Below is a list of Class 100 Clean Rooms manufacturers from St. Peters, Missouri. Class 100 clean rooms are the third highest classification in Federal Standard 209 standards. In order to meet regulations, a Class 100 standard clean room must never exceed 100 particles per cubic foot (the particles being 0.5 microns or larger). As a reference point for just how small 0.5 microns is, the average human hair is approximately 75-100 microns in width.