Rooms whose cleanliness is measured by the number of particles of a given size per cubic foot of room volume. For example, a class 100,000 clean room may have no more than 100,000 particles onehalf micron or larger per cubic foot. Similarly, for class 10,000 and class 100 rooms. In addition, a class 10,000 room may have no more than 65 five-micron particles per cubic foot, while class 100,000 may have no more than 700.¨