Airlock Pressure Regimes: A Technical Guide to Bubble, Sink, and Cascade Design

Airlock Pressure Regimes

A Technical Guide to Bubble, Sink, and Cascade Design

In critical environments, airlocks serve as the physical and aerodynamic barrier between cleanroom grades. Choosing the correct pressure regime is a mechanical necessity dictated by whether you are protecting the product, the personnel, or the adjacent corridors. Standard GMP practice dictates that doors should open into the higher pressure room to maintain seal integrity.

1. Comparative Matrix

Type	Pressure Logic	Primary Use Case
Bubble	P_Airlock > P_Adjacent	Sterile defense (Injectables, Sterile Fill).
Sink	P_Airlock < P_Adjacent	Potent compound containment (Hazardous APIs).
Cascade	P1 > P_Airlock > P2	Directional airflow between different Cleanroom Grades.

2. Interactive Design Simulator

1. Regime Selection

Bubble Sink Cascade

2. Interlock Override

Room A Door Room C Door

3. Status

COMPLIANT

0s

Cleanroom
Grade B

15 Pa

Airlock
Grade B

30 Pa

Corridor
Grade C

15 Pa

Technical Compliance Note:
• Door Swing: Hinges are fixed to open into the higher pressure room to ensure seal integrity via pressure-assisted closure.
• Transit SOP: Staff transit must not exceed 3–5 seconds (Maximum allowable duration for door opening).
• Recovery: System is validated to restore ΔP setpoints within 15–30 seconds of door closure.

3. Regulatory Audit Checklist

Standard	Target ΔP	Audit Focus
WHO TRS 961	15 Pa recommended	Prevents flow reversal due to turbulence. Evaluates recovery alarms.
EU GMP Annex 1	10–15 Pa minimum	Strict continuous monitoring required between sterile grades.
ISO 14644-4	5–20 Pa range	Calculates required air volumes to compensate for structural leakage.

CED Field Insight: A perfect design fails if VAV recovery is too slow. If your Building Management System (BMS) cannot restore the pressure setpoint within the validated alarm delay (usually 15-30 seconds), you risk cross-contamination and an immediate audit violation.

From Theory to Calculation

Mastering the pressure regime is only the first step. To ensure your HVAC system is perfectly sized to maintain these differentials, you must calculate the precise air leakage through your specific door clearances. Use our interactive ASHRAE-standard tool to derive the required Volumetric Flow Rate (CFM/Lps) for your design.