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What is a Cleanroom

The most important characteristic of a cleanroom is forcing the airflow continuously to guarantee the presence of very pure air.  

Cleanrooms are ranked by their decreasing concentration level of suspended dust particulates. 

Internationally, the term “cleanroom” designates an atmospheric pressure and particulate contamination controlled room.

When defining and testing the specifications of a cleanroom, the UNI EN ISO 14644-1 regulation is used.  

In this article, we are going to list the cleanliness classes and the maximum particulate level for each one of them. 
We are also going to specify which methods are used to collect and elaborate data in the usage of cleanrooms. 

Cleanroom Classification

The quality and cleanliness of the air are the two fundamental elements for a clean room, and they’re measured by controlling of the number of particles within the environment itself.

During the design phase of a cleanroom, the air cleaning classes are defined, based on the needs of the production process that will be carried out. Since 1963 and in the following years, different classification models have been developed:   

  • Federal Standard 209D, 209E  
  • British Standard 5295  
  • EU GMP  
  • VDI 2083 

However, among all the regulations for clean rooms, the one that today is considered as a reference at a global level is UNI EN ISO 14644-1. 

The classification of cleanrooms is done by counting microparticles of 0.5 μm in a given volume of air; the fewer particles are suspended in the air, the more purified the cleanroom is. The systems operate at low speeds and force into the room a laminar flow of air, previously filtered by HEPA filters, passing through grids placed on the floor.  

The degree of cleanliness, hygiene and safety inside a clean room are extremely high. Since the purity of the air is much higher than operating rooms, the staff must wear sterile gowns, shoe covers, bouffant caps, and masks.  In rooms where very high or total air purity is required, access is allowed only to properly trained personnel. 


Cleanrooms: limits for EN -ISO 14644-1 standards

The focal points of the legislation are in the table below. The table defines the maximum concentrations of particles contained in a cubic meter of air, in relation to the different cleanroom classes. 

CLASS  ≥0.1 ΜM*  ≥0.2 ΜM*  ≥0.3 ΜM*  ≥0.5 ΜM*  ≥1 ΜM*  ≥5 ΜM*  FED STD 209E 
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 1,000 
ISO 7        352,000  83,200  2,930  Class 10,000 
ISO 8        3,520,000  832,000  29,300  Class 100,000 
ISO 9        35,200,000  8,320,000  293,000  Air in the room 

* max numbers of particulates/m³ 

The UNI EN ISO 14644-1 measuring methods

The regulation includes three different states in which a cleanroom can be tested:

  • “As built” : the workers perform the measurements in the finished clean room, but still without machinery and personnel; 
  • “At rest”: the measurements are carried out with the working machines, but in the absence of personnel; 
  • “In operation”: in this case the measurements must be carried out with machines and personnel present and normally active. 

The UNI EN ISO 14644-1 standard also establishes some fundamental points for the correct measurement of the parameters: 

  • The UNI EN ISO 14644-1 standard also establishes some fundamental points for the correct measurement of the parameters; 
  • The volume of air taken for each sampling point shall be large enough to contain at least 20 particles of the largest size considered.   
  • In any case, the volume of air must not be less than two litres and the sampling time must be higher than one minute; 
  • At least one air sample shall be taken for each point (three if there is only one measuring point). 

 Thanks to the statistical processing of this series of measurements performed at different points, it will be possible to determine the Cleanroom class.

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Other Regulation

US FED STD 209E standard

Federal Standard 209 was published in 1963 in the U.S. as "Cleanroom and Work Station Requirements, Controlled Environments". The regulation was revised several times in the following years: vA, 1966; vB, 1973; vC, 1987; vD, 1988; vE, 1992.

Fs 209 classifies Clean Environments according to the maximum number of particles between 0.1μ and 5μ allowed per Volume Unit. The table below shows the limits allowed in its latest version. 

CLASS ≥0.1 ΜM* ≥0.2 ΜM* ≥0.3 ΜM* ≥0.5 ΜM* ≥5 ΜM* ISO
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

* max number of particulates/ft³

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British Standard 5295

The British Standard 5295 was developed in England in 1989. It is divided into 5 main parts: from Part 0 to Part 4.

  • Part 0 - General introduction and definitions for clean rooms and clean air devices.
  • Part 1 - Specifications for clean rooms and clean air devices.
  • Part 2 - Method of specifying the design, construction and commissioning of cleanroom and clean air devices.
  • Part 3 - Guide to operating procedures and disciplines applicable to cleanrooms and clean air devices.
  • Part 4 - Specifications for monitoring cleanrooms and clean air devices to demonstrate continued compliance with BS 5295.

Part 1 of British Standard 5295 defines the "Specifications for cleanrooms and clean air devices"

The Standard contains ten classes of environmental cleanliness. The following table shows the classes indicated in the standard.

All classes have particulate counts specified for at least two size ranges to provide adequate confidence in the particle size range for each class.

Specifically, it is divided into 10 cleaning classes, identified by the letter C, up to the letter M. If we compare the British Standard with the ISO we will notice that the ISO 1 class is considerably cleaner than the higher class proposed by the British Standard, whose higher grade corresponds approximately to the ISO 3 and ISO 4 class.


Tavola BS 5295 Environmental cleanliness classes

Maximum permitted number of particles per m^3 (equal to, or greater than, stated size) Maximum floor area per sampling position for cleanrooms (m^2) Minimum pressure difference*
Class of environmental cleanliness 0.3 m m 0.5 m m 5 m m 10 m m 25 m m Between classified areas and unclassified areas (Pa) Between classified area and adjacent areas of lower classification (Pa)
C 100 35 0 NS NS 10 15 10
D 1 000 350 0 NS NS 10 15 10
E 10 000 3 500 0 NS NS 10 15 10
F NS 3 500 0 NS NS 25 15 10
G 100 000 35 000 200 0 NS 25 15 10
H NS 35 000 200 0 NS 25 15 10
J NS 350 000 2 000 450 0 25 15 10
K NS 3 500 000 20 000 4 500 500 50 15 10
L NS NS 200 000 45 00 5 000 50 10 10
M NS NS NS 450 000 50 000 50 10 NA


EU-GMP Standard

The GMP (Good Manufacturing Practices) have been written and published in the United States since 1968.  Subsequently, the European Union proposed its own revision which took the name of EU-GMP.

The legislation defines the classes of environmental containment, or the degrees of cleanliness required for a cleanroom, based on the type of activity carried out.  These are rules that illustrate: processing methods, equipment and production management necessary to achieve certain standards.

Annex 1 "Manufacturing of Sterile Medicinal Product" distinguishes in particular four different degrees of cleanliness:


  • "A" Areas: areas dedicated to high-risk operations such as the handling of aseptic components or that promote the growth of microorganisms.
  • "B" Areas: for environments adjacent to grade A areas, such as filling and aseptic preparations.
  • "C" and "D" Areas: for less critical activities during aseptic manipulation. In addition, the GMP regulation also provides for two different employment states: at rest and operational.
    Note that the ISO also refers to the same two states, but adds a third: “as built”.


These last three are the same that can be found in the UNI EN ISO 14644-1.

VDI 2083 “Verein Deutscher Ingenieure” standard

VDI 2083 is the acronym of "Verein Deutscher Ingenieure" or Association of German Engineers. Their standard is a series of German regulations created in 1990 with the aim of:


  • Complete some aspects not yet covered by the ISO standard
  • Explain how standards should be used
  • Offer a deeper level of operational practices.


The legislation identifies 6 classes with increasing numbers, starting from class 1, up to class 6.  These 6 classes correspond exactly to the structure of the classification proposed in Federal Standard 209.

Austria and Switzerland have also adopted VDI 2083 to promote the standardisation of cleanroom technology. It addresses some particular issues such as energy and cost efficiency; it also proposes some solutions at a technical and procedural level that guarantee potential energy savings and develops a guideline for the training of operators and cleanroom supervisors.


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