door tested airtight in a lab leaks on site if the frame/wall joint is filled with open-cell foam and hope. Specify a continuous sealant or gasketed frame detail.
  4. Hardware penetrations — lock cases, vision panel beads, louvres, cable transfers for access control. Every penetration needs a sealing detail.

Hermetic vs "airtight" vs ordinary sealed doors

  • Ordinary sealed doorset: perimeter gaskets + drop seal. Reduces air and sound transfer; no quantified guarantee unless tested.
  • Airtight doorset: designed and tested to a stated air permeability performance, typically via EN 1026 (test method for air permeability of windows and doors) and classified per EN 12207 (classes by leakage at reference pressures). Specifying a class gives you a contractual number.
  • Hermetic doorset: a sliding door that at closure drops and presses the leaf against seals on all four sides, achieving very low leakage used for operating theatres and containment zones. "Hermetic" is an industry term, not a standards classification — always convert it into a measured leakage figure at a stated pressure difference.

Pressure control and airflow strategy

Doors participate in the room pressure cascade:

  • Positive pressure suites (operating theatres, sterile preparation) push air out to protect the room; door leakage wastes conditioned air and can destabilise the cascade.
  • Negative pressure rooms (isolation, some labs) pull air in; the door seal direction matters — compression seals work best when the pressure pushes the leaf onto the seal, so orient seals relative to the pressure side.
  • Door cycling: every opening dumps the differential. Interlocked airlocks (Chapter 28) and fast automatic operators limit the disturbance. HVAC recovery time after a door opening is a room-level acceptance criterion, not a door property — but door leakage class is one of its inputs.

Trade-off: tighter sealing increases closing forces and wear. High-performance drop seals and compression gaskets need periodic adjustment and replacement; budget for it.

Defined testing criteria

Ask for documents, not claims:

Requirement Method / classification What you receive
Air permeability EN 1026 (test), EN 12207 (classification) Test report with leakage rates at stepped pressures; class per EN 12207
Smoke leakage (fire context) EN 1634-3 Leakage rates at ambient and medium temperature under 10/25/50 Pa, feeding an S-classification per EN 13501-2 (see Chapter 30)
Room-level cleanliness ISO 14644-1 Room classification — depends on the whole envelope, not the door alone

For cleanroom-adjacent doors, a pragmatic site verification is a pressure-hold or room leakage test on the completed enclosure, which catches the frame-to-wall defects that laboratory door tests cannot see.

Common mistakes

  • Specifying "hermetic" without a leakage number and test pressure.
  • Ignoring the frame-to-wall joint — the lab-tested door leaks through the builder's gap.
  • Drop seal cut short at the latch side, leaving an unsealed corner.
  • Adding a transfer grille to a door in a pressure-controlled suite (destroys the seal; use ducted transfer paths).
  • Seals incompatible with site disinfectants, hardening and cracking within a year. Ask for chemical resistance data.

Practical checklist

  • [ ] Leakage requirement expressed as a number at a stated ΔP (e.g. per EN 1026 test, class per EN 12207)?
  • [ ] Seal materials compatible with disinfectants and temperature?
  • [ ] Bottom gap sealed without a trip-hazard threshold?
  • [ ] Frame-to-wall sealing detail on the construction drawings?
  • [ ] Seal orientation checked against room pressure direction?
  • [ ] Site room-leakage or pressure-hold test included in commissioning?

Sources

  • iTeh / CEN, EN 1634-3:2004 — Smoke control test for door and shutter assemblies — standards.theiteh.com
  • ISO, ISO 14644-1:2015 — Classification of air cleanliness by particle concentration — www.iso.org