This part of ISO 14644 covers the classification of airborne molecular contamination (AMC) in cleanrooms and associated controlled environments, in terms of airborne concentrations of specific chemical substances (individual, group or category) and provides a protocol to include test methods, analysis and time weighted factors within the specification for classification. This part of ISO 14644 currently considers only concentrations of AMC between 100 and 10-12 g/m3 under cleanroom operational conditions. This part of ISO 14644 is not relevant for application in those industries, processes or production, where the presence of airborne molecular substances is not considered a risk to the product or process. It is not the intention of this part of ISO 14644 to describe the nature of airborne molecular contaminants. This part of ISO 14644 does not give a classification of surface molecular contamination.