TECHNICAL INFORMATION

Laminar Airflow Versus Turbulent Airflow

We offer a range of contamination control equipment which have HEPA (High Efficiency Particulate Air) or ULPA (Ultra Low Penetration Air) filters as the final filtration stage. These filters are generally located as close as possible to the desired clean area i.e. in cleanrooms they are used as terminal ceiling filtration devices. In order to achieve unidirectional airflow (or laminar airflow) within an enclosed workspace, room or enclosure at the ISO CLASS 4 or ISO CLASS 5 cleanliness levels, careful attention must be paid to the ceiling layout - especially the lighting. At these cleanliness levels total HEPA/ULPA ceiling coverage is required and therefore the lighting is generally tear-drop (See Figure 1). Essentially, the airflow is “once-through” and all particulates or aerosols introduced into the airflow by personnel, equipment or processes are immediately swept out of the enclosure. The cleanliness level of the room is therefore maintained within the ISO CLASS 4 or ISO CLASS 5 thresholds at all times. For some applications, turbulent airflow (or non-laminar airflow) ISO CLASS 5 environments may be satisfactory (See Figure 2). In these cases when particulates or aerosols are introduced into the clean enclosure they will be recirculated within the enclosure, and the cleanliness level may temporarily deteriorate. The time frame for the room to purge itself (i.e. its recovery time) depends on many factors including the number of filtered air changes per unit time. For some clean storage or work areas where equipment or products are properly enclosed or shielded, this impingement or fall-out of contamination and the associated longer recovery times may be acceptable. The ISO CLASS 5 level is generally maintained within these turbulent airflow areas only during the “as built” and the “at rest” conditions.