HVAC Air Balancing and Differential Pressure Cascades in OSD Cleanrooms

Principles of Cleanroom Pressure Cascades

In oral solid dosage (OSD) pharmaceutical manufacturing, airborne dust generation during dispensing, granulation, compression, and coating poses a continuous risk of cross-contamination.

Maintaining validated differential pressure cascades between process cubicles, personnel airlocks (PAL), material airlocks (MAL), and clean corridors is the fundamental defense mechanism mandated by WHO-GMP and ISO 14644-4.

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Pressure Cascade Regimes for OSD Manufacturing

1. The Clean Corridor Regime (Positive Pressure Corridor)

In standard multi-product OSD facilities, the central corridor is maintained at the highest relative positive pressure (+30 Pa to +45 Pa), while individual process cubicles (e.g. tablet compression suites) are held at lower positive pressure (+15 Pa).

[ Corridor: +30 Pa ]  ── (Air flows inward) ──►  [ Compression Cubicle: +15 Pa ]
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                                                   [ Dedicated Dust Extraction ]

• Advantage: If a cubicle door is opened, clean corridor air flows into the processing cubicle, preventing powder dust from escaping into the shared corridor.

2. Air Change Rates (ACPH) by Cleanroom Class

| Cleanroom Classification | Minimum ACPH | HEPA Filter Grade | Target Recovery Time | |---|---|---|---| | Class D (ISO 8) | 20 to 25 ACPH | H13 (99.95% @ 0.3 µm) | < 20 minutes | | Class C (ISO 7) | 30 to 45 ACPH | H14 (99.995% @ 0.3 µm) | < 15 minutes | | Class B / Grade A | Unidirectional (0.45 m/s) | H14 / U15 | Instantaneous |

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Diagnostic Troubleshooting for Pressure Drift