The contaminated air in a cleanroom enters the AHU via coarse dust and fine dust filters and is reintroduced into the cleanroom via an absolute filter. The build-up is necessary to avoid the need to replace the absolute filter quickly. An absolute filter is commonly referred to as a HEPA or ULPA filter.
HEPA (high efficiency particulate air):
Stops particles 0.3 µm in diameter with an efficacy of 99.97%.
ULPA (ultra-low penetration air):
Stops at least 0.1 µm diameter particles with an effectiveness of 99.999%.
There are several methods for bringing air into the cleanroom, including:
- Via Filter boxes in the ceiling grid of various kinds
- Via air-sockets
- Via Filter Fan Units
- Via open plenum
When a HEPA / ULPA filter becomes saturated, it should be replaced without delay. Even the slightest damage during installation can seriously impair the performance of a HEPA / ULPA filter and is immediate cause for replacement!