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Air flow pattern for "Turbulent
Cleanroom" |
Air flow pattern for " Laminar Flow Cleanroom" |
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| Cleanroom air flow principles |
| Cleanrooms maintain particulate-free air through the use of either
HEPA or ULPA filters employing laminar or
turbulent air flow principles. Laminar, or unidirectional, air flow systems
direct filtered air downward in a constant stream towards filters located on
walls near the cleanroom floor. Laminar air flow systems are typically employed
across 80 percent of a cleanroom ceiling to maintain constant air processing.
Stainless steel or other non-shed materials are used to construct laminar air
flow filters and hoods to prevent excess particles entering the air. Turbulent,
or non-unidirectional, air flow uses both laminar air flow hoods and
non-specific velocity filters to keep air in a cleanroom in constant motion,
although not all in the same direction. The rough air seeks to trap particles
that may be in the air and drive them towards the floor, where they enter
filters and leave the cleanroom environment. |
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| Cleanroom
classifications |
| Cleanrooms are classified according to the number and size of particles permitted per volume of air. Large numbers like "class 100" or "class 1000" refer to FED-STD-209E, and denote the number of particles of size 0.5 µm or larger permitted per cubic foot of air. The standard also allows interpolation, so it is possible to describe e.g. "class 2000". Small numbers refer to ISO 14644-1 standards, which specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per cubic metre of air. So, for example, an ISO class 5 cleanroom has at most 105 = 100,000 particles per m³. Both FS 209E and ISO 14644-1 assume log-log relationships between particle size and particle concentration. For that reason, there is no such thing as zero particle concentration. The table locations without entries are non-applicable combinations of particle sizes and cleanliness classes, and should not be read as zero. Because 1 m³ is approximately 35 ft³, the two standards are mostly equivalent when measuring 0.5 µm particles, although the testing standards differ. Ordinary room air is approximately class 1,000,000 or ISO 9. |
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| US FED STD 209E
Cleanroom Standards |
| Class |
maximum particles/ft³ |
ISO
equivalent |
| ≥0.1 µm |
≥0.2 µm |
≥0.3 µm |
≥0.5 µm |
≥5 µm |
| 1 |
35 |
7 |
3 |
1 |
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ISO 3 |
| 10 |
350 |
75 |
30 |
10 |
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ISO 4 |
| 100 |
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750 |
300 |
100 |
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ISO 5 |
| 1,000 |
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1,000 |
7 |
ISO 6 |
| 10,000 |
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10,000 |
70 |
ISO 7 |
| 100,000 |
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100,000 |
700 |
ISO 8 |
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| US FED STD 209E was officially cancelled by the General Services Administration of the US Department of Commerce November 29, 2001,but is still widely used. |
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