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Cleanroom classes according to ISO 14644-1 and GMP

What distinguishes one cleanroom from another?

Cleanroom class tables as pdf for download

Theoretically, a cleanroom can be any room in which precautions are taken to ensure that the product or application remains free of contamination.

But what then distinguishes one cleanroom from another?

This is where cleanroom classifications and cleanroom classes come into play. The classification of a cleanroom depends on how clean the air inside the room is. The lower the particle concentration, the higher the classification of the cleanroom. 

But beware: with a higher classification, the ISO cleanroom class label decreases. A cleanroom of cleanroom class ISO 5 therefore fulfils a higher level of cleanliness than a cleanroom ISO 7. GMP cleanroom classes, on the other hand, are marked with letters A-D. More on this later.

To classify a cleanroom, air samples are taken at various points in the room with a particle counter and it is measured how many particles are found. Based on these measurements, the classification of the cleanliness of the room is completed. The classification into cleanroom classes describes the exposure of the room atmosphere to particles of different sizes per room volume. The qualification of the cleanroom standard is done according to a cleanroom class table.

An international standard for classifying cleanrooms is provided by ISO 14644-1. The International Organisation for Standardisation - ISO for short - is an independent organisation dedicated to setting international standards for procedures.

The ISO cleanroom classes are identified by the numbers 1-9.
An ISO 1 cleanroom is considered to be the cleanest possible room, while an ISO 9 cleanroom corresponds to almost normal room air.

So if you want to achieve the cleanest of all cleanrooms, you need an ISO 1 classification. To achieve this, samples must be detected that have 10 or fewer particles with a size of 0.1 micrometres per cubic metre.

From there on, the scale allows for more and larger particles.

In the case of an ISO class 5, which corresponds to the very strict requirements in microchip production, for example, up to 100,000 particles of 0.1 micrometres may be measured. Particles of 1.0 micrometres may not exceed 823.

ISO 9 is the "worst" cleanroom class and is considered normal room air. In these rooms, particle sizes of 0.1 micrometres are no longer considered. Allowed here are 8,320,000 or fewer particles of 1 micron and 293,000 or fewer particles of 5 microns.

Typical applications for an ISO 8 cleanroom are the automotive industry, for an IS0 7 cleanroom medical technology, for an ISO 6 cleanroom the optical industry and for an ISO5 cleanroom electronics and semiconductor technology. However, a classification differs depending on the process and requirement and must always be determined individually.

In the pharmaceutical industry, separate GMP cleanroom classes A, B, C and D are defined, which are based on the ISO standards in terms of particle concentration levels, but additionally show limit values for harmful microorganisms.  Cleanroom class D permits the most particles, cleanroom class A the fewest.


The permitted number of airborne particles is shown in cleanroom class tables. For ISO 5-9 and GMP A, B, C and D you can download a cleanroom class pdf here:

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