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Manufacturers invest hundreds—even thousands—of dollars per square foot of cleanroom space to meet ISO-proscribed particle counts. Shouldn't the same standards be required of the people who enter and potentially contaminate this ultra-clean environment?
Proper cleanroom garments, including hoods, face masks, booties and gloves, help to contain particles that people emit. Yet improper gowning procedures can negate your investment in cleanliness and threaten yields of sensitive semiconductor devices. Once a garment is contaminated—violated by contact with a dirty surface—it spreads particles everywhere it goes.
You can train personnel on proper garmenting procedures, but how do you guarantee compliance? A violated garment doesn't set off alarms, and few facilities can afford quality control monitors to supervise every person through every washing and dressing stage. Yet if strict controls are not observed, dirty gloves and coveralls almost certainly will come in contact with clean operations.
The simplest and most economical approach to this dilemma is a correctly designed gowning area, complete with well-designed cleanroom furniture, that keeps personnel on a clean track.
This design starts with a room with pressure greater than that of the outside air, but lower than the cleanroom. This cascading pressure differential reduces the opportunity for contaminants to enter each controlled space. It includes a laminar flow of HEPA-filtered air, typically emitted through ceiling filter/fan units. This continuous wash of clean air immediately removes personnel-emitted contaminants, as well as particles present even in cleanroom-laundered garments (see Figure 1). Failure to maintain the desired particle standard in the change area will lead to contaminating clean garments.
|Activity||No. of particles|
|Person emits during garmenting process||3,000,000/min.|
|Cleanest skin (hands)||10,000,000/ft2|
|Employee street clothes||10,000,000 to |
|Floor and bench surfaces||> 10,000,000/ft2|
|Garments supplied by cleanroom laundry||1,000,000/ ft2|
|Figure 1: Gowning Area Particle Generators|
Source: Encyclopedia of Clean Rooms, Bio-Cleanrooms and Aseptic Areas,
Dr. Philip Austin, P.E., 2000
The Change Room illustration below depicts an effective floor plan that places the proper gowning stations in appropriate locations. Although many variations on this layout are possible, they should support these key garmenting guidelines:
|Figure 2: Austin Contamination Index|
Particles >= 0.3µm emitted per minute in garment indicated
Source: Encyclopedia of Clean Rooms, Bio-Cleanrooms and Aseptic Areas, Dr. Philip Austin, PE, 2000
Note: Light/heavy movement refer to partial body movements (motioning with arm, tapping toes, etc.).
Change of position refers to whole body motion (standing up, sitting down, etc.).
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