- Clean rooms can be very large. Entire manufacturing facilities can be contained within a clean room 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 clean room from outside is filtered to exclude dust, and the air inside is constantly re circulated through high-efficiency particulate air (HEPA) and/or ultra-low penetration air (ULPA) filters to remove internally generated contaminants.
- Staff enter and leave through airlocks (sometimes including an air shower stage), and wear protective clothing such as hoods, face masks, gloves, boots and coveralls.
- Equipment inside the clean room is designed to generate minimal air contamination. Even specialized mops and buckets exist. Clean room furniture is also 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; however, alternatives are available. Clean rooms are not sterile (i.e., free of uncontrolled microbes) and more attention is given to airborne particles. Particle levels are usually tested using a particle counter.
- Some clean rooms 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.
- Some clean room HVAC systems control the humidity to low levels, such that extra equipment (“ionizers”) are necessary to prevent electrostatic discharge (ESD) problems.