What is a Clean Room ?
A clean room is an area that has an especially small amount of airborne pollutants. This includes vapors, bacteria, particles, dust, and aerosols. It is not possible to completely eliminate the presence of these pollutants from the air, but a clean room has a controlled amount of these pollutants, specified by a specific amount of particles per cubic meter.
Despite the tightly controlled nature of a clean room, the technology has gotten to the point where the controlled area can be very large. An entire manufacturing facility, with thousands of square meters of space, can qualify as a clean room. Some of the industries that use them extensively include biotechnology, manufacturing of tiny parts such as microchips, and biological experiments that could be disturbed by the presence of contaminants.
Any air that enters a clean room is filtered, and the air within the facility is also continuously filtered in order to remove any contaminants that are produced on the inside of the facility. Personnel who enter this type of facility first travel through an airlock, which may also include an air shower. They also wear protective gear in order to avoid contaminating the facility.
The equipment inside of the facility is specifically built to prevent contamination, including specially designed mops and buckets. The furniture is also built in this manner. Despite all of this, it is not accurate to refer to a clean room as being "sterile," because the focus is entirely on eliminating airborne contaminants.
In some cases, a clean room is pressurized from the inside so that if there is a leak of any kind, the air will leak out of the facility, instead of into it. The humidity may also be kept so low that ionizers will be required in order to prevent an excess of static electricity.
In addition to this, there are some facilities that use some of these techniques in order to keep a facility clean, but do not go to the extent of requiring people to wear protective gear or to classify it as a clean room specifically.
The air inside of a clean room is kept in a state of constant motion so that contaminants that emerge are quickly removed and filtered out of the room. This motion may be circular, or it may be all in one direction.