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Clean Rooms - Federal Standard 209

Clean rooms are maintained virtually free of contaminants such as dust or bacteria

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Clean room maintained virtually free of contaminants, such as dust or bacteria, are used in laboratory work and in the production of precision parts for electronic or aerospace equipment.

The air quality of a clean rooms are described in Federal Standard 209 "Airborne Particulate Cleanliness Classes in Clean Rooms and Clean Zones" (A through D) where the classes are named after the maximum number of particles of 0.5 micrometers or more in diameter which is acceptable in air.

Maximum Number of Particles in Air (particles per cubic foot air)
Class	Particle Size
Class	0.1 μm	0.2 μm	0.3 μm	0.5 μm	5.0 μm
1	35	7.5	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

clean room classes and number size particles diagram

In a clean room rated as "Class 10,000" there may not exists more than 10,000 particles larger than 0.5 microns in a cubic foot of air.

Classes and their Typical Uses

Class 1 & 10 - production laboratories for electronic integrated circuits ..
Class 100 - production areas for photo labs, medical implants ..
Class 10,000 - production locales for TV tubes, hospital operating theaters ...
Class 100,000 - production of ball bearings

Federal Standard 209 E uses metric units and the classes are defined as:

Maximum Number of Particles in Air (particles per volume unit)
Class		Particle Size
Class		0.1 μm		0.2 μm		0.3 μm		0.5 μm		5 μm
SI	English	(m³)	(ft³)	(m³)	(ft³)	(m³)	(ft³)	(m³)	(ft³)	(m³)	(ft³)
M 1		350	9.91	75.7	2.14	30.9	0.875	10.0	0.283
M 1.5	1	1,240	35.0	265	7.50	106	3.00	35.3	1.00
M 2		3,500	99.1	757	21.4	309	8.75	100	2.83
M 2.5	10	12,400	350	2,650	75.0	1,060	30.0	353	10.0
M 3		35,000	991	7,570	214	3,090	87.5	1,000	28.3
M 3.5	100			26,500	750	10,600	300	3,530	100
M 4				75,700	2,140	30,900	875	10,000	283
M 4.5	1,000							35,300	1,000	247	7.00
M 5								100,000	2,830	618	17.5
M 5.5	10,000							353,000	10,000	2,470	70.0
M 6								1,000,000	28,300	6,180	175
M 6.5	100,000							3,350,000	100,000	24,700	700
M 7								10,000,000	283,000	61,800	1,750