Clean Room Classicification

The following is adapted from Rockwell Automation and from FILT AIR

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 US 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 clean room has at most 105 = 100,000 particles per m³.

US FED STD 209E cleanroom standards

Class	≥0.1 µm	≥0.2 µm	≥0.3 µm	≥0.5 µm	≥5 µm
	maximum particles/ft³
1	35	7	3	1
10	350	75	30	10
100		750	300	100
1,000				1,000	7
10,000				10,000	70
100,000				100,000	700

NOTE: US FED STD 209E was canceled November 29, 2001

ISO 14644-1 cleanroom standards

Class	≥0.1 µm	≥0.2 µm	≥0.3 µm	≥0.5 µm	≥1 µm	≥5 µm
	maximum particles/m³
ISO 1	10	2
ISO 2	100	24	10	4
ISO 3	1,000	237	102	35	8
ISO 4	10,000	2,370	1,020	352	83
ISO 5	100,000	23,700	10,200	3,520	832	29
ISO 6	1,000,000	237,000	102,000	35,200	8,320	293
ISO 7				352,000	83,200	2,930
ISO 8				3,520,000	832,000	29,300
ISO 9				35,200,000	8,320,000	293,000

Cleanroom class comparison

Because 1 m³ is approximately 35 ft³, the following classes are mostly equivalent, although the testing standards differ.

ISO 14644-1	FED STD 209E
ISO 3	1
ISO 4	10
ISO 5	100
ISO 6	1,000
ISO 7	10,000
ISO 8	100,000

BS 5295 cleanroom standards

Class	≥0.5 µm	≥1 µm	≥5 µm	≥10 µm	≥25 µm
	maximum particles/m³
Class 1	3,000		0
Class 20	300,000		2,000	30
Class 3		1,000,000	20,000	4,000	300
Class 4			200,000	40,000	4,000

Note that Class 1 also requires that the greatest particle present in any sample does not exceed 5 μm