A pressure cascade is a design of clean room HVAC where areas with higher grades are kept at a higher pressure than lower graded areas.
This pressure difference ensures clean air flows into dirty areas instead of dirty air into clean areas preventing dust ingress.
A pressure cascade is required to be monitored by some Environmental Monitoring System to prove compliance and alert to excursions.
To prevent large tubulance and backdraft in a room when a door opens between a pressure cascade, Pressure Relief Dampers are commonly used.