Clean rooms are defined as a specially constructed enclosed area, environmentally controlled with respect to airborne particulates, temperature, humidity, air pressure, air flow patterns, air motion, vibration, noise, viable (living) organisms, and lighting.
Particulate control includes:
- Particulate and microbial contamination
- Particulate concentration and dispersion
Particulate/Contaminants must be continually removed from the air. The level to which these particles need to be removed depends upon the standards required. These standards are
- “Federal Standard 209E” defines a clean room as a room in which the concentration of airborne particles is controlled to specified limits.
- “British Standard 5295”defines a clean room as a room with control of particulate contamination, constructed and used in such a way as to minimize the introduction, generation and retention of particles inside the room and in which the temperature, humidity, airflow patterns, air motion and pressure are controlled.
Airborne particles occur in nature as dust, pollen, bacteria, miscellaneous living and dead organisms, and sea spray. Industry generates particles from combustion processes, chemical vapors, and friction in manufacturing equipment. People in the workspace generate particles in the form of skin flakes, lint, cosmetics, and respiratory emissions. All these particulates are either to be eliminated, diluted or prevented from settling on to the product surfaces.
The purpose of the clean room air-conditioning system is to supply airflow in sufficient volume and cleanliness to support the cleanliness rating of the room. Air is introduced into the clean room in a manner to prevent stagnant areas where particles could accumulate. The air must also be conditioned to meet the clean room temperature and humidity requirements. In addition, enough conditioned makeup air must be introduced to maintain the specified positive pressurization.
HEPA filters are a critical component in clean rooms. Clean room environments require highly filtered air that is frequently changed and delivered at precise conditions. Air-Handling units for clean room application require specific custom units that accommodate laminar air flow, HEPA and ULPA filtration, and sealed-insulation construction.
Applications of Clean Rooms
Clean rooms are typically used in manufacturing, packaging and research facilities associated with the following industries
- Semiconductor ; this industry drives the state of the art clean room design and this industry accounts for a significant number of all operating clean rooms.
- Pharmaceutical ; clean rooms control living particles that would produce undesirable bacterial growth in the preparation of biological, pharmaceutical and other medical products as well as in genetic engineering research.
- Aerospace; the manufacturing and assembling of aerospace electronics, missiles and satellites were the first application of clean rooms. Large volume clean room spaces with extreme cleanliness are involved.
- Miscellaneous applications; other uses include advanced materials research, laser and optic industries, microelectronic facility, paint room and in some aseptic foods production. Also in some high infection risk areas of hospitals.
Control of contaminants
Control is primarily through airflow design. Construction finishes; personnel and garments; materials and equipments are sources of particulate contaminations that must be controlled. Important control precautions include:
- Walls, floors, ceiling tiles, lighting fixtures, doors and windows are construction materials that must be carefully selected to meet clean room standards.
- People must wear garments to minimize the release of particles into the space. The type of garments depends on the level of cleanliness required by a process. Smocks, coveralls, gloves and head and shoe cover are clothing accessories commonly used in clean spaces.
- Materials and equipments must be cleaned before entering the clean room.
- Room entrances such as sir locks and pass through are used to maintain pressure differentials and reduce contaminants.
Air shower is used to remove contaminants from personnel before entering the clean spaces.