The standard DIN EN ISO 14644-1 divides cleanrooms into classes ISO 1 to 9. Purity class 1 is the purest, meaning the maximum permitted particle concentration is at the lowest possible level. Class 9, on the other hand, denotes high impurity. For most applications in the ISO range, cleanroom classes 7 and 8 are sufficient. ISO Class 5 complies with purity class A according to the EC-GMP guideline and meets particularly high purity requirements.