States that the layout of the production line in any clean rooms is likely to change in accordance with the production process, and that this poses a problem for post clean room maintenance. One of the many problematic issues often found in the clean room environment is air velocity, and the ongoing problem should be addressed at upgrade time. The paper looks at the characteristics of airflow distribution within a clean room, as a result of changes to the production process. The study was conducted for a class 100 clean room at a manufacturing firm for disk drives.