The standard DIN EN ISO 14644-1 divides cleanrooms into classes ISO 1 to 9. Purity class 1 is the purest, i.e. the maximum permitted particle concentration is the lowest. Class 9, on the other hand, achieves the lowest purity. 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.