Standards for classification of cleanrooms (February 2005)
Cleanrooms are classified by the cleanliness of their air. This is done according to ISO 14644-
1. This is an international standard, having been adopted by the European Union in 1999, and
the USA in 2001. However, the most easily understood classification of cleanrooms is the
obsolete Federal Standard 209 of the USA; it is still widely used.
1 Federal Standard 209
The first Federal Standard 209 was published in 1963 in the USA, and titled "Cleanroom and
Work Station Requirements, Controlled Environments". It was revised in 1966 (209A), 1973
(B), 1987 (C), 1988 (D) and 1992 (E), and withdrawn in 2001. The cleanroom class limits,
given in the earlier 209 A to D versions, are shown in table 1. The class of a cleanroom is
found by measuring the number of particles
0.5 µm in one cubic foot of room air, and
determining which class limit is not exceeded; this is the cleanroom classification.
Table 1 Federal Standard 209 class limits

Class
Particles
/ ft
3
0.1 µm
0.2 µm
0.3 µm
0.5 µm
5.0 µm
1
35 7.5 3 1
NA
10
350 75
30 10
NA
100
NA 750 300 100
NA
1,000
NA NA NA 1,000
7
10,000
NA NA NA 10,000
70
100,000
NA NA NA 100,000
700

the nomenclature shown in table 1 is likely to be used for many years.
2 ISO Standards
A range of cleanroom standards is being produced by the International Organization for
Standardization (ISO). Various committees of experts, nominated by countries throughout the
world, are writing these standards.
The standards that have been published, or are being written at the time of publication of
this information are as given below. Information about the current status of these standards is
given at
2.1 ISO 14644
This consists of the following parts, under the general title `Cleanrooms and Associated
Controlled Environments':
Part 1: Classification of air cleanliness
This gives the airborne particle limits for different classifications of cleanrooms. This
standard also gives the methods that should be used to measure the airborne particles when
testing a cleanroom to determine its class.
Part 2: Specifications for testing and monitoring to prove continued compliance with ISO
14644-1