Cleanroom airlock design: bubble, cascade and sink

By ZY Cleanroom · Updated 2026-11-01 · Sources at the end of the page

The three types

These are common names for pressure arrangements. Annex 1 para 4.14 allows positively or negatively pressurised airlocks where a hazardous material must be contained.

Pressure values

Doors closed. Values are guidance, not a fixed rule.

Doors, flushing and layout

Annex 1 para 4.13 says airlock doors should not open together. It asks for interlocks into grades A and B, and a visual or audible warning into C and D. Add a time delay where segregation needs it.

Para 4.12 asks for personnel and material airlocks to be separate where possible, flushed with filtered air, with the final stage at the same grade at rest as the room it serves. In general, hand washing belongs only in the first stage. Para 4.9 bars sinks and drains in grades A and B.

The CDC and NIH BMBL asks for two consecutive self-closing doors at BSL-3 entry, with a visual device that confirms airflow direction.

Pass-through hatches and cascades

Annex 1 para 4.12 asks that pass-through hatches protect the higher grade, for example by flushing with an active filtered air supply, and that only approved items go through. HTM 03-01 Table 6 shows a cascade in practice: supply only in the clean room, with air leaving through pressure stabilisers to rooms of lower classification.

HTM 03-01 (para 8.18) separates closed-door protection, where leakage flows from clean to less clean, from open-door protection, where airflow through the doorway replaces the lost pressure. Design for both.

Worked example: door leakage

HTM 03-01 Appendix 4 gives closed single-door leakage, assuming gaps of 4 mm at the bottom and 3 mm at top and sides.

What it means for supply air

Example only, calculated from those figures. A bubble airlock 3 m by 2 m and 2.7 m high has 16.2 m³. At a 10 Pa step, two doors leak 2 × 0.05 = 0.10 m³/s, or 360 m³/h. That is 22 air changes before any flushing target.

Pressure does not protect an open door. HTM 03-01 (para 8.17) says a 1.4 m doorway may pass 0.19 m³/s each way with no temperature difference. This is why interlocks and time delays matter.

Who approves the room

Your regulator or customer auditor judges the facility, not the contractor. The contractor builds to your room data sheet and supplies test data. To have a room list reviewed, send it to ZY Cleanroom, a cleanroom design-and-build contractor with its own panel factory in Tianjin, China.

Related guides

• How to audit a cleanroom panel factory, on site or by video
• Cleanroom wall and ceiling finishes: coving, sealants, joints and stainless steel
• Gowning room design: airlocks, zones and sequence
• Modular operating theatres: scope, air and pressure standards
• Turnkey cleanroom contractor
• Room list builder

Sources

• EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (published 25 August 2022; applied from 25 August 2023, and from 25 August 2024 for point 8.123; checked 31 October 2026)
• FDA, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing Practice (September 2004, nonbinding; checked 31 October 2026)
• NHS England, Health Technical Memorandum 03-01, Specialised ventilation for healthcare premises, Part A (published 22 June 2021; checked 31 October 2026)
• CDC and NIH, Biosafety in Microbiological and Biomedical Laboratories, 6th edition (revised June 2020), Section IV, Biosafety Level 3, pages 43 to 51; checked 31 October 2026