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(ISO 8, ISO 7, ISO 6, ISO 5)
The basis of cleanroom standards is the micrometer, or micron for short (µm), which is the size of the particles to be filtered. As stated before, cleanrooms are classified by how clean the air is, according to the quantity and size of particles per volume of air. The cleanroom classification table below shows the maximum concentration limits (particles/m3 of air) for particles equal to and larger than the considered sizes shown.
Some classifications do not require certain particle sizes to be tested because the respective concentrations are too low or too high to be tested, but they should not be zero.
For ISO 7, particles smaller than 0.5 microns (≥0.1 µm, ≥0.2 µm, ≥0.3 µm) are not taken into consideration. The concentration of particles of ≥0.5 µm and above should be below 352,000, for particles of 1 micron and above 83,200 or lower and for particles of 5 microns and above 2,930 or lower.
Air cleanliness is achieved by passing the air through HEPA filters. The more often the air passes through the HEPA filters, the fewer particles are left in the room air. The volume of air filtered in one hour divided by the volume of the room gives the number of air changes per hour.
|ISO Class||Average number of air changes per hour|
|ISO 5||240–360 air changes per hour (unidirectional airflow)|
|ISO 6||90–180 air changes per hour|
|ISO 7||30–60 air changes per hour|
|ISO 8||10–25 air changes per hour|
|Conventional building||2–4 air changes per hour|
The above-suggested air changes per hour are only a design rule of thumb. They should be computed by an HVAC cleanroom expert, as many aspects must be taken into consideration, such as the size of the room, the number of people in the room, the equipment in the room, the processes involved, the heat gain, etc.
This article will help you understand the basic differences between an ISO 5, ISO 6, ISO 7 and ISO 8 cleanroom as per ISO 14644. Please note that this information is only provided for educational purposes. The definitions in this article are oversimplified in order to assist with understanding. This article will not help you decide which cleanroom classification you must reach. If help is needed in this respect, seek the advice of an expert in your industry (pharmaceutical, medical devices, sterile compounding, electronics, etc.).