What is Clean Room Classification?

A cleanroom is usually used for manufacturing or scientific research. It is a controlled environment with low levels of pollutants such as dust, airborne microorganisms, aerosol particles, and chemical vapours.

To be precise, the pollution level of a cleanroom is specified by the number of particles per cubic meter of specified particle size. The outdoor ambient air in a typical urban environment contains 35,000,000 particles per cubic meter with a diameter of 0.5 microns and larger, which corresponds to the ISO9 clean room, which is the lowest level of the cleanroom standard.

Ⅰ. The principle of cleanroom airflow

The cleanroom maintains particle-free air by using HEPA or ULPA filters that use the principle of laminar or turbulent airflow. The laminar flow or unidirectional airflow system directs the filtered air downward with constant airflow. Laminar airflow systems are usually used for 100% ceilings to maintain constant unidirectional airflow. Laminar flow standards are usually specified in portable workstations (LF enclosures) and are mandatory in clean rooms classified as ISO-1 to ISO-4.

The correct clean room injection molding design includes the entire air distribution system, including providing adequate downstream air return. In a vertical flow room, this means using low-wall air recirculation around the area. In horizontal flow applications, it requires the use of air recirculation at the downstream boundary of the process. The use of return air mounted on in the ceiling is inconsistent with the correct cleanroom system design.

Ⅱ. Cleanroom classification

1. Cleanrooms are classified according to the cleanliness of the air

In the US Federal Standard 209 (A to D), the number of particles equal to or greater than 0.5μm in one cubic foot of air is measured, and clean rooms are classified by this count. The latest 209E version of the standard also accepts this metric nomenclature.

The newer standard is TC209 from the International Standards Organization. Both standards classify clean rooms based on the number of particles found in the laboratory air.

The cleanroom classification standards FS 209E and ISO 14644-1 require specific particle count measurements and calculations to classify the cleanliness level of a cleanroom or clean area. British Standard 5295 is used to classify clean rooms.

2. The cleanroom is classified according to the number and size of particles allowed per volume of air

Large numbers such as "class 100" or "class 1000" refer to FED_STD-209E, which indicates the number of particles with a size of 0.5 µm or greater per cubic foot of air. The standard also allows interpolation, so "Class 2000" can be described, for example.

The small number refers to the ISO 14644-1 standard, which specifies the decimal logarithm of the number of particles of 0.1 µm or larger allowed per cubic meter of air. So, for example, an ISO Class 5 cleanroom has a maximum of 105 = 100,000 particles per cubic meter.

Both FS 209E and ISO 14644-1 assume a logarithmic relationship between particle size and particle concentration. Therefore, there is no such thing as zero particle concentration. Ordinary indoor air is about Class 1,000,000 or ISO 9.

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