Cleanrooms are designed to minimise the ingress of airborne particles (achieved through HEPA or ULPA filters) and to control what happens to particles generated within the cleanroom. Good air flow design — such as turbulent flow — helps to prevent particles from being deposited onto surfaces (particles settle by two primary mechanisms: gravitational sedimentation and turbulent deposition)1. The removal of these particles is achieved through the extraction of room air with the addition of clean air into the room (air exchange rates). The flow of particles in air from a less clean area can also be blocked from entering an area of a higher cleanliness level through positive pressure differentials.
These design principles of cleanrooms (observable through airflow visualisation studies) are well understood and have been in place for decades, enhanced through advances in technology aimed at improving control.2 What is less well-defined are specifications for the equipment being placed into cleanrooms.
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