positive pressure

Positive pressure maintains higher atmospheric pressure inside the cleanroom than outside, preventing contaminated air from entering. **Principle**: Air flows from high to low pressure. Positive pressure ensures any leakage flows outward, not inward. **Typical pressure**: 0.03-0.05 inches water column (7-12 Pa) higher than adjacent areas. **Pressure cascade**: Multiple cleanliness zones with highest pressure in cleanest areas. Air flows from clean to less clean. **Implementation**: Supply more air than exhaust. HVAC system maintains setpoint. Airlocks and interlocks at boundaries. **Monitoring**: Pressure differential sensors at zone boundaries. Alarms if pressure drops. **Door management**: Airlocks between zones maintain pressure during personnel transit. Interlocks prevent simultaneous door opening. **Failure response**: Low pressure alarm triggers investigation. May indicate filter loading, door issues, HVAC problems. **Gowning rooms**: Intermediate pressure between outside and cleanroom. Progressive cleanliness. **Energy impact**: Makeup air requires conditioning (temperature, humidity, filtration). Significant HVAC load. **Critical importance**: Without positive pressure, particles enter through any gap. Foundation of cleanroom contamination control.