Cleanroom Classes: Distinctions and Classification Features
Last updated: 05. March 2026
A cleanroom is a specially controlled work area in which the concentration of airborne particles (dust, microorganisms, aerosols) is kept extremely low. Depending on the particle density, it is divided into special cleanroom classes or cleanliness classes. Cleanrooms are subject to strict, standardized requirements for the maximum permissible particle concentrations, particles per m³ of air, and particle size are classified according to the degree of air purity. In the following standards, the limit values for the respective cleanroom classes are defined: DIN EN ISO 14644-1, VDI 2083, and the EU-GMP Guide, Annex 1. To determine the cleanroom class, special particle measurements are carried out in the room. This is checked both before commissioning and at regular defined intervals during operation.
Industry and authorities have defined various classification systems that focus on different aspects of purity. In the fields of aerospace and semiconductor technology, for example, the number of particles occurring per cubic meter generally plays a role, while in medical and food technology, the focus is primarily on the amount of microorganisms and germs occurring in the air. The different classification systems take into account the differences between the respective catalogs of requirements.
Standards and classification systems for distinguishing different cleanroom classes
In the classification of cleanrooms, the two standards already mentioned above play a role in particular:
- DIN EN ISO 14644-1
- EU GMP Guide (EudraLex Vol. 4), especially Annex 1
Annex 1 is an annex to the EU GMP Guide and deals with sterile manufacturing – it is not to be equated with the entire GMP Guide. Furthermore, in Germany, the standard VDI 2083 defined by the Association of German Engineers is occasionally used. VDI 2083 supplements ISO 14644-1 with practice-oriented requirements for planning, qualification, and operation. Rarely, references can still be found to the old US standard US FED STD 209E, which has been classified as "deprecated" (i.e., obsolete) since November 2001 and is no longer used for new products and projects.
ISO 14644-1 and EU GMP Annex 1: Classification criteria
The two decisive reference documents are ISO 14644-1 (classification of cleanrooms) and the EU GMP Guide, Annex 1 (manufacture of sterile medicinal products). Annex 1 references ISO 14644-1 for classification, but it is a regulatory guideline – not a pure classification standard.
Cleanroom classes: The limit values according to ISO 14644-1
The ISO standard defines a total of nine different classes. The classification is based on the maximum permissible number of particles per cubic meter of air. While in the pharmaceutical industry (GMP) the particle size ≥ 0.5 µm is usually decisive, for the extremely pure classes ISO 1 to 3, smaller particles are used as a reference:
- ISO 1 to ISO 3: These classes are reserved for semiconductor research. Here, even the smallest particles (≥ 0.1 µm) are almost completely eliminated.
- ISO 4: Maximum 352 particles (≥ 0.5 µm). Used mostly in high-precision optics.
- ISO 5: Corresponds to the particle concentration of Grade A (at rest and in operation). In Rommelag BFS systems, the critical filling zone (the filling point) is locally protected by a Grade A UDAF system.
- ISO 6: Maximum 35,200 particles.
- ISO 7: Corresponds to Grade C at rest. This is the typical background environment for BFS systems in aseptic processing. In the operating state, ISO class 8 is permissible here according to GMP.
- ISO 8: Corresponds to Grade D at rest or the operating state of Grade C. Grade D is the typical environmental requirement for BFS systems if the product is subsequently terminally sterilized.
- ISO 9: Maximum 35,200,000 particles. Corresponds to a controlled industrial area (CNC).
Unlike the classification according to ISO 14644-1, the GMP audit does not only assess the purity of the room in the at-rest state. In the case of GMP classification Grade A, the same strict limit values must be maintained during operation as in the at-rest state. This applies in particular to areas with aseptic operations, such as filling or sealing. At the lower classification levels, less strict requirements apply for measurements in the operating state.
Factors influencing the classification
Typically, inspectors take air samples at various points in the cleanroom using particle counters to carry out the classification according to ISO 14644-1 or the EU GMP Guide. For a cleanroom to be classified in a certain class, all(!) recorded samples must meet the requirements of the respective guideline. The number of sampling points is determined by room area according to ISO 14644-1 Annex A.
In the case of higher-class classifications, the inspectors also classify the ventilation technology. In cleanrooms of classes ISO 1 to ISO 5, low-turbulence displacement ventilation is usually used. This means that the system generates a directed, low-displacement air flow (UDAF – Unidirectional Airflow). This ensures that no turbulence occurs and the existing room air does not immediately mix with the fresh air. Any microparticles occurring during operation are thus removed directly from the critical area and do not spread throughout the entire room. In the lower ISO classes six to nine, the air in the room may also be turbulent.
Areas of application
Cleanrooms according to DIN-EN-ISO classification are used in a wide variety of industries. In the automotive industry, for example, cleanrooms of classes eight and nine are frequently used. Server/data centers are often kept at ISO 8 level according to ASHRAE recommendation. In medical technology, rooms of class seven are widespread, in the optical industry class six.
In the semiconductor industry, cleanrooms play a particularly important role. Especially rooms of classes ISO 4 and ISO 5 are important here. The even stricter requirements of ISO classes one to three are primarily significant in the field of research. The pharmaceutical industry, on the other hand, usually relies directly on classification according to the EU GMP Guide, the requirements of which it must comply with during the manufacture of medicines for regulatory reasons.
Specifically, the choice of cleanroom class depends heavily on the individual application within the industry. Even in the automotive industry, there can be uses for more strictly classified cleanrooms. Conversely, in the field of the semiconductor industry, it is sometimes sufficient to use a cleanroom with a lower cleanliness class.