Never put hoods under HEPA filters, as the filter can disrupt airflows of the hood — it then becomes nearly impossible to properly test the HEPA filter for leaks or volumetric flow with a flow hood.
Cleanroom Tip: Buffer Room Concerns in Cleanrooms — Part I
Cleanroom design needs to take into consideration the testing of the HEPA filters, hood locations, and the return locations. Cleanrooms depend on gravity to pull heavy particulate to the floor, so low-level returns need to be placed in appropriate locations around the room to capture these particles before people enter and stir them into the…