Clean room raised floor

Merry Christmas


Plano, Texas
Under a raised floor in a clean room is generally used for a return air plenum and as such should fall under the "other space used for environmental air" rules. A customer wants to install a vacuum pump under the floor. It is totally enclosed but definitely not listed for use in air-handling space nor low smoke rated. As such I plan to say it is against code restrictions. Do any of you know of any exceptions or other code I am overlooking?