Dear Sir,
In ISO - 14644 -3 , the recovery study has not been recommonded for ISO -8 and ISO - 9 class.
But in WHO guideline it has been mentioned to carry out the Recovery ( Clean Up ) study with ref. of ISO-14644.
So is there need to do this study for USFDA or other audit preparation. Kindly explain ?
Regards,
Vinod 
The air samplers are very sensitive to handle particulates. If you see ISO class 5 and 7 and comapre with 8&9 the particle cound is almost increasing by 100 folds.
The particulate samplers do not have that capability to handle soo many particulates.Hence its not given in ISO.
Comming back to USFDA , they will check the AHU design and filtration design and number of air changes in this 2 areas. This should be minimum 20 airchanges perr hour.Direction of air flow will be properly questioned.