Equations have been recently derived by Whyte, Lenegan and Eaton for calculating the airborne
concentration of particles and microbe-carrying particles in non-unidirectional airflow cleanrooms.
These equations cover a variety of ventilation systems, and contain the variables of air supply rate,
airborne dispersion rate of contamination from machinery and people, surface deposition of particles
from the air, concentration of contamination in fresh make-up air, proportion of fresh air, and air
filter efficiencies. The relative importance of these variables is investigated in this present research
paper, with particular regard to the removal efficiency, location, and number of air filters. It was
shown that air filters were important in ensuring low levels of contamination in cleanrooms but the
types of filters specified in current cleanroom designs were very effective in ensuring a minimal
contribution to the cleanroom’s airborne contamination especially when a secondary filter is used in
addition to a primary and terminal filter. The most important determinants of airborne
contamination were the air supply rate and the dispersion rate of contamination within the
cleanroom, with a lesser effect from deposition of airborne particles onto cleanroom surfaces. The
information gathered confirmed the usefulness of the equation previously used by Whyte, Whyte,
Eaton and Lenegan to calculate the air supply rate required for a specified concentration of airborne
contamination