A cleanroom or clean room is an environment, typically used in manufacturing or scientific research, that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a cleanroom has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size. To give perspective, the ambient air outside in a typical urban environment contains 35,000,000 particles per cubic meter in the size range 0.5 μm and larger in diameter, corresponding to an ISO 9 cleanroom, while an ISO 1 cleanroom allows no particles in that size range and only 12 particles per cubic meter of 0.3 μm and smaller.
The modern cleanroom was invented by American physicist Willis Whitfield. An employee of the Sandia National Laboratories, Whitfield created the initial plans for the cleanroom in 1960. Prior to Whitfield's invention, earlier cleanrooms often had problems with particles and unpredictable airflows. Whitfield designed his cleanroom with a constant highly filtered air flow to flush out impurities. Within a few years of its invention in the 1960s, sales of Whitfield's modern cleanroom had generated more than $50 billion in sales worldwide.
Cleanrooms can be very large. Entire manufacturing facilities can be contained within a cleanroom with factory floors covering thousands of square meters. They are used extensively in semiconductor manufacturing, biotechnology, the life sciences and other fields that are very sensitive to environmental contamination.
The air entering a cleanroom from outside is filtered to exclude dust, and the air inside is constantly recirculated through high-efficiency particulate air (HEPA) and/or ultra-low penetration air (ULPA) filters to remove internally generated contaminants.
Equipment inside the cleanroom is designed to generate minimal air contamination. Only special mops and buckets are used. Cleanroom furniture is designed to produce a minimum of particles and to be easy to clean.
Common materials such as paper, pencils, and fabrics made from natural fibers are often excluded, and alternatives used. Cleanrooms are not sterile (i.e., free of uncontrolled microbes); only airborne particles are controlled. Particle levels are usually tested using a particle counter.
Some cleanrooms are kept at a positive pressure so that if there are any leaks, air leaks out of the chamber instead of unfiltered air coming in.
Low-level cleanrooms may only require special shoes, with completely smooth soles that do not track in dust or dirt. However, for safety reasons, shoe soles must not create slipping hazards. Access to a cleanroom is usually restricted to those wearing a cleanroom suit.
In cleanrooms in which the standards of air contamination are less rigorous, the entrance to the cleanroom may not have an air shower. There is an anteroom (known as a "gray room"), in which clean-room clothing must be put on, from which a person can walk directly into the room (as seen in the photograph on the right).
Air flow principles 
Cleanrooms maintain particulate-free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward in a constant stream towards filters located on walls near the cleanroom floor or through raised perforated floor panels to be recirculated. Laminar air flow systems are typically employed across 80 percent of a cleanroom ceiling to maintain constant air processing. Stainless steel or other non-shed materials are used to construct laminar air flow filters and hoods to prevent excess particles entering the air. Turbulent, or non-unidirectional, air flow uses both laminar air flow hoods and non-specific velocity filters to keep air in a cleanroom in constant motion, although not all in the same direction. The rough air seeks to trap particles that may be in the air and drive them towards the floor, where they enter filters and leave the cleanroom environment.
Cleanroom classifications 
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 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, for example, "class 2000".
A discrete-particle-counting, light-scattering instrument is used to determine the concentration of airborne particles, equal to and larger than the specified sizes, at designated sampling locations.
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 cleanroom has at most 105 = 100,000 particles per cubic metre.
Both FS 209E and ISO 14644-1 assume log-log relationships between particle size and particle concentration. For that reason, zero particle concentration does not exist. The table locations without entries are non-applicable combinations of particle sizes and cleanliness classes, and should not be read as zero.
Because 1 m³ is approximately 35 ft³, the two standards are mostly equivalent when measuring 0.5 µm particles, although the testing standards differ. Ordinary room air is approximately class 1,000,000 or ISO 9.
US FED STD 209E cleanroom standards 
|≥0.1 µm||≥0.2 µm||≥0.3 µm||≥0.5 µm||≥5 µm|
ISO 14644-1 cleanroom standards 
|Class||maximum particles/m³||FED STD 209E
|≥0.1 µm||≥0.2 µm||≥0.3 µm||≥0.5 µm||≥1 µm||≥5 µm|
|ISO 3||1,000||237||102||35||8.3||0.29||Class 1|
|ISO 4||10,000||2,370||1,020||352||83||2.9||Class 10|
|ISO 5||100,000||23,700||10,200||3,520||832||29||Class 100|
|ISO 6||1.0×106||237,000||102,000||35,200||8,320||293||Class 1,000|
|ISO 7||1.0×107||2.37×106||1,020,000||352,000||83,200||2,930||Class 10,000|
|ISO 8||1.0×108||2.37×107||1.02×107||3,520,000||832,000||29,300||Class 100,000|
|ISO 9||1.0×109||2.37×108||1.02×108||35,200,000||8,320,000||293,000||Room air|
BS 5295 cleanroom standards 
|Class||≥0.5 µm||≥1 µm||≥5 µm||≥10 µm||≥25 µm|
BS 5295 Class 1 also requires that the greatest particle present in any sample does not exceed 5 μm.
GMP EU classification 
|At Rest||At Rest||In Operation||In Operation|
|0.5 µm||5 µm||0.5 µm||5 µm|
See also 
- Air Quality Index
- Data recovery lab
- Secure environment
- ISO 14644
- ISO 14698
- Contamination control
- Pneumatic filter
- Semiconductor device fabrication
- "Sandia physicist, cleanroom inventor dies at 92". KWES (Associated Press). 2012-11-26. Retrieved 2012-12-03.
- In NASA’s Sterile Areas, Plenty of Robust Bacteria New York Times, 9. October 2007
- Cleanroom Clothing
- Your Cleanroom Supplier :: Hutchins & Hutchins, Inc
- Cleanroom Forum
- Cleanroom Air Flow Principles
- Cleanroom Classification / Particle Count / FS209E / ISO TC209 /
- Cancellation of FED-STD-209E - Institute of Environmental Sciences and Technology
- http://www.wbdg.org/ccb/FEDMIL/notices.pdf, page 148
- Market Venture Philippines Inc. web site
- Pharmaceutical equipment and technologies
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