The criteria that must be measured in order to validate a clean room include: the volume and quality of air supplied, air movement between the clean room and other rooms, air movement within the clean room and the particle counts in the clean room, including microbiological if necessary.

Some of the principles of cleanroom validation :

Air movement in the clean room should be sufficient to ensure that no areas within the room collect high concentrations of contamination.
Air supply to the clean room is high quality and will not add significantly to the contamination in the room.
Air supplied to the clean room is of sufficient quantity to dilute or remove contamination generated in the room.