Clean Room Standards

Clean rooms are classified by the cleanliness of their air. The method most easily understood and most universally applied is the Federal Standard 209 of the USA. In this old standard, the number of particles equal to and greater than 0.5 mm is measured in one cubic foot of air and this count used to classify the room. The most recent 209E version has also accepted a metric nomenclature. In the UK, the British Standard 5295, published in 1989, is also used to classify clean rooms. This standard will shortly be superseded by BS EN ISO 14644-1.

0.1 0.2 0.3 0.5 5.0
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

In the new 209E published in 1992, the airborne concentrations in the room are given in metric units and the classifications of the room defined as the logarithm of the airborne concentration of particles ³ 0.5 mm. For instance, a Class M3 room has a particle limit for particles ³ 0.5 m of 1,000/m3. This is shown in Table 2:

Maximum permitted number of particles per m3 (equal to, or greater than stated size) Maximum floor area Minimum pressure difference
Class of environmental cleanliness 0.3 u m 0.5 u m 5 u m 10u m 25 u m Per sampling Position For clean rooms (m2) Between classified area and unclassified area (Pa) Between classified area and adjacent classification (Pa)
C 100 35 0 NS NS 10 15 10
D 1000 350 0 NS NS 10 15 10
E 10000 3500 0 NS NS 10 15 10
F NS 3500 0 NS NS 25 15 10
G 10000 35000 200 0 NS 25 15 10
H NS 35000 200 0 NS 25 15 10
J NS 350000 2000 450 NS 25 15 10
K NS 3500000 20000 4500 500 50 15 10
L NS NS 200000 45000 5000 50 10 10
M NS NS NS 450000 50000 50 10 NS


BS EN ISO Standard

Because of the large number of clean room standards produced by individual countries, it is very desirable that a single worldwide standard of clean room classification be produced. The first ISO standard on clean rooms was published (June 1999) as 14644-1 ‘Classification of Air Cleanliness’. It is soon to be adopted as a European standard and hence a standard for all EU countries. This standard is available from standard organizations worldwide, and is available in the UK from the BSI. Table 4 shows the adopted classification.

Table 4. Selected ISO 209 airborne particulate cleanliness classes for clean rooms and clean zones:

Classification numbers Number (N) Maximum concentration limits (particles/m3 of air) for particles equal to and larger than the considered sizes shown below
0.1 u m 0.2 u m 0.3 u m 0.5 u m 1 u m 5 .0 u m
ISO 1 10 2
ISO 2 100 24 10 4
ISO 3 1000 237 102 35 8
ISO 4 10000 2370 1020 352 83
ISO 5 100000 23700 10200 3520 832 29
ISO 6 1000000 237000 102000 35200 8320 293
ISO 7 352000 83200 2930
ISO 8 3520000 832000 29300
ISO 9 35200000 8320000 293000

The table is derived from the following formula:


Cn represents the maximum permitted concentration ( in particles/m3 of air ) of airborne particles that are equal to or larger than the considered particle size. Cn is rounded to the nearest whole number. N is the ISO classification number, which shall not exceed the value of 9. Intermediate ISO classification numbers may be specified; with 0.1 the smallest permitted increment of N. D is the considered particle size in m m. 0.1 is a constant with a dimension of m m. Table 4 shows a crossover to the old FS 209 classes e.g. ISO 5 is equivalent to the old FS 209 Class 100.

The occupancy state is defined in this standard as follows:


As built: the condition where the installation is complete with all services connected and functioning but with no production equipment, materials, or personnel present.

At-rest: The condition where the installation is complete with equipment installed and operating in a manner agreed between the customer and supplier, but with no personnel present.

Operational: The condition where the installation is functioning in the specified manner, with the specified number of personnel present and working in the manner agreed upon. The standard also gives a method by which the performance of a clean room may be verified i.e. sampling locations, sample volume etc. These are similar to FS 209. It also includes a method for specifying a room using particles outside the size range given in the table 4. Smaller particles (ultrafine) will be of particular use to the semiconductor industry and the large (³ 5 mm macro particles) will be of use in industries such as parts of the medical device industry, where small particles are of no practical importance.

The method employed with macro particles is to use the format:

‘M(a; b);c’


a is the maximum permitted concentration/m3

b is the equivalent diameter.

c is the specified measurement method.




Grade Types of operations for aseptic preparations
A Aseptic preparation and filling
B Background room conditions for activities requiring Grade A
C Preparation of solution to be filtered
D Handling of components after washing



Grade Types of operations for terminally sterilized products.
A Filling of products, which are usually at risk
C Placement of filling and sealing machines, preparation of solutions when usually at risk. Filling of product when unusually at risk.
D Moulding, blowing ( pre- forming) operations of plastic containers, preparations of solutions and components for subsequent filling



Grade Air sample Cfu/ Settle plates (dia. 90mm.Cfu/2hrs. Contact plates(dia.55mm) cfu per plate Glove points(five fingers)cfu per glove
A <1 <1 <1 <1
B 10 5 5 5
C 100 50 25
D 500 100 50

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