A clean room is an environment that is used for the manufacturing of precision equipment or conducting of scientific research that has a strictly controlled level of contamination. Clean rooms use specifically designed equipment to control the amount of particles per cubic meter at a specified particle size in the room. In some cases even air temperature and humidity controls are needed.
Air Filtration
Regardless of cleanliness class, the air to all clean rooms is filtered thru HEP (High Efficiency Particulate Air) or ULPA (Ultra Low Particulate Air) filters. These filters are rated for 99.99 percent efficiency on 0.3 micron particles (HEPA) and 0.128 micron particles UULPA). Cleanliness is a function of how much clean air is mixed with the contaminated air in the room. The more clean air, the greater the contaminant dilution, and the higher the level of cleanliness. Clean rooms also take advantage of another feature of the filters and that is the pleating of the media in the manufacturing process. This pleating effect causes the air passing thru the filter to be delivered in a jet stream. The collective results of these multiple air streams produces a column of clean air moving uniformly away from the filter face.
Humidity Control
Temperature Control
The process within the space generally dictates the temperature range that can be tolerated. If there are non-specific requirements, the human factor usually will guide the selection.
Humidity Control
Often overlooked in the design of a clean room is the stringent humidity requirement. This can vary, again depending on the process involved. Between 40 percent to 60 percent is typical with a variation usually not greater than 5 percent.
Walls
Walls can be constructed of any non-shedding material that can be wiped down easily and kept clean. Walls can be gypsum board with a seamless coating on metal studs or they can be modular. Modular walls have a tax advantage in they are considered tangible property and can be taken down and moved.
Floors
The best clean room floors are poured seamless systems, seamless sheet vinyl, epoxy, or vinyl tile in that order. Products that limit dust penetration and can be easily maintained are required.
Ceilings
Most clean rooms are designed with positive pressure plenums, or ceiling spaces. This requires a special grid system that is usually factory gasketed or it can be a gel system on the more stringent rooms. The grids typically support the HEPA filters, lights, and panels and can weight as much as 12 pounds per squire foot. 12 gauge wire is used to support the grid.
HEPA Filter Units
The heart of any clean room design is the filtration that is required. Some are ducted but the most common are fan powered units. The typical 2' x 4' unit has a capacity of 700 to 800 cfm, with a 1/3 hp motor. Latest designs also include energy efficient watt motors.
Clean Room Lights
Lights are specially constructed for clean rooms so they are sealed air tight. They also produce heat which must be taken into account. Typical lighting is 70 to 100 foot candles.
Variables
While we know what the hardware mentioned above produces in regards to release of microbes, heat etc., the one element that changes daily is human element. It has been said that "absolute cleanliness" cannot be maintained with man's involvement, that robots are the only way to eliminate this source of particulate pollution. Even fully gowned, workers are constantly shedding skin particles. Gowning is required.
Gowning
Garments can include hair covering, beard or mouth covering, body covering, shoe covering and gloves with any combination of the above. Garments should be put on in a gowning room. This room should also be HEPA filtered.
Testing and Certification
Once the room is completed, most specifications call for testing and certification. Some requirements state that the room should be test annually also. Testing is usually conducted by an independent testing agency using the ISO Standards. It is also imperative for the owner to purchase a clean room monitor in order to determine the daily status of the room.
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