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What is Cleanroom?

A cleanroom is an area or enclosure in which the air has to be cleaned to a defined particle limit, usually in "particles per cubic foot". In the United States most cleanrooms are discussed in terms of Classification Limits. For example, a "Class 1000" cleanroom means that a maximum of only 1000 particles 0.5 microns in size would be allowed in a cubic foot of air. A micron is equivalent to one millionth of a meter
.
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 meter of air. Typical office building air contains from 500,000 to 1,000,000 particles (0.5 microns or larger) per cubic foot of air. A Class 100 cleanroom is designed to never allow more than 100 particles (0.5 microns or larger) per cubic foot of air. Class 1000 and Class 10,000 cleanrooms are designed to limit particles to 1000 and 10,000 respectively.
 
Note that both FS 209E and ISO 14644-1 are based on assumed log-log relationships between particle size and particle concentration. For that reason, there are no "zero" particle concentrations listed. The table locations without entries are N/A ("not applicable") combinations of particle sizes and cleanliness classes. They 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 approx. class 1,000,000 or ISO 9.

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

 

ISO 3

10

350

75

30

10

 

ISO 4

100

 

750

300

100

 

ISO 5

1,000

 

 

 

1,000

7

ISO 6

10,000

 

 

 

10,000

70

ISO 7

100,000

 

 

 

100,000

700

ISO 8

ISO 14644-1 cleanroom standards

Class

maximum particles/m³

FED STD 209E
equivalent

≥0.1 µm

≥0.2 µm

≥0.3 µm

≥0.5 µm

≥1 µm

≥5 µm

ISO 1

10

2

 

 

 

 

 

ISO 2

100

24

10

4

 

 

 

ISO 3

1,000

237

102

35

8

 

Class 1

ISO 4

10,000

2,370

1,020

352

83

 

Class 10

ISO 5

100,000

23,700

10,200

3,520

832

29

Class 100

ISO 6

1,000,000

237,000

102,000

35,200

8,320

293

Class 1000

ISO 7

 

 

 

352,000

83,200

2,930

Class 10,000

ISO 8

 

 

 

3,520,000

832,000

29,300

Class 100,000