International Organization for Standardization
ISO 14644 standard can be found in here. ISO 14644 is a series of documents, being developed as International Standards,
concerned with cleanrooms and associated controlled environments.
Federal Standard 209E download website
Federal Standard 209E is a US standard for airborne
particulate cleanliness classes in cleanrooms and clean zones.
But It was canceled and superseded by ISO Standards.
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) is one of a leading edge in the arts and sciences of heating, ventilation, air conditioning and refrigeration.
The NEBB (National Environmental Balancing Bureau) is a US contractors organization for the heating, ventilating and air conditioning (HVAC) industry.
It is a website for engineering units conversion.