Federal Standard 209E

Federal Standard 209E was a set of official guidelines established by the U.S. government to classify cleanroom environments based on their cleanliness levels. It used a numerical system, such as Class 100, to indicate how many particles of a specified size (like dust or microbes) could be present in a cubic foot of air. Lower class numbers meant cleaner environments. Although replaced by ISO standards in 2001, 209E helped standardize manufacturing conditions in industries like aerospace and electronics to ensure product quality and safety.