Before global cleanroom classifications and standards were adopted by the International Standards Organization (ISO), the U.S. General Service Administration’s standards (known as FS209E) were applied virtually worldwide. However, as the need for international standards grew, the ISO established a technical committee and several working groups to delineate its own set of standards.
FS209E contains six classes, while the ISO 14644-1 classification system adds two cleaner standards and one dirtier standard. The "cleanest" cleanroom in FS209E is referred to as Class 1; the "dirtiest" cleanroom is a class 100,000. ISO cleanroom classifications are rated according to how much particulate of specific sizes exist per cubic meter (see second chart). The "cleanest" cleanroom is a class 1 and the "dirtiest" a class 9. ISO class 3 is approximately equal to FS209E class 1, while ISO class 8 approximately equals FS209E class 100,000.
By law, Federal Standard 209E can be superseded by new international standards. It is expected that 209E will be used in some industries over the next five years, but that eventually it will be replaced internationally by ISO 14644-1.