Q: What do the clean room class ratings mean?

A: The classes, according to ISO/TC209 14644-1 are a level of airborne particulate cleanliness. A class 5 means that less than 3,520 particles (0.5 microns in size) are present per cubic meter (which equals 100 particles per cubic foot). A class 6 indicates less than 35,200 particles per cubic meter. The higher the class number the more particles present.

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