Another major source of contamination in cleanroom manufacturing is bacteria. Bacteria are a natural part of the environment and may act as either a chemical or a particulate contaminant, or in the worst case both.
While a clean environment minimizes the number of bacteria that are initially in the air, this ignores potential operator contributions of bacteria to the clean environment. For example, a sneeze or a cough will generally put both bacteria and aerosol particles into the air. Bacteria are on everyone’s skin and scratching exposed skin will place both skin flakes and bacteria into the air.
Another problem is the ability of bacteria to mutate; thus it is not uncommon for bacteria to grow in water systems and the like. In light of their size, it is not surprising that bacteria are particulate contaminants. But, how are they chemical contaminants? Recall that they are alive and contain a vast array of chemicals. Included among these chemicals are electrically charged molecules called ions.
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