Cleanroom Classes: Distinctions and Classification Features

What are cleanroom classes?

In industry and research, cleanrooms are crucial for protecting production and other processes from contamination. Depending on the application area, rooms with different levels of cleanliness are required. In everyday language, people typically distinguish only between cleanrooms and ultra-clean rooms. In reality, there are many more gradations between these variants. To differentiate them, various cleanroom classes have been defined. Depending on the class, a cleanroom ensures that particles or microbes of a certain size either do not occur at all or only in minimal quantities in the air and on surfaces.

Industry and regulatory bodies have defined different classification systems that focus on various aspects of cleanliness. In aerospace and semiconductor technology, for example, the general number of particles per cubic meter is essential. In contrast, in medical and food technology, the concentration of microorganisms and germs in the air is the key factor. Different classification systems, such as the EU Good Manufacturing Practice (GMP) guideline or ISO Standard 14644-1, reflect these differences in requirements.

Standards and Classification Systems for Cleanroom Classes

The classification of cleanrooms is mainly based on two standards:

• DIN EN ISO 14644-1
• EU GMP Guidelines (EudraLex Vol. 4), in particular Annex 1

Annex 1 is an appendix to the EU GMP Guidelines, specifically addressing sterile manufacturing, and should not be considered equivalent to the entire GMP Guidelines. 

Additionally, Germany often refers to the VDI 2083 standard, which is defined by the Association of German Engineers. VDI 2083 supplements ISO 14644-1 with practical requirements for design, qualification, and operation.

Occasionally, references are still made to the old U.S. standard US FED STD 209E, which has been considered deprecated since November 2001 and is no longer used for new products or projects.

ISO 14644-1 and EU-GMP Annex 1: Classification Criteria

The two key reference documents are ISO 14644-1 (classification of cleanrooms) and the EU GMP guidelines, Annex 1 (manufacture of sterile medicinal products); Annex 1 references ISO 14644-1 for classification and monitoring, but is a regulatory guideline – not a classification standard. 

The ISO standard defines nine classes, labeled ISO 1 through ISO 9. ISO 1 is the strictest, allowing a maximum of 10 particles ≥ 0.1 µm per cubic meter. In contrast, an ISO 9 cleanroom may contain over 35 million particles larger than 0.5 µm per cubic meter.

GMP Class A roughly corresponds to ISO Class 5, though it is based on independent limits and measurement methods. According to EU-GMP Annex 1, a Class A cleanroom must not exceed 3,520 particles ≥ 0.5 µm/m³ in a static state; the limit for≥ 5 µm is not specified. In monitoring, 29 particles/m³ is considered a guideline value. The GMP guideline also defines Classes B through D, with progressively less stringent criteria. Generally, GMP classification requires stricter and more frequent re-certification and monitoring than ISO classification.

Unlike ISO 14644-1, the GMP assessment evaluates not only the static state but also the operational state. For Class A, the same strict limits apply during operation as in the static condition—especially in aseptic areas such as filling or sealing processes. Lower GMP classes allow more relaxed limits during operation.

Factors Influencing Classification

Inspectors typically take air samples at multiple points within the cleanroom using particle counters to verify compliance with ISO 14644-1 or EU-GMP guidelines. To achieve classification for a given class, all measured samples must meet the respective limits. The number of sampling points is determined based on the room area, in accordance with ISO 14644-1 Annex A.

At higher classification levels, ventilation systems are also assessed. Cleanrooms in Classes ISO 1–5 typically employ low-turbulence displacement ventilation, which supplies filtered air uniformly and creates laminar airflow, thereby preventing turbulence and minimizing air mixing. This ensures that any particles generated during operation do not spread throughout the room. Lower classes (ISO 6–9) allow turbulent airflow.

Areas of Application

Cleanrooms classified according to DIN EN ISO standards are used in a wide range of industries. In the automotive industry, for example, cleanrooms of Class 8 and 9 are often employed. Servers/data centers are usually maintained at the ISO 8 level in accordance with ASHRAE recommendations. In medical technology, Class 7 cleanrooms are commonly used, whereas in the optical industry, Class 6 is frequently employed.

In the semiconductor industry, cleanrooms play a vital role. Rooms of ISO Classes 4 and 5 are especially relevant here. The even stricter requirements of ISO Classes 1 to 3 are primarily significant in research settings.

The pharmaceutical industry, on the other hand, typically follows the classification system defined by the EU-GMP guideline, whose requirements must be met for regulatory reasons in the manufacture of medicinal products.

Ultimately, the choice of cleanroom class depends heavily on the specific application within a given industry. Even in the automotive sector, there may be use cases that require more stringent cleanroom classifications. Conversely, in the semiconductor industry, it can sometimes be sufficient to use a cleanroom with a lower cleanliness class.