Classification of Air Cleanliness

Clean room maintained virtually free of contaminants, such as dust or bacteria, are used in laboratory work and in the production of precision parts for electronic or aerospace equipment.

In the clean room standard ISO 14644-1 "Classification of Air Cleanliness" the classes are based on the formula

Cn = 10N (0.1 / D)2.08 (1)

where

Cn = maximum permitted number of particles per cubic meter equal to or greater than the specified particle size, rounded to whole number

N = is the ISO class number, which must be a multiple of 0.1 and be 9 or less

D = is the particle size in micrometers

ISO
Class Maximum Number of Particles in Air
(particles in each cubic meter equal to or greater than the specified size)
Particle size
> 0.1 μm > 0.2 μm > 0.3 μm > 0.5 μm > 1 μm > 5 μm
ISO Class 1 10 2
ISO Class 2 100 24 10 4

ISO Class 3 1000 237 102 35 8
ISO Class 4 10,000 2,370 1,020 352 83
ISO Class 5 100,000 23,700 10,200 3,520 832 29
ISO Class 6 1,000,000 237,000 102,000 35,200 8,320 293
ISO Class 7 352,000 83,200 2930
ISO Class 8 3,520,000 832,000 29,300
ISO Class 9 35,200,000 8,320,000 293,000

ISO Cleanroom Standards

ISO-14644-1 Classification of Air Cleanliness
ISO-14644-2 Cleanroom Testing for Compliance
ISO-14644-3 Methods for Evaluating & Measuring Cleanrooms & Associated Controlled Environment
ISO-14644-4 Cleanroom Design & Construction
ISO-14644-5 Cleanroom Operations
ISO-14644-6 Terms, Definitions & Units
ISO-14644-7 Enhanced Clean Devices
ISO-14644-8 Molecular Contamination
ISO-14698-1 Biocontamination: Control General Principles
ISO-14698-2 Biocontamination: Evaluation & Interpretation of Data
ISO-14698-3 Biocontamination: Methodology for Measuring Efficiency of Cleaning Inert Surfaces