ISO 14644-1 :This is a non-governmental standard developed by the International Organization for standardization (ISO). This standard applies to clean rooms in general (see table below);
Table above provides a comparison of classifications between ISO14644-1 and FS209E. Because 1m3 is approximately 35ft3, the two standards are mostly equivalent when measuring 0.5μm particles, although the testing standards differ. Ordinary room air is approximately ISO Class9, or Class 1,000,000.
US FED STD 209E
US FED-STD-209E was a United States federal standard. It was officially cancelled by the General Services Administration on November 29, 2001, but is still widely used.
EU GMP classification
EU GMP guidelines are more stringent than others, requiring cleanrooms to meet particle counts at operation (during manufacturing process) and at rest (when manufacturing process is not carried out, but room AHU is on).
(All above information & Data are derived from Book records of Filtration Standards & Other related standards, research papers and its related webpages)