Non-unidirectional airflow cleanrooms are supplied with filtered air to minimise the contamination
of a product or process by airborne contamination. The effectiveness of the ventilation system in
providing the required type of airflow in the cleanroom that will minimise airborne contamination
can be assessed by measuring ventilation effectiveness indexes. This article provides information on
what ventilation effectiveness indexes are suitable for cleanrooms, and how they can be obtained by
test methods in common use in cleanrooms. Three methods of measuring ventilation effectiveness are
discussed, namely, the Contamination Removal Effectiveness (CRE) index, the Air Change
Effectiveness (ACE) index and the Performance Index (PI), and it was considered that the ACE index
and PI were the most suitable for use in cleanrooms.
The decay rate and recovery rate of airborne contamination in relation to the air change rate in
non-unidirectional cleanrooms is also considered, and it is demonstrated that when measured at the
same location, the three rates are identical. Also considered is the measurement of these rates in
cleanrooms and how they can be used to obtain the ACE index
