Whitfield's solution was to constantly flush out or "sweep" a room with highly filtered air. In an initial model, Whitfield designed a workbench along one wall. Clean air entered the room from a bank of filters that were 99.97 percent efficient in removing particles larger than 0.3 microns. For example, cigarette smoke blown in one side comes out the other as clean air.
The air was circulated in the room at a rate of 4,000 cubic feet or about 10 changes of air per minute. The resulting linear speed of the air is slightly more than 1 mph, which is about the same as that felt walking through a still room.
In a later modification, the air was passed down over the work area instead of across, letting gravity help carry troublesome particles into the floor, which was covered with grating. Filters underneath clean the air and it is circulated back around to re-enter the room.
Disbelief, then wonder as invention was announced
When the first cleanroom was tested instruments that counted the dust particles registered zero, causing Whitfield and others to assume they were broken, Whitfield said in 1993.
The laminar-flow cleanroom created a work environment that was more than 1,000 times cleaner than the cleanrooms in use at the time. According to tests at the time, the laminar-flow cleanroom's work area contained an average of 750 dust particles one-third of a micron in size or larger per cubic foot of air. (A micron is equal to 40-millionths of an inch.) That's compared to average dust counts of more than 1 million particles per cubic foot of air in one of the best conventional cleanrooms in use at the time.
RCA and General Motors Co. were early adopters of the cleanroom, and the predecessor to
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DOE/Sandia National Laboratories