Though there are many different construction methods for cleanrooms, all manufacturers have to follow the guidelines of ISO 14644-1, ISO 14698-1, and FED STD 209E. In some cases, modular and portable cleanrooms are specially designed to assist testing facilities. When planning Cleanroom construction, there are several factors that need to be considered, which include
1. Surfaces
2. Equipment
3. Air control system
4. Number of personnel
5. Lighting
6. Doors
7. Viewing panels
8. Humidity control
Each of these factors are described below
1. Surfaces
Cleanroom surfaces are smooth and impervious and will not peel, flake, corrode, create dust, or have places for microorganism to grow. They must be able to be easily cleaned and accessible. In microelectronic and semiconductor Cleanrooms, surfaces are required to be smooth and free of potential . ESDs Surface materials are shatter, dent, and crack resistant as well as crease repellen.
Floors in Cleanrooms are either epoxy resin or PVC. Resin floors are used where there is high mechanical loads since resin has high resistance and strength. The most common use of resin floors is in rooms that have water or high humidity.
PVC floors are more economical and are laid out in tiles. They are used in low little traffic areas where there aren‘t heavy loads.
2. Equipment
Cleanroom equipment is manufactured from easy-to-clean materials such as stainless steel, polycarbonate, or plastic laminates. The type of equipment used in a cleanroom is anything that is not attached to the walls or floor, which includes a wide range of items from simple hand tools to showers and pass throughs.
3. Air Control Systems
Cleanrooms require a great deal of air and sometimes need to have the temperature and humidity controlled. Air handling units (AHU) use 60% of a sites power. The cleaner the room the more power that is used. To control the expense of air control units, systems are designed to recirculate the air, which keeps the temperature and humidity stable.
Air control system is the most essential part of a cleanroom. Cleanrooms have positive air pressure, which results in air exfiltrating into adjoining spaces with lower pressure and leaves through electrical outlets, light fixtures, window frames, ceiling and floor interfaces, and doors. In the majority of cases, leakage is at a rate of 1% to 2%.
When planning a cleanroom, it is necessary to study how much exfiltration there is, or the amount of air that will escape the room. In a supply, return, and exhaust system, there needs to be a 10% difference between supply and return airflow.
A common exit path is through doors. The amount of exfiltrating through a door is determined by the size of the door, pressure across the floor, and how well the door is sealed. For a normal door, air exfiltrates at 190 cfm to 270 cfm.
The airflow needs to be balanced where the amount exfiltrating matches the amount of infiltrating. During the startup of a cleanroom, adjustments need to be made for exfiltration. Turbulence, eddies, equipment, and pressure influence the air exchange rate, which is the key factor in airflow design.
The diagram below shows the exfiltration and infiltration or the air exchange rate of a unidirectional air flow system, where 1 represents the infiltration and 2 is exfiltration. These two factors are critical for the development and construction of the air control system.
Related: HEPA Filter in Pharmaceutical Industry
4. Number of personnel
The major source of cleanroom contamination is from the people who work in them since a person sheds one billion skin cells per day that are 33 µm x 44 µm x 4 µm 10% of which carry microorganisms. The amount of possible contamination from people makes controlling their numbers a critical consideration.
According to academic studies, only select and trained personnel should be allowed in a cleanroom. Added to this factor is the need for adequate training in cleanroom procedures such as proper attire and protection. Studies indicate that the higher the number of personnel, the greater the amount of contamination.
5. Lighting
Cleanroom lighting is designed to meet specialized environmental requirements. Unlike the air control system, lighting represents 1% of the total cost of operating a cleanroom. Since instruments in a cleanroom are highly precise, the foot-candle, light intensity at one lumen per square foot, is very high. Each type of cleanroom has lighting specifically designed for its purposes.
Related: Lux Level in Pharmaceutical Industry
6. Low Humidity
The relative humidity (RH) for a cleanroom should be between 30 to 60% at a balanced level to protect against overly moist or dry conditions. Well balanced humidity suppresses the potential for electrostatic discharge (ESD) that could ruin products. Humidity control is necessary as a means of preventing bacterial growth. Two methods of humidity control are air conditioning and desiccants, a substance that induces dryness.
Air conditioning lowers the surface temperature in a cleanroom, while the desiccant process absorbs moisture in the air. Desiccants significantly reduce dew points to five times lower than an HVAC system. Below is a diagram of a desiccant humidity filter.
7. Doors
Cleanroom doors are responsible for keeping the room sealed from external contaminants and maintaining the controlled environment. As with every detail of a cleanroom, the doors have to be specially designed to exacting standards. Below are some of the details to consider when examining a cleanroom door. The first thing to note, as with all cleanroom surfaces, doors have to be smooth and impenetrable.
- Completely flat
- Easy to integrate into any Cleanroom
- Resistant to bending and shock with a thickness of 60 mm or 2.36 in.
- Air tightness
- Resistant to strong chemicals in cleaning products
- Safety glazed glass
- Resistant to ESDs
- Swing into the room
- High quality hardware
- Able to be locked
- Closed cell non-organic core
- Seamlessly molded
- Fire resistant
8. Viewing Panels
The purpose of viewing panels is for operators to work more efficiently and have visual contact. They are strategically located for ease of access for supervision inspection and the elimination of the supervisor performing entry protocols.
Viewing panels must be flush to both sides of the wall, shatter proof, with a drying agent in the void between the glass panels, and fire resistant. In ultraviolet lit rooms, they have a coating that filters the ultraviolet wavelengths.
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